I would worry about the road salt more than the space. If in a container, it would need to be quite large such as a whiskey half-barrel and be moved to a cold (but not far below freezing) area for the winter. Instead I would plan on annual vines such as scarlet runner beans or Black-eyed Susan vine (Thunbergia).

I would build up the edges with wood like 2X6's stacked two or three on their edges to make a raised. Leave the bottom and posdibly even the back open. That would help keep the salt out of it.

I am not sure that most clematis will survive winters there in a raised bed which will most likely freeze solid for the coldest part of the year and also in spring and fall do quite a bit of freeze-thaw cycling. Jessica is a bit warmer than I am, but I am not certain that she is warm enough for a raised bed or container grown clematis without winter protection. I couldn’t grow one since almost nothing survives winter here in containers.