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Real – Time Data Improves Traffic Flow on City Streets

You are heading home from a late night dinner on Aurora Avenue N and the traffic signals seem to be working in your favor. Cruising at the speed limit, you are getting through each intersection on green lights. If you are sitting at the light on a side street like N 77th Street , you may be wondering why the light isn’t changing for you since there is no vehicle in sight on Aurora and no pedestrian crossing Aurora from N 77th.

SDOT has begun changing the timing of lights on selected major corridors so that you won’t experience the delay from the side street as described above. How? Well, SDOT is taking away the guess work of signal timing by adding technology using wireless magnetometers which are embedded in the pavement. The magnetometers collect data and feed the information to SDOT’s traffic signal system as well as the department’s Traveler’s Information Map.

With this equipment and data, SDOT is implementing what is called Traffic Responsive Operations. This operation not only takes away the guess work, but also uses the data to adjust the timing pattern to fit the need. The length of rush hour depends not only upon traffic volumes, but also upon the day, weather, and incidents on the roadway. In the past, rush hour operations were fixed and the signal system would use an internal clock to change the timing pattern to a lower cycle. However, because the Traffic Responsive Operation collects the presence and volume of traffic in “real time,” the cycle for a signal is lowered as soon as the volume drops. A lower cycle means pedestrians and cyclists will get the go ahead signal sooner. The combination of using Traffic Responsive Operation and wireless magnetometers on the main arterial reduces delays for all users, including vehicles on the side streets. Increasing the efficiency of the intersection and on the arterial minimizes the number of vehicles that are idling and emitting greenhouse gases and thereby improves air quality.

The technology driven signal operations completed at the end of last year and planned for this year are made possible with mitigation funding from the Alaskan Way Viaduct and other federal funding. The corridors were identified as most likely to experience impacts from the viaduct replacement construction.

In 2010, the following corridors were outfitted with these operations: Elliott Avenue W/15th Avenue W from W Harrison Street to W Armour Street; First Avenue S from S Royal Brougham Way to S Spokane Street; and Fourth Avenue S from S Royal Brougham Way to S Spokane Street.

In 2011, we plan to add the technology to the following corridors: E Marginal Way S from S Idaho Street to the First Avenue S Bridge; 15th Avenue NW from Market Street to NW 85th SW Street/Holman Road NW ; and Aurora Avenue N from Winona Avenue N to N 145th Street.

This real-time traffic technology is a winner for everyone balancing the needs of all users – pedestrians, bicyclists, motorists, transit and freight – while minimizing the impact on the environment.