Try telling people in St. Louis Park this summer that the state needs more money for road construction. With Interstate 394 and Hwy. 100 both pinched for major repairs, they're seeing about all the highway spending this year that a motoring citizen can stand.

I bet I'd also hear a cry of "Enough, already!" from I-35E commuters into downtown St. Paul from points north, including Little Canada, Vadnais Heights and White Bear Lake. Or from those who miss the Snelling Avenue/Hwy. 51 bridge over I-94, and can't remember whether I-94 is closed going westbound or eastbound, this weekend or next, to accommodate its replacement. (This weekend, it's closed going eastbound between Hwy. 280 and I-35E, the Minnesota Department of Transportation advises.)

And how about folks in the western 'burbs who drive I-494 between I-394 and I-694: Are you detecting any shortage of orange plastic barrels and road construction rigs?

I could go on, because this year's list of MnDOT projects runs on. Projects in Greater Minnesota this season require eight tiny-typefaced pages to enumerate; the metro area's road work catalog this summer consumes four similarly jam-packed pages.

That's not to mention all the local projects that also offer drivers frequent opportunities for close examination of the rear bumper of a fellow motorist's vehicle. Getting into downtown Minneapolis from the east has been a particular pain, as construction of the shrine to the NFL takes precedence over the mobility needs of mere mortals in Downtown East.

All in all, it's a $1.1 billion year for Minnesota highway construction, third most costly in the modern era (see accompanying chart). For those (including editorial writers) who argue that Minnesota needs more transportation money, "it challenges our credibility," MnDOT government affairs director Scott Peterson commiserated last week.

Peterson rose to the challenge by trotting out MnDOT's forecasts. They show that if the 2016 Legislature does not provide an infusion to the Trunk Highway Fund, by 2018 Minnesota motorists will see far fewer striped orange cones around the state. State spending on road construction will start declining next year, fall off dramatically in 2018, and keep shrinking each year thereafter unless new revenue appears, MnDOT's charts show.

That shrinkage might sound fine to those who are spending too much of this beautiful summer stuck in traffic. But Minnesotans need to know that if transportation spending shrinks, over time, so will this state's transportation-dependent economy.

"You want improvements in the roads, like an extra lane? That'll be the first thing to go," Peterson said. For example, Hwy. 14, long deemed ripe for full expansion to four lanes as a key commercial conduit across southern Minnesota, won't see that improvement without new money.

Bridge safety — a tender topic this weekend, the eighth anniversary of the I-35W collapse — will be an increasingly costly priority as the majority of interstate highway bridges simultaneously come due for replacement, he continued. That will squeeze out basic road maintenance — and as that happens, roads will degrade to the point that repairs will no longer suffice to keep them safe. They'll need to be rebuilt, at much higher costs.

An expert panel concluded three years ago that an additional $250 million per year is required to keep the existing highway-and-bridge network in its current condition. With each passing year of legislative inaction, that figure grows, Peterson said.

Minnesotans have seen so much construction in the last three years because of a series of one-time funding bursts that carry time limits and aren't likely to recur, Peterson said. The largest among them was $1.8 billion in bonding authorized by the 2008 transportation bill, which also yielded the only state gas tax increase in the last quarter century. Next year is the last in which those bonds can be issued, he said — but the debt service they require will be a drain on transportation budgets for the next 20 years. As a result, he said, "we are at the upper limit of what we are able to borrow."

With the state budget well into surplus territory, another one-time infusion of funds is possible from the 2016 Legislature. I'd argue that paying cash for, say, a new freeway bridge would beat a bunch of other possible uses for that money, and is surely better than no new transportation money at all.

But Peterson and other transportation advocates plead for a steady, predictable stream of new money that would give MnDOT planners a chance to sequence and stage projects in a cost-efficient and traffic-efficient manner. On this point, Minnesota drivers, MnDOT folk and transportation editorial writers would likely agree: Construction spurts like this year's aren't desirable.

Lori Sturdevant, an editorial writer and columnist, is at lsturdevant@startribune.com.