There’s a suggestion on dublin.ie‘s Virtual Institute of Simplicity to “put a kerb on the outside of cycle lanes”. It’s pointed out that they do this in Paris, but the roadways in Paris are generally wider than in Dublin. My concern is that a concrete kerb would take space away from cyclists, rather than motorists. Also, it may further enforce the “ghettoisation” of cyclists, whereby motorists don’t expect to see cyclists in any part of the roadway other than the cycle lane.
In any case, comments and votes are being accepted at http://www.dublin.ie/simplicity/ideaDetails.asp?id=315