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Benefits of ATDM

ATDM overhead signs help manage traffic during an incident.

Collision and congestion management
Active Traffic and Demand Management signs allow WSDOT to quickly alert drivers to changing roadway conditions and direct drivers to reduce speeds and move away from a lane closure or get around a collision.

There is not enough data to adequately estimate congestion reduction at this time. Congestion, like collisions, can vary greatly from year to year. Several years of travel time data may be needed before we can measure whether there is a change in congestion levels attributable to ATDM. You can read more about collision results and congestion management in the Grey Notebook (pdf 2 mb).

Emergency response
Emergency responders report high compliance with the “lane blocked/lane closed” symbols. These control symbols, including red X’s and yellow merge arrows provide extra time for vehicles to move over and provide a gap between emergency responders and moving traffic. WSP troopers patrolling the corridors report feeling safer when working on the roadway.

Emergency management
The system is helpful in managing weather events as well as managing other emergency situations. For example, during the week of January 16, 2012, WSDOT traffic engineers used ATDM to give drivers advance warning of the major snow storm forecast for Western Washington. When the snow fell, the signs were used to lower the speed limits for snow conditions. This same approach has been used on Snoqualmie and Stevens passes with success and is now used in the Seattle metropolitan area.