Low-income drivers in 16 Texas counties will soon be eligible for financial aid to replace old vehicles.

By the end of the year, the state will begin offering up to $3,500 in vouchers to replace pre-1996 vehicles, which are some of the heaviest polluters on the roads.

The program will be available in 14 Texas counties surrounding the Dallas-Fort Worth and Houston areas, as well as Travis and Williamson counties.

Owners who agree to "retire" their vehicles will get $3,000 vouchers that can be used toward buying a new car or truck or a late-model used vehicle. If they opt to buy a hybrid, they can get $3,500. The program is voluntary.

Sen. Kip Averitt, R-Waco, led the bill through the legislature. He estimates that old cars and trucks emit 20 to 30 times as much pollution as a new vehicle. Environmental Defense regional director Jim Marston estimates the number is closer to 10 times as much pollution.

Vehicles must have passed a state inspection within the last 15 months, and their owners' annual income cannot exceed $61,000 to qualify.