I've been setting up a lot of crashes lately, and one thing I don't like is trying to time starting a vehicle so it hits another one at an intersection or something. What I would like to see is a trigger UI app. The idea is that you place a point on the terrain, like a small, invisible checkpoint, and when a vehicle crosses it, a green light appears on the UI app letting you know to start moving if you want to hit the other vehicle. It would also be really cool if you could reverse the idea, when you cross the trigger point, it can start a path AI vehicle moving down it's path. This would make setting up large wrecks a lot easier and much more fun.
I think you should be able to do this already using the FlowGraph system ( https://www.beamng.com/threads/flowgraph.63201/ ) Maybe not the UI App, but using a trigger to start another action
Alright I finally gave the FlowGraph thing a try, and was able to accomplish exactly what I wanted. Thanks for the advice. Here's what I did in case anyone is looking to do something similar: