902.2 Traffic Control Signals (MUTCD Chapter 4B)
- 1 902.2.1 General (MUTCD Section 4B.01)
- 2 902.2.2 Basis of Installation or Removal of Traffic Control Signals (MUTCD Section 4B.02)
- 3 902.2.3 Advantages and Disadvantages of Traffic Control Signals (MUTCD Section 4B.03)
- 4 902.2.4 Alternatives to Traffic Control Signals (MUTCD Section 4B.04)
- 5 902.2.5 Adequate Roadway Capacity (MUTCD Section 4B.05)
902.2.1 General (MUTCD Section 4B.01)
Support. Words such as pedestrians and bicyclists are used redundantly in EPG 902 to encourage sensitivity to these elements of “traffic.”
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.
902.2.2 Basis of Installation or Removal of Traffic Control Signals (MUTCD Section 4B.02)
Guidance. The selection and use of traffic control signals should be based on an engineering study of roadway, traffic and other conditions.
Support. MoDOT’s general policy is to own, operate and maintain all traffic signals and flashers installed or constructed on the state highway system.
When the installation of a traffic signal is warranted, the cost of the signal (excluding emergency and school signals), installation and maintenance, and electrical power for operation, unless otherwise stated, will be borne by the Commission. Where possible, MoDOT takes advantage of any reduced power rates by including in the municipal and/or county agreement a phrase the city will pay for the power, with reimbursement to be made by the state. Where city/county power is not available, MoDOT pays for the power directly.
The need for signalizing an intersection will normally be recognized and initiated at the district level. 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 EPG 902.3, that define the minimum conditions under which installing traffic control signals might be justified.
Meeting the warrant requirements of the MUTCD alone is not necessarily a sufficient reason to install traffic signals. Since the installation of traffic control signals will operate either to the advantage or disadvantage of vehicles and persons controlled, the selection and use of traffic control devices is to be preceded by a thorough engineering study of the roadway and traffic conditions.
Guidance. There are locations where, due to changes in the traffic conditions, the need for a traffic signal is no longer present. Several obvious locations would be where a school or commercial development has a signal at an entrance and the facility has closed or relocated. It is also possible traffic signals at intersections of public streets can no longer be justified due to changes in traffic patterns, such as new roadway construction or changes in the neighborhood. In any case, it can be a very difficult decision to remove an existing signal.
If the removal of an existing traffic signal is to be successful, misperceptions by the general public are among the greatest hurdles to overcome. While these can be very high hurdles, they are possible to clear if the proper engineering considerations are made and supported.
There are four major considerations that need to be reviewed before the removal of an existing signal: warrants, crash experience, sight distance and pedestrians.
A. Warrants. If traffic volumes are so that the highest activity day is only 50 percent of the required volumes to meet any of the MUTCD warrants, then removal can be considered. For example, Warrant 1 requires 150 side street vehicles per hour for any eight hours of an average day to be considered warranted. If there are 75 or fewer this would not be considered a warranted hour. If none of the hours of a normal day meet this level, then the signal could be a candidate for removal. Care must be taken when evaluating the main-line volumes because if they are at or are significantly higher than the warrant requirements, removal could be more difficult.
B. Crash Experience. Crash experience, both historical and expected, can be a very tough issue when considering a signal for removal. A thorough review of the crash history at the intersection is to be done to determine what has been occurring at the intersection. Historically, the removal of an unwarranted signal can cause a 90 percent decrease in rear-end type collisions, a 30 percent increase in right angle crashes, 10 percent increase in left turn crashes, and 10 percent increase in pedestrian crashes.
The nature of the crashes that could be expected after the removal of the signal is influenced by the type of control that will replace the signal. If a multi-way stop is used then, in general, an increase in crashes would not be expected. If, however, a two-way stop control is planned then the percentage changes described above can be expected.
Regardless of the traffic control that is planned after the signal is removed, a detailed before/after review is to be documented.
C. Sight Distance. The sight distance available to the side street, particularly if two-way stop control is proposed, is very important to the removal decision. If the sight distance available for the side street is less than the stopping sight distance for the mainline approach speed, signal removal should not be considered without providing for the recommended sight distance.
D. Pedestrians. Consideration for pedestrians using the existing signal must be made using appropriate warrants. If a signal is removed, alternate pedestrian accommodations should be considered.
E. Other Considerations. If the four above considerations indicate removal of the signal is favorable, other considerations should be reviewed when appropriate.
- Cost Savings. The removal of an unwarranted signal can result in cost savings to the public, that includes: reduced delays, reduced energy and fuel consumption and reduced emissions. Quantifying the annual savings to the public might help with the removal of the signal.
Standard. After all of the above considerations have been evaluated and if the decision is made to proceed with the removal, the following steps shall be taken:
- 1. Central Office Traffic shall be advised and documentation of the above noted evaluations provided to support the decision.
- 2. Public notice of the intention to remove shall be made. This can consist of news releases, public hearings and presentations at city council meetings or canvassing parties affected by the removal. This is a very important step and the district must be prepared to answer any questions that might arise.
- 3. Establish a date for the signal to be turned off and notify Central Office Traffic.
- 4. Flash the signal heads for a minimum of 30 days. After the flash period, cover the signal heads for no less than 60 days. The type of flash used shall compliment the type of traffic control selected for the intersection, yellow/red for two-way stops and red/red for four-way stops.
- 5. After the 90 day transition period has been successfully completed, the physical removal of the signals can be initiated. A comprehensive removal shall be completed with all concrete foundations and bases removed to at least flush with the ground. Consideration shall be given to filling or securing any pull boxes.
Guidance. When a temporary traffic control signal is removed the appropriate traffic control to be used after removal of the signal is to be determined and any sight distance restrictions removed.
902.2.3 Advantages and Disadvantages of Traffic Control Signals (MUTCD Section 4B.03)
Support. 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 advantages:
A. They provide for the orderly movement of traffic.
B. They increase the traffic-handling capacity of the intersection if:
- 1. Proper physical layouts and control measures are used, and
- 2. 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.
C. They reduce the frequency and severity of certain types of crashes, especially right-angle collisions.
D. They are coordinated to provide for continuous or nearly continuous movement of traffic at a definite speed along a given route under favorable conditions.
E. 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 disadvantages:
A. Excessive delay,
B. Excessive disobedience of the signal indications,
C. Increased use of less adequate routes as road users attempt to avoid the traffic control signals, and
D. Significant increases in the frequency of collisions (especially rear-end collisions).
902.2.4 Alternatives to Traffic Control Signals (MUTCD Section 4B.04)
Guidance. 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.
Option. These alternatives may include, but are not limited to, the following:
A. Installing signs along the major street to warn road users approaching the intersection;
B. Relocating the stop line(s) and making other changes to improve the sight distance at the intersection;
C. Installing measures designed to reduce speeds on the approaches;
D. Installing a flashing beacon at the intersection to supplement STOP sign control;
E. Installing flashing beacons on warning signs in advance of a STOP sign controlled intersection on major- and/or minor-street approaches;
F. Adding one or more lanes on a minor-street approach to reduce the number of vehicles per lane on the approach;
G. 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;
H. Revising the geometrics at the intersection to add pedestrian median refuge islands and/or curb extensions;
I. Installing roadway lighting if a disproportionate number of crashes occur at night;
J. Restricting one or more turning movements, perhaps on a time-of-day basis, if alternate routes are available;
K. If the warrant is satisfied, installing multi-way STOP sign control;
M. Installing a roundabout; and
N. Employing other alternatives, depending on conditions at the intersection.
902.2.5 Adequate Roadway Capacity (MUTCD Section 4B.05)
Support. 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 effectively.
Guidance. 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 flow.
Other methods of increasing the roadway capacity at signalized locations that do not involve roadway widening, such as revisions to the pavement markings and the careful evaluation of proper lane-use assignments (including varying the lane use by time of day), should be considered where appropriate. Such consideration should include evaluation of any impacts that changes to pavement markings and lane assignments will have on bicycle travel.