LANSING — Gov. Gretchen Whitmer on Tuesday proposed raising Michigan's gas tax by 45 cents per gallon by Oct. 1, 2020 — an action she said would raise more than $2 billion annually to fix Michigan's crumbling roads.

Whitmer's proposal, which would give Michigan the highest fuel taxes in the United States, has some motorists wondering what happened to the last road funding package — a $1.2-billion-a-year plan approved by lawmakers in 2015.

The 2015 plan, which combined fuel tax and registration fee increases with injections of general fund money, won't be fully implemented until 2021 and was expected to raise about $880 million this year.

Michigan Department of Transportation officials say the 2015 plan was never going to be sufficient to solve Michigan's road funding problems and has only slowed the rate at which Michigan roads are deteriorating.

Whitmer's proposal would hike taxes for both regular and diesel fuel by 15 cents on Oct. 1, another 15 cents on April 1, 2020, and a further 15 cents on Oct. 1, 2020.

Did Whitmer promise such a big fuel tax increase during her campaign?

No. In fact, she scoffed at the idea of an increase less than half as big.

Whitmer talked about raising an extra $2 billion in state funding for roads and hoping to leverage an additional $1 billion from the federal government, but she gave little in terms of specifics about exactly how that money would be raised.

She said that if the Legislature would not approve unspecified “user fees,” she could go to the voters to ask them to approve major borrowing to fix the roads.

During a televised Oct. 12 debate in Grand Rapids, Whitmer’s Republican opponent, then-Attorney General Bill Schuette, accused her of wanting to increase the fuel tax by 20 cents a gallon.

“That’s ridiculous,” Whitmer said.

“No, it’s not,” Schuette protested.

“It’s nonsense, and you know it,” Whitmer fired back.

Whitmer told reporters after her Tuesday budget presentation that such a large increase in the gas tax was not always her plan, but she determined it was the best option after assessing various other alternatives.

Didn't gas taxes just go up?

Michigan fuel taxes last increased on Jan. 1, 2017, as a result of the 2015 legislation. The tax on regular fuel increased 7.3 cents per gallon and the tax on diesel fuel increased 11.3 cents per gallon, equalizing both taxes at 26.3 cents per gallon.

The higher fuel taxes were expected to generate about $400 million this year for the Michigan Transportation Fund, which is primarily spent on road repairs at the state and local level.

What else was included in the 2015 road funding package?

The package also hiked most vehicle registration fees by 20 percent, also effective Jan. 1, 2017. That change was expected to raise about $217 million this year, with those revenues also going to the Michigan Transportation Fund.

Finally, the package earmarked specified annual amounts of income tax revenues for road repairs, starting with $264 million this year and increasing to $600 million in 2021 and every year after that.

Whitmer wants roads paid for primarily through user fees, and her plan would replace the general fund money earmarked for roads under the 2015 plan with gas tax money.

The proposed return to the general fund of income tax revenue earmarked for road repairs contributed to varying estimates of the net impact of the gas tax increase. Whitmer said her proposal would raise $2.5 billion for roads, though budget documents pegged the net new revenue at $2.1 billion in 2021. A House Fiscal Agency analysis released Thursday said the net increases from the fuel tax hike would be $797 million in 2020 and $1.9 billion in 2021.

Has other extra money gone to road repairs since 2015?

Yes, the Legislature has appropriated surplus general funds for road repairs each year, including about $357 million this year.

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Is the money from the 2015 package being spent on roads?

For the most part, yes.

Of the $880 million in extra funds the package was expected to raise this year, $319 million was to be spent on state trunk lines (the ones with an "I", "M", or "US" in front of their names); $312 million on county roads; and $173 million on city and village roads. Another $69 million is going to the Comprehensive Transportation Fund, which supports public transit, about $6 million to recreation, and $3 million to rail.

That's according to a 2015 House Fiscal Agency analysis of the 2015 road funding package, adjusted to account for a 2018 law that boosted the amount of general fund revenue going to roads in 2019.

So why does the gas tax need to go up again?

Transportation Department officials say they knew when the 2015 legislation was passed that it wasn't nearly enough to fix the roads.

They say that by itself, the 2015 money only slows a steady decline in the quality of the roads, and they point to a series of studies they say support that position.

A 2012 report by former state lawmakers Rick Olson, R-Saline, and Roy Schmidt, D-Grand Rapids, said an extra $917 million was needed for state trunk lines.

Adjusted for inflation, that would equate to a little over $1 billion today.

But after accounting for increased road funding resulting from the 2015 package, which was enacted after the Olson-Schmidt report was published, the shortfall in state trunk line funding is about $681 million today and should shrink to about $551 million by 2021.

Whitmer’s proposal would provide an additional $431 million to state trunk lines in 2020 and just over $1 billion in 2021, according to budget documents.

Based on those numbers, Whitmer’s proposal provides about $250 million less for state trunk lines in 2020 than what the 2012 report said is needed today, and about $449 million more in 2021 than what the report said would be needed.

The department also points to the more recent report of former Gov. Rick Snyder’s 21st Century Infrastructure Commission, published in November 2016.

That report identified a $2.2-billion-a-year road and bridge funding gap, after the 2015 package is fully implemented, of which about $1.6 billion would apply to state trunk lines and “principal arterials.”

That’s almost exactly what the Whitmer proposal would provide in 2021 — $1 billion for state trunk lines and $641 million for “principal arterials” — highly traveled roads, many of which are under MDOT jurisdiction, but some of which are local roads.

So does that settle it?

Not necessarily.

Many people, including many lawmakers, don't accept the numbers in the 2012 or 2016 reports and say less money would be needed if the Michigan Department of Transportation spent existing dollars more efficiently.

Among the concerns is the quality of work, the use and enforcement of warranties with road contractors, and the amounts spent on contractors for services such as engineering.

Another concern for many Michiganders is Michigan's highest-in-the-nation gross truck weights. Many say roads and bridges, even if brought up to top condition, will not stay that way for long unless truck weight limits are lowered.

Among those who agree with how much extra road money Michigan must raise, many disagree with raising the full amount through a gas tax, rather than using other options.

Some see it as a regressive tax that would hit low and middle-income workers hard.

There are also concerns that such a major gas tax increase would put gasoline stations near the Indiana and Ohio borders — where fuel taxes are much lower -- out of business.

Contact Paul Egan: 517-372-8660 or pegan@freepress.com. Follow him on Twitter @paulegan4.