LAYTON — They've determined the "why." Now comes the "what" and "where."

The Utah Department of Transportation is entering the next phase of its West Davis Corridor study, designed to figure out ways to meet transportation needs through the year 2040 in western Davis and Weber counties.

Having determined something has to be done to reduce traffic congestion in the area, UDOT is moving on to figuring out what the alternatives are. It's a phase that UDOT project manager Randy Jefferies calls "the heart of the public involvement and community participation."

"Those solutions may be transit solutions; they may be roadway solutions; they may be new corridors; they may be existing corridors that need to be widened," Jefferies told the Davis County Council of Governments this week. "We're looking north-south, east-west. Right now, everything is on the table."

The study area is bounded by the Great Salt Lake on the west, I-15 on the east, Parrish Lane in Centerville on the south and 12th Street in Marriott-Slaterville on the north.

Looking at alternatives is part of an $8 million "environmental impact statement" process expected to take a few years. Three open houses are set for early August for UDOT to get ideas from the public.

By year's end, options will be narrowed to a final group of three to four that "we'll really put a magnifying glass on," Jefferies said.

"We have a high degree of congestion" in the study area, he told the council. "In fact, by the year 2040, our traffic congestion is projected to triple, and our delays will increase by 140 percent by the year 2040 if no corridor is defined and constructed."

The area's population is projected to grow by 75 percent by 2040; north-south roadway congestion is expected to increase by 269 percent and east-west congestion by 131 percent during that period.

UDOT is conducting the study in cooperation with the Federal Highway Administration. The federal agency will make the final decision on the matter. A draft EIS will be prepared in 2011, followed by a final EIS in 2012 and a final decision in 2012 or 2013.

The West Davis Corridor concept first appeared on local planning maps during the 1960s, and it has gone by several names since then under various studies: West Davis Highway, North Legacy and the Legacy Parkway (or state Route 67) extension.

UDOT is using the "West Davis Corridor" essentially to look at the situation through fresh eyes, but it also has said it expects one alternative to be a recommended corridor from a 2001 North Legacy study.

That study was the basis for the Davis County Council of Governments to begin buying parcels of land within the corridor before the land is developed, thus saving the government from having to buy more expensive land in the future. The money comes from approximately $2 million collected annually in special vehicle registration fees.

Details about the West Davis Corridor are at www.udot.utah.gov/westdavis.

e-mail: bwallace@desnews.com