An overturned tanker truck shut down the Beltway at the American Legion Bridge on Thursday evening for 12 hours. (Fairfax County Fire and Rescue)

It happened again. A single incident — this time a crash — gridlocked traffic in much of the region for hours.

As highway debacles go, the overturned tanker truck that caused havoc Thursday was pretty much a worst-case scenario. It happened on the Inner Loop of the Capital Beltway near the American Legion Bridge, the worst traffic bottleneck in a metro area filled with them. Because cleanup was complicated — personnel had to mop up leaking fuel and transfer what was left in the tanker — the northbound lanes were shut for more than 12 hours.

The crash, which a preliminary investigation has blamed on reckless driving and defective brakes, reminded everyone that we don’t have enough ways to get across the region’s biggest natural barrier, the Potomac River.

It was hardly a unique occurrence. In June, the region’s roads were jammed for much of the day after a fatal crash involving a tractor-trailer on the Wilson Bridge, the Beltway’s other Potomac River crossing. In 2016, an electrical fire in a Metro tunnel caused huge delays on three rail lines, crippling the commute. That same year, less than an inch of snow jammed highways from the afternoon rush until after midnight.

So what can be done to avoid such fiascoes, and why hasn’t it been done already?

These chronic meltdowns highlight two truths. One, we have not invested enough in our transportation infrastructure to keep up with the region’s population growth. This is largely because of people’s unwillingness to pay, either in taxes or, increasingly, tolls.

It’s a nationwide problem, but it is particularly acute in our prosperous region, which attracts a steady influx of newcomers. Delays on the American Legion Bridge have increased 40 percent from 2010 to 2017.

It will get worse if, as some expect, the region experiences a boom as Amazon’s selection of Arlington for its new headquarters facility prompts other tech companies to move or expand here to take advantage of the talent pool.

“Our transportation system truly isn’t resilient,” said Joe McAndrew, director of transportation policy at the Greater Washington Partnership. “We need to think about how to invest in ways that give people options, either in a vehicle or other means.”

The partnership, an alliance of chief executives from many of the region’s largest companies, has recommended a package of ambitious, costly measures to reduce chronic traffic congestion, including expanding commuter rail service and adding both tolled highway express lanes and dedicated bus lanes.

In addition, because of political resistance, we have not fully committed to a model for how to shape the region’s development in a way that would end or at least reduce gridlock.

At risk of oversimplifying, this is a lifestyle choice. Do we want newcomers to live in the District and inner suburbs, in multifamily buildings served mainly by transit? Or do we want a significant number of them to move into single-family homes in the outer suburbs — where housing is often more affordable — and be dependent on cars to get around?

That question is at the center of most political battles over transportation and land use in our region. A quick way to judge a person’s viewpoint is to ask whether they favor or oppose building a new Potomac bridge north of the American Legion bridge, to link Loudoun and northern Montgomery counties.

Thursday’s commuter nightmare injected a bit of life into that long-standing debate, where opponents of a new bridge have the upper hand.

The crash and resulting hours-long commute home for many of the region’s residents “goes to show the importance of . . . providing more connectivity and redundancy in our system by building a second bridge,” said Jason Stanford, executive director of the Northern Virginia Transportation Alliance, which represents developers and other interests who for years have advocated for a new span.

In most proposals, a new bridge would connect Route 28 in Virginia north of Sterling, to a road in Maryland south of Poolesville. In general, the proposal has more support in Virginia than in Maryland, partly because it would almost certainly run through part of Montgomery’s Agricultural Reserve.

Opponents say a new bridge would be too expensive and too far north to do much good, and would create a host of environmental problems. They won a significant victory last year when the region’s Transportation Planning Board voted against including a new bridge in its long-range construction plan, “Visualize 2045.”

Transit supporters say a better way to add a Potomac River crossing in that part of the region would be to build a new Metro line between Tysons and Bethesda or Rockville, or extend the light-rail Purple Line across the river. But there’s not enough money available for either, at present.

“Frankly, [Thursday’s incident] shows the great vulnerability of our completely auto-dependent transportation system,” said Stewart Schwartz, executive director of the Coalition for Smarter Growth. “I could imagine a region that has a better balance between its subway system and its roads, and its bus and bus rapid transit systems would likely have more resilience, more options.”

He said authorities also should do a better job to ensure safe driving and to communicate quickly with the public when accidents occur.

“To the extent that they are the result of safety issues, the most effective thing we can do is set lower speed limits, end distracted driving, improve enforcement,” Schwartz said.

Several analysts said they hoped the tanker crash would highlight the need to rebuild and expand the American Legion Bridge. That has broad support, in theory, but faces political obstacles in Maryland.

Montgomery’s Democratic politicians are wary of Republican Gov. Larry Hogan’s plan to widen the bridge, the Beltway and Interstate 270 by adding toll lanes using a public-private partnership. Many say they would prefer an increased investment in transit.

Some supporters of Hogan’s plan, and of a second crossing north of the American Legion Bridge, urged a compromise between transit and highway advocates.

“It’s not an either-or. We still need both,” said Emmet Tydings, vice chair of the Suburban Maryland Transportation Alliance. “We can’t build our way out of the problem with transit alone.”

But transit supporters see that argument as a trap.

“ ‘Both’ doesn’t in practice generally mean ‘both,’ because jurisdictions have built so much more road infrastructure,” said David Alpert, founder of pro-transit organization Greater Greater Washington.

He’s not sure there is a way to avoid incidents like Thursday’s.

“If we have a transportation network that’s overbuilt, people would say it’s wasteful,” Alpert said. “If we have one that just meets our need, then it’s going to be susceptible to problems.”