Serious train and bus accidents are rare. But when they happen, passengers and their bags have almost none of the protections considered standard on planes and cars.

The National Transportation Safety Board has long recommended a variety of measures to improve passenger safety, including installing lap-shoulder seatbelts, requiring riders to buckle up and improving window safety and overhead baggage restraints.

“Current safety standards for locomotive cabs and rail passenger cars are inadequate,” the N.T.S.B. said in February when it unveiled its “most wanted” list of safety improvements for trains. “Protecting passengers and crews from injury requires keeping rail car windows intact and maintaining their structural integrity during an accident, and includes occupant restraint systems, such as seatbelts, to mitigate the severity of passenger injuries.”

But regulators of Amtrak, Greyhound and a host of national and regional transportation carriers have generally not adopted the recommendations.