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Eastside HOV Evaluation - Hours of Operation

Central Puget Sound HOV Map
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In 2002, the State Transportation Commission directed WSDOT to implement an evaluation of central Puget Sound freeway HOV lanes to determine if they could be operated any more efficiently.

One of the results of this evaluation was a demonstration project which opened freeway HOV lanes to all traffic on freeways east of I-405 between the hours of 7 pm and 5 am. This changed freeway HOV
lane hours on all of I-405 and SR 167, and the portions of SR 520 and I-90 that lay east of I-405. The affected HOV lanes are shown in a lighter green color on the HOV webmap.

I-5 HOV lanes were excluded from the proposal
because they are more heavily traveled and the cost of improvements that would have been required to meet safety standards was in excess of $50 million. SR 520 west of I-405 was excluded because this segment of HOV lane cannot hold higher volumes due to safety reasons. On I-90, the HOV Reversible Express Lanes between Rainier Avenue South and Island Crest Way are already open to solo drivers.

The Eastside Hours of Operation demonstration project was designed to determine whether changing the hours of operation would have an effect on traffic speed, volumes, safety, or HOV use. To prepare for the demonstration project, the Federal Highway Administration required WSDOT to make about $1.2 million of safety improvements including new guard rails, rumble strips, raised lane markings, and updated signs.

WSDOT gradually opened eastside freeway HOV lanes to all traffic at night throughout the summer of 2003. We have closely monitored the lanes to study the effect of this change. In June 2006 we issued a final report on the results of the demonstration project. The major findings were:

  • Slight improvement in congestion.  A slight improvement in congestion has been noted around 7 pm since the new hours of operation have been in place.
  • Slight improvement in speeds. 
  • There has been a correspondingly modest increase in speeds of between two to four mph.
  • HOV lanes are being used by general purpose traffic. 
  • The HOV lanes are being used by general traffic during the evening and early morning hours. There has been about a ten percent increase in the number of solo drivers in most of the carpool lanes between 7 pm and 5 am, and even higher usage on those segments of I-405 and SR 167 which experience regular evening congestion. Only one location, southbound I-405 near Renton, has had lower volumes in the HOV lane after 7 pm.
  • No safety problems. 
  • Overall there has been little or no adverse effect on collision rates from this project. The safety improvements which were made prior to the nighttime opening may have contributed to a lower rate of run-off-the-road type collisions.
  • Slight increase in violations. 
  • There was an overall increase in violations during transition periods (right before and after HOV-only hours) of between one and four percent. There were also some areas where violation rates went down.
  • Public support. 
  • Responses to a public opinion survey suggest between 26 and 32 percent felt that maneuverability, safety, or speeds were somewhat or much improved as a result of this change. Agreement with the new policy was at 68 percent. The new policy also improved opinion of the HOV system in general for almost 39 percent of the respondents.

Although the demonstration project is now officially over, these new hours of operation have been successful and are expected to continue so long as operations remain positive.


Updated March 2010.