Network map Current system map (includes Metro and local/regional trains), valid from December 2020 The Copenhagen S-train (Danish: S-tog), the S-train of Copenhagen, Denmark, is a key part of public transport in the city.

It is a hybrid urban-suburban rail serving most of the Copenhagen urban area, and is analogous to the S-Bahn systems of Berlin, Vienna and Hamburg.

The trains connect the Copenhagen inner city with Hillerød, Klampenborg, Frederikssund, Farum, Høje-Taastrup and Køge.

There are 170 km (110 mi) of double track[2] with 87 S-train stations, of which eight are in neighbouring towns outside greater Copenhagen.

[3] The judges' panel cited a long list of possible explanations for the "S" in S-tog, including: "state railways" (statsbaner), "city railway" (stadsbane), "Greater Copenhagen" (Storkøbenhavn), "sun" (sol), "lake" (sø), "forest" (skov), "beach" (strand), "snow" (sne), "skiing" (ski), "skating" (skøjteløb), and "sleigh" (slæde), all of which start with an S in Danish.

The names, though, demonstrate that the initial marketing of the S-trains emphasized recreational day trips from the city to the countryside.

[5] The network consists of a central section through downtown Copenhagen that splits into three radial lines at each end, reaching the outer suburbs and neighbouring towns.

The system is designed so that a train from any southern radial can continue along any of the three northern and vice versa.

A, B, C and F run all week, E and H Monday to Friday, and Bx is a support line that operates only during the rush hour.

[7] The S-tog along with buses, regional trains, and Copenhagen metro uses Rejsekort, an electronic ticketing system across Denmark.

The price is the same no matter if you take a bus, train or S-Train, and a 20% discount is applied when traveling outside of peak times if using Rejsekort.

[10] Proposals to extend the Vestbanen (West) line from Høje Taastrup to Roskilde along existing tracks, have been discussed on several occasions, and was under investigation as of 2019.

[11] Extension from Klampenborg to Elsinore (converting the Kystbane railway to S-train standard) would prove more difficult, but the issue has been mentioned.

The Danish Transport Authority (Trafikstyrelsen) has suggested converting the F-line of the S-train network to metro standard as an M5 line,[when?]

The voltage is 1,500 or 1,650 volts DC (negative overhead wire), indicating that it varies considerably with the loading and distance from a feeder station.

Varying the combination of frequencies allowed up to 15 different instructions or commands – such as stops and permitted speeds – to be indicated to the train.

Lineside signals were provided for use when the HKT system was inoperative or when a non-equipped train needed to be driven on the line, but line capacity was significantly reduced as these signals only protected full-length blocks and had to be placed according to conservative braking distance assumptions.

In 2011, infrastructure operator Banedanmark awarded Siemens Mobility a contract to replace HKT with its Trainguard MT communications-based train control system (CBTC), on the grounds that the HTK installation was reaching the end of its life and becoming increasingly unreliable.

[13][14] The CBTC system employs the moving block principle, whereby a central controller continuously tracks the precise location and speed of every train on the line and adjusts the instructions issued to drivers accordingly.

On the S-train network this has allowed a reduction in minimum separation between consecutive trains ('headway') from 120 seconds to only 90.

[14] Hillerød–Jægersborg was the first section to be converted, as its F-HKT installation ('simplified' HKT) had the oldest hardware and did not deliver the same level of train protection as the other parts of the system.

[13][16] Further conversions continued through to 2022, when in late September the final three routes (Valby–Frederikssund, Valby–Høje Taastrup, and Sydhavn–Køge) were switched over to CBTC operation.

They are the longest serving S-train rolling stock to date, in continuous service for 44 years.

Two variants are in use, one of eight cars referred to as Class SA [da] (formed of vehicles SA-SB-SC-SD-SD-SC-SB-SA) and one of four cars referred to as Class SE [da] (formed SE-SF-SG-SH) These are articulated units supplied by Alstom-LHB and Siemens with prefabricated friction stir welded aluminium roof panels made by Marine Aluminium from Sapa extrusions, and were manufactured from 1996 to 2007.

These trains introduced air conditioning in the interior and regenerative braking to the network, increasing energy efficiency.

These 4-car units (DSB class SE-SH, also known as Litra SE) can run solo in low-traffic intervals.