Back to Expert-Tool Page > City--Population 500,000 or more > Reduce Congestion

Determine where and why it occurs.Ê

• Put in place a system to monitor traffic at congested locations.Ê If such a system is already in place, confirm that all surveillance devices are providing accurate and reliable information. If they are not, repair them. To achieve continuing accuracy and reliability, develop a system to check for errors and to repair malfunctioning equipment promptly.ÊÊ
  
  
• Use the surveillance system to determine or confirm the cause of the congestion, at what times it occurs, how severe it is, and what strategies might be effective in reducing it. Use it to measure the effectiveness of any strategies that are applied.

Manage traffic

• If traffic conditions are variable, consider establishing a transportation management center (TMC) to manage incidents and adjust traffic signals and variable message signs in response to traffic in key areas. Consider linking it to traffic management centers in adjacent cities and highway districts.ÊÊÊ
  
  
• Consider establishing communications links between signal controllers, variable message signs, and the transportation management center so that signals and signs can be operated remotely. Consider installing pan-tilt-zoom closed-circuit TV to observe traffic in key locations and to provide information for remote management.ÊÊÊ
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• If traffic varies from day to day, consider using a traffic adaptive control program such as the Urban Traffic Control Systems (UTCS) developed by the FHWA.
  
  
• For full control of a large traffic signal system in a congested city, consider a UTCS-type system that can be modified from a central location, such as the TMC.

Advise travelers

• Provide information on congestion and incidents to travelers via the Internet and radio. On the Internet, provide information on travel times and travel time variance at all times of day so that travelers who can adjust their departure time are encouraged to travel when it is least congested.Ê

Reduce arterial congestion

• 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.Ê Use variable message signs that suggest using an alternate route and that give the time savings on 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.Ê
  
  
• If there is delay because of some sort of bottleneck, consider diverting traffic to a less congested arterial during congested periods using 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 for each of the routes could also be posted on variable message signs on the main arterial. Consider moving traffic affected by the bottleneck into one lane earlier so that it does not interfere as much with through traffic or traffic exiting on other streets.Ê Use overhead variable message signs to indicate the proper lane.
  
  
• 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 a vehicle arrives on the cross street.
  
  
• If there is good transit on the arterials, consider measures to encourage transit use, such as improved information regarding transit services and travel times on the web.

Congestion due to events or traffic surges

• Consider developing a routing plan to facilitate the movement of event traffic without unreasonably restricting other traffic. Implement it with a combination of changes in signal timing to facilitate the movement of the traffic surges and variable message signs to route event traffic and through traffic through and around the event area. For periodic large events, consider a portable traffic management center.Ê
  
  
• Consider noting major events on traffic congestion maps on the web.

Congestion 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.ÊÊ

Congestion 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, and to divert non-freeway traffic around the backup. Post travel times for each of the two routes.
  
  
• For large numbers of cars exiting the freeway, consider changing the signal timing to facilitate their movement away from the freeway as well as using variable message signs to divert other traffic around the congestion.ÊÊ
  
  
• If traffic is congested because of an incident on the freeway that causes travelers to divert to city streets, consider altering signal timing on the streets to facilitate the movement of the additional traffic until the incident is cleared.Ê

Congestion due to incidents

• Consider using portable variable message signs, broadcast radio, and highway advisory radio to divert traffic from the incident.Ê
  
  
• If congestion is often caused by incidents, record the locations and causes and attempt to reduce their frequency through the use of safety measures.Ê Consider installing closed-circuit TV in locations where incidents occur frequently to facilitate detection and clearance.
  
  
• Develop response plans for various incidents in advance to reduce the time needed to clear them.

Congestion 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 øthis could minimize both arterial delays during commute hours and downtown area delay during the mid-day. Traffic adaptive signal systems designed to minimize overall traffic are available.
  
  
• Consider diverting through traffic away from the downtown area during congested periods by using variable message signs, lane control and route guidance on the web.
  
  
• If downtown congestion is extreme, consider a toll to enter the area during the congested period as is done in Singapore; Trondheim, Norway; and London. The toll can be varied according to the level of congestion at different times of day.
  
  
• If parking is difficult to find, consider installing a parking availability system that monitors spaces at various parking facilities and guides travelers to available parking using fixed and variable message signs.