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Determine where the congestion and freeway bottlenecks are located at various times during the congested period. One method is to make a contour plot of speeds on a time-space diagram with freeway location on the vertical axis and time of day on the horizontal axis. Bottlenecks are located where speeds immediately downstream are abruptly higher than upstream speeds. Speeds can be obtained from floating cars, probe vehicles, or a system of road-based detectors such as inductive loops or road-side cameras.

Then determine the causes of the congestion.

Traffic Management Center and traffic monitoring

• If incidents frequently cause increased congestion in your area, consider establishing a traffic management center (TMC) to manage them. The center can also manage recurrent, everyday congestion. Consider linking it to traffic management centers in adjacent cities and highway districts.  
   
• If it does not already exist, put in place a system to monitor traffic at the most congested locations. Test its accuracy and reliability.  To achieve continuing accuracy and reliability, develop a system that checks the system for errors and repairs malfunctioning equipment promptly.  
  
  
• Use the system to determine when congestion occurs, how severe it is, and what strategies might be effective in reducing congestion. 
  
  
• Consider establishing communications links between the traffic management center and field devices, such as traffic surveillance devices and variable message signs. Link the traffic management center to the sources of incident information and channels for providing traveler information. Consider installing pan-tilt-zoom closed circuit TV to observe traffic in key locations, confirm suspected incidents, and provide information for remote management.
  
  
• 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 less congested. 

Strategies to reduce or manage recurrent congestion

• If a bottleneck is caused by traffic entering from an on-ramp, consider metering the ramp to increase flow through the bottleneck as well as diverting entering traffic to an on-ramp that will not cause a bottleneck. A traffic simulation model such as FREQ or Paramics can be used to model the effects of such changes on freeway and arterial traffic before they are implemented. During the congested period, the metering scheme should maintain the flow through the bottleneck at capacity and should move exiting vehicles off the freeway as quickly as possible.  This will minimize delay at the bottleneck. 
  
  
• For a bottleneck caused by traffic exiting the freeway at an off-ramp, consider channeling exiting traffic into the exit lane earlier so it has less effect on through traffic. Use variable message signs to control movement from one lane into another. Also consider working with the destination jurisdiction to move traffic away from the freeway more quickly. This might involve increasing the green time on the street leading from the freeway and diverting cross traffic around this street during the congested period. 
  
  
• If there are alternate routes to the freeway that are as fast as the freeway during congested times, consider posting both routes' travel times on variable message signs on the freeway to encourage drivers to take the alternate route.
  
  
• If there are underutilized HOV lanes, consider converting them to high-occupancy toll lanes or mixed flow lanes.
  
  
• If traffic is very congested, consider converting the road or a single lane of the road to a toll road with congestion pricing, such that tolls increase with the level of congestion in order to reduce demand so that it does not exceed capacity and cause delay.  Use electronic toll collection.   
  
  
• For congestion at toll facilities, consider electronic toll collection. 
  
  
• Consider archiving travel times by freeway link and by time of day and using this archived data to provide internet-based travel time estimates (including the variance in travel time) for travelers. Travelers could enter their origin, destination and departure time window and receive estimates of travel times by various routes and modes for the times within their time window. The object would be to reduce peak freeway congestion by causing people to travel at less congested times, to take less congested routes, or to travel by transit.  
  
  
• If some freeway trips could be made via transit, encourage use of transit by improving transit service and reliability by better tracking of transit vehicles, giving them signal priority, providing advanced fare payment, and improved information on services and arrival times.

Strategies to manage congestion caused by incidents

• Keep records of the locations and causes of incidents, and attempt to tailor solutions to the information. For example, on a particularly critical section of freeway, such as a bridge, there might be a fine for running out of gas or dangerous conditions might be corrected at locations where accidents often occur.
  
  
• If there are many incidents, consider a freeway service patrol to remove disabled vehicles  and to detect incidents. The patrol vehicles should be deployed immediately upstream of bottlenecks so that they can give first priority to incidents that might restrict flow through the bottleneck.
  
  
• Consider installing pan, tilt, and zoom CCTV with a link to the TMC at locations where incidents occur frequently to reduce the time needed to confirm and correctly respond to them. 
  
  
• Consider installing an automated phone system to shift calls regarding a major incident to a separate line to prevent the system from being overwhelmed and to reduce the time needed for incident managers to receive the information.
  
  
• Develop response plans for various types of incidents in advance to reduce the time needed to clear them.  
  
  
• If practical alternate routes exist upstream of an incident, use portable variable message signs and other communications channels to advise people to take them, with instructions on where they can return to the freeway downstream from the incident. Also utilize permanent changeable message signs, highway advisory radio, broadcast radio and the internet.