Installing stop signs or traffic signals where they are not needed can cause significant disruption of traffic flow and increase intersection delay for drivers. The delay increases travel time, annoys drivers, and the starts and stops cause increased fuel consumption and production of carbon monoxide, nitrous oxide, particulate matter, and other pollutants.
WHAT IS THE HARM IN INSTALLING A STOP SIGN?
Two-way stop signs assign the right-of-way at an intersection. The warrants for the installation two-way stop signs in the Manual for Uniform Traffic Control Devices (MUTCD) are listed below. Because a stop sign causes substantial inconvenience to motorists, it should be used only where warranted. It may be warranted where the following conditions exist:
- The intersection of a less used road with the main road where the normal right-of-way rule is hazardous;
- A street entering a through highway or street;
- An 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 with a stop sign.
The amount of delay created by the stop sign depends on both major and minor street flows. The gaps in the major flow traffic stream must be adequate to allow the stopped traffic to move through, or turn right or left through the intersection. The term "critical gap" is often used to describe the median gap accepted by drivers for specific turning maneuvers and roadway characteristics. According to the 1997 Highway Capacity Manual, typical critical gaps are 6.2 to 6.9 seconds for right turns from a minor roadway, and 7.1 to 7.5 seconds for left turns from a minor roadway. Left-turning movements take longer, and left-turning drivers must cross more traffic streams. Additional delay for minor street vehicles is also determined by the vehicle arrival rate. The arrival rate of vehicles on the minor street is related to how long drivers will wait in the queue to get to the stop line.
The delay times at stopped approaches can become excessive if either major or minor flow is high. The advantage of a two-way stop is that the major flows do not have to stop and they incur almost no delay at the intersection (i.e., the majority of the traffic does not have to stop).
Four-way stop control is often controversial as it can often confuse motorists and can cause more average delay than other types of control. The multiway stop sign should only be used where the volume on all approaches to the intersection is approximately equal and the traffic volumes are relatively low. However, the four-way stop sign can be useful in situations where two-way stop control has not solved the safety problems, but signalization is not yet warranted.