Westcott said:
Imagine a summit on a main line where banking was required up both sides.
What trackwork would heve been used at the summit to seperate the banking locos from the trains?
Or did they just carry on down to the bottom at the other side?
The solutions varied by site Hamish and whether the assisting engine was physically coupled to the train. Of course it also depends on whether the assisting engine is on the front or rear of the train. There were/ are no fixed rules. Also depends on whether we are talking UK practice or elsewhere.
Although it's only a unidirectional hill for banking engines, Lickey has one of the more interesting layouts. Assisting engines are not coupled, so at the summit they simply brake to a stand clear of trailing points which can take them into a long central siding between the main running lines. They can stand clear there until a free path is available back down to Bromsgrove.
Some UK examples
1) On the ascent to Shap from the south, assisting engines were traditionally added at Tebay, pushing the train north without being coupled to it. They then halted on the main line at the summit and waited to either be turned onto the southbound main line via a trailing crossover to return to Tebay or whisked into a siding to await a path. Where assisting engines were used on southbound trains I recall them working through.
2) On the south Devon banks, assisting engines were attached to the front of the train at either Plymouth or Newton Abbot and continued with the train throughout.
3) On the Settle & Carlisle, Hawes Junction was used in both directions by the Midland Railway as the point of detachment for assisting engines. The Midland always had such engines coupled on the front of the train, so a train had to stop, detach the loco which would head for a loco yard to be turned to return whence it came.
- but they were also sometimes coupled to a goods train going down the incline to assist with braking effort. 
