The signalling system used on the standard-gauge railway network in Sweden is based on that of the traditional mechanical semaphore signals. Currently only colour-light signals are used, together with the Automatic Train Control system.
The main signals (huvudsignaler) display the following aspects:
The aspects may seem a little inverted, since a single green light means proceed 80, two green lights Proceed 40, caution and three green lights stands for Proceed 40, short route. In other words: more green means more cautiously. The speed limits apply to trains without Automatic Train Control (ATC) equipment. ATC signalling typically allow higher speeds.
On some routes, for example the City Tunnel in Malmö, a simpler signal system is in use until ERTMS will be in full use.
This system uses two light signals with blue number signs (instead of yellow/white in normal signalling) and can show the following aspects:
These signals should not be confused with normal main signals with two lights. They have yellow number signs, while the "Two light signal" have blue ones.
Distant signals (försignaler) are informational signals used to give an advance warning about the next home signal. Distant signal are typically located 800 to 1,200 meters (2,625 to 3,940 feet) in advance of the home signal in question.
Before the entry/home signal of a station, there always is a free standing distant signal, with the signature for the station on a board placed under the signal.
The aspects a free-standing distant signal can display are:
The signal indication is the same as for the combined aspects in the main signals.
Dwarf signals (dvärgsignaler) are used as shunting signals and can show the following aspects:
There are also types of dwarf signals, called "Main Dwarf signals" (Huvuddvärgsignal) used as stand-ins for home signals in stations with lot of shunting or where there are a lot of switches that needs a signal.
Road crossing signals (Vägkorsningssignaler (V-signaler)) are used at road crossings. They tell the driver if the crossing is clear (lights flashing, bells ringing or, if available, gates are closed) They can show the following aspects
The same aspects are also used at moveable bridges, but with another sign under the signal.
Some road crossing signals have a distant signal (Vägkorsningsförsignal (V-försignal)), placed at a distance (usually not breaking distance) from the road crossing signal.
The distant road crossing signal is nicknamed "skull" (döskalle).
Because the aspects are in reverse with more green lights meaning slower the aspects are not fail safe, so lamp proving is needed to prevent lamp failure giving a faster aspect.
Single and Double Green signals work the other way with Norwegian railway signalling and it would be unsafe for drivers to cross the border, unless ATP were fitted.