While Traveling through the tunnels, I find it difficult to spot Speed Limit signs while Driving without the HUD. IRL, the Trains Headlights Reflect off of the Speed Limit Signs making it easier for the Operator to see them. Also, the signs need to be moved a little higher.
I would just love brighter headlights. Ive spoken to people in London (one is actually a train driver on the underground) and they've stated that the headlights are indeed brighter than in the game.
