In 2002, the State Transportation Commission directed the Washington State Department of Transportation (WSDOT) to implement an evaluation of all Puget Sound HOV lanes in order to determine if they could be operated any more efficiently.
One of the results of this evaluation was a demonstration project to open HOV lanes to all traffic on freeways east of Lake Washington between the hours of 7 pm and 5 am. This changed HOV lane hours of operation 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 Project Map. Interstate 5 HOV lanes were excluded from the proposal because they are more heavily traveled and the cost of improvements that would have been needed to meet safety standards was exorbitantly high.
The project was designed to determine whether changing the hours of operation would have an effect on traffic speed, volumes, safety, or carpool lane use. To prepare for the demonstration project, WSDOT spent about $1.2 million to enhance safety with guard rails, rumble strips, raised lane markings, and updated signs to meet Federal Highway Administration standards.
Throughout the summer of 2003, WSDOT gradually opened Eastside freeway HOV lanes to all traffic at night. 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 segments of I-405 and SR 167 with 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 opening the HOV lanes may have contributed to a lower rate of run-off-the-road type collisions at night.
- 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 overall. 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. 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, the new hours of operation will continue. A policy to formally adopt these new hours on Eastside freeways will be made soon.