The state laws require that by the 1998 model year, 2 percent of every auto company's sales be "zero-emission vehicles," presumably electric cars.

"While New York is very committed to zero-emission vehicles, they do have technology constraints," she said.

By 2003, 10 percent of the cars in New York would have to be so-called zero-emission vehicles, probably electric cars.

Freight bicycles are used as low-cost, zero-emission vehicles to haul cargo.

Although they welcome hybrids, environmentalists say the ultimate goal should be zero-emission vehicles.

Under California clean air rules, 10 percent of the vehicles sold in the 2003 to 2008 model years must be electric or "zero-emission vehicles."

The mandate, which once called for 10 percent of a company's sales to be zero-emission vehicles, has already been weakened twice.

The standards also require "zero-emission vehicles," presumably cars that run on electricity.

New York and Massachusetts, for example, have both passed laws that will require certain percentages of low- or zero-emission vehicles to be sold over time.

Low or zero-emission vehicles are also includes in Tokyo 2016's plan.