States are being urged to require motorcycle riders to wear proper helmets.
Members of the National Transportation Safety Board have unanimously approved safety recommendations.
Michigan is one of 20 states that require riders to wear helmets.
Motorcycle deaths increased for the ninth straight year in 2006 when just over 4,800 motorcycle riders died. Nearly 4,600 died in 2005.
Transportation officials say non-helmeted riders are three times more likely to suffer a brain injury in a crash than those wearing a helmet.
But motorcycle groups question the ability of helmets to provide complete protection and prevent internal injuries in a crash. They say more rider education programs are needed.