I- 90 Lane Conversion Evaluation

The purpose of the project is to evaluate the effectiveness of converting a general purpose traffic lane to an HOV lane on Interstate 90 between Issaquah and Bellevue Way. The research effort included consideration of vehicle occupancies, travel time, safety, and public support. A successful lane conversion would demonstrate the potential to save the cost of constructing new highway lanes when existing highway lanes were available for conversion.

From an operational perspective, we can conclude that the HOV lane conversion did not have an adverse impact on travel speeds or travel times. Moreover, a reduction in speed variance was observed after the HOV lane conversion, which suggests a possible improvement in safety. Finally, an analysis of speed-flow relationships showed that the HOV lane had a significant impact, but the adverse consequences of this impact would be felt only in highly congested conditions. A relatively low HOV violation rate of 4.6 percent was observed, possibly indicating that the benefit gained from using the HOV lane may have been minimal. No change was noted in the average vehicle occupancy for the overall facility. The accident investigation was limited because of the time constraints and hampered by outside factors; nearly half of the accidents were possibly attributable to unrelated construction.

From a public opinion standpoint, the I-90 lane conversion in the Seattle area can be classified as a qualified success. While a slight majority of commuters oppose the conversion, public opinion for and against is surprisingly close. It appears that with effective marketing and careful implementation, lane conversions can be successfully undertaken. However, it is important to recognize that significant opposition may arise from young commuters, from regular SOV users, and from commuters who will be forced to make departure time changes. To reduce their opposition, commuters who fit this mold should be addressed through informational campaigns and other strategies.

Publication Date: 
Wednesday, February 1, 1995
Publication Number: 
WA-RD 362.1
Last modified: 
10/12/2016 - 15:41
Soon Gwan Kim, Jodi Koehne, Fred Mannering.
Washington State Transportation Center (TRAC)
Number of Pages: 
Attitudes, Commuters, High occupancy vehicle lanes, Measures of effectiveness, Public opinion, Traffic lanes, Transportation safety, Travel surveys, Travel time, Vehicle occupancy.