Access to Roadrunner has always been slightly tricky. The police once stopped and challenged me about what I was doing. When I explained that I had no intention of climbing anyway near the road, they seemed satisfied and said begrudgingly that it was okay, but that they expressly did not want anybody driving around the cycle track or parking on it.
I told the copper that we always parked in the layby 200 metres back down towards the roundabout (Bangor direction). He seemed happy with this.
I know there is a lot of building work in the area at the moment (there has been off and on for years), but I doubt very much that anybody will be challenged if they visit putside of a normal working day. Weekends are probably okay as well.
Crossing the road in a low key manner is a problem when the road is busy, but if people use a bit of common sense I don't see a problem. Just make your passage quick and efficient. Don't sit on the wall and don't draw attention to yourself once in the cave.
Whatever you do, don't follow the access details in the Rockfax N Wales Limestone guide - this could lead to a formal banning of the crag.
Apologies if this sounds like a preaching session, its just that, whilst RR might suit everyone's taste, it does have some loyal followers who would hate to see it banned, or filled in.
