Quantification of Incident and Non-Incident Travel Time Savings for Barrier-Separated High-Occupancy Vehicle (HOV) Lanes in Houston, Texas

This project examined barrier-separated high-occupancy vehicle (HOV) lane travel time savings during incident conditions in Houston, Texas. Travel time studies, due to cost and manpower, are typically conducted infrequently and under non-incident conditions. Due to the high occurrence of incidents in large urban areas, travel time studies conducted under non-incident conditions underestimate the benefit of HOV lanes. During 2003, only an average of 17% of AM peak and 10% of PM peak periods were found to be incident free in the four HOV corridors studied: I-10 Katy, I-45 North, I-45 Gulf, and US-59 Southwest Freeways. Characteristics of the 9506 incidents reviewed from the incident database are detailed by corridor and direction, cross-section location, severity, number of vehicles, time of day, day of week, month of year, and weather conditions. A total of 341 incidents in these corridors were identified for further analysis and stratified into an incident matrix for each corridor with the extent of lane blockage versus duration of incident. Historical Automatic Vehicle Identification (AVI) data for these incident peak periods were analyzed using a Travel Time Generator software program developed in this project. This software used the AVI data to calculate segment and corridor mainlane and HOV lane travel times for 5-min periods during the AM peak (6:00-9:00 AM) and PM peak (3:30-6:30 PM) periods. Travel time savings during incident conditions were compared to non-incident conditions for the range of incidents in the matrix. The additonal benefit of HOV lane travel time savings during incident conditions over non-incident travel time savings was estimated at 74% combining all corridors and peak periods. An important benefit of HOV lanes is shown in the travel time graphs detailing mainlane and HOV lane travel time comparisons for the range of incidents in the matrices. In comparison to average travel time savings over the entire 3-hr peak period, maximum travel time savings during incident conditions ranged up to 64 min in the AM peak and 49.5 min in the PM peak. An analysis of the entire year of 2003 AVI data (incident and non-incidnet conditions) estimated the benefit of HOV lanes in these four corridors during the combined AM and PM peak periods at approximately $146,000 per day or approximately $38 million per year. The Katy Freeway HOV lane showed the greatest incident and non-incident savings at nearly $80,000 per day or $20.5 million per year.