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This section of the manual is intended for use as a guide in the planning
and design of the electrical portion of a traffic signal installation
that conforms to Department policy. It will provide a means of developing
uniformity in the design and plan preparation of traffic signals. The
term "traffic signals" can include many types of control signals:
pedestrian signals, lane-use control signals, hazard identification
beacons, school sign flashing beacons, moveable bridge signals, priority
control signals, and railroad pre-emption. However, certain general
Design Criteria can be applied to all traffic signals.
Complying with all of the design criteria is sometimes difficult. It
will require some judgment on the part of the designer to draw the necessary
balance. However, it is necessary that the criteria be followed as closely
as possible in order to achieve uniformity of traffic signal design.
It is recognized that situations will occur where good engineering judgment
dictates deviation from this Department policy. Any such deviation shall
be detailed in writing and submitted for approval to the Manager in
the Office of Traffic
Signal and Safety Engineering.
It is not the intent of this section to reproduce all the information
that is adequately covered by textbooks and other publications that
are readily available to the designer. This section, when used in conjunction
with engineering knowledge of traffic signal design and good judgment,
should enable the designer to perform their job more efficiently.
The terminology used in this section, unless stated otherwise, is as
defined in the current addition of
National
Electrical Manufacturers Association (NEMA) Standard Publication
No. TS-1, Part 1, entitled, "Traffic Control Systems".
All publications shall be the latest edition.
12.03.1 Warrants for
Traffic Signals 
All traffic signal installations must be warranted in accordance with
the
MUTCD.
The Traffic
Signal and Safety Engineering Unit is responsible for review and
approval of the traffic signal warranting analysis. The designer shall
have the Office of Traffic
Signal and Safety Engineering’s approval for the design prior to
starting the actual electrical design of the traffic signal.
12.03.2 Traffic Signal
Controller
The current Department standard is an eight phase fully actuated traffic
signal controller. The controller is a microprocessor based digital
unit with dual ring quad left or sequential operation, as specified
in the current NJDOT
Specification Nos. EB-TSC-ITB-8 and EB-TSC-8CL.
The designer shall review the timing sequence to insure that an eight
phase traffic signal controller can perform it. The controller shall
not require external timers or timing relays to perform the timing sequence.
The designer shall, in all cases, consider and utilize the overlapping
pedestrian movement or concurrent traffic movements. The timing schedule
shall be on a separate plan sheet.
The controller is the most important component of the traffic signal;
therefore, the designer must use extreme care in choosing a location
for the controller at the intersection. As a minimum, the following
criteria shall be adhered to:
- The controller shall be offset as far as possible from the traveled
roadway within the right-of-way, allowing adequate work area for maintenance.
- The controller location shall provide the maintainer the best possible
visibility of the signal indications when working on the cabinet.
- The controller location shall be the least vulnerable to vehicular
accidents and shall not restrict sidewalk areas.
12.03.3 Traffic Signal
Standards
Types, designs and certain typical installation details for traffic
signal standards and their foundations are included in the NJDOT
Standard Electrical Details.
Traffic signal standards and transformer bases shall be of aluminum
alloy to support traffic signal mast arms with a length of 25 feet or
less. When the mast arm exceeds 25 feet, the traffic signal standard
shall be steel. They shall be mounted on foundations as follows:
| Traffic Signal Standard |
Foundation |
| Type "C" |
Type "SFT" |
| Type "K" |
Type "SFK" |
| Type "S" |
Type "STF" |
| Type "T" |
Type "SFT" |
| Type "SC" |
Type "STF" |
Foundation Type "SFX" shall be installed in center barriers only and
shall be used in special cases only. The designer must justify its use
and obtain approval in writing. In conjunction with the installation,
a small transformer base, Part No. NJTB-30 as shown on NJDOT
Standard Electrical Details No. L-1501, shall be used. The Traffic
Signal Standard Type "C" shall also be used when 12" signal face(s)
of three sections or more are suspended at the end of the mast arm to
obtain the minimum roadway overhead clearance.
When 12" signal face(s) of four sections or more are suspended at the
end of the mast arm, the Traffic Signal Standard Type "T" shall not
be used. The roadway overhead clearance of the signal head shall be
examined and calculated when a traffic signal standard, particularly
Type "T", is installed at the low side of a banked section of roadway.
When a single free swinging indication is to be installed at the end
of a mast arm, an aluminum signal head shall be used.
Traffic Signal Standard Type "K" shall be used for 25 foot mast arms.
The designer is responsible for loading calculations necessary to verify
that the standard and arm will support the signal indications and signs.
When the loading of a traffic signal standard or traffic signal arm
is approaching its limit, a warning note "consult Traffic
Signal & Safety Engineering for additional load" shall be shown
near the installation on the plan.
Mast arm signs shall be free swinging in accordance with the standard
details.
Traffic signal standards shall be located as follows:
- The minimum offset shall be 32" from face of curb or edge of pavement
to center of the standard.
- Steel traffic signal standards should be located as far off the
roadway as possible. A minimum of 5 feet from the face of the curb
to the center of the steel traffic signal standard should be maintained.
- Traffic signal standards shall not be located in areas of handicap
ramps nor shall they obstruct the crosswalks.
- Traffic signal standards, where feasible, shall also be used to
support pedestrian signals and push buttons.
- Traffic signal standards shall not be located on the traffic side
of (in front of) the guide rail or any natural or manmade deflecting
barrier. The location should provide the distance necessary for rail
deflection when struck and a reachable distance for pedestrians to
push the pedestrian push button. Exceptions on a case by case basis
may be made only with approval of the Electrical Engineer in the Office
of Traffic
Signal and Safety Engineering.
- Traffic signal standards shall not be located near the curve of:
a. A corner with a radius of less than 15 feet, or;
b. A corner with a radius of less than 30 feet provided where trucks
and buses turn right occasionally, or;
c. A corner with a radius of less than 50 feet provided where large
truck combinations and buses frequently turn right.
- The designer is responsible for locating and identifying the horizontal
and vertical clearances of the utility companies primary (750 volts
or more) and secondary power lines and shall assure that the minimum
clearances are in accordance with the NEW JERSEY ADMINISTRATIVE CODE
CHAPTER 25 UTILITY ACCOMMODATION, Section 16:25-5.3 (c) and Section
10 of the NJDOT Procedures Manual. The designer shall coordinate the
electrical design work with the present and future plans of the utility
companies. All overhead and underground utilities must be shown on
the plans. There shall be no conflicts with the lighting installation.
See Figure 11-C.
12.03.4
Traffic Signal Indications
The location and type of indications shall be approved and/or determined
by the Traffic Engineer in the Office of Traffic
Signal and Safety Engineering. The Department currently maintains
the following signal indications:
| Type |
Specification No. |
| Polycarbonate 8" Signal Head |
EB-TS-1 |
| Polycarbonate 12" Signal Head |
EB-TS-1 |
| Aluminum 8" Signal Head |
EB-TS-1A |
| Aluminum 12" Signal Head |
EB-TS-1A |
| 12" Fiberoptic Bi-modal Arrows |
EB-TS-3 |
| Pedestrian Signal |
EB-PS-1 |
| Optically Programmed |
EB-TS-2 |
| 8"/12" Red LED Module |
EB-REDLED-TSM |
| 8"/12" Green LED Module |
EB-GRNLED-TSM |
| 12" BI-Modal LED Module |
EB-LED-BTAM |
| 12" GRN, AMBER,RED LED Arrows |
EB-LED-GARTAM |
12.03.5 Intersection Lighting
Intersection lighting shall be included as part of the traffic signal
design at all signalized intersections and shall conform to Section
11-08, "Lighting At Intersections". The intersection lighting shall
be installed on Traffic Signal Standards, Type "C", Type "SC", or Type
"K" with a "KE" extension.
12.03.6 Conduits
Rigid metallic conduits, 3" in diameter, shall be used throughout for
all traffic signal circuits. Conduits for loop detector cables shall
be 1-1/2" in diameter. Conduits for overhead electrical services and
telephone services shall be 2" in diameter or as required by the utility
company. Consult the utility company for any special requirements. Typical
details regarding conduit installations are included in the standard
electrical details.
Rigid nonmetallic conduits (RNMC) may be used for interconnect conduits
between intersections or for conduits to control "Red Signal Ahead"
signs. A ground wire shall be installed.
Multiple runs of conduits shall be placed in a common trench. When
they are installed in a common trench cut in an existing roadway, only
one conduit shall be classified as type CUR. All others shall be classified
as type CUG.
Conduits installed under existing concrete sidewalk or bituminous concrete
shall be classified as type CUR.
When a conduit run is installed as a combination of type CUG and type
CUR, both construction items shall be indicated on that run. The construction
quantities of each item shall be calculated.
12.03.7 Cables and Wires
All cables and wires, including neutrals, to be used for traffic signal
circuits and incoming secondary service shall conform to the SPECIFICATIONS
and shall be fully color coded. The designer shall provide a block wiring
diagram as shown on NJDOT
Sample Plans E-2 and E-3. The block wiring diagram shall indicate
the cable letter for each cable extending from the controller to the
base of the traffic signal standard. The letters shall be assigned sequentially
to cables terminating at the far corner first, then to cables terminating
at the next corner as the first group passes through (east corner then
north corner; south corner then west corner, as shown in the NJDOT
Sample Plans E-2 and E-3).
The designer shall calculate the wire fill
of all conduits to insure conformance to the
National
Electrical Code. The following cable areas shall be used:
| Cable |
Cross Sectional Area |
| 10/C #14 |
0.322 sq. in. |
| 5/C #14 |
0.166 sq. in. |
| 2/C #14 |
0.105 sq. in. |
All the Department's solid state controllers with solid state load switches
are also equipped with conflict monitors. In order for the monitor to
perform correctly, it is important that a separate neutral be provided
for each phase and overlap of the vehicular signals.
The designer shall provide sufficient wire from each traffic signal
standard to the controller; however, in order to avoid a redundancy
in the wiring system, the following traffic signal faces may be wired
in parallel in the base of an individual traffic signal standard:
- Traffic signal faces of a main street or side street on the same
phase, provided there is exclusive left turn signal phase.
- Traffic signal faces of a minor side street, provided they are on
the same phase and most likely they will not be on separate phases
or will not have an exclusive left turn phase in the future.
The signal cable shall then be brought directly to the controller.
The designer shall observe the following criteria:
- All vehicular indications shall be wired on a 10/C #14 cable. A
5/C #14 may be used when only one indication is on the pole.
- All pedestrian indications shall be wired on a 5/C #14 cable.
- All push buttons shall be individually wired on a 2/C #14 cable.
- All loop detectors shall be wired with a 2/C (twisted pair) #14
cable. Each loop detector shall have its own twisted pair of detector
lead-in wires and shall be connected separately to a channel of the
detector unit.
- Each traffic signal circuit of a load switch must be less than 10
amperes; calculations should be provided for the circuits of more
than 7 amperes.
- Lighting circuits installed as part of the traffic signal installation
shall utilize the same conduit system as the traffic signal circuits
and conform to Section
11, "Roadway Lighting Systems". The wire size shall
be #8 AWG or as required.
12.03.8 Vehicular Detection
The Department installs inductive loop detectors (ILD) as the primary
type of detection. A series of short loops shall be installed to cover
the area of detection determined by the traffic engineer. Other types
of detectors are used only in areas where the loops could not be installed,
such as a steel bridge deck.
The installation of inductive loop detectors shall conform to the following
guidelines:
- Under normal conditions a diamond shaped loop, which is approximately
6’ x 6’ in the direction of travel, shall be utilized to cover the
area of detection. The largest loop shall be no greater than 6’ x
18’.
- Loops directly behind the stop line shall always be designed as
small as possible to guarantee the detection of motorcycles stopped
directly behind the stop line. See Figure 12-B.
- The designer should first try to use a series of four short loops.
Where the area of detection cannot be covered with a four-loop layout,
additional loop(s) should then be considered as shown in Figures
12-A, 12-B,
12-C
and 12-D.
- The longitudinal spacing between two loops shall be in the range
of 5 feet to 16 feet. The spacing shall decrease gradually as a vehicle
approaching the intersection reduces its speed.
- Except in areas of parking, the side edge of a loop shall have a
lateral spacing of 3 feet from a curb or pavement edge and 3 feet
from a painted double yellow line or a white line.
- Under normal conditions the front edge of the loop immediately behind
the stop line shall be no more than 2 feet from the top of the stop
line. The maximum spacing between loops adjacent to the stop line
shall be 5 feet. A spacing of less than 5 feet for these loops may
be used to meet the requirements set forth in the next item (7.).
- The distance from the front edge of the area of detection to the
intersection shall be as shown on Figures
12-A, 12-B,
12-C
and 12-D.
In the case of a skewed intersection, the dimension shall be measured
perpendicular from the extension of the curbline to the front loop.
In no case shall any portion of the loop extend beyond the extended
curbline into the intersection area. In some cases, depending upon
the skew angle, a supplemental loop should be required to insure that
vehicles overriding the stop line will not leave the area of detection.
- When a loop is used mainly as a system loop or a dual function loop
(local intersection detection and system detection), it shall be a
6’ x 6’ rectangular shaped loop and installed in the center of the
traveling lane in which volume counts are to be taken.
- A force-off loop and motion loop shall be of rectangular shape and
installed at locations determined by the traffic engineer.
- All loops shall be identified alphabetically and in sequence as
a vehicle approaches the intersection.
The designer shall field check each intersection to select proper loop
locations. This field check shall consider driveway locations, pavement
conditions, manhole locations, width and skew of the roadway, power
sources and other electrical equipment that will interfere with proper
loop operation.
In summary, the final decision concerning the size, shape, spacing
and location of loop detectors for proper traffic control is a combination
of analytical procedures and application of good engineering judgment.
When detection is needed on bridges, the use of probes, preformed loops,
microwave, video and infrared detectors shall be investigated.
12.03.9 Junction Boxes
18" x 36" junction boxes shall be used for the traffic signal.
17" x 30" junction boxes may be used only for loop wires and loop detector
lead.
Junction boxes shall not be installed in handicap ramp areas. The placement
of junction boxes should also avoid sidewalk areas whenever possible.
In order to facilitate cable pulling and splicing, a junction box shall
be installed adjacent to traffic signal standard(s), the controller,
loop detectors and at each end of conduit crossings under roadways.
The location of conduit crossings should be so arranged that the junction
boxes at terminals of such conduits could also be used as service points
to the above noted facilities. Junction boxes are designed to accept
a maximum of six conduits. In cases where the number of conduits and
cables are in excess of the junction box capacity, except in front of
the controller where two junction boxes may be installed, the design
should be re-examined.
12.03.10 Incoming Service
The secondary service, obtainable from the local utility company's pole
or manhole, shall be used to service the complete installation at each
intersection. Standard services shall be single phase, 3-wire, 120/240-volt,
#6 AWG wire shall be installed. When service is obtained from a manhole,
the designer shall consult the utility company for the size, location,
material and termination of the service conduit, and the installation
of the service wire, which usually is provided by the utility company.
The designer shall prepare a written preliminary request for service
to the local utility company indicating the required service and obtain
their written approval including any utility company assigned request
number. Information on the continuous load and payee of the energy charge
shall also be provided in the letter.
When an existing traffic signal is affected by the construction, they
shall be revised as follows:
- Where possible, all existing equipment should be left in place while
the proposed signal is constructed. The designer shall provide a scheme
of the construction to verify that the equipment can be left in place.
A scheme shall be provided for each stage of construction, which includes
detailed temporary wiring and any safety protection, if required.
- A temporary signal shall be included in the contract whenever an
existing signal must be removed prior to the completion of the new
signal.
- If a signal is being removed as part of the design and not replaced,
the designer shall indicate the stage of construction that the signal
will be removed.
- When an existing signal is part of a "system", the ITS
Engineering Unit shall also be notified and the system aspect of the
signal shall be their responsibility.
The designer shall investigate and provide a report of a total system
design concept in each project. The Department currently utilizes several
types of traffic signal systems as follows:
- Closed Loop - continually monitoring a minimum of 30 local
intersection operations and system performance. The system is also
capable of traffic responsive operation and providing maintenance
reports.
- Time Base - Time base coordination, when installed at a group
of intersections, provides a coordinated system without the use of
interconnecting cables.
- Isolated Intersection Control - Isolated intersection control
is only utilized when coordination is not required.
- When the design of a project includes the installation or modification
of a computerized closed loop traffic signal system, the ITS Engineering
Unit shall be contacted for the proper system design criteria.
All plans shall be completed in accordance with Section 16.4 and 16.6
of the NJDOT Procedures Manual.
If during the reconstruction of the roadway, an existing traffic signal
can no longer adequately control the intersection or the stage construction
warrants a traffic signal to safely control traffic, a temporary traffic
signal shall be provided for in the plans (NJDOT
Sample Plans E-4).
The designer shall provide plans, timing, details and certified structural
calculations supporting the design and the material to be used. The
certification shall be by a Professional Engineer licensed in the State
of New Jersey. The plans shall take into consideration the construction
staging and any adjustments to the temporary traffic signal system shall
be shown.
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