Lateral Bridge Clearances
The major cross section elements considered in the design of streets and highways include the pavement surface type, cross slope, lane widths, shoulders, roadside or border, curbs, sidewalks, driveways, and medians. Due consideration should be given to the motoring and non-motoring users in designing the cross section.
Pavement surface type is determined by soil conditions, traffic volume, traffic composition, material availability, initial cost, and the extent and cost of maintenance. All of these affect the relationship of cost to traffic service.
Generally, all roadways in the State are surfaced with hot mix asphalt materials or Portland cement concrete. These pavements provide good riding qualities, help to maintain the cross section, and adequately support the expected volume and weights of vehicles without failure due to fatigue. In considering cyclists and pedestrian traffic, other roadway surfaces include textured and colored asphalt, textured and colored concrete, and brick and other unit pavers. As part of urban design, landscape or streetscape treatments, these are used in crosswalks, bike lanes, shoulders, and traffic calming devices.
Important characteristics in relation to geometric design are the ability of a surface to sustain its shape and dimensions, the ability to drain, and the affect on driver, bicyclist, and pedestrian behavior.
The cross slope of the pavement is the slope of the pavement surface measured transverse to the centerline of the highway. The high point of a normal cross slope of a roadway is known as the crown. Undivided pavements on tangents or on flat curves have a high point (crown) in the middle of the traveled way and slope downward toward both edges.
The minimum cross slope for concrete pavement and hot mix asphalt pavement should be 1.5 percent. The cross slope shall be uniform across the pavement section, from the high point to the edge of lane. The cross slope in each successive lane should be increased by 0.5 percent. However, it may be increased on each successive pair of lanes by 0.5 to 1 percent in order to cause the least disturbance to the existing border area, to limit the amount of resurfacing weight on a structure, or to minimize the cross slope in the outer lane when more than three lanes are sloped in the same direction.
In addition, if the cross slope of the left-turn lane is in the same direction as the adjacent lane, the adjacent lane cross slope may be used.
On a divided highway, each one way pavement may be crowned separately, as on a two lane highway, or it may have a unidirectional slope across the entire width of pavement, which is almost always downward to the outer edge.
A cross section where each roadway has a separate high point (crown) has an advantage of rapidly draining the pavement as shown in the top two drawings of Figure 5-A. In addition, the difference between high and low points in the cross section is kept to a minimum. The disadvantage is, additional drainage inlets and subsurface drainage
lines are required. In addition, treatments of at grade intersections are more difficult because of the creation of several high and low points on the cross section. Preferably, use of such sections should be limited to regions of high rainfall. A cross section having no curbing and a wide depressed median are particularly well suited for high rainfall conditions.
Roadways that slope only in one direction provide more comfort to drivers because vehicles tend to be pulled in the same direction when changing lanes (As shown in the bottom four drawings of Figure 5-A). Roadways with a unidirectional slope may drain away from or toward the median. Providing drainage away from the median may affect a savings in drainage structures and simplify treatment of intersecting streets. Advantages of drainage toward the median are:
1. An economical drainage system, in that all surface runoff is collected into a single conduit.
2. Outer lanes, used by most traffic, are freer of surface water.
A major disadvantage of drainage toward the median is all the pavement drainage must pass over the inner, higher speed lanes. Where curbed medians exist, the drainage is concentrated next to and on higher speed lanes. This concentration of drainage, when the median is narrow, results in annoying and undesirable splashing onto the windshields of opposing traffic.
The rate of cross slope on curves as well as on tangent alignment is an important element in cross section design. See Section 4, “Basic Geometric Design Elements,” for speed curvature relationships to determine pavement superelevation on curves.
Lane widths have a great influence on driving safety and comfort. The predominant lane width on freeways and land service highways is 12 feet.
While lane widths of 12 feet are desirable on land service highways, circumstances may necessitate the use of lanes less than 12 feet. Lane widths of 11 feet in urban areas are acceptable. Existing lane widths of 10 feet have been provided in certain locations where right of way and existing development became stringent controls and where truck volumes were limited. However, new or reconstructed 10 foot wide lanes would not be proposed today, except in traffic calming areas.
On land service highways, where it is not practical to provide a shoulder adjacent to the outside lane, the outside lane width shall be 15 feet to accommodate bicyclists. Where alternate bike access is provided, the outside lane width should be 1 foot wider than the adjacent through lane width. The designer should strive to accommodate the bicyclist and pedestrian on all projects.
When resurfacing existing highways that have lane widths of 10 feet or less, the existing lanes should be widened to either 11 foot minimum or 12 foot desirable.
Auxiliary lanes at intersections are often provided to facilitate traffic movements. Such lanes should be equal in width to the through lanes but not less than 10 foot wide when constructed adjacent to a shoulder. When there is no right shoulder adjacent to a new or reconstructed auxiliary lane, the width of the auxiliary lane shall be designed to accommodate the bicyclist. Where alternate bike access is provided, the auxiliary lane width should be 1 foot wider than the adjacent through lane width. The criteria in this paragraph shall also apply to auxiliary lanes at interchanges on land service highways.
On Interstates and freeways, the width of the auxiliary lane shall be 12 feet. Lane widths for specific types of highways are enumerated as part of the typical sections illustrated at the end of this section.
For the width of climbing lanes and left-turn lanes, see Section 4, “Basic Geometric Design Elements” and Section 6, “At-Grade Intersections,” respectively.
A shoulder is the portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles, for emergency use, and for lateral support of subbase, base and surface courses.
Some of the more important advantages of providing shoulders are:
1. Space for the motorist to pull completely off the roadway for emergencies.
2. An escape zone to allow motorists to avoid potential accidents or reduce accident severity.
3. An aid to driver comforts by creating a sense of openness; improves highway capacity.
4. An improvement in sight distance in cut sections.
5. A provision to enhance lateral clearance for the placement of signs, guide rails, or other roadside appurtenances.
6. Space for pedestrians where there is no sidewalk and for bicycle usage.
New Jersey shoulder pavement design is based on the following engineering considerations.
A. The New Jersey state highway system constitutes the heart of our state’s surface transportation network. As a corridor state, the New Jersey highway system is subjected to the highest traffic count and loading in the nation.
B. New Jersey highways continue to be faced with a serious backlog of deficient pavements in poor to fair condition. As such, many of the pavements are in the process of or will eventually be rehabilitated or reconstructed.
C. Due to frequent traffic encroachment over the longitudinal joints next to the shoulder and the need to stage traffic on shoulders during rehabilitation, progressive shoulder deterioration will result if adequate shoulder pavement strength is not provided in the original construction.
D. Shoulders of adequate pavement strength will carry traffic during the future construction of additional lanes, and the widening, resurfacing, rehabilitation and recycling of the existing lanes. The shoulders will also be used as an additional riding lane during peak hours relieving traffic congestion, such as in the case of “bus/shoulder” lanes.
The following shoulder pavement design policy is based on the above consideration. The term “Full Pavement Shoulder” is a shoulder pavement equal to that of the mainline pavement.
Full pavement shoulders shall be used as follows:
Full pavement shoulders shall be used for all new construction, reconstruction and widening on all portions of the NJ highway system.
For mainline pavement rehabilitation projects, shoulder pavement shall be designed to carry mainline traffic for a minimum period of 2 years or the following minimum section (whichever is greater):
2” Hot Mix Asphalt ___ Surface Course
3” Hot Mix Asphalt ___ Intermediate Course
8” Dense Graded Aggregate Base Course
Desirably, a vehicle stopped on the right shoulder should clear the pavement edge by at least 1 foot, preferably by 2 feet. On land service highways, in difficult terrain, or in areas where right of way is restricted due to roadside development or environmental factors, a minimum 8 foot wide shoulder may be provided. On 3R projects, the existing shoulder width may be reduced to 8 feet to provide wider lanes. New or reconstructed shoulders on heavily traveled and high speed land service highways, especially those carrying large numbers of trucks (250 DHV), where turning volumes are high or dualization is anticipated, should have usable shoulders at least 10 feet and preferably 12 feet wide. Shoulders should be provided adjacent to all new acceleration and deceleration lanes at interchanges, where practical, in major new construction or reconstruction projects along major land service highways having an AADT of 10,500 per lane (DHV of 1,500 per lane) or greater, for the project design year. "Practical" is defined as given consideration to social, economic, and environmental impacts in concert with safe and overall efficient traffic operations.
Shoulder widths on freeways and Interstate highways shall be 10 feet minimum. However, where truck traffic exceeds 250 DDHV, a 12 foot shoulder should be provided. A 10 foot shoulder shall be provided adjacent to all new or reconstructed auxiliary lanes. Where no right shoulder exists, the existing auxiliary lane width may be maintained on Interstate and freeway resurfacing, restoration and rehabilitation (3R) projects. However, whenever practical, a 10 foot desirable or a 6 foot minimum shoulder should be provided on Interstate and freeway 3R projects.
Shoulder widths for specific types of highways are enumerated as part of the typical sections illustrated at the end of this section.
Although it is desirable that a shoulder be wide enough for a vehicle to be driven completely off the traveled way, narrower shoulders are better than none at all. Partial shoulders are sometimes used when full shoulders are unduly costly, as on long span bridges or in mountainous terrain. Regardless of the width, a shoulder should be continuous where feasible.
Left shoulders are preferred on all divided highways. The desirable median shoulder width on a 4 lane and 6 to 8 lane highway is 5 feet and 10 feet respectively. The minimum left shoulder width on land service highways is 3 feet and on a freeway is 4 feet. In order to provide wider lanes on 3R projects, the left shoulder width on an existing divided multilane land service highway may be reduced to 1 foot (Programmatic Design Exception).
Shoulders on structures should have the same width as the usable shoulders on the approach roadways, both right and left. This design is essential on freeways, and is desirable on all arterials where shoulders are provided. Long span, high cost structures usually warrant detailed special studies to determine feasible dimensions. Wherever practicable, full shoulders should be included, but as has been indicated, for some cases, it may be judged proper to use only partial width shoulders.
Shoulders are important links in the lateral drainage systems. A shoulder should be flush with the roadway surface and abut the edge of the through lane/auxiliary lane. On a divided highway with a depressed median, all shoulders should be sloped to drain away from the traveled way. With a raised narrow median, the median shoulder may slope in the same direction as the traveled way. All shoulders should be pitched sufficiently to rapidly drain surface water.
Desirably, a shoulder cross slope should not be less than 4 percent to minimize ponding on the roadway. As a minimum, a shoulder cross slope should not be less than 2 percent. However, when a left shoulder is less than 5 feet in width and the median slopes away from the roadway or where the median and adjacent lane both slope toward the median gutter, the shoulder cross slope may be at the same rate and direction as the adjacent lane for ease of construction.
On 3R and reconstruction projects, shoulder cross slope may be increased to 6 percent to minimize impacts on existing curb, drainage, adjacent properties, access, etc. But, shoulder cross slope should not exceed 5 percent where a curb ramp is present since the angle of incidence between a mobility devise descending a curb ramp and the counter slope of the gutter must be limited to avoid catching the mobility devise footrest.
Shoulder on the high side of a superelevated section should be designed to drain away from the adjacent traffic lanes. A shoulder cross slope that drains away from the paved surface on the high side of a superelevated section should be designed to avoid too great a cross slope break. The cross slope of the shoulder shall be as follows:
1. The shoulder cross slope should be 4 percent where the superelevation rate is 3 percent or less.
2. For superelevation rates greater than 3 percent and less than 5 percent, a maximum rollover rate of 7 percent will be used to establish the shoulder cross slope.
3. When superelevation rates range from 5 percent to 6 percent, the shoulder cross slope will be 2 percent.
On an existing superelevated curve where there is a history of run off the road accidents, the location should be evaluated for proper clear zone, sight distance, superelevation, and signing. The shoulder cross slope on the outside of the curve may be constructed in the same direction as the adjacent lane. However, consideration should be given to snow storage in border area (snow melting in border area then draining and refreezing on roadway surface) by sloping the border away from roadway or by providing slotted drainage along shoulder.
The shoulder on the inside of a curve or on the low side of a superelevated section should be sloped at 4 percent, or equal to the superelevation of the adjacent lane, whichever is greater.
It will not always be economically feasible to provide desirably wide shoulders continuously along the highway through high cut areas or along steep mountainsides. In such cases, consideration should be given to the use of intermittent sections of shoulders or turnouts that can be placed at favorable locations along the highway. Where intermittent shoulders or turnouts are provided, the length of the transition section should be approximately 50 feet to encourage usage and to permit safe entry and exit.
The area between the roadway and the highway right of way is referred to as the roadside or border. The term "roadside" generally applies to freeways and the term "border" applies to land service highways. The distance between the outside edge of roadway and the hinge point may be less than the width of the roadside or border area.
The right-of-way width on rural and urban freeways is typically 300 feet and 150 feet respectively. Depending upon the median, traveled way and shoulder widths, the roadside width is in the range of 70 feet for rural freeways and 25 feet for urban freeways.
Desirably, the width of the border should be sufficient to permit the placement of utility poles and all fixed obstructions beyond the clear zone area. Normally an additional 5 feet should be added to the clear zone distance to provide the necessary placement of the utilities within the highway right-of-way yet beyond the clear zone recovery area. The acquisition of additional right-of-way should be considered if it is economically and socially feasible. If right-of-way is acquired, it should accommodate all current project needs and any foreseeable future widening.
See Section 8 for the required clear zone distance for various design speeds.
When it is not practical to provide for the clear zone width, a border width on land service highways of 15 feet is preferred. The designer should determine the practical border width by taking into account pedestrian needs, bicyclist needs and the proper placement of roadside appurtenances such as longitudinal barriers, longitudinal barrier end treatments, utility poles, signal pole foundations, signs and foundations, existing and/or future sidewalks, underground utilities, etc. A border width would typically range from 10 feet to 15 feet on land service highways. The border can be adjusted more or less on a property by property basis. In order to avoid obstacles and preclude unnecessary right-of-way acquisitions, the border width may be reduced at spot locations or random length sections. For example, you may want to reduce the 15 feet proposed border on one property to a 12 feet border in order to avoid a parking lot or a building. These reduced border areas will need to provide for safe and feasible accommodations of all roadside appurtenances.
The goal should be to provide the optimum border width considering all project costs, such as construction, utilities, permits, design, right-of-way, etc.
For freeways, interstates and expressways continuous fencing should be included in order to effectively preserve access control. Chain link fence as per the Standard Construction Details and Standard Specifications should be used. If another type of fence is required, it should be the most cost-effective type suited to the specific adjacent land use. Fencing should be located on either the right-of-way or access-control line, unless it has been established that such fencing is not necessary in order to effectively preserve access control. Engineering judgment should dictate exceptions in areas of precipitous slopes or natural barriers. However, in addition to vehicular access control, pedestrian or animal movements should also be considered. For additional fence design criteria, refer to Subsection 5.9.3, Median Fencing on Land Service Highways, Subsection 10.8.9, Fence Positioning at Culverts and Head Walls and Subsection 10.11.4E, Stormwater Management Facility Design Features (basin fencing policy).
The type and location of curbing appreciably affects driver behavior, which affects the safety and utility of a highway. Curbing may be used to separate pedestrian walkways from the roadway, to control drainage and to control ingress and egress from roadside development. Where required, curbing may be permitted at intersections for channelization or for sustaining the integrity of pavement (ex: curb at intersection radius returns). To fit the definition of “curb,” some raised aspect or vertical element is required. Curbing is not a substitute for pavement markings.
Curb is used extensively on urban land service highways. However, on rural land service highways, caution should be exercised in the use of curb. In the interest of safety, new installations of vertical curb shall not be constructed on freeways and Interstate highways; however, sloping curb may be used for drainage control.
The two general classes of curb are vertical curb and sloping curb. Each may be designed as a separate unit, or integrally with the pavement. Vertical and sloping curb may be designed with a gutter to form a combination curb and gutter section.
Sloping curb is designed to allow an errant vehicle to cross it readily without further loss of vehicular control. It is low with a flat sloping face. On a land service highway, sloping curb can be used at the median edge to discourage a vehicle from illegally crossing a grass median or to outline channelizing islands in intersection areas. Sloping curb may also be provided at the outer edge of the shoulder. It is the preferred treatment for left-turn slots. Sloping curb permits a vehicle with large off-tracking to have a less damaging effect to both vehicle and curb. However, vertical curb may be used on left-turn slots where there is existing vertical curb in the median.
Vertical curb and a safety walk may be desirable along the faces of long walls, bridges, and tunnels, particularly if full shoulders are not provided.
New installation of vertical curb shall not be constructed on freeways and Interstate highways; and are considered undesirable on other high speed arterials. When accidentally struck at high speeds, it is difficult for the operator to retain control of the vehicle. In addition, most vertical curbs are not adequate to prevent a vehicle from leaving the roadway. Where positive protection is required, such as along a long narrow median or adjacent to a bridge substructure, suitable median barrier or guide rail should be provided.
Generally, vertical curb should not be provided inside the face of bridge parapets. A preferred and more widely used method is to design the parapet in the shape of the Department’s concrete barrier curb. On an urban street, vertical curb may be used on bridges with the same curb height as the approach roadway curb. Inlets should be provided in the gutter or the curb, or both.
Generally, it is not practical to design a gutter section to contain all of the runoff, even from frequent rains, and some overflow onto the traveled surface can be expected. The spread of water on the traveled way is kept within tolerable limits by the proper spacing of inlets. Grate inlets and depressions or curb opening inlets should not be placed in the travel lane because of their adverse effect on drivers and bicycle riders who veer away from them. Warping of the gutter for curb opening inlets should be limited to the portions within 4 feet of the curb to minimize adverse driving effects. See Section 10, "Drainage Design" for the proper spacing of inlets.
Curb introduced intermittently along a street should be offset 3 feet from the edge of lane if there is no shoulder: where the curb is continuous, the offset should be at least 1 foot. See Figure 6-D for offsets of curbs for islands with and without shoulders.
For new installations of sloping curb, the overall curb height shall not exceed 4 inches.
For new installations of vertical curb, the curb height (face) shall conform to the following:
1. For posted speeds greater than 40 mph, the curb height shall not exceed a 4 inch face.
2. For posted speeds less than or equal to 40 mph, the desirable curb height is 4 inches. Where sidewalks are to be constructed, a 6 inch face may be used.
3. For traffic calming areas a 6 inch face may be used.
4. For curb on bridges with sidewalk, the desirable curb height should be 6 inches to accommodate future resurfacing and/or conduits throught the sidewalk.
When curb is used in conjunction with guide rail, see Section 8, “Guidelines for Guide Rail Design and Median Barriers,” for the placement of guide rail.
Where posted speeds are 40 mph or less and no guide rail exists, an 8 inch face vertical curb may be used to discourage parking of vehicles in the border area of the highway.
When resurfacing adjacent to curb, the curb should not be removed unless it is deteriorated or the curb face will be reduced to less than 3 inches. A curb face less than 3 inches is permissible, provided drainage calculations indicate the depth of flow in the gutter does not exceed the remaining curb reveal.
When replacing short sections of existing curb or installing short sections of new curb, the curb face should match the adjacent existing curb face. A short section of curb is approximately less than 100 feet long at each location. When there are closely spaced short sections of curb to be replaced, install the entire run of curb at the standard curb height and type as specified above.
The Americans with Disabilities Act (ADA) of 1990 is a civil rights statute that prohibits discrimination against people with disabilities. Designing and constructing pedestrian facilities in the public right-of-way that are usable by people with disabilities is an important component of highway design.
ADA accessibility provisions apply to the entire transportation project development process including planning, design, construction, and maintenance activities.
The requirements of ADA include:
• New construction must be accessible and usable by persons with disabilities.
• Alterations to existing facilities, within the scope or limits of a project, must provide usability to the extent feasible.
On new roadway construction, roadway rehabilitation, roadway reconstruction, new bridge construction, bridge replacement and bridge widening projects, sidewalk, where feasible, should be provided on both sides of land service highways and structures in urban areas. All of these projects should have some type of walking facility out of the traveled way. A shoulder will provide a safer environment for a pedestrian than walking in the live lane.
Generally, sidewalks will not be provided in rural areas. However, sidewalks shall be considered where there is evidence of heavy pedestrian usage. Sidewalks may be provided to close short gaps in existing sidewalk and where there are major pedestrian traffic generators such as churches, schools, hospitals, public transportation facilities, etc., adjacent to the highway or where there is a worn pedestrian path. A worn path is an indicator of pedestrian traffic that requires a sidewalk. Individuals tend to walk in locations where continuous sidewalk connections are provided. A lack of pedestrian activity in a location with discontinuous sidewalks is therefore not necessarily an indication of a lack of pedestrian demand. Future development should also be considered for possible major traffic generators. Sidewalk should not be constructed along undeveloped land, unless a maintenance jurisdiction agreement or a resolution of support with the municipality can be obtained.
A sidewalk may be omitted from a project where there is insufficient border width or there is no anticipated pedestrian traffic due to the land use adjacent to the roadway.
In order to ensure that sidewalk installations provide satisfactory linkages and contribute to system connectivity, all designers should take the following actions:
1. When project limits are established, continuity of pedestrian travel should be a consideration relating to the ends of the project including addressing arrival and departure curb ramps at pedestrian street crossings. For example: Where resurfacing only the northbound side of a divided highway, and the intersections(s) have sidewalk on both bounds, then curb ramps will be addressed on the entire intersection.
2. Sidewalks should extend to common destinations and logical terminal points.
Sufficient clear zone width, drainage patterns and infrastructure, grade issues, and the presence or future likelihood of bus transit stops are all key considerations of where to install sidewalks. The location of drainage ditches, buildings, retaining walls, utility poles, bus stops, vegetation, and significant roadside grade changes should be carefully coordinated with sidewalk alignment where possible to provide adequate sight distance and separation between pedestrians and vehicular traffic.
In general, sidewalks should be placed within the highway right of way. However, the exact alignment can vary throughout the section and practical considerations should be given to:
• maintaining adequate storm water runoff
• following the Americans with Disabilities Act Accessibility Guidelines (ADAAG)
• designing around roadside features that cannot or should not be removed or relocated. At times, providing for adequate pedestrian and traffic safety and/or pedestrian continuity may warrant locating sidewalks outside of the highway right of way, and within easements.
• Note: Where sidewalks are not warranted by existing or latent demand, or cannot be constructed due to right of way, utility, environmental or other considerations, roadway shoulders designed to NJDOT standards should be provided.
On a bridge project in urban and rural areas where there is no existing or proposed sidewalk at the approaches to a structure and the structure is to be replaced or widened, sidewalk may be provided on the new structure where additional width would be required to maintain traffic during future bridge deck reconstruction.
Urban and rural areas shall be those identified in the current State Highway Straight Line Diagrams.
A Complete Street is defined as means to provide safe access for all users by designing and operating a comprehensive, integrated, connected multi-model network of transportation options, such as sidewalks, bike lanes, paved shoulders, safe crossings and transit amenities. The NJDOT Policy No. 703 implemented a Complete Street policy through the planning, design, construction, maintenance and operation of new and reconstructed transportation facilities enabling safe access and mobility of pedestrians, bicyclists, and transit users, of all ages and abilities. Limited Scope projects are not required to comply with the Complete Streets policy. See Policy No. 703 for more information on how to address Complete Streets on new and reconstruction projects and what qualifies for an exemption.
Walking is a fundamental form of transportation that should be accommodated on streets and land service highways in New Jersey. The capacity of roadways to accommodate pedestrians safely and efficiently, particularly in urban and developing suburban areas, depends on the availability of sidewalks, intersection and mid-block crossing provisions, and other general characteristics such as roadway width and design speed.
When a sidewalk will be provided only along one side of the highway, the designer should include provisions to accommodate pedestrian crossing of the highway to access the sidewalk if there is a substantiated existing or future need. Such provisions should include one or more of the following: signing, painted cross walks, at grade pedestrian signals, pedestrian overpasses, etc.
Sidewalks should provide a continuous system of safe, accessible pathways for pedestrians. Sidewalks on both sides are desirable for pedestrian-compatible roadways.
The following widths apply in situations of pedestrian traffic typical in suburban, or rural areas, or traditional residential neighborhoods. In urbanized areas, especially downtowns and commercial districts, sidewalk width should be increased to accommodate higher volumes of users. Refer to the Highway Capacity Manual to calculate the desirable sidewalk width given current or projected pedestrian volumes. The designer should consider local input prior to any installation of new sidewalk.
The desirable width of a sidewalk should be 5 feet (4 feet minimum) when separated by a buffer strip. If a sidewalk width less than 5 feet is used, consideration of 5 feet by 5 feet passing areas at 200 feet intervals should be given during the planning and design of the project. The 5 foot width accommodates continuous, two-way pedestrian traffic. Where the border width is 10 feet, the width of the buffer strip should be a minimum of three feet with a 4 feet wide sidewalk. However, where the border width is 15 feet, the minimum width of the buffer strip should desirably be 5 feet with a 5 feet wide sidewalk or 6 feet with a 4 feet wide sidewalk. If the border widths are other than 10 or 15 feet, look at the conditions out in the field to determine the widths of the sidewalk and buffer strip. Where no buffer strip is provided, the desirable width of the sidewalk should be 7 feet (6 feet minimum), especially where there is no shoulder (aids in preventing truck overhangs or side view mirrors from hitting pedestrians). The sidewalk width should be clear of trees, signs, utility poles, raised junction boxes, hydrants, parking meters and other similar appurtenances. Where utility poles, sign supports, fire hydrants, etc., are provided in the sidewalk, the minimum useable width of sidewalk shall be 3 feet to allow for mobility device passage.
On rehabilitation or reconstruction projects where improvements are constrained by the existing border and right-of-way areas, the desirable sidewalk width would be implemented where feasible.
It is recognized that on rehabilitation or reconstruction projects existing roadway elements such as beam guide rail, signs, utility poles, slopes, etc. may become problematic in implementing the desirable width.
When the improvements would be considered technically infeasible or environmentally sensitive, the use of 4 feet minimum sidewalk widths would be acceptable.
Sidewalk Border Design
Where sidewalks are adjacent to swales, ditches or other vertical drop offs, there should be a minimum of two feet of clear space between the edge of the sidewalk and the top of the slope. This clear space should be graded flush with the sidewalk.
Sidewalk Buffer Design
Designers should strive for a desirable quality of service for pedestrians. The width and quality of buffer between the sidewalk and the roadway influence the pedestrian’s sense of protection from adjacent roadway traffic. Physical barriers between the sidewalk and roadway such as trees and other landscaping, parked cars, and concrete barriers and guide rail may increase pedestrian safety and comfort, and therefore encourage higher levels of walking.
The minimum width of a buffer strip is 3 feet (measured from the face of curb to the nearest edge of the sidewalk). The desirable width should be increased up to 6 feet when feasible.
Grades and Cross Slopes
The maximum sidewalk cross slope is 2%. The maximum grade is 12:1 (8.33%), however, the longitudinal grade of the sidewalk should be consistent with the grade of the adjacent roadway. If the 12:1 grade is not feasible due to topography and other physical constraints, then the grade should be developed to the extent feasible. When sidewalk grades steeper than 12:1 for a maximum distance of 30 feet are unavoidable, a level 4 foot long landing should be included if feasible (or at a distance that is practicable).
The sidewalk should have a firm, stable slip resistant surface. A concrete surface is preferred; brick or concrete pavers may be used if they are constructed to avoid settling or shifting of bricks. Hot mix asphalt sidewalks may also be used. It is important to avoid ponding on sidewalks.
The ADA Law under 28 CFR Part 35.151(e) provides general direction for the placement of curb ramps:
• Crosswalks can be marked or unmarked but where crosswalks are marked curb ramps should be wholly contained within marked pedestrian crosswalks to enable ramp use to be incorporated as part of the established pedestrian control at the intersection.
• Curb ramps are not limited to intersections and marked crosswalks but should also be considered at other appropriate points of pedestrian concentration or access such as refuge medians/islands, mid-block crossings, parking areas and other traffic separation islands.
• Adequate visibility is required to ensure safe pedestrian movement. A sight distance evaluation is recommended to ensure that curb ramps are not placed at locations where motorists cannot see the low profile of people using mobility devices. For vehicles parking at intersections see Title 39 for parking restrictions. Parking should also be eliminated at midblock crossings to provide access from the curb ramp and to increase the visibility of the pedestrian.
Sidewalks curb ramps and roadway drainage features must be designed and constructed to prevent surface drainage from ponding at the bottom of the curb ramp. Edge of road elevations at the gutter line must be graded to ensure positive drainage. For new construction, additional inlets may be required to prevent drainage issues.
Public sidewalk curb ramps shall be provided where sidewalks permit pedestrian to cross curbs such as at:
• Painted crosswalks at mid-block locations
• Crosswalks at exit or entrance ramps
• Driveways, alleys, passenger loading zones, handicapped parking stalls
• Channelized islands, divisional islands or medians served by crosswalks
• Trail crossings
Existing substandard curb ramps shall be replaced with curb ramps designed in compliance with this section. Designers are to perform field investigation and evaluation of existing curb ramps to determine whether the ramps are substandard.
All new construction, reconstruction, major rehabilitation, widening, resurfacing (open –graded surface course, hot in-place recycling, microsurfacing/thin lift overlay, structural overlays, and mill and fill), cape seals, signal installation, and pedestrian signal installation and major upgrades, and projects of similar scale and effect are subject to the ADAAG contained in this Sidewalks subsection which includes providing curb ramps. In alterations to existing facilities where full compliance with the ADAAG is technically infeasible the alteration shall comply with these standards to the maximum extent feasible. Designers shall document the basis for their determination using Form TIF-1 (ADA Technically Infeasible Form). This form shall be submitted as part of the Final Design Submission (FDS). Form TIF-1 and its instructions are available on the Department’s website in the “Engineering” section.
Technically Infeasible means, with respect to an alteration of a building or a facility, something that has little likelihood of being accomplished because existing structural conditions would require removing or altering a load-bearing member that is an essential part of the structural frame; or because other existing physical or site constraints prohibit modification or addition of elements, spaces, or features that are in full and strict compliance with the minimum requirements.
Providing accessibility to the maximum extent feasible applies to the occasional case where the nature of an existing facility makes it virtually impossible to comply fully with applicable accessibility standards through a planned alteration. In these circumstances, the alteration shall provide the maximum physical accessibility feasible. This applies to alterations to an existing facility that cannot fully meet the standards because of existing site conditions. Existing site constraints such as existing utilities, existing structures, environmental/historic impacts or other site constraints may prohibit modification or addition of elements, spaces, or facilities from being in full and strict compliance with the standards. Reasons for providing accessibility to the maximum extent feasible may include the following constraints:
• Existing utilities
• Existing buildings, walls or vaults
• Environmental impacts
• Historic impacts
• Roadway profile slope (Terrain)
For less extensive projects, limited improvements to accessibility would generally be expected. For example, if an existing portion of sidewalk along a residential block were rebuilt or replaced, at a minimum the new portion of sidewalk would be subject to ADA compliance including curb ramps, among other things. However, compliance with these guidelines would not extend to untouched sections of sidewalk outside the planned alterations.
Based on FHWA Office of Civil Rights and the US Department of Transportation General Counsel approval, there are a number of roadway preservation and preventative maintenance projects that do not require curb ramps to be constructed. These projects may involve, but are not limited to:
• Bridge deck patching
• Fender repair
• Fiber optics
• Guide rail
• Raised pavement markers
• Signing and striping in-kind
• Minor Signal Upgrades (i.e. retiming signal installation)
• Utility work that does not alter pedestrian facilities
• Seismic retrofit
• Pavement patching
• Shoulder repair
• Restoration of drainage systems
• Crack sealing
• Bridge painting
• Scour countermeasures
• Other roadway preservation and preventative maintenance projects. The following are some examples of such projects.
1. Pavement repair
2. Joint replacement or repair
3. Bridge deck restoration and component patching
4. Chip seals
5. Diamond Grinding
6. Fog Seals
7. Joint Crack Seals
8. Scrub Sealing
9. Slurry Seals
10. Spot High-Friction Treatments
11. Surface Sealing
In most cases, the unique projects mentioned previously will not modify a pedestrian route. However, the designer should consider every project as an opportunity to further the accessibility of its pedestrian network and should not unnecessarily restrict the scope of work so as to avoid the requirements for new curb ramps.
The sight distance should be checked to ensure curb ramps are not placed in such a location that a motorist will find it difficult to perceive the low profile of a mobility device occupant crossing the roadway.
Curb ramps shall be designed to accommodate all users, thus, transitions from the sidewalk to the curb ramp or to the turning space shall be gradual. Relocation of the sidewalk at an intersection is permissible, and in some cases necessary in order to obtain the required sidewalk and curb ramp slope.
Gutters & Counter Slopes
Gutters require a counter slope at the point at which a curb ramp meets the street. This counter slope shall not exceed 5%. The change in angle must be flush, without a lip, raised joint or gap. Lips or gaps between the curb ramp slope and counter slope can arrest forward motion by catching caster wheels or crutch tips.
Turning and Clear Spaces
A curb ramp with a turning space is required wherever a public sidewalk crosses a curb or other change in level. Turning spaces are required anywhere a turning maneuver is required by a user of a mobility device. Turning spaces shall provide a nearly level area (2% cross slope or less) for mobility device users to wait, maneuver into or out of a curb ramp, or to bypass the ramp altogether. A turning space of 4 feet minimum by 4 feet minimum is required. This accommodates the length and wheelbase of mobility devices (standard wheelchairs and scooters). When one curb ramp at the center of the corner radius (corner type curb ramp) is used, the bottom of the curb ramp shall have a clear space 4’ minimum outside active traffic lanes of the roadway. The clear space should be wholly within the crosswalks. See Figure 5Q for illustration.
Landings or a level cut through should also be provided at raised medians or crossing islands.
The curb ramp shall have a running slope of 12:1 maximum. It may be necessary to limit the running slope of a parallel or perpendicular curb ramp in order to avoid chasing grade indefinitely. The curb ramp length should not exceed 15 feet. Adjust the curb ramp slope as needed to provide access to the maximum extent feasible.
Curb ramp flares are graded transitions from a curb ramp to the surrounding sidewalk. Flares are not intended to be mobility device routes, and are typically steeper than the curb ramp (10:1 max) with significant cross-slopes.
Flares are only needed in locations where the ramp edge abuts pavement. A curb edge is used where the ramp edge abuts grass or other landscaping. If the curb ramp is situated in such a way that a pedestrian cannot walk across the ramp sides, flares may be replaced with a curb adjacent to the ramp. Straight returned curbs are a useful orientation cue to provide direction for visually impaired pedestrians. (See the Standard Roadway Construction Details)
Curb Ramp Types and Placement
The appropriate type of curb ramp to be used is a function of sidewalk and border width, curb height, curb radius and topography of the street corner. There are seven curb ramp types used in street corner designs as shown in the Construction Details. In all cases, the curb ramp should be located entirely within the marked crosswalks (where they exist). Drainage grates or inlets should not be located in the area at the base of the curb ramp. Grates are a problem for mobility devices, strollers and those who use walkers. Wheelchair safe grates should be used where relocation is impracticable.
Two curb ramps are required at each corner, one on each highway within the crosswalk area. If the curb ramp cannot be constructed within the existing crosswalk, the crosswalk shall be modified to include the ramp. The preferred location for a curb ramp is usually parallel to the sidewalk and out of the normal pedestrian path. Where field conditions prohibit the placement of two curb ramps, one ramp at the center of the corner radius is acceptable. Where the travel lane is next to the curb, use a curb ramp at the center of the corner radius in order to provide for a clear space, or a Type 7 curb ramp may be used where needed to ensure that the clear space remains outside the travel way. Curb ramp designs which result in wide painted cross walks greater than 10 feet should be avoided.
The Standard Roadway Construction Detail illustrates the design criteria for public sidewalk curb ramps. The designer should take into consideration the existing conditions at a curb ramp location when evaluating project impacts. These impacts may include constructability issues, quantities and cost.
At a curb ramp location where the sidewalk is greater than 6 feet in width and there is no grass buffer strip, the approach sidewalk transition shall be as shown for Curb Ramp Type 1 and 3 in the Standard Roadway Construction Details. However, where a grass buffer strip exists between the curb and the sidewalk at a curb ramp location, the flared side slope and approach sidewalk transition should be altered as shown for Type 2 and 4 in the Standard Roadway Construction Details.
The designer may want to guide pedestrians away from crossing the mainline of a high volume and/or high speed section of highway except at signalized intersections or at a pedestrian overpass. Therefore, at unsignalized intersections along such highways a curb ramp would be required on the side street corner but not on the mainline corner. In these cases, prohibition for pedestrian crossing signage needs to be provided. Curb Ramp Type 5 and 6 in the Standard Roadway Construction Details are examples of curb ramp locations for crossing the side street. The preferred treatment for Curb Ramp Type 5 and 6 is out of the normal pedestrian path, but not necessary where right of way width cannot accommodate the offset.
Where there is limited right of way (ROW) at a curb ramp location, the approach sidewalk transition should be altered and the turning space made flush with the gutter line as shown for Curb Ramp Type 7 in the Standard Roadway Construction Details. These limited ROW locations are where the distance from the gutter line to the outside edge of sidewalk is 6 feet or less.
There are also several design solutions that a designer can utilize in order to solve "Limited ROW" constraints without actually acquiring ROW. They are contained in the Special report: Accessible Public Rights-of-Way Planning and Designing for Alterations, Public Rights-of-Way Access Advisory Committee (ACCESS Board), July, 2007, which include but are not limited to:
• Use Curb Ramp Type 3, 4 or 7 where there is not enough room for the landing behind the curb ramp:
This is basically done by employing a Type 3 or 4 type curb ramp. If there still is not enough room, try using a Type 7 curb ramp. If the side street has a high curb, try lowering the curb around the intersection corner radius. For example, if the side street has existing 8 inch curb and it also continues along the corner radius, replace this high curb along the corner radius with 4 inch or less curb and then transition to the 8 inch curb on the side street. This will make your 12:1 ramps much shorter.
• Reduce street width and provide curb ramp type 3, 4 or 7:
Check design vehicle types for turning radius requirements for the particular intersection corner. If a smaller design vehicle can be used at that corner, reduce the corner radius and provide the appropriate curb ramp. By reducing the corner radius, the new gutter line will be moved further into the street creating more room to provide the sidewalk and curb ramps.
• Lower sidewalk to street surface using blended transition:
Lower the sidewalk grade at the intersection to make the sidewalk elevation flush with the gutter elevation. Then provide 12:1 ramps at the radius returns to bring sidewalk up to existing elevation. In other words, make a Curb Ramp type 7 turning space encompass the entire intersection radius.
• Corner Curb extension:
It may be used where posted speeds are 35 MPH or below, see Section 15, “Traffic Calming.”
• Elevate intersection to sidewalk level:
A vertical raised intersection may be used where posted speeds are 35 MPH or below, see Section 15, “Traffic Calming.”
Intersections may have unique characteristics that can make the proper placement of curb ramps difficult, particularly in alteration projects. However, there are some fundamental guidelines that should be followed.
• Their full width at the gutter line (exclusive of flares) must be within the crosswalk. Aligning the ramp to the crosswalk, if possible, will enable the visually impaired pedestrian to more safely navigate across the intersection and exit the roadway on the adjoining curb ramp.
• Curb ramps should avoid storm drain inlets, which can catch mobility device casters or cane tips.
• Curb ramps should be adequately drained. A puddle of water at the base of a ramp can hide pavement discontinuities. Puddles can also freeze and cause the user to slip and fall.
• Curb ramps must be situated so that they are adequately separated from parking lanes.
Curb Ramps at Intersections
The clear width of a curb ramp should be a minimum of 4 feet, excluding flares.
The following criteria shall apply to providing curb ramps at intersections:
1. Where all the corners of an intersection have existing or proposed sidewalk, curb ramps shall be provided at each corner.
2. Where all the corners of an intersection do not have existing or proposed sidewalk, the following provisions shall apply:
a. Where there is existing or proposed sidewalk at only one corner, A only, B only, C only or D only; no curb ramp is required. If the curb at the corner with sidewalk is to be constructed or reconstructed, it is optional to provide depressed curb for future curb ramps for compatibility with other corners.
b. Where there is existing or proposed sidewalk at two adjacent corners only, such as A and B, curb ramps shall be constructed at corners A and B only.
c. Where there is existing or proposed sidewalk at two diagonally opposite corners only, such as A and C, curb ramps shall be constructed at corners A and C together with a curb ramp at one of the other corners (B or D).
d. Where there is existing or proposed sidewalk at three corners, curb ramps shall be constructed at each corner where existing sidewalk is to remain or where new sidewalk is proposed.
Where a corner at an intersection is without existing or proposed sidewalk, but with curb to be constructed or replaced or with existing curb to remain as is; it is optional to provide depressed curb for future curb ramps.
Where islands exist or are proposed at intersections with curb ramps, the following provisions shall apply:
1. Where a small channelizing island (50 to 75 square feet) is encountered at an intersection, it is not necessary to provide for a curb ramp or walkway opening for the island, but crosswalks shall be adjusted to safely accommodate a person with disabilities without encroaching into the adjacent traveled way.
2. Where a channelizing island is greater than 75 square feet, provide a 4 foot. wide walkway opening level with the street in the part of the island intersected by the crosswalk. Where the walkway opening would be long or would create drainage problems, an alternate design is to place curb ramps at both sides of the island where it is intersected by the crosswalks and have a level area of at least 4 feet. between the curb ramps.
3. At intersections where a left turn island or divisional island is encountered and the island cannot be moved back so that the nose is out of the crosswalk, provide a 4 foot wide walkway opening level with the street in the part of the island intersected by the crosswalk. See the Standard Roadway Construction Details.
At a location where a curb ramp is not presently required, the curb ramp area should be kept clear of obstructions such as light standards, traffic signals, meter boxes, controller boxes, junction boxes, utility poles, inlets, fire hydrants, guide rail, signs, planters, etc. which would interfere with future curb ramp construction.
The Department’s or local public agency’s transition plan should be reviewed to determine where future curb ramps are needed. It may be economical to include those improvements with current projects instead of through separate pedestrian improvement projects.
The surface of a public sidewalk curb ramp shall be stable, firm and slip-resistant. The surface of a concrete curb ramp (excluding turning space and flared sides) shall have a detectable warning surface. Detectable warnings shall consist of raised truncated domes and shall be the color red where the adjoining public sidewalk surface is also concrete. Where the adjoining public sidewalk surface is not concrete, the surface of a public sidewalk curb ramp shall contrast visually with adjoining public sidewalk surfaces, either light-on-dark or dark-on-light. Curb ramp surfaces shall be covered with a detectable warning surface per the Standard Construction Details and Specifications. Detectable warning surfaces are also required at pedestrian railroad crossings.
The curb ramp area (curb ramp, turning space, and approach sidewalk transition) shall be kept clear of existing and proposed obstructions such as light standards, traffic signals, meter boxes, controller boxes, utility poles, inlets, fire hydrants, guide rail, signs, planters, etc. Existing obstructions should be relocated as necessary, so as to provide maximum visibility of and for the curb ramp user. The preferred treatment for existing manholes, junction boxes, and valve boxes is to locate them outside of the limits of the curb ramp. However, as an alternate treatment, these items may remain in the curb ramp area and be reset to the slope of the curb ramp. If they are within the area of the detectable warning surface, provide more detectable warning surface to compensate for the loss of area. Wherever possible, curb ramps should be located to avoid drainage low points in the gutter grade. Gratings or similar access covers shall not be located in the area at the base of the public sidewalk curb ramp.
Accessible Pedestrian Signals, Push Buttons and Curb Ramps
If pedestrian pushbuttons are provided, they should be capable of easy activation and conveniently located near each end of the crosswalk. Curb ramps with a turning space shall allow mobility device users to access existing or proposed pedestrian pushbuttons. Where pedestrian pushbuttons have been provided at intersections with no sidewalk, curb ramps with landing areas shall be provided at both ends of the crosswalk associated with the pedestrian pushbuttons (i.e., Pedestrian pushbuttons may have only been provided to cross the wide state highway and not the narrow side street). See “Section 4E.08 Pedestrian Detectors” of the current Manual on Uniform Traffic Control Devices for guidance on locating pedestrian pushbuttons at curb ramps.
Also available for use is a ADA Curb Ramp Calculator.
Driveway terminals are, in effect, low volume intersections. The number of driveways and their location has a definite effect on highway capacity, primarily on arterial highways.
Design requirements for driveways and the process under which the Department of Transportation will handle an access permit request are contained in the Department's publication, New Jersey State Highway Access Management Code and the Memorandum to All Design Units entitled "Access Control at Jughandles and Interchanges, and Driveway Reviews", October 3, 1994.
To determine the adequacy of the sight distance at driveways, see Section 6 for sight distance at intersections.
Sidewalks across driveways shall have a 2% maximum cross slope where placing new sidewalk at driveways or reconstructing driveway aprons.
In commercial areas, conventional driveways (i.e. where there is a change in grade between the street and abutting property and the driveway entrance is connected to the street via a sloped concrete apron) are preferred over access points that resemble at-grade street intersections where there is no grade change. In the design of conventional driveways, the pedestrian right of way is established more clearly and vehicles must turn more slowly into and out of the driveway. If an intersection-style driveway is used, vehicle turns can be slowed by using a small curb radius. In addition, driveway width should be made no wider than necessary. Wide driveways allow faster turns and more exposure for pedestrians. The sidewalk at driveways should remain at grade and may have the same surface material or crosswalk delineation across the driveway so motorists know they are crossing a pedestrian access route.
The intersection of driveways and sidewalks are the most common locations for severe cross slopes for sidewalk users. Sloped driveway entrances can cause mobility device users to lose directional control, veer downhill toward the street and potentially tip over. Therefore, the following solutions are recommended:
• At locations with a buffer between the sidewalk and the street, provide a level path of pedestrian travel (as an extension of the regular sidewalk) through the driveway cut, and resume the driveway slope within the buffer.
• On narrow sidewalks against the curb, achieve a similar level landing area by moving the sidewalk back away from the highway as it crosses the driveway, where possible.
• Lower the driveway crossing to the grade of the street similar to a curb ramp type 7 as per the Standard Roadway Construction Details. (Note, although this solution is preferable to a severe cross slope, it can create steep grades on both sides of the driveway and can cause drainage problems on the landing.)
Sidewalk crossings of residential driveways and most commercial driveways should not generally be provided with detectable warning surfaces, since the pedestrian right-of-way continues across most driveway aprons and the overuse of detectable warning surfaces diminishes message clarity. However, where commercial driveways are provided with traffic control devices or otherwise are permitted to operate like public streets, detectable warnings should be provided at the junction between the pedestrian route and the street.
A median is a highly desirable element on all arterials carrying four or more lanes. It separates the traveled ways for traffic in opposing directions. The median width is expressed as the dimension between the through lane edges and includes the left shoulders, if any. The principal functions of a median are to:
1. Provide the desired freedom from the interference of opposing traffic.
2. Provide a refuge area for pedestrians and bicyclists.
3. Provide a recovery area for out of control vehicles.
4. Provide a stopping area in case of emergencies.
5. Provide for speed changes and storage of left turning and U turning vehicles.
6. Minimize headlight glare.
7. Provide width for future lanes.
8. Add open green space in an urban area.
9. Serve as traffic calming devices on low speed roadways.
For maximum efficiency, a median should be highly visible both night and day and in definite contrast to the through traffic lanes. A median may vary in scope from pavement markings to an expansive grass area of varying width between two independently designed roadways. Medians may be depressed, raised, or flush with the pavement surface.
Along with their function of controlling and directing traffic movement (usually turns), and dividing traffic streams, islands serve to increase the safety and comfort of pedestrians crossing at intersections and midblock locations by providing a refuge. When channelizing islands are designed for this purpose, they are often termed “pedestrian crossing islands” or “median refuges.” See Sections 5.7 and 6.5 for design guidance.
The effective width of a median used as a pedestrian refuge and for traffic calming purposes is the width of the raised portion. In order for a median to function as a refuge, the raised portion of the median must be at least 6 feet wide. Medians should be as wide as feasible, but of a dimension in balance with other components of the cross section. The general range of median widths is from a minimum of 6 feet, to a desirable dimension of 84 feet or more on freeways and rural areas. When not utilized as a refuge or for traffic calming, medians can be as narrow as 4 feet, in which case the detectable warning surface (DWS) should be omitted.
Desirable median width without a barrier for urban land service highways should be 32 feet to accommodate future widening (a future 12 foot lane, 3 foot shoulder in each direction with a 2 foot median concrete barrier curb) and 16 feet where no future widening is anticipated. Desirable and minimum median widths without a barrier for rural land service highways should be 46 feet (to accommodate future 12 foot lane and 5 foot wide shoulder in each direction with a 12 foot grass median) and 36 feet (to accommodate a future 12 foot lane and 5 foot shoulder in each direction with a 2 foot median concrete barrier curb), respectively grass median may have sloping curb on both sides. For minimum median widths with barrier and for median widths for freeways, see the typical sections illustrated at the end of this section.
Medians 5 feet or less in width will be paved, except where the special nature of an area might warrant the higher cost and risk involved in maintaining grass. Special areas might be parks or refined areas in towns or cities where a narrow grass strip would be in harmony with the surroundings or where shrubbery is planted to reduce oncoming headlight glare.
Where practical, nose areas shall be paved back to a point where the distance is 5 feet between curblines.
In general, the median should be as wide as can be used advantageously. As far as the safety and convenience of motor vehicle operation are concerned, the farther the pavements are apart, the better. However, economic factors limit the width of median that can be provided. Construction and maintenance costs increase generally with an increase in the width of roadbed, but the additional cost may not be appreciable compared with the cost of the highway as a whole and may be justified in view of the benefits derived. A distinct advantage of wider medians on roadways, other than freeways, is to provide adequate shelter for vehicles crossing at intersections with public roads and at crossovers serving commercial and private drives. However, wide medians are a disadvantage when the intersection is signalized. The increased time for vehicles to cross the median may lead to inefficient signal operation.
If the right of way is restricted, the median should not be widened beyond a desirable minimum at the expense of narrowed roadside areas. A reasonable roadside width is required to adequately serve as a buffer between the private development along the road and the traveled way, particularly where zoning is limited or nonexistent. Space must be provided in the roadside areas for sidewalks, highway signs, utility lines, drainage channels and structures, and for proper slopes and any retained native growth. Narrowing these areas may tend to develop hazards and hindrances similar to those that the median is designed to avoid.
Raised medians have application on arterial streets where it is desirable to regulate left turn movements. They are also frequently used where the median is to be planted, particularly where the width is relatively narrow. It must be pointed out, however, that planting in narrow medians creates hazardous conditions for maintenance operations.
Flush medians are used to some extent on all types of urban arterials. When used on freeways, a median barrier may be required. The median should be slightly crowned or depressed for drainage.
Additional discussion on median openings and intersections including emergency median openings on land service highways and freeways is discussed in Section 6, “At-Grade Intersections.”
This section pertains to the installation of fence on top of median barrier curb or in grass medians along our State land service highways. The purpose of the fence is to prohibit the unlawful and potentially dangerous crossing of the highway by pedestrians where barrier curb or a grass median exists. It is the Department's policy to provide median fencing on a case by case basis only.
Fencing in the median may be considered when there is a known pedestrian/vehicle crash history, or the Department has been requested by the local municipality to eliminate an illegal pedestrian crossing of the median. Upon notification of such a problem or when requested by the local municipality; the local municipality (township engineer, police, etc.) should be contacted for their input, accident reports should be requested and analyzed and a field review of the site should be conducted in order to determine the exact location and reason for the illegal pedestrian crossings. An example of a reason for an illegal pedestrian crossing may be that pedestrians at a bus stop are crossing the highway to get to and from their vehicles parked on the opposite side of the highway.
If the pedestrian crossing is an isolated incident, fencing or other countermeasures are not warranted. If the pedestrian crossing is an ongoing patterned problem, evaluate the following safety countermeasures for use before installing fence in the median. They can be used by themselves or in combination with each other:
• Relocate the midblock bus stop and/or crossing closer to the signalized intersection.
• Provide mid-block crossing location(s) as per Section 14-12.1
• Coordinate the adjacent pedestrian network with safe crossing locations. For example, a pathway may be re-oriented so that it leads directly to an intersection, overpass or midblock crosswalk. The site may be graded to naturally direct pedestrians.
• Contact the local police department and request that they step up policing of jaywalkers.
• Encourage safe use of crosswalks at signalized intersections by providing clearly defined crosswalks, pedestrian actuated signals and signs. Provide proper traffic signal signs for the instruction of pedestrians and drivers, see "Section 2B 37" of the current Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Provide pedestrian crossing signs to selectively aid in limiting pedestrian crossing to safe places. For proper placement of these signs, see "Section 2B 36" of the MUTCD.
• Provide a pedestrian overpass if intersection/ interchange spacing exceeds one mile and if a user benefit cost analysis warrants an overpass. A pedestrian overpass is very effective when accompanied by median fencing.
• Provide roadway lighting.
Only after the previous countermeasures are evaluated and implemented should the engineer consider providing fencing in medians. That is, fencing should be used as a last resort. Fencing in medians should stop approximately 90 percent of the pedestrian crossings; however, it has its drawbacks. If the decision is made to install median fencing, the following issues should be recognized:
• Difficulty in maintaining fence on median barrier curb.
• Potential to reduce horizontal sight distance when installed on median barrier curb.
• Litter can be a problem along fence located in grass medians adjacent to high litter generators such as shopping malls.
Median fencing should be installed in well-lighted areas so that pedestrians can see the fence prior to attempting to cross the highway at night. Where existing roadway lighting is inadequate, provide additional roadway lighting in accordance with “Section 11, Roadway Lighting Systems.”
Adequate sight distance at intersections and emergency U turns should be provided when designing limits of fencing. Therefore, fencing on barrier curb shall stop a minimum of 300 feet from the median barrier curb terminal, and fencing in grass medians shall terminate a minimum of 200 feet from the end of the grassed island. Fencing shall not be installed in medians where there is substandard horizontal stopping sight distance.
When installed on median barrier curb, chain link fabric shall be 4 feet high, with 3 inches diamond mesh.
When installed in grass medians, the chain link fabric shall be 6 feet high, with 3 inches diamond mesh. All chain link fence posts within the clear zone shall be made breakaway (i.e., breakaway coupling).
Typical sections should be developed to provide safe and aesthetically pleasing highway sections within reasonable economic limitations.
The typical sections shown in the plans should represent conditions that are "typical" or representative of the project. It is not necessary to show a separate typical section to delineate relatively minor variations from the basic typical. The most common or predominant typical section on the project should be shown first in the plan sheets followed by sections of lesser significance.
Figures 5 B through 5 J inclusive illustrate the various control dimensions for single lane and multi lane highways.
Figures 5-B, 5-B1, 5-B2, 5-C, 5-D, 5-E, 5-F, 5-G, 5-H, 5-I and 5-J all illustrate the various control dimensions for single lane and multi-lane highways.
Designers should make every effort during the early design phase to eliminate or minimize certain features on bridge decks such as, horizontal curves, vertical curves, variable horizontal widths and cross slopes. Locating these features off the structure simplifies construction, is more economical and reduces future maintenance requirements.
For further information, the designer should review Section 5.2., Geometrics on Design Manual Bridges and Structures.
It is desirable that the clear width on the bridge be as wide as the approach pavement plus shoulders.
On underpasses, the desirable treatment is to maintain the entire roadway section including median, pavements, shoulders and clear roadside areas through the structure without change.
Minimum lateral clearances are illustrated in Figures 5-K through 5-P inclusive.
On divided highways where the median width is less than 30 feet consideration should be given to eliminating the parapets and decking the area between the structures.
Vertical clearances for bridges and structures shall be in accordance with Section 3.2, Vehicular Bridge Structures, of the Design Manual Bridges and Structures.
Bridges and Structures Design should be notified of all changes in bridge clearances.
Minimum lateral clearances are illustrated in Figures 5-K, 5-L, 5-M, 5-N, 5-O and 5-P.
One method of making roadways safer is by constructing longitudinal rumble strips. The audible warning and vibration made when vehicle tires pass over rumble strips alert motorists that their vehicles have drifted out of their intended travel lane adjacent to a shoulder or the centerline, and that the driver needs to take corrective action to possibly avoid an accident. Rumble strips are constructed on the shoulders of divided highways and freeways; and on undivided roadways, rumble strips are constructed on the centerline and/or the outside shoulder of the pavement. Rumble strips shall not be constructed on bridge decks or on bridge approaches, but may be constructed on HMA overlays over bridge approaches. Do not construct rumble strips on concrete pavement. See the Standard Roadway Construction Details for rumble strip layouts and dimensions.
Along the mainline on all Interstate highways, freeways, and other limited access highways, shoulder rumble strips shall be constructed on inside shoulders that are 3 feet or greater in width and outside shoulders that are 6 feet or greater in width.
Along the mainline of land service highways, shoulder rumble strips shall be constructed on inside shoulders that are 3 feet or greater in width and outside shoulders that are 6 feet or greater in width at locations where:
• Crash data indicates an overrepresentation of roadway departure crashes as compared to the statewide average for the most recent 3 year period.
• The shoulder approaching a bridge overpass or underpass is reduced or eliminated. (In this instance, the rumble strips shall be provided a minimum of 500 feet in advance of the bridge.)
The use of shoulder rumble strips may still prove to be beneficial along the mainline of land service highways where these warrants are not met. For example, when roadside or median obstructions exist that cannot be eliminated or mitigated (Refer to Section 8). These cases must be evaluated on an individual basis, and engineering judgment shall be employed in the solution.
Shoulder rumble strips shall not be constructed 100 feet in advance of and beyond all street intersections and commercial driveways. The minimum length of rumble strip measured longitudinally along the shoulder shall be 100 feet.
In order to maintain the integrity of the hot mix asphalt (HMA) pavements, the pavement box under the rumble strips must have a minimum thickness of four inches of hot mix asphalt material.
Centerline rumble strips shall be constructed at the yellow centerline stripe location in rural and urban areas on two-lane roads and multilane undivided highways. Roadway characteristics that warrant centerline rumble strips are:
• Roads with posted speed limits of 35 mph or higher
• Minimum lane width of 10 feet
• HMA pavement must be in good condition with a surface distress index (SDI) greater than 3. Consult with the Pavement Management Unit.
Centerline rumble strips should be specified regardless of the presence of passing zones.
Centerline rumble strips shall be constructed to the end of the centerline stripe at all street intersections.
Centerline rumble strips shall not be constructed along left turn slots and continuous two-way left-turn median lanes.
The minimum length of rumble strips measured longitudinally along the centerline shall be 100 feet.
Fog seal surface treatment shall be applied after construction of the centerline rumble strips. Wait for fog seal treatment to cure based on manufacturers recommendation before application of permanent traffic stripes.