[swiftcoder]

This depends whether you have one of those barriers made of bollards that raise out of the ground (expensive, hard to retrofit on an existing parking structure), or the kind where an arm lowers across the road (cheap, trivial to retrofit)

[cjbgkagh]

I think such barriers are usually considered permanent and must always be overcome. You get over a barrier. So it is more like a wall or hurdle. In the metaphors of difficulty it is assumed there will always be some residual difficulty so there will still be a barrier, but one that is easier to get over, so it is replaced with a lower one.