AM (Automatic block) signals are placed between stations and allow for more trains to run at a time. AM signals are placed approximately 2 km apart, but can be more or less depending on the situation.

AM Signals on mainlines can show two or three aspects: Stop (one red), proceed (one green), and proceed expect proceed (two green). On some lines the signals do not pre-signal each other, so there are only two aspects together with pre-signals for pre-signalling.

AM Signals cannot be remote controlled, they are entirely autonomous. The train line between two stations must have line block (Danish: Linjeblok). The directional line block makes a directional reservation on the line which allows an exit path to be set out of the station towards the U Signal. This activates the AM Signals which check that the block is free and the aspect of the next signal in case of three aspect AM Signals. U Signals on lines with line block are technically similar to AM Signals and signal dispatchers have no control over them.

On right-hand drive lines AM Signals are dimmed to almost darkness when no train is in the block preceding the AM Signal, unless it is showing the Stop aspect. This is to extend the life of the filament in the light bulb. On bidirectional lines all AM Signals are always at full brightness.

Some lines have “Stop and passage control”. This is a system to check whether a block is free and the AM Signal has changed to the Stop aspect. If those two requirements have been met, the preceding signal may give the Clear aspect. In some cases, this doesn't happen, so the signal instead gives the “Stop and Proceed” aspect