TTI Study: HOV lanes without positive separation linked to car crashes

News AASHTO Journal July 06, 2005
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A study recently released by the Texas Transportation Institute (TTI) indicates that vehicle crash rates may rise when high-occupancy vehicle (HOV) lanes are situated next to general traffic lanes, with no physical barrier between the two, the Wall Street Journal reported.

However, TTI found that accident rates did not increase where HOV lanes and general-traffic lanes are separated by a concrete barrier – which is only the case on about 10% of HOV installations across the country, the Journal reported.

TTI’s study compared crash rates along a stretch of Dallas, Texas-area freeway before and after the addition of an HOV lane that had no barrier between the different types of lanes. HOV lanes, aimed at offering a speedier traveling experience to those driving at least two to a vehicle, have quadrupled in the U.S. over the past 15 years, to 2,500 miles of HOV’s nationally. Originally conceived of as an air-pollution reducer, some areas are converting them to congestion-priced toll lanes known as “HOT” lanes.

Dallas traffic planners are considering the placement of 2 1/2-foot-tall pylons to separate a new stretch of HOV lanes on U.S. 75 from the rest of traffic, saying there is a lack of room for larger barriers. The cost of the pylons could be up to $8 million, the Journal reported.

TTI’s study, released in April, concluded that the accident rate on freeways with non-separated HOV and general-traffic lanes has risen by as much as 56%. In a study released a year earlier, the Journal reported, researchers at the Midwest Research Institute recorded an 11% increase in vehicle wrecks in a study that covered HOV additions at several locations in Southern California. The accidents in question tend to be side-swipe and fender-bender wrecks rather than impacts causing major injury or death, the newspaper reported.

Scott Cooner, a TTI program manager, said one reason for the increased wreck rate in that particular setting is that some drivers weave back and forth from general traffic lanes into HOV lanes, or vise versa. In other cases, general-lane occupants moving more slowly than their neighbors in the HOV sometimes won’t let people wanting to merge in the general lanes into the queue.

There is another national study planned on the safety of HOV lanes this year, the Journal reported. California, New York and seven other states are spending $200,000 on the study, which is expected to lead to a handbook for transportation planners on the safest designs.

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