The latest advances in inflatable head barriers are now permitted in cars sold in the U.S. The National Highway Traffic Safety Administration (NHTSA) has revised its standards for preventing head injuries during side-impact and rollover accidents. In 1995, NHTSA issued rules for adding protection to the heads of passengers beyond what is provided by forward-mounted airbags. At first, most car makers planned to meet the requirement, which began phasing in this September 1, by adding padding to the upper interior of cars. In the interim, however, design engineers devised devices similar to airbags that expand across the roofs of cars in accidents. A problem is that the devices won't deploy through heavy padding. So NHTSA decided on a tradeoff. It will reduce the speed used in crash tests of cars with the devices in uninflated states, in favor of the bigger benefits offered in more severe crashes. But vehicles equipped with such systems also will have to comply with a new test in which the vehicle is crashed into a pole. NHTSA will use a new side-impact crash dummy in the pole test. The head injury rule applies to 10% of 1999 models, but will apply to 100% of year 2003 production models.