The rules for driving demand to keep at least enough distance to the vehicle before you, that you can safely perform an emergency break, if the vehicle should do so too.
In driving ed i learned that you need to keep at least 2seconds distance to the car in front of you, one second to react and one second to perform a similiar break maneuver like them. If your vehicle is heavier you need to increase that distance.
Whenever i drove like this the only result was people taking it as an invitation to swear in between the car in front of me and me. I want undercover cops in plain cars to just drive and record everyone violating the safe distance or takeing the space that is left as safe distance. We could resolve muncipal debt and drop the amount of deadly accidents by at least 50% this way.