Force312 is correct...it's all about blocking. The train begins it's climb at a slower rate so as to allow the third train to enter the unload station before the train climbing the lift reaches the top. Once the waiting block behind the unload station is completely clear, the next block is clear and the lift speeds up to full speed.
This is also one of the main causes for a train to stop on the lift, about two-thirds of the way from the top. If the train reaches a certain point on the lift, before the waiting block reads clear, the system stops the lift until the block does read clear.
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James Draeger
http://draegs.tripod.com/ "Legend is a wooden Jesus"