Recently the Hull - Leeds line there are some major renewals work at the moment, currently focused around Melton. This has brought a number engineering trains in for the Saturday night possesions. Finding out times can be difficult for enthusiast, but gen sites on the internet can provide the information. Even then trains like these can leave quite early. But if you get lucky the results can be rather pleasing.
One example of one of these workings was 66 099 on a long spoil train looking particularly filthy - though the dirt and dust does do an excellent job of highlighting all the details and fittings along the solebar which is very useful for modellers! The train had originated from Carlisle the previous night and was waiting to head to Doncaster.
Soon afterwards 66 154 joined 66 099 and it makes an interesting contrast for modellers looking to weather their Class 66s. Both locos were filthy but had weathered in quite different ways.
Both departed soon afterwards, both at walking pace until the reached the limits of the possession - displaying a part of rail operation that I've never seen modelled.Perhpas to be different someone could set their layout in a T3 (full blockage) possesion!?