Last I needed to place a complex train to a bend rail way for still rendering. The train based on 7 wagons (blocks). I use the flow along curve and history to get the straight train to the bend railway. The flow option was copy=yes rigid=yes local=no preservestructure=yes.
There was a problem with the connection between the wagons, but this wasn’t visible. Finally I was able to move the straight source curve to fine adjust the position of the bend train. I use the trick often in the past, since moving/animating the simple straight source curve is easier than moving the whole train.