Apologies if this has been asked already:
When crossing from fast line to slow line ( and vice versa!). How do you know when then last carriage has passed over the points in order for you to accelerate?
I can't speak for other companies, but all mainline DB Schenker locos have a 'Q-Tron' device fitted. This is basically a small computer mounted either on the central cab windscreen pillar (on a 60) or above the driver's windscreen (on a 66/67).
You enter your personal pin number, train ID and then you can enter the train length from the information provided on the train list (paperwork that accompanies each freight train). On the train list, the length is calculated in SLU's (standard length units). 1 SLU equals 21 feet, so you multiply your SLU's x 21 to find out your train length in feet, then enter this into the Q-Tron.
When you approach a crossover or speed restriction, there is a button near to the braking controls that activates the train length function of the Q-Tron. Press it once to arm it, press it again to activate it as the loco passes out of the speed restriction/crossover.
The Q-Tron then counts down the train length, plus a safety margin of about 10-15% before beeping to let you know you are across. You can also watch the length count down in feet.