Dangerous 'slip road' from cycle path onto Marston Rd

The council installed a slip road for cyclists to exit the cycle path and join the Marston Road. The road markings indicate that cyclists have priority. But, (a) the road markings are wearing out and/or (b) motorists may ignore them. So, cyclists must merge with the Marston Road traffic at their own risk. I think the council should install a barrier to divert motorists from the cyclists' entry point and also slow down motorists entering the 20mph zone there (many take no notice of the 20 sign). There are many barriers to separate cyclists and motorists along the Marston Rd between John Garne Way and the Islamic Institute. Why not have more barriers at this more crucial point, where cyclists must merge with the traffic and the 20mph zone begins?