Colorado needs $9 billion to improve roads and alleviate traffic congestion in the next 10 years — a number so large that state lawmakers are entertaining a once-unthinkable solution: a tax hike.

Democratic and Republican leaders are negotiating a measure for the November ballot to increase taxes and generate billions of dollars for transportation projects across the state, including the expansion of Interstate 25 north and south of Denver and Interstate 70 through the mountains.

The early discussions represent a significant shift in the political mood at the Capitol, particularly in a state where all tax hikes must go to the voters and conservative forces hold immense influence. The proposal, most likely a sales-tax increase, is expected to include other tax cuts in the first years as an offset.

If the legislature referred a statewide tax hike to the ballot, it would be the first of its kind in 25 years.

The only other tax hike that lawmakers put on the ballot since the approval of the Taxpayer’s Bill of Rights (TABOR) in 1992 was Proposition AA in 2013 — which voters essentially sanctioned a year earlier with the passage of a constitutional amendment legalizing recreational pot sales.

Sandra Hagen Solin with Fix Colorado Roads, an organization pushing for a deal, said lawmakers are realizing “that the public is increasingly becoming frustrated with the transportation system.”

“It’s remarkable that the conversation is occurring,” she continued. “And I think that’s why we are encouraged by the potential of a solution being brought forward before the session ends.”

Still, the initial optimism belies discord among rank-and-file lawmakers in both parties who are unhappy with the political trade-offs. And it overlooks mounting opposition from conservative organizations, such as Americans for Prosperity, the Independence Institute and the Colorado Union of Taxpayers, all of which are opposed to any tax hikes. Like years past, either factor could thwart a deal.

“If anyone thinks that another ballot proposal that starts with the line ‘shall taxes be increased’ is going to pass in 2017, they are fooling themselves,” said Michael Fields, the state director for AFP, an organization backed by the billionaire Koch brothers, which announced a petition drive Thursday to stop a tax increase.

Four citizen initiatives to increases taxes — including one for tobacco products in 2016 — failed in recent years. Even the Amendment 66 campaign to raise taxes and direct $95 million to classrooms failed in 2013, despite early enthusiasm and positive polling.

“Tax hikes have had a checkered history in this state,” said Rick Ridder, a veteran Democratic strategist who works on ballot campaigns. “The proponents will have to convince voters that the need is great, that the time is now and that the amount is little but sufficient to do the job and benefit those who are paying the tax.”

A growing urgency back home

Colorado Springs Mayor John Suthers, a Republican and the former state attorney general, knows what it’s like to push a tax hike amid blowback from members of his own party. And win.

With Suthers’ insistence, city voters approved a 0.62 percent sales tax increase for five years in 2015 to generate an estimated $250 million to fill potholes and make road repairs. Now, he’s part of the coalition urging Colorado lawmakers to strike a similar deal for the state.

“We need to hold them accountable on this issue,” he said. “This need to be done.”

His top priority is expanding a 17-mile stretch of I-25 from Castle Rock south to Monument that is a consistent bottleneck. He cited an estimate that one-quarter of people buying homes in northern El Paso County are working in the southern Denver area.

“You have two of the 40 largest cities in America within 70 miles of each other and there’s an awful lot of interaction,” he said.

The lesson Suthers learned in 2015 speaks to how the mood toward a tax hike for roads has changed at the statehouse.

“Any polling you do, people are upset about the roads,” he said. “Often times, when you go to the voters, you have to spend a lot of effort convincing them that something is an issue. Not when it comes to roads. They know roads are an issue.”

The state is adding roughly 100,000 new residents a year, meaning road conditions and traffic will get worse.

The pressure on lawmakers is coming from communities across the state — all of which have a list of favorite projects that need dollars.

Chris Romer, the president of the Vail Valley Partnership, a community development organization, is focused on I-70 in the mountains. Not only is skier traffic so bad that it deters visitors, he said local businesses rely on trucks to haul their goods down the mountain.

“The I-70 corridor is our lifeline,” he said.

Gov. John Hickenlooper and Colorado lawmakers are hearing the message and entered the 2017 term agreeing that transportation money is the No. 1 priority. But both made similar pledges in prior years only to fail to reach agreement in the end.

Tony Milo, the executive director of the Colorado Contractors Association, said this year is different. “We are finally at a point where we are at an urgency, where the legislature feels like they can’t adjourn without addressing the issue,” he said.

The reason, he continued, “is the fact that … traffic just gets worse every day and voters and motorists are at a breaking point.”

What a deal may look like

The initial conversations about a deal are occurring behind closed doors between Republican Senate President Kevin Grantham, Democratic House Speaker Crisanta Duran and Hickenlooper’s office.

The Democratic governor recently suggested the leading idea is a tax measure that generates as much as $500 million a year for road projects, most likely from a sales tax hike, as part of a bond package that would reach near $3.5 billion. But the terms are far from certain.

The opening negotiations involve three possible sources for new dollars: new taxes, current general fund money and federal gas tax revenues. Each option has its advocates and critics, and a final agreement would likely incorporate multiple levels of funding.

Hickenlooper maintains that any deal must include new revenue. Most of the attention is on a sales tax because it generates the most money. For example, an additional 0.5 percentage point increase in the 2.9 percent statewide sales tax would raise an estimated $514 million next fiscal year.

Republican lawmakers are insisting that the measure remain revenue-neutral in the first year — meaning the deal must include tax cuts that equal the initial tax hike. Two possible cuts are the gas tax or the business personal property tax.

The balance would create political cover for lawmakers who pledged not to increase taxes.

Sen. Don Coram, R-Montrose, said the U.S. 550 highway in his district is becoming dangerously crowded, and he’s prepared to make the argument for a tax hike back home.

“The ‘R’ behind my name stands for rural and we in rural Colorado have needs and requirements that can only be addressed through a taxation program,” he said.

But Colorado cities and counties are expressing caution about increasing the sales tax because they use local levies to derive most of their revenue. And even some Democrats are hesitant about a sales tax hike hitting the poor the hardest.

“I would be hesitant to rely only on a consumption tax or sales tax,” said Rep. Chris Hansen, D-Denver. “I think that can be very regressive in nature.”

Republican legislative leaders want to first look for money in the $11 billion general fund, which represents the discretionary spending in the $28 billion budget.

“We have the money in our general fund,” said Rep. Dan Nordberg, R-Colorado Springs. “We just need to prioritize transportation — and shame on us for not doing so earlier.”

To make room, conservative lawmakers are demanding cuts to health-care spending, particularly the Medicaid program that provides health insurance to low-income residents, as well as redirecting mass-transit money to road building.

“If there is not some talk about finding funding inside the current budget, there’s not going to be a tax increase that passes,” said Jon Caldara, president of the Independence Institute, a Denver think tank aligned against tax hikes. “Getting it on the ballot is easy, but getting it passed is not.”

Democratic leaders suggest reclassifying the hospital provider fee — a budget move that failed the last two years — would allow more spending for roads. And they say using existing revenue should not be part of the deal because it takes money from education and other needs.

“It’s not there. Look at the budget. There is no money,” said Rep. Diane Mitsch Bush, D-Steamboat Springs, the House transportation committee chairwoman. “And to say there is (money) is misleading the public, it’s misleading our businesses, it’s misleading our families.”

As an alternative to a tax hike, Republican lawmakers and conservative advocacy groups are renewing a push for a $3.5 billion bond package that uses half the federal gas tax revenue to cover the debt payments — a 2015 bill that failed in the Democratic House.

The proponents note that the payments to the TRANS bonds that began in 1999 end this year, freeing up about $170 million for a new bond issue. But the state transportation department argues that money is needed to cover maintenance and operations of the new roads built with the bonds.

“We’re already squeezing every penny out of our transportation revenue but efficiencies can only get us so far,” Hickenlooper told lawmakers in his State of the State address, in which called for a ballot measure this year.

The competing ideas and political factions will make reaching a deal difficult. And lawmakers are especially cognizant that putting a measure on the ballot is only the first step.

“I’m open to anything,” said Rep. Faith Winter, D-Westminster. “And I think it’s important to also talk to the voters and see what funding mechanisms they’re open to. Because ultimately, it’ll be their decision.”