|Manufacturer||Urban Transportation Development Corporation|
|Number in service||28 |
|Formation||4 car trains (2 sets of semi-permanently mated pairs)|
|Fleet numbers||3000–3027 
2 un-numbered test cars used for testing by UTDC
|Capacity||30 seated, 55 standing|
|Operator(s)||Toronto Transit Commission|
|Line(s) served||Line 3 Scarborough|
|Car body construction||Aluminum|
|Car length||41 ft 8 in (12.70 m)|
|Width||8 ft 2 in (2.489 m)|
|Doors||4 sets (2 sets per side) per car|
|Maximum speed||70 km/h or 43 mph|
|Weight||34,050 lb (1,840 kg)|
|Traction motors||3 phase AC linear motors|
|Power output||120 hp (89 kW)|
|Transmission||3 phase AC linear motor|
|Electric system(s)||600 V DC third rail (linear induction)|
|Current collection method||linear motors|
|Track gauge||1,435 mm (4 ft 8 1⁄2 in) standard gauge|
The S-series is the rolling stock of light metro trains used on Line 3 Scarborough of the Toronto subway system. They were built from 1983 to 1986 for the Toronto Transit Commission by the Urban Transportation Development Corporation (UTDC) in Millhaven, Ontario. They were based on the Intermediate Capacity Transit System (ICTS) Mark I model of trains. The line first operated with two-car units, and later as four-car units as ridership grew. A test run began in 1984 and full service began in 1985. The fleet numbers of the cars used are 3000 to 3027.
Identical trains are used by the Vancouver SkyTrain and the Detroit People Mover. However, unlike these systems which are fully automated with no human operator onboard, the TTC employs a single operator to steer S-series trains along with Line 4. Toronto subway trains on Line 1, Line 2, on the other hand, carry two personnel onboard (an operator and a guard) while in service.
Since the retirement of the remaining H-series trains in 2014, the S-series trains have been the oldest in operation on the system. They are the only rapid transit trains owned by the TTC with painted livery since the G-series trains. The trains used to have a unique logo of a lower-cased "RT", referring to the line's original name, Scarborough RT. Since 2015, the cars have been undergoing refurbishment and repainting to prolong their lifespan until at least 2023. The new exterior of each car features a blue-finish (the line's colour on route maps), the Line 3 symbol, and the names of the line's six stations written on the top edge on both sides.