Elevated yard lead

In the past, I've read some magazine articles about modelers attempting to mimic a hump operation.  The key factors seem to be height of hump, quality of switches, length of yard tracks, weight of cars, free-rolling ability of cars, and controlling the car speed after release from the engine.  The engineering and computer programming for this stuff in the real world seems very well adjusted these days after an enormous cost outlay by the railroads, but from what I remember reading, the modeling approach seems to be mostly trial and error.  For example, speed controls might be puffs of air blown through ties or paint brush bristles stuck between ties where speed needs to be reduced.  Use of metal couplers is also highly recommended.

Chuck