If people wouldn’t dine at a restaurant with a “D” grade, why would they ride a charter bus with the same grade?

That was Sen. Chuck Schumer’s point Sunday when he called on the federal Department of Transportation to better enforce existing rules regarding the display of safety grades on bus windshields, and to develop a letter-grading system similar to the city’s system for restaurants.

“On the heels of the terrible Dahlia crash ... your gut reaction is to ask what more can be done to prevent these kinds of crashes and improve the culture of safety,” Schumer said. “But in this case, we have a law I passed in 2012 that can not only help solve this problem, but can better inform the public, too. That is why I am asking the federal Department of Transportation to hit the gas on a federal letter-grade system for private bus companies.”

Today’s bus safety ratings were implemented in 2012 when a law required bus operators to post safety records on the buses, at the terminals and at the point of sale, Schumer said. But so far, Schumer said, the DOT hasn’t properly enforced it.

“The way DOT has it is not good enough,” he said. “No one knows these grades, passengers get on the buses without knowing whether they’re safe or not.”

Proper enforcement, he said, could have prevented the deadly Queens crash that killed three people and injured 16 last month.

In that crash, a Dahlia Travel charter bus slammed into an MTA bus on Sept. 18, going double the speed limit. The driver, who was killed in the crash, had been fired from the MTA in 2015 after a highway collision and was later arrested for DUI and evading arrest. Dahlia Travel also had 11 unsafe violations, according to reports.

Currently, Schumer said, the grades are posted online “in such a small, hidden way,” but no one goes on to find them.

“Today I am demanding, I’m not really just asking . . . that the DOT require these safety grades to be placed in the windshield,” he said. “It will prove an incentive to the bus companies to straighten out.

“You don’t have the A-B-C grade, then there’s one grade for the passenger and for bus safety: F-A-I-L, fail,” he added. “The safety records are there, they’re compiled, but no one knows about them. We should no longer keep them hidden.”

A representative for the DOT did not respond to a request for comment.