Four companies have made the Colorado Department of Transportation’s short list to pitch proposals for a full makeover of the Interstate 70 mountain corridor through a public-private partnership.

“It’s exciting to see that companies want to step up and partner with the Colorado Department of Transportation and do something meaningful on I-70,” said County Commissioner Dan Gibbs, who also sits on the I-70 Coalition. “This development will help figure out how you fund it, and that’s one of the biggest challenges ahead of us.”

CDOT put out a call for bids for a partnership project, following last year’s unsolicited proposal from Parsons, one of the final four, to make over the congested I-70 corridor between Denver and the High Country.

With four takers, CDOT will release an official request for proposals next month. Based on the project plans submitted, officials are expected to select a company to work with from among the four by as early as fall of this year. At that point the proposal specifics, currently kept under wraps for proprietary reasons, will be released.

The contenders are CH2M Hill, the world’s largest engineering firm, based on the Front Range; Parsons Corporation, the California-based company that instigated the current investigation of a public private partnership; HNTB Corp. out of Kansas City; and HDR Inc., an engineering and consulting firm headquartered in Omaha, Neb.

The proposals will likely mirror an improvement plan known as the “preferred alternative” that got the green light last year from both CDOT and the Federal Highway Administration. The sweeping, long-term plan envisions improvements on the corridor ranging from additional lanes between Floyd Hill and the Eisenhower Tunnel and high-speed rail to traffic management strategies and bus services.

Details recently released on one of the company’s proposals indicate tolls would likely be involved.

A high-speed rail has been a key component of plans for the I-70 corridor, but to be effective in reducing peak-season traffic, the line would have to be fast enough to tempt motorists away from the option of driving, CDOT officials have said.

But a rail system that could handle the weather, grades and sharp curves of the I-70 corridor at a high speed would likely be prohibitively expensive for the state transportation department.

Early estimates came in between $10 and $20 billion, daunting numbers for CDOT, which is already struggling to maintain Colorado’s existing highway system on its approximately $1 billion yearly budget.

But a top executive for HNTB, one of the firms submitting proposals for the I-70 corridor, recently expressed optimism for high-speed rail projects in the United States, specifically citing plans for trains connecting congested corridors in Texas and California.

“We can’t continue to build ourselves out of these areas by just building more freeways and airports,” sr. vice president and chairman of high speed rail services at HNTB Peter Gertler was quoted as saying in HSR Updates, a trade publication.

He did not mention the I-70 mountain corridor project, but did go on to state his belief that the public sector should pave the way for partnerships on infrastructure improvements with up-front investments.

“It’s pretty much in the public domain right now, which is evaluating the need, identifying the alignment and securing or getting environmental clearance,” he told HSR Updates. “After that point, when it’s ready to go into final design and construction, I think at that point there is an opportunity to explore private investment.”