MICHIGAN DEPARTMENT OF TRANSPORTATION Davison TSC Traffic Signals 101

Intersection Safety Myths The driving public has developed a number of misconceptions about traffic control solutions over the years.

Myth : Installing signals always makes intersections safer.

Reality: The installation of unwarranted signals, or signals that operate improperly, will create situations where overall intersection congestion is increased, which in turn can create aggressive driving behavior. When signal phasing causes longer waiting times, both drivers and pedestrians tend to become impatient and violate red lights, or drivers are tempted to cut through neighborhood streets. One way of improving waiting times at an intersection with a new signal is to make sure the minor street waiting times are less than they were before installation of the signal. This will encourage motorists to use signals on main roads instead of neighborhood streets.

WHY UNIFORM STANDARDS? Do you know what the color red signifies? A yellow painted line? An eight-sided traffic sign? A study of driver observance of a standard red octagonal sign with the letters “SOTP” painted on it was conducted. It was found that practically no one noticed the misspelled legend but everyone obeyed the sign. Uniformity is a critical factor relative to signalization because of the serious consequences which may result from installation of an unwarranted signal. Properly used, traffic signals reduce certain type of crashes, provide gaps in the traffic stream benefiting other access points further “downstream”. Poorly designed, ineffectively placed, or improperly operated signals perform just the opposite of what is expected of them. Intersections become clogged with cars, and motorist delay and crash potential is increased.

A set of “warrants” was established, under which signals function properly and provide the motoring public and pedestrians the most benefit. The “warrants” are used by traffic engineers nationally to evaluate the need for stop and go traffic signals.

WARRANTS – GUIDELINES FOR TRAFFIC SIGNAL INSTALLATION Signal warrants are a set of guidelines or conditions which allow careful assessment of the need for signalization. Warrant 1 – MINIMUM VEHICULAR VOLUME This warrant requires a minimum number of vehicles on both the major street and cross street for each of any eight hours during the day. Warrant 2 – INTERRUPTION OF CONTINUOUS TRAFFIC Warrant 2 provides for situations where a very high volume of major street traffic restricts entry of cross street traffic causing excessive delay. Warrant 3 – MINIMUM PEDESTRIAN VOLUME Occasionally a situation arises where very high pedestrian activity conflicts with high traffic volumes. Warrant 4 – SCHOOL CROSSING Warrant 4 provides minimum installation guidelines for traffic signals at established school crossing locations based on the number of children utilizing the crossing and the availability of adequate gaps in the traffic stream during crossing periods.

Warrant 5 – PROGRESSIVE MOVEMENT Between two widely spaced signals in a system, an intermediate traffic signal, properly located, may serve to regulate the size and speed of the traffic “platoon”. A signal maybe installed under this warrant if vehicle speeds vary and volumes are high. Warrant 6 – CRASH EXPERIENCE Certain conditions at an intersection may result in a high incidence of “right-angle” crashes. This warrant provides for a reduction in the number of vehicles required under other warrants. Warrant 7 – SYSTEMS WARRANT This allows installation of traffic signals at some intersections to encourage concentration and organization of traffic flow networks. Warrant 8 – COMBINATION OF WARRANTS Warrant 8 says when several of the preceding conditions are nearly satisfied, a signal may provide the best solution at the intersection. Warrant 9 – FOUR HOUR VOLUMES This warrant is used when volumes are very high on the major street for a minimum of four hours a day. The side street volumes can be lower than in Warrant 1.

Warrant 10 – PEAK HOUR DELAY This warrant would be applied where traffic conditions are such that for one hour of the day, the minor street traffic suffers excessive delay entering or crossing the main street. Warrant 11 – PEAK HOUR VOLUME This warrant is also intended for application where traffic conditions are such that for one hour of the day, minor street traffic suffers undue delay entering or crossing the main street. The volume requirement for this warrant is higher than for Warrant 10. These warrants have one common point; they all require certain minimum vehicular volumes.

EFFECTS OF TRAFFIC SIGNALS What, then, are the effects of traffic signals? Do they improve operation of the intersection? Are intersections safer after their installation? When located properly and operated correctly, signals offer the following advantages: 1. They can provide orderly traffic movement. 2. Where proper physical design and control measures are used, they can increase the traffic- handling capacity of the intersection. 3. They reduce the frequency of certain crash types, especially the right-angle type. 4. Under favorable conditions, they can be coordinated to provide continuous movement of traffic along a given route. 5. They can be used to interrupt heavy traffic at intervals to permit other traffic, vehicular or pedestrian, to cross.

EFFECTS OF TRAFFIC SIGNALS, cont… The following factors will result from improper or unwarranted signal installation: Excessive delay will be caused. Disobedience of signal indications is encouraged. The use of less adequate routes may be induced in an attempt to avoid the signal. Crash frequency (especially rear-end crashes) will be increased.

How a Signal Request is Evaluated TRAFFIC COUNTS This survey consists of “machine counts” (the “boxes” and rubber hoses frequently seen along state highways) taken of all vehicles entering the intersection on a typical weekday. In conjunction with the machine counts, an eight hour “turning count” is conducted during peak traffic hours in which all incoming vehicles are tabulated according to the direction they leave the intersection. CRASH RECORDS A record of all traffic crashes reported to the Michigan Department of State Police is forwarded to MDOT’s Traffic and Safety Division. The traffic engineer uses these crash reports to study the problems at the subject location and determine which crash patterns are susceptible to correction through application of various measures, including traffic signals. FIELD INVESTIGATIONS In addition, the engineer also conducts an on-site investigation to observe the intersection and its operating characteristics. Some of the points the traffic engineer looks for are type and condition of the road, schools and “school crossings”; large traffic generators, such as shopping centers; existence of parking and bus stops; and the proximity of other traffic signals.

Before and after signals crash study

Multiway Stop Applications Again, the decision to install multiway stop control should be based on an engineering study. The study will evaluate the following warrants: A. If a traffic signal is warranted, the multiway stop can be placed as an interim measure while arrangements for signal installation are being made. B. A crash problem as indicated by 5 or more reported crashes in a 12 month period that are correctable with a multiway stop installation. Such crashes include right- and left-turn collisions as well as right-angle collisions. C. Minimum volumes: Just as in signalization, volumes of vehicles and pedestrians play a large factor in multiway stop placement. Major street approaches – 300 vehicles per hour for any 8 hours Minor street approaches – 200 units per hour for the same 8 hours. These volumes are reduced when the approach speed of the major-street traffic exceeds 40mph.

CONCLUSION We hope the preceding explanation gives you a better understanding of the complexities involved in signal evaluation from first request to actual installation. The decision-making process is lengthy, though justified, since a professional traffic engineer must make decisions based on engineering studies, not snap judgments resulting from opinion. The necessary data requires time to collect. It may take four to six months to gather and analyze traffic counts and crash records. After approval, signal installation must then be engineered, estimates prepared, contractual agreements negotiated, material requisitioned, and installation crews scheduled. It is not uncommon for the process to take 12 months. Traffic signals are never denied on the basis of cost. Our primary concern is the public’s well-being.