TDOT fears hazard unless all obey smog-cutting limit

Enforcing different limits for cars and trucks would produce safety hazards, they say.

“Whatever we’re going to have to do is going to have to be done for all,” said Ed Cole, chief of planning and environment for the Tennessee Department of Transportation, which sets speed limits.

Facing federal deadlines to meet new standards for ozone pollution, regulators have identified a reduction of truck speed limits to 55 mph as one of the most effective ways of slashing emissions of smog-causing nitrogen oxides.

The reduced speed limits would be enforced only in Shelby and other mostly urban counties that have had trouble meeting the ozone standard.

In some counties, the state estimates that cars and trucks produce more than half of the emissions that help form ozone, the main component of smog.

Officials haven’t decided whether the limits would be in effect year-round, just during the warm-weather ozone season, or only on days when high pollution levels are forecast.

“We’re in favor of reducing speed limits in counties with air-quality problems. How we go about that . . . is outside our bailiwick,” said Rick Bolton, vice chairman of the state Air Pollution Control Board.

This week, the board called on Department of Environment and Conservation Commissioner Betsy L. Child to convene Gov. Phil Bredesen’s interagency task force on air quality to discuss speed limits and other smog-reduction strategies.

At its April meeting, the board plans to vote on a resolution regarding speed limits.

Cole said TDOT has advised against “differential” speed limits for cars and trucks on safety grounds. The department’s views are shared by the trucking industry.

“If you have lower speed limits just for trucks, we have a serious concern that you’re going to do damage on the safety side,” said Chris Burruss, president and chief executive officer of the Tennessee Trucking Association.

Burruss said statistics show that some states with different limits for cars and trucks have more rear-end accidents than states with uniform limits.