The government wants new passenger vehicles to provide head protection in dangerous side-impact crashes, which kill thousands of motorists every year and leave others with serious brain injuries.

The National Highway Traffic Safety Administration on Wednesday issued new rules requiring the improved safety protections in new passenger vehicles by September 2012.

The upgrades, which have been under review since 2004, are designed to reduce deaths and injuries of motorists who are struck by another car or truck along the vehicle's side. Side-impact crashes killed 9,200 people in 2005, the most recent figures available.

Changes to the safety systems could save 311 lives and prevent 361 serious injuries a year, the agency estimated, through the installation of side air bags that protect a person's chest and abdomen and window curtain air bags guarding the head.

Nicole Nason, the safety agency's administrator, said the crashes often lead to debilitating injuries. "Even people who survive the crash can end up with long-term medical costs and permanent brain injuries, so we think (the rules) are important for both injuries and fatalities," she said.

Automakers said they were receptive to the changes. In 2003, the industry agreed to install side air bags in all new passenger vehicles by September 2009 and the safety equipment is becoming more widely available.

Dave McCurdy, the head of the Alliance of Automobile Manufacturers, which represents General Motors Corp., Ford Motor Co., Toyota Motor Corp. and others, said they shared NHTSA's goal of "enhancing head protection" in side crashes.

Under the government's plan, automakers will be required to phase-in the head protection beginning with the 2010 model year, with full compliance by the 2013 model year. It will increase the average vehicle cost by $33.

The rules do not require specific types of technologies to meet the standards, but automakers will likely use side curtain air bags and air bags that protect the chest and abdomen. Nearly half of 2008 model year vehicles offer the air bag combination.

Auto manufacturers will need to comply with a new test that simulates a vehicle striking a tree or a pole in the driver's side. They will also need to conduct crash tests using dummies the size of a small woman and a more technologically advanced male dummy of average height.

Gerald Donaldson, senior research director for Advocates for Highway and Auto Safety, said the rule provided more focus on head injuries of motorists in the back seat and would take into account a wider range of people. But he said it failed to do enough to protect elderly motorists.

Safety groups have pointed to the benefits of side air bags. A study last year by the Insurance Institute for Highway Safety found that driver deaths were reduced by 52 percent in sport utility vehicles equipped with head-protecting side air bags, while the same air bags reduced driver deaths by 37 percent in passenger cars.