It would be cool to have something like this - but for the moment, you'd have to use a family instead.
So you'd put all your roadside stuff in a family, then have one event "If car collides with family" .
You'd need to maintain / update though, if you added more things / changed their behaviour.
You can't at the moment have two different types in a family, say for example, if you were using a mixture of sprites and tiled backgrounds for your collision objects.