Posted: Fri Mar 23, 2007 3:10 am
Hello,
I don't know who AG or Chris Gibb are but I doubt they were intentionally trying to lie or fob someone off. There's a good chance this is how the system had been explained to them by someone else who either didn't understand the signalling themselves or was trying to simplify the issue. Since writing my last message I have investigated further and the signal leaving Clifton in the up direction and that in the tunnel coming out (down) share the shame stick relay (for economy as previously suggested). The stick relay is what keeps a signal from reclearing when it shouldn't. The sharing of the stick relay is fine... unless you wanted to turn a train back at Clifton.
With regards to Avonmouth you are again limited by the signalling. The up platform is signalled for up trains only so only trains from Clifton can arrive at this platform, and any terminating services would have to shunt on to the single line at the St. Andrews end back in to the down platform in order to return to Clifton. The down platform can deal with through down trains bound for Clifton and thanks to the provision of a fixed red signal seen here:
http://www.bristol-rail.co.uk/images/avonmouth9.jpg
up trains coming from Clifton can terminate here (on the down platform) and return back to Clifton. Because this signal is only capable of showing a red aspect is it not possible for trains to continue beyond towards St. Andrews.
Alex
I don't know who AG or Chris Gibb are but I doubt they were intentionally trying to lie or fob someone off. There's a good chance this is how the system had been explained to them by someone else who either didn't understand the signalling themselves or was trying to simplify the issue. Since writing my last message I have investigated further and the signal leaving Clifton in the up direction and that in the tunnel coming out (down) share the shame stick relay (for economy as previously suggested). The stick relay is what keeps a signal from reclearing when it shouldn't. The sharing of the stick relay is fine... unless you wanted to turn a train back at Clifton.
With regards to Avonmouth you are again limited by the signalling. The up platform is signalled for up trains only so only trains from Clifton can arrive at this platform, and any terminating services would have to shunt on to the single line at the St. Andrews end back in to the down platform in order to return to Clifton. The down platform can deal with through down trains bound for Clifton and thanks to the provision of a fixed red signal seen here:
http://www.bristol-rail.co.uk/images/avonmouth9.jpg
up trains coming from Clifton can terminate here (on the down platform) and return back to Clifton. Because this signal is only capable of showing a red aspect is it not possible for trains to continue beyond towards St. Andrews.
Alex
