Mayor de Blasio and Gov. Cuomo are having a dumb argument over allowing self-driving cars in Lower Manhattan, though they may be inadvertently showing why we need such things: Getting emotion out of lots of areas of life, from governing to driving, would be a nice improvement.

Last week, Cuomo announced General Motors is applying to test autonomous vehicles in Gotham next year. No one told the mayor, and he wasn’t pleased when he found out. “It’s a mistake . . . It creates a danger. We are going to work vigorously to stop it,” he said.

He shouldn’t have been surprised. The law giving the state authority to take these applications was in this year’s state budget, and presumably the mayor employs someone to read the budget for him. It’s long been policy, anyway, that the state, not the city, decides who gets a license to drive a car.

Allowing driverless-car tests is a good idea. Most important for now, this test is stringent. It requires a car company to have a person with a driver’s license and autonomous-vehicle training in the driver’s seat. GM has said it’ll only put engineers in the driver’s seat, and that a second person will sit in the front passenger seat.

Beyond that, the state police will be watching; GM must send them a set route beforehand. And GM will pay for this, through a crude form of congestion pricing​: $93 to $132 each hour, depending on whether state police are on straight or overtime, plus a per-mile charge.

No, this experiment isn’t risk-free. But consider the risk of doing nothing. Traffic deaths nationwide were up 6 percent in 2016, to 40,200 people.

New York has kept deaths down — and the mayor does deserve credit for his Vision Zero plan. But we’re nowhere near zero: as of Aug. 30, 140 people died this year, compared to 159 by August last year.

Companies from GM to Google have been testing self-driving cars all around the world for five years, without any major incidents. (New York’s law allows for competition, too; GM doesn’t have an exclusive agreement.)

In California, over a three-year period, self-driving cars were involved in 30 minor accidents. Most were the fault of other drivers. In 18 cases, a driver rear-ended the test car; cars with human drivers ran stop signs or red lights.

It’s good for pedestrians and bicyclists, too, to let GM test technology here. The driverless car has to “learn” how dense cities work. That’s why London and other cities are allowing companies to test their own technology.

Driverless cars can reduce deaths and injuries, and — properly programmed — they could make driving, cycling and walking in Manhattan more pleasant.

Too many drivers let their emotions govern them in life-or-death situations. Someone is frustrated because backed-up traffic means he misses a green light — so he blows the next red light.

Some drivers diligently refrain from “blocking the box” — moving forward through the intersection only when there’s enough room. But drivers behind them will honk and honk until they give in to the bullying, making it harder to walk around.

Then, there are taxi passengers — who often harass drivers into their own bad behavior. Some passengers want their drivers to exceed the speed limit, or to drop them off in bus lanes. (I recently saw two people chatting getting into a cab as an ambulance blared behind it.)

Driverless cars can reduce emotion-governed driving. A driverless car should be impervious to bullying and impatience.

Eventually, human drivers will have to modify their behavior, too. There’s no point in giving a computer the finger because it won’t get out of your way (although, if people’s other behavior on the road is any guide, people will do it, anyway).

Yes, it would be nice if Cuomo and de Blasio got along in fixing New York’s streets. And lots could go wrong with driverless cars. There’s the potential for (more) congestion if it makes taking a cab even cheaper.

For now, though, don’t be too afraid of the future; be more afraid of the roads today.

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