Don't expect to be paying tolls on Interstate 70 anytime soon.

Even under the most ambitious timetable, it would take six to eight years to slap tolls on the 200-mile stretch of I-70 between Highway 40-61 near Wentzville and Interstate 470 near Kansas City, Missouri transportation officials say.

But there may be other political obstacles that could stop any toll road proposal in its tracks. Missouri lawmakers may be apprehensive about imposing tolls — a historically unpopular idea — especially in an election year.

And while Missouri has received federal permission to pursue tolls on existing interstates, at least one other state — Pennsylvania — ran into roadblocks trying to convert a major interstate highway to a toll road.

Missouri Department of Transportation officials say the conversion of I-70 to a toll road would add lanes and replace interchanges on the highway at a cost of $2 billion to $4 billion.

The project would be undertaken by a private consortium. Private companies would finance, rebuild and operate the highway.

While previous toll authority has been put to Missouri voters, MoDOT Director Kevin Keith and others say the latest proposal may not require a public vote.

"The need is there," said state Sen. Bill Stouffer, R-Saline County. "The question is how we finance it. The public needs to be involved in that discussion. I'm not a big fan of tolls. We need to lay the alternatives out."

Stouffer is chairman of the state Senate Transportation Committee, which would hear a toll bill. A bill could be filed as early as this week.

Stouffer said he hopes to hold a "good hearing" on the topic, bringing in experts on both sides and examining a range of funding options. He warned that it may be a mistake to bypass the voters on the I-70 issue.

During a daylong transportation summit last week in Jefferson City, Keith said Missouri's revenue from the state fuel tax has declined the past four years.

Meantime, the state highway construction program has been humming along at $1.2 billion a year, in large measure because of the passage of Amendment 3.

Passed by voters in 2004, the amendment shifted gasoline taxes to pay off bonds for highway construction and repair, and moved all revenue from motor vehicle sales taxes to a highway fund over a four-year period

But going forward, Keith said, spending levels are expected to dip to $600 million a year.

"Nobody is going to give us any more money right now," Keith said.

Rebuilding I-70 also would be a boost to the state's economy, he said, creating 10,000 jobs a year during the life of the project.

Pennsylvania twice tried to turn a stretch of Interstate 80 into a toll road. Former Gov. Ed Rendell told the U.S. Senate Finance Committee last May that the toll road would have generated $200 million for the maintenance of that highway.

The U.S. Department of Transportation refused to allow Pennsylvania to collect tolls. The only places where tolls are allowed on interstates are those stretches where collections predated the interstate system.

"For lord's sake, lift the cap (on tolling)," Rendell told the Senate panel.

One key difference between Pennsylvania and Missouri is that MoDOT has received federal permission to proceed with the I-70 toll road option.

Meantime, Brad Guilmino, chief financial consultant at HNTB Corp., said there is a "lot of talk" among U.S. states about tolls on existing interstate highways because of scarce highway funds.

"Really no road is free," Guilmino said last week during a panel discussion in Jefferson City. "There's a toll road, and there's a road you are paying for with your gasoline tax or your sales tax."

The tolling process has changed, Guilmino added. A car can pass a gantry at 70 mph and it would detect the transponder. It could be outfitted with a camera to "take 10 snapshots" of a license plates to bill the registered owner, he said.

As a result, cars wouldn't have to slow down and stop at a toll booth, he said. Not all highway trips would require paying tolls because of how the gantries are placed.

Dave Osiecki, senior vice president for policy and regulatory affairs at the American Trucking Associations, agreed that more funding is needed to rebuild U.S. highways.

But toll facilities chase drivers to other highways to bypass the toll, he said.

Diversion is "a big deal," Osiecki said, for an industry that spends a lot of time adopting technologies, training drivers, complying with federal regulations. Trucks tend to divert to less-safe roads from toll highways, he said.

The American Trucking Associations is open to tolling if it adds new highway capacity, Osiecki said. "Where we really don't like tolling is on existing capacity — existing interstates in particular."

Failure to take it to a public referendum, he added, appears to be "potentially dangerous approach."

And if open toll collections on I-70 favor local traffic at the expense of interstate traffic — such as trucks — it could unfairly discriminate against interstate commerce.

State Sen. Mike Kehoe, R-Jefferson City, said he and other lawmakers are "looking at some different concepts." Kehoe, a former state highway commissioner and vice chairman of the Senate Transportation Committee, said the bill would get the conversation going.

"I don't have any visions of grandeur that this is just going to sail right through," Kehoe said. "It's a tough conversation. And I understand both sides of this."