-15-
Method of Operation
Trains are operated through Dobbs Ferry by signal indications of an approach color lighted automatic block signal system. Each track is signaled for the current of traffic, westward on track Nos. 1 and 3 and eastward on track Nos. 2 and 4.
Signal 21.12 controls the eastward movement into the block where the accident occurred and is 3,523 feet east of the collision point.
If the block beyond an intermediate signal is occupied by a train, the signal will display the following aspect:
| Aspect | Name | Indication |
| Red over red | Stop and Proceed | Stop; then proceed at restricted speed. |
If the block governed by the signal is clear and the block in advance of that block is occupied, the signal will display the following aspect:
| Aspect | Name | Indication |
| Yellow over Red | Approach | Proceed not exceeding medium speed prepared to stop at next signal. Reduction to medium speed must commence before engine passes approach signal. Medium speed-not exceeding 30 miles per hour. |
If the block beyond an intermediate signal is not occupied, but the third block ahead of the signal is occupied, the signal will display the following aspect:
| Aspect | Name | Indication |
| Yellow over Yellow | Advance Approach | Proceed at limited speed prepared to stop at second signal. Reduction to limited speed must commence before engine passes signal. Limited speed not exceeding 45 miles per hour. |
If three blocks in advance of the signal are unoccupied, the signal will display the following aspect:
| Aspect | Name | Indication |
| Green over Green | Clear | Proceed |
(See appendix D.)
