I looked at the most recent data on traffic fatality rates per 100 million vehicle miles driven by state. The highest rate at 1.92 is in Puerto Rico which has a warm climate, followed by 1.86 in South Carolina. Mississippi and Kentucky are tied for third at 1.69.
Massachusetts has the lowest fatality rate at .63, followed by Rhode Island at .64, and Minnesota at .66. The District of Columbia is fourth best at .75 and New Jersey is not far behind at .78.
California is 1.07.
ETA: My source is the National Highway Traffic Safety Administration.