ABS Signal Simulator
Simulator Introduction
This simulation demonstrates basic Automatic Block Signal (ABS) logic operation. There are basically three things ahead of the signal head that determine its aspect: block occupancy, next signal state (or signal ahead state) and switch state. Also this simulation assumes that when a signal mast has two heads there is a switch just ahead. The upper head indicates the straight route track state and the lower head indicates diverging route track state. In addition, the signal head is shown on the right side of the track in the direction of travel.
For signal vocabulary click here.
Simulator operation - click on the block line or the switch line icon (black line) in the diagrams below to change the state.
RED - When the block ahead is occupied then the aspect is red.
YELLOW - When the aspect is not red (block ahead is not occupied) and the signal ahead is red then the aspect is yellow. Note that in this case the block ahead state may not be a reliable condition to use. This will be apparent when a switch is present.
GREEN - When the aspect is not red and the aspect is not yellow then the aspect is green.
| Direction of travel -> | ||
|---|---|---|
| Block 1 | Block 2 | Block 3 |
 |
|
|
 |
|
|
This next section demonstrates bi-directional train travel. Upper head indicates straight route and lower head indicates diverging route.
RED upper - When the block ahead (straight route) is occupied or the switch ahead is diverging route then the aspect is red. When the switch is diverging the upper head is red regardless of the blocks ahead (straight route) .
YELLOW upper - When the aspect is not red and the signal ahead is red then the aspect is yellow.
GREEN upper - When the aspect is not red and the aspect is not yellow then the aspect is green.
RED lower - When the block ahead (diverging route) is occupied or the switch ahead is straight route then the aspect is red. When the switch is straight the lower head is red regardless of the diverging blocks ahead.
YELLOW lower - When the aspect is not red and the signal ahead is red than the aspect is yellow.
GREEN lower - When the aspect is not red and the aspect is not yellow then the aspect is green.
| Direction of travel <--> | ||||
|---|---|---|---|---|
| Block 1 | Switch 1 | Block 3 | Switch 2 | Block 4 |
| Block 2 | ||||
|
|
  |
||
|
 |
|
 |
|
|
|
|
||
|
||||
|
||||