At journey start, you drive a Class 52 light engine out of the yard and climb up to cross a bridge over the other tracks, then go down the other side. As you go down the other side, the physics are most peculiar. At the start of this 1.7% down gradient you close the throttle and prepare to apply brakes as loco gathers speed. Except it doesn't. Instead, it quite rapidly slows down and stops. Then it slowly rolls up the hill a bit before stopping again. If you stop at the top of the gradient and release the brakes, the loco starts to accelerate down, then starts to slow down, then speeds up, then slows down.... It's as if it's not sure which direction gradient is going - all very odd! Edit: Just discovered that same problem occurs in GWE - Diesel Legends - journey 5A62 'Return to Old Oak Common' which also uses Class 52.