It would be nice if the Severn Bridge tolls could scraped, as have all the bridge tolls in Scotland. The problem is not that the bridges span (mostly) a border that lies between two administrative areas - handing control of both bridges to the National Assembly in 2018 could easily solve that problem.
The real problem that hard pressed commuters face is that the Department for Transport is already (no doubt) looking at any toll revenues and thinking of milking the bridge tolls for all that it can squeeze out of them (less maintenance costs). The lack of a direct rail connection between the Ebbw valley and Newport also means that most (potential commuters to Bristol and beyond) have little choice but to drive to work.
This oversight (if it can be called that) may reflect successive Welsh Governments ignoring the economic realities that drive a significant number of Welsh residents to make the long daily commute across the Severn Bridges. The day the tolls are significantly reduced or removed cannot come soon enough.