All Mainers know that Interstate 95 begins in Houlton and ends in Key West, Fla. Now, there’s a chance to prove it.

The Department of Transportation and the Maine Turnpike Authority are putting together the details of a proposal that would change exit numbers on Interstate routes. The problem is southern Maine’s. Portions of the Maine Turnpike and Interstate 295, which runs from South Portland, through the heart of Portland and on to Falmouth, share the same exit numbers.

For example, take Exit 5 off the Maine Turnpike and you wind up in Saco. Take Exit 5 off Interstate 295, and you wind up on Congress Street in Portland. The result can be confusion as to exactly which exit one should take.

The preferred method from the state for resolving the problem: Make exit numbers on the turnpike, I-295 and Interstate 95 equal the mile marker nearest their location. Naturally, the counting on I-95 would start in Houlton, where the highway begins, and end in York. The mileage markers for I-295 and the Turnpike also would begin in the north and move south. In this way, the Houlton exit might be numbered 3 and the York exit, 300 or so. An alternative plan would be for highway workers to accommodate the needed extension of I-95 to Northern Aroostook County and start Houlton with the appropriate number on what will become the longer highway.

There is a chance the state highway sign numberers were thinking of doing this backwards — counting the first mile of highway from the end of New Hampshire — a sort of no-man’s land in the national system — instead of at the official U.S. starting point in Houlton. If that is the case, they need only think of the benefits to numbering from the beginning. For instance, high numbers to the south would be a regular reminder to residents there that Maine really does extend beyond Augusta — a real help to reducing the Two Maines problem. Similarly, tourists entering the state from New Hampshire would immediately become aware that Maine stretches far beyond the usual haunts of visitors. North-south numbering would be an invitation to explore the entire state.

While there is sure to be some economic cost associated with changing highway exit numbers — a $1 million price tag for signs and associated state costs alone no matter which end the state starts at, as well as millions more for businesses to alter their stationery, business cards, advertising and the like — there could be some tangible economic benefits, too. Not to mention some intangible justice, in the form of a truly north-south highway.