you're gonna have to drop a source for that.
because, no, they're not. the Secret Service provides a driver specially trained for the risks a president might face, and very strongly insists, but they're not "prohibited" from driving simply because they're presidents.
to be clear, the secret service cannot prohibit the president from doing anything they really want to do. Even if it's totally stupid for them to do that. (This includes, for example, Trump's routine weekend round of golf at Turd-o-Lardo)