The King administration’s proposal to index gasoline-tax increases to inflation is an understandable reaction to years of fighting with legislators over penny increases to the tax, currently at 22 cents. But indexing raises problems as well as revenue and should be viewed with caution by members of the Transportation Committee, who are split over the plan.

No one who drives around Maine, especially in spring, can doubt Transportation Commissioner John Melrose when he says the state must find $92 million for the next budget to pay for road maintenance and repair programs. But he has public support, even amid grumbling about higher prices. Given the opportunity, drivers overwhelmingly support spending state money on improving roads and bridges – the large transportation bond questions pass easily each year at the polls. Lawmakers in Augusta aren’t hearing voters, however; they’re hearing lobbyists who have specific reasons for not liking any added tax. Indexing, which would tie the tax level to an inflation formula and raise the amount automatically, is a way to get around the lobbying.

But there are problems with this. The first is fairness. For instance, a large number of Maine’s mentally ill residents are in its prisons, in part because there is no place else for them, but there’s no indexing of a tax that would ensure all mentally ill are served. The same goes for domestic-abuse programs, homeless shelters, education and dozens of other crucial state services. Not that lawmakers want to look at this too closely, but it makes no more sense to even have a dedicated gas tax for roads than it does for, say, towns to restrict the use of local property taxes only to services for people with property.

Second is public accountability. It is no doubt time-consuming for state transportation officials to go before legislative committees each year and plead for money, but their testimony serves an important purpose. It gives the public details about a service they pay for. When people read newspaper stories or hear TV news accounts of transportation officials describing what they would do with the money, they gain a better understanding of where their gas-tax dollars are being spent. Automatic increases, on the other hand, lead to automatic anger.

Third, the annual testimony requires state officials to scrutinize spending and, in cases when legislators have done their homework well, to justify it. Commissioner Melrose is particularly proud of changes he began several years ago that allowed his department to pave more miles of road faster and for less money. Whether his innovations would have taken place absent that public scrutiny is open to question.

Fourth is the department’s own financial health. Automatic tax increases suggest that the department will never need more from the tax than what inflation allows. For the next several years anyway, just getting inflation raises would be of real benefit, but what about eight or nine years from now? If unexpected projects or a newly discovered backlog present themselves, the department will be forced to explain why a program that is supposed to take care of itself hasn’t, with the legislative fight much more difficult because of the lack of education along the way.

Better than automatic indexing is for the Legislature to look at the true costs of road building and repair, including the environmental costs, examine how well the department is able to carry out its policies on its current budget and set the gas-tax level to do its share to meet those policies. That is perhaps overly optimistic. At the very least, lawmakers might notice that the public wants better roads and is willing to pay for them at the polls, year after year.