Interstate 81 doesn't need separate lanes for trucks border-to-border through Virginia, a study released Tuesday suggests.

Looking at I-81 through a year-2035 lens, the study says at least one new lane will be needed both north and south, and about half of its 325 miles will need two new lanes in each direction.

The Roanoke Valley and Christiansburg Mountain are potential two-lane sites. They were included in the study, which was announced by the Virginia Department of Transportation.

Sections of I-81 at Wytheville and Harrisonburg may need to be relocated, the study said.

Tolls, and the traffic that would avoid I-81 because of them, also were evaluated.

Possible state-financed railroad improvements also were analyzed.

The question most people have about I-81 is "when will construction begin," and the study doesn't answer that. It's a step in the process that eventually could lead to widening the highway.

Called a draft environmental impact statement, the study took almost two years, and it is only a first-level review. A second phase called Tier 2, may begin in 2007.

Public meetings will be held starting in January for people to give VDOT their comments on the study's findings.

No construction can begin until the Tier 2 study wins approval. But whenever that happens, dirt could start to fly in locations that don't have sensitive environmental issues requiring detailed study and protective measures.

The phase-one environmental study did not formally determine any specific number of lanes, and it did not propose any ways of financing improvements.

Nevertheless, VDOT Chief Engineer Mal Kerley called it "an important milestone in planning the future of Interstate 81 in Virginia."

Its finding that a single new lane in each direction would meet needs in 2035 dampened a proposal by the Star Solutions builders' consortium that suggested an eight-lane highway with four truck-only lanes financed by truck tolls.

Star Solutions isn't giving up, though. It is still negotiating a contract with VDOT to make whatever improvements they can agree on.

Environmental issues raised in the study will be the key factor in determining what those improvements can be, Kerley said.

Separate lanes for trucks remain a possibility in some locations, said Star Solutions spokesman Tyler Bishop in Richmond.

"We still very much believe that truck lanes are warranted to improve safety on the corridor as a whole. It's obvious the environmental process will determine what we can and can't do. The lanes might not all be separate, but a majority might be separated," Bishop said.

An environmental group's spokesman said he was glad the study supports a varying number of lanes depending on location.

Trip Pollard of the Southern Environmental Law Center said "the congestion and safety problems are primarily found in certain hot spots."

"Improvements are clearly needed to I-81, but they need to be targeted improvements rather than a one-size-fits all approach such as the Star Solutions proposal," Pollard said. "And they need to be coupled with other reasonable, long-term solutions."

One of those solutions in the VDOT report was an upgrade to railroad tracks in the I-81 corridor, with a goal of moving more freight by rail instead of trucks.

Truck traffic will increase faster than cars in the next 30 years, the study said. Upgrading rail lines to make trains faster would absorb some of that truck growth, the study said, but I-81 still will be heavily congested unless it is widened.

Star Solutions endorsed the rail concept in a statement. "The Star Solutions team continues to believe that rail should be part of a multimodal approach to relieving congestion in the corridor," it said. The report suggested an ideal solution for I-81 might include an upgrade to Norfolk Southern Railway tracks from Lynchburg through Winchester.

About $500 million in public funds for rail improvements, coupled with a two-lane upgrade of I-81, would cost $8.3 billion in 2005 dollars. By 2015, the cost likely would rise to $12 billion, the study said.

The report's summary also mentions a proposal by Rail Solution, a group that advocates a major rail upgrade as an alternative to widening I-81. The group's suggestion for two tracks along the NS lines from Bristol to Winchester would cost $3.7 billion, and doesn't offer enough benefits to justify the cost, the study said.

The study's summary pays considerable attention to tolls and the number of drivers who might switch to U.S. 11 to avoid having to pay.

Unless I-81 is widened, traffic on U.S. 11 will be extremely heavy in 2035, the study says.

If I-81 is widened and a low toll is charged, traffic on U.S. 11 will be less than if nothing is done, the study says.

If I-81 is widened and a high toll is charged, traffic on U.S. 11 would be worse than if nothing is built, it says.

Regardless of whether anything is done to I-81, U.S. 11 will need improvements by 2035, the study adds.

It did not say how much a low toll or high toll would be.

The summary presents a fairly glossy picture of toll effects, repeatedly saying that toll-inspired diversions would have a "slight" impact.

The "actual traffic impacts on these roads resulting from the number of additional vehicles would be low," it says.

Of the vehicles that would avoid a tolled I-81, about half would switch to U.S. 11, the study said. Most of those are likely to be driven for shorter distances, possibly 100 to 300 miles.

Longer-haul trucks, hauling freight from the Deep South to markets in the Northeast, have other options.

They can choose to go north via Interstate 95, or by way of Interstates 65, 64 and 79 through the Ohio Valley.

"About 14 percent of freight traffic diverted off of I-81 would use I-95 as an alternate route, and approximately 15 percent would use" the Ohio Valley corridor, the study said.

"These diversions are not expected to have a measurable impact to traffic operations on parallel interstates," the study says.

Missing from the summary was information on the number of vehicles that could be expected to divert to the alternate routes.