They can. Looking left to right, they start in the town, out of sight. Behind the church on the backscene below. There are two entrance/exits , one just above the Atlantic and the other above the 6 wheeler behind it. From there they can loop under the bridge, stop in front of the engine works and then back round the back, or they can go up to the station and loop round behind the buildings at the main entrance.
To get to the other end of the layout, they turn left under the bridge and into the garage building you can see on the right here. This was taken in 2017 before it was fully operational, so the entrance is blocked off with perspex.
From there they run along thre length of the engine shed out of sight before emerging onto Springfield Road and immediately left to pass under the bridge. Where the horses and carts have been posed below.
This is where it gets really clever - Andrew has devised and installed working traffic lights as it's only a single track road under the bridge. You can see it working here - it's a thing of wonder. Vehicles stop at the red light and wait for traffic coming from the factory side, then proceed when it clears to green. Traffic from the Great North Road waits out of sight about half way along the factory building, just in front of Paul.
Without all the bits and bobs, the video also shows how vehicles then climb up the Great North Road bridge, turn and wait out of sight until they're released by the next one passing behind the Ruston Hornsby factory. They then start the circuit again.
It's not totally flawless....
... but on the whole it works really well and provides another slice of entertainment for the punters.