No matter where we are or how quiet it is.. My DD (3.5) and Ds3 (5) always hold my hand when in a car park or crossing the street..

Generally you just teach your children the dangers of moving vehicles and I also teach my kids not to hop or run or jump near roads. NOt because they will go on it but it might scare the drivers.. Think to when you are driving and you see a child playing on the sidewalk (eg) I always find my heart skips a beat if they are jumping or hopping ect.. (does that make sense)

A few times Ds2 (7) has been a bit silly so for the next few days he has to hold my hand when in a car park ect..