After a school bus rolled on a West Virginia highway two years ago, forcing one boy to have his leg amputated and seriously injuring two other children aboard, police quickly discovered the driver was drunk.

But the National Transportation Safety Board then discovered something even more troubling: School bus drivers driving impaired was not an isolated problem.

That’s why the NTSB on Thursday recommended for the first time that all new school buses be equipped with alcohol detection systems that can disable the bus if they detect the driver might be impaired. Similar systems are already used on school buses in parts of Europe.

“There’s a higher expectation for school bus drivers than many other types of drivers,” said Kris Poland, deputy director of the NTSB’s Office of Highway Safety. “We expect that the drivers are attentive, not fatigued, not impaired and are driving as safely as possible.”

The agency didn’t estimate the cost of adding the detection systems to buses or say who would foot the bill. The kind of ignition interlock device that people charged with DUIs are routinely required to get costs about $75 to $150 to install and roughly $100 a month to monitor.

Federal regulators or states could require the technology, but Congress would have to pass legislation to ensure widespread adoption. The NTSB recommendation focuses on alcohol and not drugs because they determined that was the probable cause of this crash and there aren’t similar tests available for other drugs like marijuana. There also aren’t clear legal standards for exactly how much of other drugs is enough to impair a driver.

It follows a previous recommendation by NTSB that Congress adopted to require alcohol detection systems in all new passenger vehicles. But that rule has yet to be rolled out because it is still caught up in the rulemaking process.

The NTSB has long been concerned about drunken driving because alcohol is a factor in one-third of the roughly 37,000 traffic deaths each year. Investigators struggled to nail down exact stats on how common a problem this is among school bus drivers, but they found enough evidence to convince them that alcohol detection systems are needed.

A report by the news service Stateline.org in 2020 showed at least 118 school bus drivers had been accused of driving under the influence of alcohol or other drugs over the five previous years, said Meg Sweeny, the primary author of the NTSB report on the West Virginia bus crash.

In that crash, the driver lost control of the bus after hitting a driveway culvert off the right side of a rural road. All 19 children aboard were hurt, but most had only minor injuries. The driver was sentenced last year to up to 110 years in prison.

Data from the National Highway Traffic Safety Administration shows that 407 school bus drivers were involved in fatal crashes between 2020 and 2024. Only two of those tested positive for alcohol, and only one of them had a blood alcohol level above the legal limit.

The number of drunken driving cases among bus drivers is alarming even though it remains a small portion of all drivers, said Peter Kurdock, who is general counsel for Advocates for Highway and Auto Safety.

“Children going to and from the schoolhouse are America’s most precious passengers,” Kurdock said. “So we should be doing all we can to make the bus as safe as possible.”