Larry Hogan, right, speaks with Senate President Thomas V. Mike Miller before taking the oath of office Jan. 21 to become the 62nd governor of Maryland. (Patrick Semansky/AP)

Maryland Gov. Larry Hogan’s bill to cancel upcoming gas-tax increases would sap nearly $3 billion from planned road and transit projects over the coming six years, according to a draft document from the state Department of Transportation.

The legislation — Hogan’s boldest bid so far to provide tax relief — presents another challenge to the bipartisan cooperation that has been promised by both the Republican governor and the Democratic-controlled General Assembly.

Democratic leaders are fiercely resisting the governor’s bill, saying it and other funding changes that Hogan is proposing would be a fatal blow for the light-rail Purple Line in the Washington region and kill most major road improvements across the state that are not underway.

“I don’t know who he’s expecting to vote for this,” said House Speaker Michael E. Busch (D-Anne Arundel). “If this bill passes, it would leave you barely enough money for filling potholes.”

Hogan is attempting to undo key parts of a 2013 law championed by then-Gov. Martin O’Malley (D) that phases in a 5 percent sales tax on gasoline over three years and includes a provision that increases the existing gas tax each year based on the rate of inflation. By mid-2017, legislative analysts say, the increases would cost the typical driver more than $80 a year.

Hogan’s bill would cancel the three percentage points on the sales tax that have yet to take effect and put an end to automatic increases based on inflation. Beyond providing tax relief, Hogan’s legislation reflects an important principle: that lawmakers should have to vote each time a tax goes up, spokesman Doug Mayer said.

“Everyone agrees that transportation infrastructure is essential for growing the state’s economy, but there seems to be a somewhat shortsighted assumption that there is no room for greater efficiency as we look at future projects,” Mayer said. “The governor and every member of the Cabinet are reviewing a variety of projects initiated over the last few years to determine what can be achieved in a more cost-effective manner.”

The 2013 bill was projected to generate $4.4 billion over six years for transportation projects at a time when state officials said they had barely enough money to maintain existing road and transit systems, much less pay for the Purple Line and another major light-rail project — the Red Line — planned for Baltimore.

The draft document by the Transportation Department estimates that Hogan’s bill would result in nearly $3 billion less for new projects, including planned borrowing, over the coming six years. Erin Henson, a spokeswoman for the department, confirmed the authenticity of the document, which was obtained by The Washington Post, and said a final version would be released in coming weeks.

Hogan has proposed passing on a greater share of state transportation dollars to counties and municipalities for local projects. He is also proposing to pay for some previously planned environmental projects with transportation funds. Those changes could reduce the amount of funding available for state transportation projects by an additional $1.5 billion during the six-year period, according to the document, leaving little money for projects in the state transportation fund.

Senate President Thomas V. Mike Miller Jr. (D-Calvert) said Hogan’s gas-tax legislation stands no chance of passage in his chamber. He described the bill as an effort by Hogan — who is also fighting the legislature over school funding — to be able to say that he attempted to fulfill his campaign promise to deliver broad tax relief.

“He wants to tell his constituents that he tried and the Democrats thwarted him,” Miller said.

The need to maintain transportation funding was “brought home” this week, Miller said, when a motorist’s windshield was hit by chunks of concrete that fell from an overpass in Prince George’s County. Acting transportation secretary Pete K. Rahn has asked the State Highway Administration to inspect 27 state-owned bridges of similar age and condition.

Hogan’s office declined to say Friday projects that might be at risk if his bill passes, a posture that brought a rebuke from Busch. “I think if you’re going to be honest with everyone, tell them the projects you’re not going to fund,” Busch said.

In addition to the Purple and Red lines, the major projects that are slated for construction in coming years include a $95 million widening of a portion of the Baltimore Beltway, a new $156 million interchange at I-270 and Watkins Mill Road in Montgomery County and a new $157 million exchange at Maryland Route 4 and Suitland Parkway in Prince George’s. Hogan has asked Rahn to look at the costs of the light-rail projects and recommend whether to move forward.

Ralph Bennett, president of Purple Line Now, a coalition of business, labor, environmental and civic groups that is pushing for the completion of the light-rail line, described Hogan’s proposal as “ridiculous.”

“For him to do this is vandalism,” Bennett said. “It really is outrageous.”

Montgomery County Executive Isiah Leggett (D) said Hogan’s proposal is inconsistent with the governor’s message of wanting to boost the economy.

“If you want to create jobs and expand the tax base, in order for us in Montgomery, Prince George’s and Baltimore to do so, we need assistance in transportation, and most importantly in transit,” Leggett said.

House Minority Whip Kathy Szeliga (R-Baltimore County) said she supports Hogan’s bill for the same reason she voted against the gas-tax increases in 2013. No tax increase should be automatic, she said.

“If a politician thinks it’s a good idea to raise someone’s taxes, they should have a vote so people know who is supporting it and who isn’t,” she said. “A tax that automatically increases is tyrannical.”

She said Democrats’ predictions about the effects of Hogan’s bill were “hyperbole.”

House Minority Leader Nicholaus R. Kipke (R-Anne Arundel) said Hogan’s proposal is in line with what Maryland residents want. “[The voters] overwhelmingly agree that our legislators should only be raising taxes if it is absolutely essential,” Kipke said.