Real-time travel information helps customers navigate around congestion and shows the public when agencies know about and are working to clear traffic problems.
Real-time traffic information deployment in Seattle has both been a customer service and customer relations success, in Bellevue, Washington the real-time travel map is one of the most viewed city websites.

NCHRP Synthesis 447: Active Traffic Management for Arterials

Summary Information

This synthesis documents the state of the practice associated with designing, implementing, and operating active traffic management (ATM) on arterials. Information for this synthesis was gathered through a literature review of advanced ATM methods for arterials and in-depth telephone interviews of agencies selected through a screening interview. The study has provided information on strategies used to actively manage traffic and congestion on arterials; situations and operating conditions in which ATM strategies have been successfully and unsuccessfully deployed on arterials; and system and technology requirements associated with implementing the strategies.

Real-Time Travel Information

Bellevue, Washington has a large arterial data collection infrastructure in place and wanted to develop a means of providing this information to the public for informational purposes. The agency reports the level of congestion at intersections on a travel map using green, yellow, red, and black color codes. Colors are determined through detector occupancy. Collected data is also published to an FTP site where it can be accessed by developers, who could create their own applications to assist in route guidance, which is what many travelers want. The agency is converting the system into a GIS-based system, which will make overlays possible so developers can overlay Bellevue’s traffic data onto traffic maps. In addition to the traffic map, Bellevue has 55 cameras around the city showing local conditions. The city hopes the information will cause drivers to better spread congestion among different routes and times throughout the day.

Seattle, Washington provides traveler information via a web-based travel map, dynamic message signs (DMS), and travel cameras. This information is offered via an online portal, mobile application, and social media. The web-based traveler information map is color coded based on occupancy data collected by magnetometer sensors throughout the city, using green, yellow, red, and black. Sensors are carefully sited so they are not affected by traffic signals. Each location required a lot of fine-tuning to interpret and assign values reflecting the appropriate color codes. The 22 DMSs in Seattle warn drivers of significant transportation events while traveling, such as incidents, construction, and drawbridge openings. While these messages are the primary purpose of DMSs, some also provide travel time information to key points in the city. Travel times are measured by license plate readers (LPRs) that pair captures of the same license plates between two points and calculate the amount of time between the two captures. The web portal also has links to 130 traffic cameras. The cameras are set up in places where they have good views up and down the corridors. Most of the cameras are still shots updated every few minutes. The web portal may be accessed at:



  • In Bellevue, performance of the traffic map is measured by web site views. The traffic map is consistently in the top five of all viewed city web pages. The city also has noted the number of unique visitors jumps dramatically for severe weather events or incidents.
  • In Seattle, the system successfully informs motorists about detours and other construction-related information. It has also been good from a media relations standpoint because when something happens, the city can now show the problem is being actively managed. Public officials are pleased with the system and the results. They are also getting a number of requests to use the system from various project managers in support of road closures.
  • In Seattle, showing travel times on the DMSs was not a planned part of the project, but this function has been found to be an extra benefit. But consequently, not all message signs have LPRs, which means travel times cannot be shown at locations without LPRs.
  • One major benefit to ITS technologies are that they can be adjusted to match the budget by simply changing the number of devices installed. As design proceeded and cost estimates were made, Seattle was able to add and subtract devices based on available funding.