The government’s highway safety agency is proposing voluntary safety guidelines for self-driving vehicles.

Preliminary tests by a University of Nebraska road safety research facility and the U.S. Army Corps of Engineers point to concerns that the nation’s roadside guardrails are no match for new heavy electric vehicles.

A large U.S. government study has found that more than half the people injured or killed in traffic crashes had one or more drugs, or alcohol, in their bloodstreams.