Safe follow distance is usually measured in time, not distance. It's a function of human reaction time plus your vehicle's ability to brake, which is mostly a f

Safe follow distance is usually measured in time, not distance. It's a function of human reaction time plus your vehicle's ability to brake, which is mostly a function of its velocity (also greatly affected by tires and weight but there's far less variance there in passenger cars compared to personal variance in velocity). Most DOTs claim around 1.5s for reaction time, and then up to another 1.5s for braking at typical highway cruising speeds. So, 2-3s follow distance in total. Adjust down for low velocity and up for poor driving conditions.