Opponents of the proposed Legacy Parkway say the traffic model used to determine the need for the Davis County road is still flawed, despite attempts to fix it.

An analysis by two University of California-Davis professors, funded by the Utah Chapter of the Sierra Club and five other organizations opposing the proposed road, found the travel-demand model developed by the Wasatch Front Regional Council is biased in favor of building highways."The model is insufficiently accurate for plan or project analysis," wrote Caroline Rodier and Robert Johnston of UC-Davis' department of environmental science and policy.

"We can only conclude that the model is inadequate to evaluate the travel effects of the proposed I-15 North corridor (reconstruction) and the Legacy Parkway."

Bob Adler, a member of the local Sierra Club's legal committee, said the model of mathematical formulas evaluating current and future growth patterns does not take into account induced travel or land-use changes.

"If you build more highway lanes, people tend to drive more and longer, so you end up with more capacity but more demand," Adler said. "You're chasing your tail."

The professors also found the model ignores trends suggesting that highway construction leads to sprawled development and additional vehicle trips.

"They didn't consider those things at all," Adler said of the regional council. "They consider the same land-use patterns whether or not you build the highway and actually show less traffic after you build the highway than before."

Mick Crandall, project manager for the regional council, said he is not aware of any projection of less traffic after the $401 million Legacy Parkway is built.

And as for adjusting land-use patterns, that is a matter for local communities, Crandall said. The regional council included in its model the master plans already developed by Davis County communities, he said, and felt it improper to do otherwise.

"We have tried to do everything that was suggested (by critics) last spring," Crandall said of recent adjustments to the traffic model. "We made a lot of changes. We spent a fair amount of money."

Crandall said the full revision of the travel model, to be included in the upcoming final Environmental Impact Statement, has not even been released.

Adler said the Sierra Club, which has been involved in the reworking of the travel model, gathered enough documentation to review the new model before an official release.

The Sierra Club has waged a public battle against UDOT and its partners in an attempt to stop the 12-mile, four-lane highway from being built parallel to I-15 in southern Davis County.

Marc Heileson of the Sierra Club said the organization remains confident that once UDOT and the regional council "put a good-faith effort into studying transit alternatives," they will discover there are more environmentally friendly alternatives to road building in the wetlands-rich Davis County corridor.

The regional council, the Utah Department of Transportation, the Sierra Club and others are scheduled to meet Wednesday morning to discuss the travel model and the EIS. Crandall said many of the Sierra Club's concerns can be discussed at that time.

"They should have sat down and talked, listened to what was there before they issued a press release," Crandall said of the Sierra Club. "They reacted to some materials that they got, I don't know when. A month ago, two months ago. I think there are some things that are different" about the model now.

Crandall said no matter what changes are made to the traffic model, it is clear to the regional council that the Legacy Parkway is needed.

"I don't think there's any question," he said. "You look out here today. You need a highway today."

Carlos Braceras, UDOT's Legacy Parkway project director, said the travel model was identified as "state-of-the-practice" even before a peer review by the Federal Highway Administration. That review suggested a number of changes, which were made, Braceras said.

UDOT officials will meet with Federal Highway Administration and Army Corps of Engineers officials later this week and hope to issue the final EIS by the second week in June. A public hearing would be held a month later.

A record of decision from the Federal Highway Administration and a decision on the Clean Water Act permit by the Corps are expected in October.

If UDOT gets the green light in each case, it could hire a contractor in December and the Legacy Parkway could be under construction by July of next year.

You can reach Zack Van Eyck by e-mail at zman@desnews.com