The California law enabling single-occupant access to the HOV lanes was meant to stimulate sales for fuel-efficient, ultra low-emission vehicles, with the goals of reducing dependence on foreign oil and saving money at the gasoline pump. Between August 2005 and June 2011, California law allowed owners of hybrid vehicles achieving at least 45 mpg (5.2 l/100 km) to purchase a Clean Air Vehicle Sticker for $8, allowing them to drive on carpool lanes regardless of the number of occupants in the car. However, two-thirds of the sticker registrants had hybrid cars already on the road, the authors noted; in other words, the stimulus effect was lower than expected.

While the original clean air sticker policy expired in 2011, a new HOV-exception program with 40,000 stickers for electric, hydrogen fuel cell, and plug-in hybrid vehicles started in 2012.

While adding a single hybrid to any HOV lane at 2 a.m. creates no congestion or social costs, said the researchers, adding one hybrid driver at 7 a.m. on weekdays to an already congested road such as Interstate 10 in the Los Angeles area appends $4,500 per car in annual costs (in pollution and time) to society.

With the addition of solo-driver hybrids on already congested highways, HOV lane traffic climbs above 30% beyond socially optimal levels, according to the research. Thus, carpooler congestion costs substantially outweigh the green benefits of hybrids, the researchers concluded.

The economists suggested several alternatives:

• Instead of letting the solo-driver hybrids into rush-hour carpool lanes, the state should provide a tax credit for hybrid vehicles, much like the federal government.

• Policymakers could ration HOV access via congestion pricing, which could relieve congestion and improve air pollution.

• Having commuters use buses may represent the win-win in terms of pollution and congestion that policymakers were hoping with the CAVS [sticker] policy, the researchers suggested in the paper.

Even if vehicles were truly zero emission, policies that promote their adoption at the expense of exacerbating congestion still generate substantial losses of time for high-occupancy vehicle commuters, they explain in the paper.

To reduce congestion in that interstate corridor and to be fair to commuters in high-occupancy vehicles, the economists suggest a congestion toll of 45 cents per mile, and for hybrid and low-emission vehicles, a reduced congestion toll amounting to 38 cents per mile.

Resources

• Antonio Bento, Daniel Kaffine, Kevin Roth and Matthew Zaragoza-Watkins (2014) “The Effects of Regulation in the Presence of Multiple Unpriced Externalities: Evidence from the Transportation Sector,” AEJ: Policy Volume. 6, Issue 3 doi: 10.1257/pol.6.3.1