Efforts to Reduce Road Congestion May Create Smog : Pollution: A new computer model indicates that emissions appear to rise as cars accelerate beyond 20 to 35 m.p.h. The findings may cause planners to rethink some transportation projects.

Creeping through sluggish rush-hour traffic makes cars spew out more pollutants.

To relieve pollution-causing congestion, transportation planners and pollution regulators have budgeted millions of dollars each year to build car-pool lanes, subways, trolley lines and other improvements.

Now, however, the California Air Resources Board has developed a new computer model that suggests that longstanding efforts to reduce congestion may, under certain circumstances, create more pollution.

The board’s computer-generated “emission factors” indicate that emissions do drop as average freeway speeds rise to between 20 and 35 m.p.h. But they also appear to start rising again as cars accelerate much above that speed.

The implication for transportation planners is potentially significant. Under the Clean Air Act, the Environmental Protection Agency can withhold federal grants to projects that increase air pollution. If, as the board’s computer model suggests, freeway improvements and train lines are found to increase pollution, hundreds of millions of federal dollars could be at stake.

EPA officials said they doubt that the new emission factors will endanger major federally funded transit projects such as the Metro Red Line subway or the Century Freeway. But officials believe that it could force the review of some new freeway construction projects--such as toll roads in Orange County--or the addition of car-pool lanes that are reserved for commuters several hours each day.

“I find it hard to conceive that we would sanction a subway project,” said one official, who asked not to be named because he is involved in deciding how to apply the emission factors to Southern California’s pollution-control plan. “And I think the same is true of (car-pool) projects that are really designed to increase . . . the number of people who use car pools.”

The full effect of the Air Resources Board’s new data will take time to sort out, he added.

“It’s a pretty fluid discussion at this point,” he said. “There are some very sensitive negotiations going on at this point.”

The potential effects on freeway building and widening projects, some car-pool lane construction and other improvements has led the state’s three largest transportation agencies--Caltrans, the Los Angeles County Transportation Commission and the Metropolitan Transportation Commission in the Bay Area--to challenge the methodology behind the emission factors.

Meanwhile, the county transportation board is scheduled to consider a committee recommendation Wednesday under which the board would enlist other agencies to join the commission in petitioning the Air Resources Board to convene an unusual public hearing to reconsider the emission factors.

At issue is the state board’s computer estimation of how much cars pollute when driven in ordinary traffic. This estimate--generated by using computer models developed at the California Institute of Technology and elsewhere--is applied to regional plans that predict how many cars will be on the road in years to come.

Multiplying the number of cars by the average amount of pollution lets planners anticipate whether the region will meet its goal of complying with federal clean air standards by early next century.

These factors help planners set goals for how many cars they need to try to get off the region’s streets and highways--by diverting drivers into other travel modes, such as car pools, trains, buses or bicycles.

It has long been known that cars pollute somewhat more at higher speeds, but earlier Air Resources Board models predicted that the amount of added pollution was so low that congestion relief programs would not backfire and significantly increase smog.

The new state board model, however, changed that.

In the past, carbon monoxide and hydrocarbon pollution were not predicted to increase until a car accelerated beyond 55 m.p.h.--or about 45 m.p.h. for nitrogen oxide pollution. Now, the state board believes that carbon monoxide and hydrocarbon pollution jump when cars reach 35 m.p.h.--or 20 m.p.h. for nitrogen oxide pollution.

“The implication of these new emission factors is that any project or program which improves the traffic speed, directly or indirectly, will increase emissions,” staff air quality scientist James Ortner recently warned the County Transportation Commission.

“Thus, . . . highway projects, (car-pool) lanes, even transit projects which allow highway speeds to increase could be delayed or not built because of the models yielding emission increases.”

Richard Spicer, principal air quality planner for the Southern California Assn. of Governments, agreed.

“If the transportation capital improvement plan is found to be not in conformity with the Clean Air Act,” he said, “then federal funds for transportation facilities might be held up.”

At the very least, they said, the state board data may greatly complicate regional planning and the political process of deciding which transportation projects to build. Instead of doing things to reduce congestion and pollution, some decisions could come down to whether planners want to reduce congestion or pollution.

“Traditionally, we’ve always thought that emissions drop as speeds increase, so there is a common goal for environmental and transportation planners, which is to relieve congestion,” the EPA official said. “This reverses some of that thinking.”

“It changes a lot of our assumptions,” Spicer said. “It goes right to the basis of our planning. We may not always be able to serve both goals.”