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Minnesota lawmakers might soon vote to spend as much as $8 billion over the next decade on the state’s roads and bridges. The political fight over the taxes that it would require could be the fiercest dispute of the legislative session.

But the road system is massive and complex, controlled by hundreds of governmental bodies across the state and paid for by billions of dollars flowing from fund to fund. Experts say most people understandably haven’t paid a lot of attention to the transportation system’s intricacies.

“I have a sense that they probably don’t understand a whole lot about how it’s funded or how extensive it is, or who owns which road they’re driving on,” said Scott Peterson, the Minnesota Department of Transportation’s director of government affairs.

Even experts don’t know a lot of key details about the system, such as the quality of the state’s minor roads. Many local governments don’t track this in any comprehensive way, and MnDOT only knows for sure how good its own roads are.

But details such as that could make a big difference in what lawmakers decide to do about Minnesota’s roads this year — which could make a big difference in what Minnesotans pay in taxes.

Gov. Mark Dayton, Democratic-Farmer-Labor Party lawmakers and a coalition of interest groups have backed a series of tax increases to raise hundreds of millions of dollars per year. Their plan would raise taxes on gasoline and cars to fund additional road and bridge work, as well as a sales tax hike in the metro area to pay for mass transit.

It’s a comprehensive plan that Dayton says is necessary to address “antiquated and inadequate” roads — both to repair the existing system and build new infrastructure for Minnesota’s growing population.

Republicans aren’t so sure. They acknowledge that Minnesota isn’t spending enough money to repair its current system but aren’t sure about how much the state should spend on new infrastructure.

“We really need to gather the data,” said Rep. Tim Kelly, R-Red Wing, chair of the House Transportation Policy and Finance Committee. “I don’t have the answers right now.”

DFL lawmakers say policymakers already have enough answers from recent studies to know the state needs a comprehensive long-term solution. But with Republicans controlling the state House of Representatives and the DFL the Senate and governor’s office, the two sides will need to agree on the data in order to agree on a solution.

Here’s what you need to know about Minnesota’s road system as lawmakers debate major improvement plans:

HOW MANY ROADS ARE THERE? (Back to top)

There are about 142,914 miles of road, and they crisscross almost the entire state except for some uninhabited northern forests. If you count each lane separately — so a mile of two-lane highway has two lane-miles and a mile of four-lane interstate has four lane-miles — Minnesota has about 293,589 lane-miles.

But not all roads are created equal.

Almost 80,000 of Minnesota’s road miles are dirt or gravel paths carrying very little traffic per day. Interstate highways — with fewer than 1,000 miles in the state — account for 80 times less mileage but carry five times more traffic than all the dirt and gravel roads combined.

“Pretty much every trip is either begun or ended on one of those local roads, whether you’re going to your house or you’re going to your place of business,” said Sen. Scott Dibble, DFL-Minneapolis, chair of the Senate’s Transportation and Public Safety Committee.

Those rural roads face bigger burdens than their traffic numbers would indicate, however — literally. Washington County engineer Wayne Sandberg noted that small rural roads often carry heavier traffic, such as trucks or farm equipment, which chews up roads faster than passenger cars.

“The number one thing that really beats up our roads or degrades our roads is the heavy truck traffic,” Sandberg said.

Despite having dense grids of urban streets, the seven-county Twin Cities metro area has only 12 percent of Minnesota’s total miles of roads. But it carries 47 percent of the state’s traffic.

WHO PAYS FOR THESE ROADS? (Back to top)

There’s no one answer to this question. Except for a handful of private roads, almost all of Minnesota’s roadways are paid for by governments. But a typical morning commute might involve driving over roads paid for by four or five governments.

In general, though, there are three ways that Minnesota roads are paid for:

The state-run highway system is about 29,000 lane-miles, or 10 percent of all the lane-miles in Minnesota. But these roads — the interstates, U.S. highways and state highways — carry about 58 percent of Minnesota’s traffic. These roads are paid for by drivers across Minnesota, with a healthy assist from the federal government.

The local road system consists of 184,000 lane-miles, or 62.5 percent of the state total. They have only about 12 percent of the state’s total traffic. They’re paid for entirely by cities, counties and townships out of local revenue — frequently property taxes, along with vehicle registration taxes. Most of the smaller city and county roads fall into this category, along with all the township roads.

Most of the remaining Minnesota roads are hybrids — funded partially by local taxpayers and partially by statewide taxpayers. These are the city and county “state-aid” roads, and are usually the bigger, more heavily traveled roads in a city or county. In St. Paul, for example, University Avenue is a state-aid street, while the adjacent side street Sherburne Avenue is the city’s sole responsibility.

WHAT CONDITION ARE OUR ROADS IN? (Back to top)

State roads are actually pretty good — for now.

Only 7.5 percent of Minnesota’s pavement is in “poor” condition, according to federal statistics, though the situation is much worse for major urban streets, of which 12.4 percent are in poor condition.

Just under half of Minnesota’s roads are in “good” condition with extremely smooth rides.

Because roads deteriorate over time, the system needs regular maintenance to shore up poor roads.

“The need for investment never really ends,” MnDOT’s Peterson said. “You can reach some high points.”

Peterson said Minnesota’s state bridges, at least, might be at such a high point right now because of federal stimulus money and a 2008 increase in the state gas tax.

But for many of the roads in the state – those miles and miles of low-traffic city, county and township roads – no one really knows.

MnDOT doesn’t have a centralized database of road quality around the state. In fact, though the agency knows where each road in the state is, it doesn’t even know for sure which roads are paved and which are dirt or gravel.

Peter Morey, director of data systems and coordination for MnDOT, said that when a local government builds a new road, state data technicians sometimes assume it has the same pavement as other roads in that jurisdiction.

The department used to hire interns every summer to drive the state’s roads and record data about them. But that program was canceled decades ago for budgetary reasons, and now the state’s database doesn’t note whether road information derives from observations or assumptions.

Counties have the option to hire the state to drive special equipment over their roads and measure pavement quality and other characteristics. But that costs money, and generally only the bigger counties do this.

So while big counties in the metro area may have detailed data about every inch of their roads, small, rural counties may not — to say nothing of townships and small cities.

“It’s also a credit to (local governments) that they’ve handled their road system as well as they can by themselves, really,” Rep. Kelly said.

Kelly and Dibble said they didn’t have firm data but have been told by local leaders that their roads are in bad shape.

HOW MUCH DOES IT COST TO FIX A ROAD? (Back to top)

Anywhere from $167,000 to $3.7 million or more per lane-mile.

If the road’s substructure is in good condition, then rough pavement can be fixed by just applying a new surface. A typical asphalt resurface costs about $167,000 per lane-mile — meaning double that for a two-lane road and more if the road is wider. Concrete is sturdier but more expensive: a new concrete surface costs about $488,000 per lane-mile, according to MnDOT.

If a road deteriorates to the point where its substructure also needs replacement, fixing it becomes a lot more expensive. A full reconstruction costs about $1 million per lane-mile for a rural road, and $2.2 million per lane-mile in a town.

Because of the denser population in the Twin Cities, metro-area projects can be significantly more expensive — up to 70 percent more. That means more than $3.7 million for a lane-mile — or $7.5 million per mile for a two-lane city street.

Other factors can increase these average costs by making road work more difficult, such as steep hills, sharp turns or unstable terrain.

HAS IT ALWAYS BEEN THAT EXPENSIVE? (Back to top)

Roads have never been cheap, but they’ve been getting pricier.

Inflation has reduced the purchasing power of the dollar, meaning most commodities cost more dollars today than they did 10 or 20 years ago. But the cost of road construction has increased even faster than the rate of inflation, because of changes in the price of equipment, labor and materials such as oil, concrete and gravel.

“Since 2008, the cost of construction and the materials we use to build roads has gone up by over 70 percent,” engineer Sandberg said. “What used to cost $1 million in 2008 is almost $2 million now.”

WHERE DOES THE MONEY COME FROM? (Back to top)

Three taxes provide most of the money Minnesota uses for roads. In 2013, the 28.6-cent-per-gallon gas tax brought in $860 million, while the vehicle-registration tax collected $622 million and the state share of the motor vehicle sales tax raised $359 million.

That all goes into the state’s Highway User Tax Distribution Fund, which then distributes that money — $1.84 billion in 2013 — to specific purposes:

59 percent, or $1.08 billion in 2013, goes to pay for state roads.

27.5 percent, or about $500 million, goes toward county state-aid highways.

8.5 percent, or $157 million, goes toward city state-aid roads.

2.6 percent, or about $50 million, goes into a flexible spending account.

1.5 percent, or $28 million, helps townships with their roads.

Less than 1 percent, or $15 million, helps townships with bridges.

That means — with a few minor exceptions — that for every dollar raised in extra transportation taxes, 59 cents goes to the state, 27.5 cents to counties, 8.5 cents to cities and about 2.4 cents to townships.

In addition, the federal government every year provides money for state and local roads. In 2013, that was $550 million more for state highways, and $170 million for local roads.

HOW CAN ONE TELL HOW A ROAD WAS PAID FOR? (Back to top)

The first thing to determine is what type of road it is, information that’s placed on periodic roadside signs. If it’s an interstate, U.S. highway or state highway, then the money comes entirely from the state and federal governments.

If it’s a county road, then the county pays for some or all of it, while city roads are cities’ responsibilities.

There’s no easy way to tell whether state aid helps pay for a road other than by asking the local road department. But generally speaking, the busier roads are likely to receive state aid, while back streets are likely to be purely local.

All township roads are in the same category, paid for by the townships with a little support from the state.

How much state aid a county or city gets varies from government to government. A complex formula in state law assigns state aid to cities and counties based on factors including need, population, road-network size and how much tax revenue a county contributed to the system.

WHO DECIDES WHICH ROADS TO BUILD AND REPAIR? (Back to top)

Local governments build their own transportation plans based on need, resources and other factors they choose to consider.

The state traditionally distributes its funds based primarily on which roads and bridges need repair — though MnDOT will let some less-traveled highways “go to a lower quality before we fix them,” Peterson said. But two years ago, lawmakers passed a plan called “Corridors of Commerce,” which directed more than $300 million to pay for road work aimed at economic development, relieving congestion and other factors besides degrading road and bridge quality.

HOW MUCH MORE MONEY DOES THE STATE’S ROAD SYSTEM REALLY NEED, IF ANY? (Back to top)

Republicans and DFLers, along with local governments, agree that Minnesota isn’t spending enough to maintain its current system.

“We’ve got a lot of maintenance to do,” Sen. Dibble said. “There’s a lot of backlog, and it’ll only grow over time, of fixing what we’ve got.”

A study commissioned by Dayton recently found the state needed to spend about $250 million more per year just to keep up with maintenance on its state-run highway system. County, township and city roads required hundreds of millions more.

Kelly said Republicans agree on the need for more maintenance spending, even though they’re not eager to raise taxes.

“We may have failed in that effort over the last several years,” Kelly said. “If we don’t do that, it just gets more expensive in the future.”

The governor’s study also recommended spending more than double that to create a “world-class” system. That’s what Dayton and DFL lawmakers are aiming for with their comprehensive proposal — and what Republicans are balking at.

David Montgomery can be reached at 651-224-5064. Follow him at twitter.com/dhmontgomery.

UPDATE: This story has been edited to improve formatting and layout.