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Stop Signs and Traffic Signals

Related Pages: Public Works & Parks » Engineering » Parking & Traffic

Stop signs and traffic signals are placed at strategic locations to provide safe and efficient movement of the travelling public, including pedestrians. The placement of stop signs and traffic signals are governed by a Federal Government publication: The Manual on Uniform Traffic Control Devices (MUTCD). Worcester follows the Commonwealth of Massachusetts in complying with the MUTCD.

The following are frequently asked questions and the DPW&P response.

Q:
Why can't we have stop signs to reduce speeding along my street?
 A:

One of the most frequent complaints that people have in residential areas is that vehicles constantly speed by the front of their house. They are concerned about the safety of their children. These residents frequently request the erection of additional stop signs. The addition of a stop sign, however, usually does not solve the problem.

A stop sign is an inconvenience to motorists. Because of this, stop signs should only be placed if they meet a Manual on Uniform Traffic Control Devices (MUTCD) warrant. Stop signs are frequently violated if unwarranted. In certain cases, the use of less restrictive measure or no control at all will accommodate traffic demands safely and effectively.

Warrants for a Stop Sign:
Because a stop sign is an inconvenience to through traffic, it should be used only where needed. A stop sign may be warranted at an intersection where one or more of the following conditions exist:

  • intersection of a less important road with a main road where application of the regular right-of-way rule is hazardous;
  • street entering a through highway or street;
  • unsignalized intersection in a signalized area;
  • other intersections where a combination of high speed*, restricted view and serious accident record indicates a need for control by the stop sign.

Existing sign installations should be reviewed to determine whether the use of a less restrictive control or no control at all could accommodate the existing and projected traffic flow safely and more effectively.

*Speed, in this warrant is directly related to sight distance and its relationship to vehicles/drivers approaching an intersection.

Q:
Can stop signs control speed?
 A:

Many studies have shown that stop signs are not an effective measure for controlling or reducing midblock speeds. In fact, the overuse of stop signs may cause drivers to carelessly stop at the stop signs that are installed. In stop sign observance studies approximately half of all motorists came to a rolling stop and 25 percent did not stop at all. Stop signs can give pedestrians a false sense of safety if it is assumed that all vehicles will come to a complete stop at the proper location. Engineering studies also show that placing stop signs along a street may actually increase the peak speed of vehicles, because motorists tend to increase their speed between stop signs to regain the time spent at the stop signs.

Q:
What is the harm in placing stop signs in our neighborhood to reduce speed?
 A:

Installing stop signs can do more harm than good. Too many stop signs may also actually discourage good driving habits. Studies have shown that if stop signs are overused or are located where they don't seem to be necessary, some drivers become careless about stopping at them. This can be especially dangerous for pedestrians and bicyclists who may have a false sense of safety from the existence of a stop sign.

Additionally, unwarranted stop sign locations can increase the number of motor vehicle accidents. Studies have shown that stop signs placed where drivers do not expect them can increase the number of 'rear-end' accidents because the average driver does not expect, or anticipate, the need to stop.

Q:
Why can't we have a four-way stop to reduce accidents?
 A:

Four-way stop signs are not always the answer to reducing intersection crashes. Crash analysis is very complicated and usually identifies multiple causes. Stop signs delay drivers, and many times the drivers become impatient. Impatient drivers may cause crashes. Not all four-way stop intersections are dangerous, but they must be warranted.

Q:
What is required for the installation of four-way stop control?
 A:

The addition of four-way stop control is an inconvenience to all the drivers using the intersection. For this reason, three warrants have been developed and are listed in the Manual on Uniform Traffic Control Devices (MUTCD). A multiway stop control installation may be warranted at an intersection if any of the following conditions exist:

  1. Traffic signals are warranted and urgently needed, and the multiway stop signs are an interim measure that can be installed quickly to control traffic while arrangements are being made for the signal installation.
  2. A crash problem, as indicated by five or more reported accidents of a type susceptible to correction by a multiway stop installation in a 12-month period. Such accidents include right- and left-turn collisions as well as right-angle collisions.
  3. Minimum traffic volumes. (a) The total vehicular volume entering the intersection from all approaches must average at least 500 vehicles per hour for any eight hours of an average day; and (b) the combined vehicular and pedestrian volume from the minor street or highway must average at least 200 units per hour for the same eight hours, with an average delay to minor street vehicular traffic of at least 30 seconds per vehicle during the maximum hour; but (c) when the 85-percentile approach speed of the major street traffic exceeds 40 miles per hour, the minimum vehicular volume warrant is 70 percent of the above requirements.

A four-way stop installation should only be used when traffic volumes on the intersecting roadways are approximately equal. However, if volumes are particularly large a traffic signal may be more appropriate. Investigating the warrants listed above will require an extensive traffic engineering study. This study may indicate whether or not a multiway stop control installation is appropriate.

Q:
Won't crashes be reduced if a stop sign is installed?
 A:

One of the multiway stop control warrants is crash related. If an intersection meets this requirement and it has approximately equal approach volumes, a multiway stop control installation may be warranted for safety purposes. However, the overall results of the traffic engineering study and the professional judgment of the engineer should also be considered. In fact, research has shown that under certain conditions other traffic control measures may be more effective and safer than the addition of a multiway stop sign. A study conducted by the City of Irvine, California, indicated that simply improving intersection visibility can sometimes be a successful approach to crash reduction at intersections.

Q:
Can we get a traffic signal at our intersection?
 A:

Justification of signal installation requires considerable data collection and analysis.

The MUTCD lists 11 warrants for the placement of traffic signals. These warrants are summarized below (please refer to the MUTCD for the engineering details). If none of these warrants are met, a traffic signal should not be placed. In addition, the fulfillment of a warrant or warrants also does not in itself justify the installation of a signal.

  1. Minimum vehicular volume. The volume of intersecting traffic must be above a certain value.
  2. Interruption of continuous traffic. The traffic volume on a major street is so significant that the traffic on the minor street cannot safely merge, enter or cross the major street.
  3. Minimum pedestrian volume. The volume of pedestrians crossing a major street exceeds a certain value.
  4. School crossing. At an established school crossing, a signal can be placed if it is shown that there are not enough gaps in the traffic for the children to safely cross.
  5. Progressive movement. To maintain the proper grouping of vehicles and to effectively regulate the group speed.
  6. Accident experience. When less restrictive remedies and enforcement has failed to decrease the accident rate below levels expected with signalization.
  7. Systems warrant. A common intersection that serves a principle network for through traffic flow.
  8. Combination of warrants. If warrants 1 and 2 are each satisfied by 80 percent of the stated values, a signal placement could be justified.
  9. Four-hour vehicular volume. The traffic volumes on the major and minor streets exceed a certain value for each of any four hours on an average day.
  10. Peak hour delay. The minor street traffic suffers major delay in entering or crossing the major street for only one hour of an average weekday.
  11. Peak hour vehicular volume. The traffic volumes on the major and minor streets exceed a certain value for only one hour of the day.

Installing a traffic signal at a low-volume intersection can significantly increase crashes and delays.

Again, the increase in delay and stops then translates into higher fuel consumption, increased travel times and higher point source pollution. The length of delay is directly related to a number of factors. Cycle length is one factor, for example, that is influenced by traffic volumes and the need to safely accommodate pedestrians. The pedestrian crossing time constraints could significantly increase the necessary cycle lengths.

Although traffic signals can reduce the total number of collisions at an intersection, research has shown that certain types of crashes (e.g., rear-end collisions) may actually increase after a signal is installed. For this reason, the type and number of crashes at an intersection should be considered before the installation of a signal.

Traffic signals can represent a positive public investment when justified, but they are costly. A modern signal can cost $150,000 to $200,000 to install. In addition, there is the cost of the electrical power consumed in operating a signalized intersection 24 hours a day and general maintenance.

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