Effects of Incidents on Buffer-Separated High-Occupancy-Vehicle Lanes in Dallas, Texas

High-occupancy vehicle (HOV) lanes should provide travel time savings and offer more trip reliability to users. Historically, the determination of travel time savings on HOV lanes as compared to general-purpose lanes is calculated using data collected on days without incidents. This paper examines the effect of incident conditions on travel time to users of Dallas' IH-635 buffer-separated HOV lanes. Incidents blocking one or more of the general-purpose lanes showed a maximum additional travel time savings to HOV users of 10 minutes per vehicle for incidents with a lane blockage of nearly 1 hour. Shorter duration incidents produced less travel time savings. Incidents causing the HOV lane to be blocked, due to the incident itself or by responding emergency vehicles, resulted in HOV users experiencing a maximum delay of 10 minutes. Incidents in which both the HOV lane and adjacent general-purpose are blocked delay HOV users a maximum of 14 minutes. The overall net benefit offered to concurrent flow HOV lane users when both non-incident and incident days are included in the calculation equates to only 1 minute round trip travel time savings per vehicle per day. An unanticipated result of this research is the realization of the importance of proper incident response for maintaining HOV lane operation during incidents. Suggestions for incident response techniques are offered for maintaining HOV lane operation, including preferred placement of emergency vehicles and proactively directing traffic.