Stop‐and‐go science: By better understanding traffic flow, researchers hope to keep down highway congestion

W elcome to Los Angeles. The year is 2020. The traffic is, well, worse. Average commuting times are twice what they were in the 1990s. Drivers endure a stop-and-go crawl over almost half the miles they travel. Peak speeds on the region's roads have tumbled. The average rush-hour, roadway speed is 24 miles per hour. These bleak predictions from the Southern California Association of Governments may paint a more troubled picture for L.A. than what's expected for many metropolitan areas. However, the rest of the world's cities won't be far behind. Officials at all levels of government are sorting through a queue of proposals to lessen congestion. They include, for example, better mass transit systems, new road-use fees to influence driver choices, and construction of separate highways for cars and trucks. Meanwhile, scientists and engineers around the globe are trying to figure out how to cram more vehicles onto the existing roadways without putting highway speeds into a nosedive. "We can't just build more and more roads, so basically we have to try to use the existing capacity more efficiently," says Peter Molnar, a traffic scientist at Clark Atlanta (Ga.) University. It's a two-pronged undertaking in which researchers are generating mathematical and computer models of traffic flow and at the same time devising ways to reduce congestion. Some of the new mathematical models, advanced mainly by physicists, deDict traffic as more comDlex and unpredictable than traditional traffic experts, mainly civil engineers, believe it to be. These models have sparked intense controversy. Other, relatively simple models, which are based on computer simulations rather than differential equations, are winning acceptance for their ability to generate artificial traffic networks that behave like real ones. Researchers have also begun applying their findings in new ways, such as combining simulations with actual traffic data to predict and avert delays. In the next few years, traffic-forecasting systems linked to intelligent highway controls, such as on-ramp metering lights, will become more common, the scientists say. Then, the benefits of their investigations should start to kick in.