NCPA - National Center for Policy Analysis


June 30, 2005

High-occupancy vehicle (HOV) lanes, have become a fixture of many urban freeways as way to alleviate traffic congestion and improve air quality. But in its attempt to do a good deed, there is evidence that adding HOV lanes can lead to more accidents, say observers.

According to the Texas Transportation Institute (TTI), accident rates have increased since the addition of HOV lanes in Dallas:

  • When the HOV lanes first opened in 1996 on I-635, the accident rate per 100 million vehicle-miles increased from 32 to 50.
  • In 1997, when 3.8 miles of HOV lane was added (equaling 11.1 miles), the accident rate increased from 44 to 62.
  • Additionally, the rate of accidents increased 56 percent for stretches of Dallas freeway that have HOV lanes adjacent to regular lanes without a concrete barrier.

Rates have also increased in other states, including California, where accident rates have grown 11 percent in locations where HOV lanes were added, narrowed, or both.

One reason HOV safety hasn't received a lot of attention is that the accidents tend to be minor, like side-swipes and fender benders, say observers; nonetheless, serious accidents do occur. So why might HOV lanes cause accidents?

  • Lanes are not separated by concrete barriers so drivers often illegally weave between the regular and HOV lanes. Nationwide only 10 percent of HOV lanes actually have barriers.
  • Drivers stuck in gridlock tend to be resentful of their faster-moving counterparts and won't let them merge back onto the regular freeway, causing accidents.

In response to the increase in accidents, Dallas traffic planners are considering using 2.5-feet-tall pylons to separate a new stretch of HOV lanes on U.S. 75; these pylons could add up to $8 million to the initial cost of the project.

Source: Russell Gold, "HOV Lanes Linked to Rise In Car Crashes," Wall Street Journal, June 21, 2005; based upon: A. Scott Cothron et al., "Crash Data Identify Safety Issues for High-Occupancy Vehicle Lanes in Selected Texas Corridors," Texas Transportation Institute, March 2005.

For text (subscription required):,,SB111931048375764610,00.html

For study:


Browse more articles on Environment Issues