We don’t know why a New Jersey Transit train crashed at high speed into the Hoboken train station last Thursday, killing 34-year-old Fabiola Bittar de Kroon and injuring 114, just a month after a New Jersey Transit bus collision killed two people.

But we do know this: States are best prepared to handle a disaster when they’re doing well before it happens — and when they’ve built up some public goodwill, too.

New Jersey doesn’t fit that bill: It doesn’t run its transportation well on a day-to-day basis.

And without big changes, it’s going to get worse.

Without New Jersey Transit, the Garden State withers. Last year, 272.3 million people took its trains or buses — up from 237.4 million a decade ago. 32.7 million people took the Hoboken line, up 41 percent from the 23.2 million who took it back then.

More people are commuting for a few reasons: taking the car is more expensive and harder, as tolls go up and buses take up more of the Hudson crossings. Last month, the Port Authority hinted at the idea of a second bus-only lane on the highway to the Lincoln Tunnel.

Increasingly, too, the jobs are in New York. As New Jersey Transit itself notes, “New Jersey’s economy . . . fared significantly worse than its neighbors” after the 2008 recession. Employment dropped by 6 percent, twice as much as in New York City. New Jersey didn’t recover its lost jobs until last year, four years later than New York.

So you’d think the state would care about its transit system. It sure isn’t acting like it: Between 2001 and 2006, New Jersey Transit spent $4.1 billion, in today’s dollars, on major capital projects like train, station and track upgrades. Between 2011 and 2016, it spent only $3.4 billion.

And until recently, it’s been spending almost nothing. Over the summer, Jersey’s transportation fund ran out of money. (It still takes in $1.2 billion a year, including from the gas tax, but it must spend all of that money on its existing debt.)

New Jersey continues to squander the infrastructure money it does have on trifles and amusements.

New Jersey Gov. Chris Christie and lawmakers couldn’t agree on how to find more money: some lawmakers wanted to raise the gas tax, but Christie said they had to cut another tax in return. So they spent the summer bickering over whether to cut the sales tax or the estate tax.

As the money ran out in August, Christie signed an emergency order diverting money from the state’s overall budget to pay for critical transportation projects — stuff like filling in potholes, not funding better track and signaling systems.

Of course, when you have no money, raising one tax only to cut another one makes no sense. But the day after the crash, that’s exactly what New Jersey did — raising its gas tax but cutting a slew of other taxes, including both the sales tax and the estate tax, in return. Noting the average family would see an overall tax cut, Christie said “it’s the first statewide tax cut . . . that affects all New Jerseyans since 1994.”

Realistically, though, Jersey is dead broke — it can’t make even half of its necessary payments to pension funds. Christie is using this tragedy, then, to pretend to do something responsible about infrastructure while boasting about tax cuts.

Would investment in better technology have averted Thursday’s crash? It’s impossible to know. New York and Amtrak aren’t flat broke like New Jersey is, but they’ve been slow, too, in rolling out automated-stop technology.

Capital investments would give people a better day-to-day commute — and could avert a future disaster. New Jersey needs to fund about $5 billion out of the $20 billion cost of building a new tunnel across the Hudson River to do major repairs to the existing, century-old tunnel. But it has no idea where it’s going to get that money.

Just how bad are the decisions state officials have been making? New Jersey continues to squander the infrastructure money it does have on trifles and amusements. Last month, as the Bond Buyer reported, the state made plans to issue $1.2 billion in debt to fund a long-delayed “megamall” in East Rutherford.

Using scarce tax dollars to fund a mall made no sense in 2002, when the state launched the bizarre project, and it makes less sense today. Maybe, though, Christie and lawmakers can prod the mall’s owners to add an indoor miniature train to the planned indoor ski slope and water slide.

At least, then, the state could say it’s working on some train project.

Nicole Gelinas is a contributing editor to the Manhattan Institute’s City Journal.