NCPA - National Center for Policy Analysis


January 23, 2006

Giving people incentives to carpool is the underlying rationale for HOV lanes. But growing evidence is accumulating that this policy is accomplishing less than many people believe, says Robert W. Poole Jr. of the Reason Foundation.

In a recent study on virtual exclusive bus lanes, Poole and his colleagues found:

  • Despite the quintupling of HOV lane-miles between 1990 and 2000, the fraction of commuters who carpool declined from 13.4 percent to 12.2 percent.
  • Between 33 and 75 percent of carpoolers (depending on the city) are members of the same family, raising the question of how much real change in trip-making behavior the HOV lanes are bringing about.
  • Vehicle occupancy is lowest for work trips (and commuting is the focus of most ride-sharing efforts); every other category of trips has higher vehicle occupancy.
  • Vehicle occupancy is also lowest during commute hours; it's significantly higher in the evenings and on weekends.

So the policy of promoting ride-sharing to ease peak-period congestion does not seem at all well-targeted.

Furthermore, according to Pravin Varaiya of the University of California-Berkeley, HOV lanes increase congestion in two ways:

  • By keeping non-HOV vehicles out of that lane, the policy adds to congestion in the general-purpose lanes.
  • Since nearly all HOV facilities use a single lane in each direction, those lanes have less inherent capacity than regular freeway lanes, and hence operate almost as slowly as general-purpose lanes.

Source: Robert W. Poole Jr., "But Should We Continue with HOV Lanes?" Reason Foundation, January 2006; and Robert W. Poole Jr. and Ted Balaker, "Virtual Exclusive Busways: Improving Urban Transit While Relieving Congestion," Reason Foundation, September 2005.

For text:

For Reason study:


Browse more articles on Environment Issues