Bus and high occupancy vehicle lanes

A high-occupancy vehicle (HOV) lane is a restricted traffic lane that is usually reserved for vehicles with two or more occupants. High-occupancy vehicle lanes are implemented to promote higher vehicle occupancy, and reduce traffic congestion and air pollution.

A study was undertaken to determine the circumstances that would motivate commuters to shift to carpools and buses. A model was developed to calculate the benefits, defined as reduced person-delay and reduced emissions, for four alternatives: adding a high occupancy vehicle lane, adding a general purpose lane, converting an existing lane to a high occupancy vehicle lane, and doing nothing. The results of the study showed that adding a high occupancy vehicle lane to a three lane freeway would be more effective than adding a general purpose lane only if the initial maximum delay was 35 minutes or more and the proportion of high occupancy vehicles comprised at least 20% of the vehicle fleet (Dahlgren, 1998).

A pilot project that aimed to achieve travel time savings, reduced collision rates and lower air emissions was implemented in 1999 by the British Columbia Ministry of Transportation and Infrastructure. One of its project initiatives involved the widening of the Trans Canada highway from four to six lanes to provide two HOV lanes, over a distance of 16 km from Burnaby to Coquitlam. The results of the study showed that traffic volumes in the central portion of the HOV section increased by approximately 55% in the peak hour directions, and by about 15% in the off-peak hour directions. Average vehicle occupancy increases ranged from 2.5% to 9.4% along selected sections of the HOV lanes. An examination of collision related claims before and after construction of the HOV lanes indicated that the numbers of claims decreased by 25% in the year after the HOV lanes were constructed (BC Ministry of Transportation and Infrastructure, 1999).

A 2007 Canada Newswire report on HOVs on highways 403 and 404 in the Toronto area indicated that between 37% and 40% of carpoolers were commuting to work on those highways. Average rush hour speeds on these roads range from 50 to 60 km/h in general purpose lanes compared to 70 to 100 km/h in HOV lanes, providing carpoolers with considerable time savings per trip.

A two year study evaluated the performance of HOV lanes following their implementation on a section of interstate highway in Utah. The analysis assessed the freeway operations before the HOV lanes opened and throughout the first year of operation. The results of the study indicated that during the afternoon peak period, the HOV lane moved the same number of people as each general-purpose (GP) lane with only 44% of the vehicles. The HOV travel lanes provided a 30% travel time savings during the afternoon peak period and a 13% travel time savings during the morning peak period. Vehicle occupancy on the interstate corridors with HOV lanes increased by 17%, whereas average vehicle occupancy on comparison interstate sites without HOV lanes remained the same before and after the HOV lane opening (Martin et al, 2004).

In Texas, a study to better understand the safety issues associated with HOV lanes, particularly buffer-separated concurrent flow HOV lanes, evaluated multiple years of crash data, before and after the implementation of HOV lanes on three interstate corridors. The analysis showed that the number of crashes remained unchanged on the interstate corridor where a moveable barrier-separated contra flow HOV lane was implemented. However, the analysis of the data on the two interstate corridors where buffer-separated, concurrent flow HOV lanes were implemented showed that injury crash rates increased by 56% and 41%, respectively. The authors of the study found that many of the crashes occurred in the buffer-separated concurrent flow HOV lane and the adjacent general purpose lane. The speed differential between the two buffer-separated HOV lanes, which usually operated at the speed limit and the congested general purpose lanes which usually operated at slower speeds was cited as the likely cause for the increased injury crash rates (Cothron et al., 2004).

An assessment of the effectiveness of California’s HOV system provided mixed results. The study, which used several months of peak-hour data, showed that HOV lanes were under-used as determined by vehicles per hour per lane traffic versus lane capacity. HOV lane travel times were more reliable than GP lanes; however they offered limited travel time savings. The mean savings over a random 10-mile route on an HOV lane versus the adjacent GP lane was 1.7 minutes. Many HOV lanes experienced degraded operations (vehicle speed drops below 45 mph for 10% of the peak hour during a six-month period). 18% of all HOV miles during the AM peak hour and 32% during the PM peak hour had speeds below 45mph for more than 10% of weekdays. The authors of the study determined that HOV lanes reduced overall congestion slightly only when the general purpose lanes became congested. The authors concluded that operating the freeway system efficiently through the maintenance of free flow traffic would be more beneficial than adding HOV lanes (Kwon et al., 2006).

Support for HOV facilities is not universal. Heavy congestion on some portions of HOV network in California prompted the California Department of Transportation to examine potential solutions including the conversion of high occupancy vehicle lanes (HOV2+) to higher occupancy (HOV3+) vehicle lanes or to high occupancy toll (HOT3+) lanes (CTC & Associates, 2013).

Scope of the Problem

• Dahlgren, J. (1998). High occupancy vehicle lanes: Not always more effective than general purpose lanes, Transportation Research Part A: Policy and Practice, Volume 32, Issue 2, Pages 99-114. Retrieved from http://www.sciencedirect.com/science/article/pii/S0965856497000219

Evidence

• BC Ministry of Transportation and Infrastructure (1999) High Occupancy Vehicle Lanes (HOV) Evaluation Summary, Phase II HOV Evaluation and TMP Baseline. Retrieved from http://www.th.gov.bc.ca/publications/reports_and_studies/hovsummary/summary.htm#first
• Canada Newswire (2007). McGuinty Government Opens High Occupancy Vehicle Lane on Highway 404. Retrieved from http://www.newswire.ca/en/story/74075/mcguinty-government-opens-high-occupancy-vehicle-lane-on-highway-404
• Martin, P., Perrin, J., Wu, P., and Lambert, R. (2004). Evaluation of the Effectiveness of High Occupancy Vehicle Lanes. University of Utah. Retrieved from http://www.mountain-plains.org/pubs/pdf/MPC04-158.pdf
• Cothron, A. S., Ranft, S. E., and Walters, C.H. (2004), Crash Analysis of Selected High-Occupancy Vehicle Facilities in Texas: Methodology, Finding and Recommendations, (Report No. FHWA/TX-04/0-4434-1), Texas Transportation Institute. Retrieved from http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/0-4434-1.pdf
• Kwon, J., and Varaiya, P. (2006). Effectiveness of California’s High Occupancy Vehicle (HOV) System. California State University, East Bay and University of California, Berkeley. Retrieved from http://paleale.eecs.berkeley.edu/~varaiya/papers_ps.dir/HOV_summitv6
• CTC & Associates (2013). Impacts of Increasing Vehicle-Occupancy Requirements on HOV/HOT Lanes. Prepared for Caltrans Division of Research and Innovation. Retrieved from http://www.caltrans.ca.gov/newtech/researchreports/preliminary_investigations/docs/HOV_and_HOT_Lanes_Preliminary_Investigation_03-25-13.pdf