Salt Lake's population surges by 131,180 every workday, giving it the third-highest commuter-to-resident ratio of cities its size or larger nationwide.

Commuting increases Salt Lake's daytime population to an estimated 312,923 from an estimated 181,743, giving it a ratio of 2.45 commuting workers to every resident worker, according to the first-ever U.S. Census Bureau estimates of the daytime populations. Washington, D.C., ranks first with a ratio of 2.57, followed by Irvine, Calif., with 2.45.

The findings are based on 2000 Census data from more than 6,400 places across the country.

Census Bureau Director Louis Kincannon said in a statement that the information is important for planning purposes, "including those dealing with transportation and disaster relief operations . . . the data can provide a clearer picture of the effects of disasters such as Hurricanes Katrina and Rita."

The places where the largest percent increases in daytime over nighttime populations occur tend to be those with small resident populations. For example, among medium-size cities, Greenville, S.C., has a daytime population 97 percent higher than its nighttime population.

The report also shows that commuting increases Park City's population by 91 percent. Other small Utah cities with high daytime increases are South Salt Lake, Murray (36 percent) and Vernal (28 percent).

Demand strapped officials with the Utah Department of Transportation and Utah Transit Authority say they're not surprised by the ranking.

"We're doing our very best to keep up," said UTA spokesman Justin Jones, who said an average 50,000 passengers rode light rail each weekday in September, and standing room on buses to town from as far away as Payson and Brigham City is regularly taken.

Jones said a new planned 44-mile commuter rail from Weber County should help meet the demand.

Meanwhile, UDOT spokesman Nile Easton said the number of vehicles on the road and miles those vehicles are traveling is rapidly increasing. UDOT has in the past three years added a carpool lane on I-15 and is working to extend that through Provo, and has added traffic cameras.

The agency is also studying the possibility of tolls to allow single drivers to use the carpool lane.

"We keep facing a curve we can't get ahead of," he said. "We're trying to be creative."

Roger Borgenicht, chairman of Future Moves Coalition, a part of Utahns for Better Transportation, said the census numbers indicate a need for a regional transportation network "so that people have more choices."

He said if people are commuting regularly they need a convenient and reliable way to get downtown.