THE EFFECTS OF INCIDENTS ON CONCURRENT FLOW HIGH OCCUPANCY VEHICLE LANE DELAY ON IH-635 (LBJ FREEWAY) IN DALLAS, TEXAS

High Occupancy Vehicle (HOV) lanes provide travel time savings and offer a more reliable trip time 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. The objective of this research is to determine the effect on travel time to users of Dallas' concurrent flow buffer-separated HOV lanes on IH-635 (LBJ Freeway) during incident conditions. The research results will supplement research on Houston's barrier-separated HOV lanes on the same topic which is documented in Report 0-4740-1, developed concurrently. The data used to determine HOV lane user benefits/disbenefits during incidents included video data of actual peak period incidents from Dallas' Traffic Management Center and corresponding speed and travel time data in the corridor. Only a few incidents were available for intense data analysis due to the unanticipated speed and travel time data limitations. Incidents blocking one or more of the general-purpose lanes showed a maximum additional travel time savings to HOV lane users of 10 minutes per vehicle for incidents with a lane blockage of nearly 1 hr. Shorter duration incidents produced less added travel time savings. Incidents blocking the HOV lane, due to the incident itself or by responding emergency vehicles, resulted in the HOV lane users experiencing a maximum delay of approximately 10 min. Incidents in which both the HOV lane and Lane 1 are blocked delays HOV lane users a maximum of approximately 14 min. 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 about 1 min 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 operation of the HOV lane during times of incidents. Simply stated, the HOV lane during certain general-purpose lane incidents appeared to be operating effectively until emergency vehicles came on the incident scene. Suggestions for incident response techniques are offered for maintaining HOV lane operation, including preferred placement of emergency vehicles and directing traffic proactively.