‘Fuzzy Logic’ is answer to gridlock

Sure, in November Seattle was ranked third among U.S. cities for the amount of time drivers spend stuck in traffic. And recently, the intersection of Interstate 5 and Interstate 90 was named one of the worst in the nation.

But next time you’re suffering oh so slowly through the rush-hour mess, ponder this: It would likely be a lot worse if a new “fuzzy logic” regulating system weren’t in the driver’s seat.

Although it sounds imprecise, fuzzy logic can deliver exacting answers about the ever-changing status of area freeways to help move traffic more efficiently, according to researchers at the University of Washington. After several months of testing at selected on-ramps last spring, the system performed so well that it now dictates traffic flow on all 126 metered freeway on-ramps in the Seattle area. And UW researcher Cynthia Taylor said she’s getting calls from traffic engineers throughout the country interested in learning more about her method.

“There seems to be a lot of interest,” said Taylor, a research engineer with the UW’s Department of Electrical Engineering. “We are very pleased with how well it seems to be working.”

On I-90, the fuzzy-logic system produced an 8.2 percent reduction in freeway congestion - significant enough to be noticeable on a day-to-day basis. It also prevented a bottleneck near the Eastgate on-ramp, a task at which the old algorithm failed. Results show that traffic flow was 4.9 percent better with fuzzy logic.

On I-405, fuzzy logic produced slightly higher freeway congestion and slightly higher flow. The trade-off was that lines at the on-ramps were much shorter using fuzzy logic. According to test data, unacceptably long on-ramp lines occurred nearly twice as often using the old system as they did with fuzzy logic. So fuzzy logic significantly decreased the ramp congestion while maintaining mainline efficiency.

Numerous factors, including weather, accidents and daily variations in traffic, make an exact comparison difficult, Taylor said. But the test results indicate that, as a whole, fuzzy logic reduces travel time and increases flow. It’s also very easy to adjust, so traffic engineers can readily fine-tune it to meet current needs - a big plus in a freeway system as large and variable as Seattle’s.

Seattle transportation officials opted to begin implementing the fuzzy-logic algorithm after test results were available at the end of the summer.

Taylor said she believes the key to fuzzy logic’s success lies in its flexibility - its ability to cope with imperfect input and adapt as the situation changes.

“It’s really more complex to be vague,” Taylor said. “This algorithm is able to use that vagueness to achieve a precise answer. By considering shades of gray and all factors simultaneously, you get a better answer, one that is more suited to the situation.” ¶

Rob Harrill, News & Information