The government is urging owners of older Hondas and Acuras to stop driving them and get them repaired after tests found that their Takata air bag inflators are extremely dangerous.
The National Highway Traffic Safety Administration says it has new data showing that chances are as high as 50 percent that the inflators can explode in a crash.
Transportation Secretary Anthony Foxx says the vehicles should be fixed as soon as possible before they cause more deaths or injuries.
Takata inflators can explode with too much force, blowing apart a metal canister and sending shrapnel into drivers and passengers. At least 11 people have died and more than 100 have been injured.
The advisory covers vehicles from the 2001 to 2003 model years.