Back to Expert-Tool Page > City--Population 50,000 -499,999 > Reduce Congestion

Determine where and when congestion occurs. Then analyze why it occurs.

Speeds can be estimated from vehicle flows and densities. A number of surveillance devices are available for determining these. Some are portable and can be moved from place to place. Travel times can be measured by floating cars. Instrumented cars that automatically record travel times may be available on loan from a state highway department.

On arterials

• If there are delays at signalized intersections because the signals along the arterial are not coordinated, consider coordinating signals and optimizing cycles using a simulation program such as Transyt. If optimal cycles vary over the course of the day, consider using different timing plans at different times of day.
  
  
• If the signal system is already optimized, consider diverting traffic to a less congested arterial by using variable message signs that recommend an alternate route and give the time saved by using the alternate route.
  
  
• If there are delays at signals because of left or right turns, consider a left turn pocket or a right turn lane.
  
  
• If there is delay because of some sort of bottleneck, consider diverting traffic to a less congested arterial during congested periods by using either fixed signs for fixed hours of diversion or variable message signs if the congested times vary by time of day. The latter should be coupled with some type of traffic monitoring that will activate the sign when traffic becomes congested. Travel times via each route could also be posted on variable message signs on the main arterial.
  
  
• If there is a delay at an isolated signal (nearest signal over 1 mile away), consider a traffic-actuated signal that is green for arterial traffic except when actuated by a vehicle arriving at the cross street.

Due to events or traffic surges

• Consider a combination of changes in signal timing to facilitate the movement and variable message signs to route through traffic around the congested area during special events or other causes of surges in traffic. For periodic large events consider a portable traffic management center.

At rail crossings

• If there are delays at rail crossings and there is a grade-separated crossing nearby, consider using variable message signs to route vehicles to that crossing when a train is approaching or crossing.

Due to freeway traffic

• For backups at a freeway on-ramp, consider using variable message signs to divert travelers to other on-ramps, to channel freeway-bound traffic into one lane, or to divert non-freeway traffic around the backup. Post travel times for each of the routes.
  
  
• For large numbers of cars exiting the freeway, consider changing the signal timing to facilitate their movement away from the freeway and using variable message signs to divert other traffic around the congestion.

Due to incidents

• Consider using portable variable message signs and broadcast radio, if available, to divert people away from the incident site.

In a downtown area

• The goal may be to minimize stops and delay throughout the downtown area rather than on a single arterial. Signal timing should be adjusted to suit traffic conditions throughout the day-this could minimize both arterial delays during commute hours and downtown area delays during the mid-day. Traffic adaptive signal systems designed to minimize overall traffic are available.