====== Signal aspects ======
For advtrains, a **signal aspect** can contain the following information:
  * The main signal aspect,
  * Whether the train may proceed as shunt move,
  * Whether a train in shunt mode may proceed under the main aspect, and
  * The main signal aspect of the next signal ("distant signal", not used).

The main and distant signal aspect can show one of the following:
  * Do not proceed ("danger")
  * Proceed with the given speed limit
  * Proceed while retaining the current speed limit
  * Proceed without any speed limit

Trains in shunt mode have the speed restriction of 6.