| Always | |
| If the weather permits | |
| Never | |
| If it improves your ability to see or hear an approaching train |
| Safe for cars but not necessarily for buses | |
| Safe for buses, cars can exceed this speed | |
| Safe for all conditions | |
| Safe for both cars and buses |
| Must be kept closed and locked at all times | |
| Can be locked fully open for fresh air | |
| Can be locked partially open for fresh air | |
| Can be left open as a regular practice |