The above is a simple layout of two ovals, built for St Albans South Signal Box (currently under restoration). The inner oval is plain track and has colour light signals operated by relays activated by reed switches under the track; a magnet on th rear of the 'bubble car' running round operates these in sequence.
Of greater interest, however, is the outer circle. The signalling is semaphore and will eventually be worked from a model lever frame with proper interlocking. This oval has two sidings, one permanently connected to the traditional 12v controller and one to the steam system. The main part of the oval may be switched between either system. This allows a 12v train to run round while the steamer is being prepared; it's then shunted into the siding and the steamer bought out of its siding to do its stuff.
This was seen by over half the 1080 people who visited St Albans signal box during the September 2008 'Heritage Open Days' and received numerous comments for the 'hot oil' smell etc!
PS for more information about the signal box see St Albans South SignalBox, work on a 1:1 scale in our signalling sub-forum.