The plaintiffs agreed they wouldn't sue again, but couldn't promise no one else would. They agreed to a provision that would allow UDOT to pull out of the agreement in the face of a serious legal or administrative challenge from others.

"This was a particularly difficult issue," said Robert Adler, the University of Utah law professor who worked with the plaintiffs. "The value of a settlement to the state is in part that they don't have to fight a lawsuit."

But the unusual escape clause not only does nothing to prevent lawsuits, says Rep. David Ure - it's a road map to more litigation and spells the eventual demise of the agreement.

"I don't think this is the end of lawsuits, but the start of lawsuits," said the Kamas Republican, who vowed to vote against the resolution approving the settlement during Wednesday's special legislative session.

It's not known how much support the measure has in the Legislature.

Adler says the escape clause allows each side to wield equally strong hammers, but doesn't see much risk.

"What does it all add up to? Probably zero," he said.

Ure said he's already heard of people, whom he wouldn't name, who are considering legal action against the settlement to see if they can get UDOT to bolt.

The escape provision also spells out how the six main plaintiffs in the lawsuit - the Sierra Club, Utahns for Better Transportation, the League of Women Voters, Friends of Great Salt Lake, Future Moves Coalition and Great Salt Lake Audubon - could be released from their promise not to sue again.

In his 25 years of crafting environmental law settlements, Adler said he's never seen a lawsuit come from an outside party; still, he said, it is unusual to see such a clause written in.

"We felt it was pretty necessary," said UDOT spokesman Tom Hudachko. "It gives us the option to stand down."

If that happened, "everybody could sue everybody else," an undesirable end to negotiations that Gov. Jon Huntsman Jr. initiated shortly after taking office in January.

Legislative approval of the settlement would mean the Legacy Parkway, stalled since 2001 when the 10th U.S. Circuit Court of Appeals agreed that the state's environmental study was deficient, could begin construction in May and open in 2008 and relieve severe rush-hour traffic congestion between Salt Lake City and Farmington.

The 27-page agreement outlines how the roadway would be constructed to minimize harm to Great Salt Lake wetlands while also alleviating traffic jams on Interstate 15. Key components include a ban on semitrailers and billboards, a maximum speed of 55 mph and rubberized asphalt to dampen road noise. The parkway would be just four lanes wide for at least the next 15 years.

Sen. Sheldon Killpack, R-Syracuse, who supports the compromise, said that critics claiming they oppose the settlement on principle are making allegations that simply aren't true. That has helped keep emotions churning as the special session comes closer.

"I'm hopeful in the end that cooler heads will prevail," he said.

Ure says he will oppose the deal when it comes to the vote Wednesday because he objects to the way negotiations were conducted out of the public and legislative eye. He said he thinks the ban on semitrailer trucks is fundamentally unfair and finds the design principles frivolous.

That doesn't mean he is against building the highway.

"Don't you ever insinuate I don't want this road. I do," he said. "I believe we can build the Legacy Highway just as fast without the compromise as with the compromise."

Ure, the House parliamentarian, has emerged as one of the more high-profile critics of the settlement made public this week. He has joined up with Friends of Legacy, a group that claims a dozen or so members who oppose the Legacy settlement. Started by activist Dave Owen, the organization has been running ads on KSL radio claiming "a handful of environmentalists" are setting the state's road-building agenda.

Ure wrote an opinion piece published in Thursday's Deseret Morning News calling the deal "blackmail," and told The Salt Lake Tribune the settlement "has so many holes in it you could drive a semi through it."

Semis won't be allowed to drive on the parkway, however, a restriction that Utah Trucking Association president Dave Creer spells serious difficulty for the Salt Lake Valley.

Creer pointed out that semitrailers with 80,000-pound capacities haul food, fuel and clothing on I-15 are using an international freight corridor known as Canamex serving the entire Western Hemisphere.

Creer isn't buying UDOT reassurances that the Legacy Parkway will claim 30 percent of the interstate traffic, making it easier for truckers to make their runs. Truck traffic on I-15 is estimated to grow 6 percent per year, or double in 20 years, he said. And freeway traffic is bound to grow because of northern Utah population increases.

The Legacy settlement would allow exemptions to the big-rig ban in case of an emergency on I-15. But in the modern trucking world, where routes are set by computer long before freight starts rolling, if a road isn't permanently available it isn't even on the map.

With companies, including Wal-Mart, building huge distribution centers on the outskirts of urban Utah, "what we're going to be facing down the road is a real crisis in getting goods into this valley," Creer said.

Would the trucking association legally challenge the settlement?

"Emphatically no," Creer said. "We're not going to sue."

But they do want the conservation groups to know that if they try to ban trucks on any other roadway, "they're going to hear from an organized group," Creer said. "They've awakened a sleeping giant."