This is an example of the relay logic used to operate a railroad wayside signal at a control point for a signalled siding. The switches act as control signals coming from the dispatcher desk. One of these indicates the position of the turnout switch at the control point. The rest are block authorization which gives the signal the appropriate aspect.
Aspects available are Stop, (red/red/red) Approach, (yellow/red/red) Advance Approach, (yellow/yellow/red) Clear, (green/red/red) Medium Approach (red/yellow/red) and Medium Approach Medium. (red/yellow/flashing green)
