British Rail Class 399

The Class 399 is a dedicated tram-train unit. The primary purpose of the type is to operate the tram-train service between Sheffield and Rotherham; as such, it is designed to run on both the National Rail and Supertram networks.[5] Each vehicle is composed of three articulated sections, which are fitted with a total of three motorised bogies and one unpowered trailer bogie, complete with a pneumatic suspension system. They are bi-directional units, which eliminates any need for turnaround facilities to be installed; rear-view camera displays are also present in the driver's cab for improved visibility and situational awareness.[5]

To suit the two different networks, the Class 399 are dual voltage vehicles, capable of operating on both the 750 V DC OHLE of Supertram's network, and the 25 kV 50 Hz AC OHLE that is the standard on the National Rail network. Although the route to Rotherham will be electrified to the 750 V DC standard used on the rest of the Supertram network, the installation of dual voltage capability is to allow the vehicles to be future-proofed if the Midland Main Line north of Sheffield is electrified.[17][5] The process for switching between the two different power supplies is automated by an integrated Automatic Power Control (APC) system. This system is triggered by a series of magnets which have been embedded at key locations on the ground outside of the track, while the two power supplies are intentionally separated by a neutral section of track.[5] In practice, the vehicle travels over the first magnet to trigger the circuit breakers to open, after which it coasts through the short neutral section before the new voltage is detected and the circuit breakers are closed again. While the APC provides an automated process for this, there is a manual override allowing the driver to close the circuit breaker if circumstance ever requires this to be done.[5]

The Supertram lines and the National Rail network also use vastly different signalling systems.[5] When travelling on the Supertram network, signals are primarily provided to the driver visually; the tram-trains also make use of the same vehicle identification system (VIS) as used by the conventional trams. In addition, for compatibility with running upon the National Rail network, the tram-trains are fitted with Train Protection & Warning System (TPWS) and GSM-R equipment.[5] While TPWS is to be active during all operations, manual intervention by the driver is required for the activation of the GSM-R terminal each time one of the vehicles is driven onto the heavy rail line.[5]

In order for the vehicle to be capable of running on both on-street tramways and the National Rail network, the profile of the wheels were required to suit the particularities of the rails on both systems.[5] The design team collaborated with the University of Huddersfield, to develop a specially-designed wheel that fits both rail head profiles, which is claimed to reduce the rate of wear and mitigate against the risk of derailment. However, as the wheel profile was non-standard, permission had to be obtained from the Rail Safety and Standards Board before the new design could be adopted and subject to real-world testing.[5] As a result of the vehicles being operated upon a heavy rail line, they are subject to higher crashworthiness standards than had been imposed upon the rest of Supertram's fleet. As a result, these units will be the only ones capable of operating the tram-train service to Rotherham.[10][18]

Being tested at Donetsk Way, April 2017

In January 2016, the first tram-train commenced active testing on the Supertram network.[5] On 14 September 2017, the first Class 399 officially entered passenger service in a ceremony attended by the Parliamentary Under-Secretary of State for Transport Paul Maynard and various transport officials and representatives from Sheffield Children's Hospital.[19][20] Tram 399202 was named Theo, after the mascot of the city's children's hospital charity; in addition, tram passengers who travelled over the next two days made donations to the charity in place of the standard fare.[19]

In addition to their tram-train functionality, the fleet has also been used to strengthen Supertram's existing assets, which has not been previously expanded since having been originally commissioned in 1992. The vehicles have been fully integrated into Supertram's fleet, and are maintained by the manufacturer at the main Nunnery depot.[21] The Rotherham service operates three times per hour between Cathedral and Rotherham Central, before terminating at a new stop at Rotherham's Parkgate retail park, with a total journey time of approximately 25 minutes.[12] A total of three vehicles will be required for this service level; three of the remainder will be used to increase capacity on the rest of the network, with the seventh in maintenance.[17]

Initially however, four of the seven vehicles will be dedicated to the Rotherham service, with the other three used for fleet expansion. This is owing to the different wheel profile required for running on National Rail tracks as opposed to Supertram's own. This is envisaged to be the case until Supertram has completed its full track replacement programme.[22] In May 2018, testing began on the tram-train aspects of the vehicle itself.[23] The full Rotherham service started running on 25 October 2018.[24]

• On 25 October 2018, unit 399204 was badly damaged after hitting a lorry near Woodbourn Road tram stop.[25]
• On 30 November 2018, unit 399202 was damaged in a collision with a car at the same junction as the previous collision.[26]
• On 9 April 2019 a fault was found on the Class 399 units and they were withdrawn to undergo safety checks. Tram-train service was suspended,[27] but resumed during the next day.[28] Work to refit the bogie covers which were removed continued until 11 June 2019.[29][30]
• On 14 December 2019 the fleet was withdrawn from service on the advice of the manufacturer[31] as a result of a hydraulics issue.[32] and services resumed on 17 December 2019.