In conceiving, scoping and designing projects, the NJDOT will consider the needs of all road users and neighbors. This includes pedestrians, bicyclists, and neighbors, such as residents, and businesses, as well as drivers. One of the key steps in accomplishing this is to carefully and systematically decide on the appropriate functional classification of the roadway, and the appropriate target operating speed (a.k.a. the posted speed limit) during Concept Development, or at least prior to the start of Scoping. Properly selected design criteria should result in motorists driving freeways like freeways, arterials like arterials, collectors like collectors, and local streets like local streets.
In deciding the appropriate functional classification and target operating speed for an existing roadway, one of the most important considerations will be the consistency of the existing geometry and surrounding context of the roadway, and how they relate to the existing operating speed and the posted speed limit. Target operating speeds cannot be determined arbitrarily, but must be consistent with conditions along the roadway and subject to reasonable enforcement. The designer may proactively alter the existing geometry and roadway environment in an attempt to decrease the operating speed and enhance the safety of pedestrians and bicyclists, or the viability of downtown or residential areas, in balance, not competition, with the safety of motorists.
Roadway design should lead the driver to adopt a driving behavior appropriate to local conditions. The designer thus should carefully consider the appropriate target speed for a roadway section based upon land use conditions, building densities, the environment and the disparate needs of users of the facility. It should be recognized that streets do not only serve transportation related functions but are also places of commercial and social encounter. Therefore, a designer should also consider the non-vehicular uses of a roadway and seek consistency between all aspects of the roadway, its environment, and the chosen Design Speed.
What does this mean? Historically, in NJDOT, the Design Speed has set the lower limit for design features. If a physical, environmental or other impediment posed an obstacle to a project, the Design Speed established the limit below which it would be difficult to compromise, in effect, the maximum safe speed. If, however, no such obstacles exist on one or more stretches of road, the design would be to optimum standards, potentially yielding an infinite Design Speed. This could lead to inconsistencies between the Design Speed, posted speed, and desirable vehicle operating speed, and result in drivers making inappropriate decisions. If this occurred in downtown or "Main Street" environments, where the intent of the designer and/or the community may have been for a slower pace of traffic, compatible with pedestrian and downtown type activity, serious pedestrian safety, quality of life, and socioeconomic issues could arise.
The NJDOT's Design Philosophy takes into account functional classification, existing or intended land use, and the context of the project, and then uses an appropriately selected Design Speed as the basis for all of the design elements. If there are no physical or environmental impediments to alter the geometry of a roadway, the designer may consider introducing design elements that reinforce and encourage the intended operating speed, which should be based on the needs of all road users. There is a wide range of options available to the designer to do so, including some that fall under the umbrella "traffic calming." These include neckdowns, rotaries, speed humps, etc.; however, these could also include narrow lanes and shoulders, curvilinear alignments, etc. These items may be controversial and have downsides; and become increasingly inappropriate when design and operating speeds increase. As such, the NJDOT generally will not consider traffic calming features along segments of roadway where the posted speed limit is above 35 mph. Therefore, the designer will need to carefully weigh whether the use of these elements creates a desirable balance between the competing interests. The idea of making sure that all elements of design compliment each other and send a consistent message to the motorist is not just a Context Sensitive Design concept that applies to Main Street, New Jersey. This concept is applicable on all roads.
In summary, NJDOT designs in the 21st Century should represent the product of reasonable people making reasonable decisions that reflect consideration of the needs of all road users, and social and environmental impacts. Highway designs must reflect a thoughtful understanding of the context of the project, in addition to adherence to standards and guidelines.
BDC announcement BDC15MR-01
(November 18, 2015) and
(April 26, 2016)
- Section 1 - Introduction
- Section 2 - General Design Criteria
- Section 3 - Definitions and Terminology
- Section 4 - Basic Geometric Design Elements
- Section 5 - Major Cross Elements
- Section 6 - At Grade Intersections
- Section 7 - Interchanges
- Section 8 - Guide Rail Design and Median Barriers
- Section 9 - Crash Cushions
- Section 10 - Drainage
- Section 11 - Highway Lighting Systems
- Section 12 - Traffic Signal Design
- Section 13 - Ground Mounted Sign Supports
- Section 14 - Traffic Control Plans and Details
- Section 15 - Traffic Calming
Roadway Design Manual