Active Traffic Management (ATM) is a strategy used by the Washington State Department of Transportation to reduce collisions associated with congestion and blocked lanes. About 50% of traffic congestion is due to events like collisions or disabled vehicles.
How does it work?
The system uses overhead lane signs to provide advance notice of traffic conditions:
- Variable speed limit signs direct drivers to incrementally reduce their speeds.
- Symbols direct drivers to change lanes when a lane is blocked.
- Overhead message signs warns drivers of slowdowns, backups and collisions ahead.
The system decreases last second avoidance maneuvers and panic braking, primary factors contributing to collisions.
Current Active Traffic Management Corridors
- Interstate 5
- Interstate 90 Seattle/Bellevue
- Interstate 90 Snoqualmie Pass
- State Route 520 Seattle/Bellevue
Active Traffic Management is a new technology. WSDOT is the first state transportation agency to use the system in the United States. Considered a work in progress, analysis of existing traffic management corridors for safety and congestion relief could lead to additional locations like Joint Base Lewis McChord in Tacoma
These applications are consistent with WSDOT’s Moving Washington strategy which emphasizes the efficient operation of existing highways by deploying strategies that reduce collisions and maximize traffic flow.
Active traffic management signs allow WSDOT to quickly alert drivers to changing roadway conditions, reduce speeds and direct drivers away from a lane closure and around a collision.
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 providing a gap between emergency responders and moving traffic. WSP troopers patrolling the corridors report feeling safer when working on the roadway.
During the week of January 16, 2012 WSDOT traffic engineers used ATM 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 limit 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. The system was helpful in managing the snow event and will be extremely helpful in managing other emergencies.
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 ATM
The SR 99 Alaskan Way Viaduct Replacement Project paid for the signs on I-5 to help manage increased traffic on I-5 while the new tunnel is built and the viaduct demolished.
The active traffic management system was used extensively during a nine day closure of SR 99 in October 2011 when the southern mile of the viaduct was demolished.
During the closure, I-5 experienced a significant increase in traffic. To manage the increased volume, the electronic signs notified drivers of the heavy on-ramp traffic, particulary from Spokane Street. The signs advised drivers traveling in the lane where ramp merged to use caution. Observations showed many drivers moved out of the lane to provide gaps for merging traffic. The improved merge action aided in the overall management of construction traffic congestion.
During the viaduct closure, active traffic management signs also gave drivers information on alternate routes. When congestion was severe, WSDOT used the signs to tell drivers to use major city arterials. The system helped direct drivers to faster routes. Management of traffic during the closure was successful with no major collisions.