When you see the Saltsjöbanan for the first time, you will probably think the trains look familiar. And you will be right – they are old underground trains converted to serve the 15,000 or so passengers who commute from the seaside to the centre of Stockholm every day.

Although the Saltsjöbanan line is a railway, it is served by trains that were originally ordered for the underground. Today there are 30 vehicles plying the 23 km route.


First to use CTC

This line was one of the first in the country to be electrified, in 1913. Another innovation pioneered by the Saltsjöbanan was CTC (centralised traffic control), which allowed the whole line to be remote-controlled from the control centre.


The challenge

The challenge for Cactus was to integrate modern technology with parts of the old equipment from 1938. Cactus and SL have worked together to establish very effective communication between the interlocking system and the control centre. Here, modern fibre-optic cabling and redundant modems with continuous monitoring have been used.


An unusually smart solution

The solution for integrating new technology was very smart. It also provided for extremely quick and safe commissioning.

The trick was to use exactly the same interface between the remote control station and the interlocking system. In this case, the interface was an 80-pole connector. By connecting the new remote control system through the old interface, we ensured that everything would work.

The technology made it easy to test and hook up new units. Station after station could be tested at night. Any faults were fixed on the spot. Commissioning was then almost a formality