Chapter 4B. Traffic Control Signals—General
Section 4B.01 General
A traffic control signal (traffic signal) shall be defined as any
highway traffic signal by which traffic is alternately directed
to stop and permitted to proceed.
Traffic shall be defined as pedestrians, bicyclists,
ridden or herded animals, vehicles, streetcars, and other conveyances
either singularly or together while using any highway for purposes
Words such as pedestrians and bicyclists are used redundantly in
selected sections of Part 4 to encourage sensitivity to these elements
Standards for traffic control signals are important
because traffic control signals need to attract the attention of
a variety of road users, including those who are older, those with
impaired vision, as well as those who are fatigued or distracted,
or who are not expecting to encounter a signal at a particular location.
Section 4B.02 Basis
of Installation or Removal of Traffic Control Signals
The selection and use of traffic control signals should be
based on an engineering study of roadway, traffic, and other conditions.
A careful analysis of traffic operations, pedestrian and bicyclist
needs, and other factors at a large number of signalized and unsignalized
locations, coupled with engineering judgment, has provided a series
of signal warrants, described in Chapter 4C,
that define the minimum conditions under which installing traffic
control signals might be justified.
Engineering judgment should be applied in the review of operating
traffic control signals to determine whether the type of installation
and the timing program meet the current requirements of all forms
If changes in traffic patterns eliminate the need
for a traffic control signal, consideration should be given to removing
it and replacing it with appropriate alternative traffic control
devices, if any are needed.
If the engineering study indicates that the traffic control signal
is no longer justified, removal may be accomplished using the following
- Determine the appropriate traffic control to be used after removal
of the signal.
- Remove any sight-distance restrictions as necessary.
- Inform the public of the removal study, for example by installing
an informational sign (or signs) with the legend TRAFFIC SIGNAL
UNDER STUDY FOR REMOVAL at the signalized location in a position
where it is visible to all road users.
- Flash or cover the signal heads for a minimum of 90 days, and
install the appropriate stop control or other traffic control
- Remove the signal if the engineering data collected during the
removal study period confirms that the signal is no longer needed.
Instead of total removal of the traffic control signal, the poles
and cables may remain in place after removal of the signal heads
for continued analysis.
Section 4B.03 Advantages
and Disadvantages of Traffic Control Signals
When properly used, traffic control signals are valuable devices
for the control of vehicular and pedestrian traffic. They assign
the right-of-way to the various traffic movements and thereby profoundly
influence traffic flow.
Traffic control signals that are properly designed,
located, operated, and maintained will have one or more of the following
- They provide for the orderly movement of traffic.
- They increase the traffic-handling capacity of the intersection
- Proper physical layouts and control measures are used,
- The signal operational parameters are reviewed and updated
(if needed) on a regular basis (as engineering judgment
determines that significant traffic flow and/or land use
changes have occurred) to maximize the ability of the traffic
control signal to satisfy current traffic demands.
- They reduce the frequency and severity of certain types of crashes,
especially right-angle collisions.
- They are coordinated to provide for continuous or nearly continuous
movement of traffic at a definite speed along a given route under
- They are used to interrupt heavy traffic at intervals to permit
other traffic, vehicular or pedestrian, to cross.
Traffic control signals are often considered a
panacea for all traffic problems at intersections. This belief has
led to traffic control signals being installed at many locations
where they are not needed, adversely affecting the safety and efficiency
of vehicular, bicycle, and pedestrian traffic.
Traffic control signals, even when justified by
traffic and roadway conditions, can be ill-designed, ineffectively
placed, improperly operated, or poorly maintained. Improper or unjustified
traffic control signals can result in one or more of the following
- Excessive delay;
- Excessive disobedience of the signal indications;
- Increased use of less adequate routes as road users attempt
to avoid the traffic control signals; and
- Significant increases in the frequency of collisions (especially
Section 4B.04 Alternatives
to Traffic Control Signals
Since vehicular delay and the frequency of some types of crashes
are sometimes greater under traffic signal control than under STOP
sign control, consideration should be given to providing alternatives
to traffic control signals even if one or more of the signal warrants
has been satisfied.
These alternatives may include, but are not limited to, the following:
- Installing signs along the major street to warn road users approaching
- Relocating the stop line(s) and making other changes to improve
the sight distance at the intersection;
- Installing measures designed to reduce speeds on the approaches;
- Installing a flashing beacon at the intersection to supplement
STOP sign control;
- Installing flashing beacons on warning signs in advance of a
STOP sign controlled intersection on major- and/or minor-street
- Adding one or more lanes on a minor-street approach to reduce
the number of vehicles per lane on the approach;
- Revising the geometrics at the intersection to channelize vehicular
movements and reduce the time required for a vehicle to complete
a movement, which could also assist pedestrians;
- Installing roadway lighting if a disproportionate number of
crashes occur at night;
- Restricting one or more turning movements, perhaps on a time-of-day
basis, if alternate routes are available;
- If the warrant is satisfied, installing multiway STOP sign control;
- Installing a roundabout intersection; and
- Employing other alternatives, depending on conditions at the
Section 4B.05 Adequate
The delays inherent in the alternating assignment of right-of-way
at intersections controlled by traffic control signals can frequently
be reduced by widening the major roadway, the minor roadway, or
both roadways. Widening the minor roadway often benefits the operations
on the major roadway, because it reduces the green time that must
be assigned to minor-roadway traffic. In urban areas, the effect
of widening can be achieved by eliminating parking on intersection
approaches. It is desirable to have at least two lanes for moving
traffic on each approach to a signalized location. Additional width
on the departure side of the intersection, as well as on the approach
side, will sometimes be needed to clear traffic through the intersection
Adequate roadway capacity should be provided at a signalized location.
Before an intersection is widened, the additional green time pedestrians
need to cross the widened roadways should be considered to determine
if it will exceed the green time saved through improved vehicular
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