Average velocity equals distance over time. The distance measurement comes from the train of cars. While in the loading station, measure the length of the train. This can be done quickly by measureing from the back of one train car to the back of the adjacent train car. Then multiply this distance by the number of cars in the train.
Average velocity equals distance over time.
The distance measurement comes from a known length of track. Most tracks are constructed from track cross ties that are some equal distance apart from each other. Either get this distance form the park, measure or estimate it.