I don’t see a rule in Junk’d that it’s legal to share a space with another vehicle. But I don’t see a rule that it’s illegal. Does this mean if I’m behind someone in the same lane that I can roll Engine and blow past them? Or if I’m in the same segment that I can roll Tires and jump over them?
In my games I handle it like this: cars can occupy the same space with other vehicles as the result of an action, but you can only overtake cars via another lane by rolling tires or successfully shooting the car before you to junk in the same lane.