Institute of Transportation Studies Friday Seminar: Lessons Learned from Spatiotemporal Studies of Freeway Carpool Lanes


Late August means the end of summer is nigh, students are back, classes are in session, and it's the return of the Friday Transportation Seminars. This semester there are some changes to the seminars - Cookie Hour and the seminar will take place in the same location in 290 Hearst Memorial Mining Buidling. We also encourage you to follow along (and participate) with the Twitter hashtag #itsberksem

This week's Friday Seminar features ITS's own Professor Michael Cassidy presenting, "Lessons Learned from Spatiotemporal Studies of Freeway Carpool Lanes."

The presentation explores how the segregation of distinct vehicle classes on a roadway can improve travel conditions for all of the classes. Insights come using freeway carpool lanes as case studies. Spatiotemporal study of real sites shows (i) how the activation of a continuous-access carpool lane triggers reductions in vehicle lane-changing maneuvers, and (ii) how the reduced lane-changing can “smooth” and increase bottleneck discharge flows in a freeway’s regular lanes. Theoretical analysis predicts that, thanks to this smoothing effect, even underused carpool lanes can diminish both the people-hours and the vehicle-hours traveled on a freeway. Relevance to bus lanes is briefly discussed. Further insights come via critiques of certain practices that degrade the effectiveness of carpool lanes. Spatiotemporal traffic data reveal that a policy aimed at improving carpool-lane speeds has backfired, owing to a friction effect. The policy mandates the eviction of select fuel-efficient hybrid vehicles from carpool lanes. These evictions have caused queues to expand in regular lanes during the rush. And these expanded queues, in turn, slow vehicles in the adjacent carpool lanes. Spatiotemporal data further show that efforts to combat the friction effect by deploying limited-access carpool lanes can also backfire, because the designs for these lanes are prone to creating bottlenecks.

The Friday Seminar takes place on August 29, 2014 from 4:00-5:00 PM in 290 Hearst Memorial Mining Building. Cookie Hour immediately precedes it at 3:30 PM in the same location. (Note: Cookie Hour is not in the library!) There will be a no-host Happy Hour at LaVal's at 5:00 PM.