the driver, 23-year old briana disaia of texas - miraculously walks away unscathed. her life saved because she was wearing her seatbelt. arizona authorities say she was driving too close to the vehicle in front of her and didn't have enough time to react to the mattress. how long does it take to respond? >> a total of a second and a half to see something react appropriately. >> that doesn't sound like much. does it make a difference? >> it can when you're traveling at high ee half means that you may have covered 100 feet or so in that time that your brain is processing this. that's precious distance you have lost. >> a rule of thumb, give three seconds of following distance. to measure, find a fixed object like a telephone pole. when the car in front passes, count one 1,000, two 1,000, three 1,000. when you get to the marker before three, you're too close. police saying tailgating doesn't save you time, that greater role. >> thank you. when we come back. could the key to a national health problem be hiding in the homes of the amish? the medical headline tonight. reme