The purpose of this study was to measure time headway between moving vehicles. We observed 2,004 vehicles running on suburban and city roads at night and daytime. We analyzed time headway from the viewpoints of location, time, lane, weather, 'fleet', and type of vehicles. The safe distance at 60 km/h, recommended by driving schools in Japan today, was tentatively equivalent to a time interval of 2.7 seconds. From the overall standpoint, nearly 8027774225220f 2,004 vehicles maintained an unsafe and risky time headway. When adopting the safe criterion in the UK, 9227774232060f vehicles in Japan kept unsafe time gaps under rainy condition. We proposed ""how to maintain safe distance between moving vehicles"" using time headway in concrete terms.