Background and specifications

In 2012, Transport for London announced its intention to procure a fleet of new, longer DMUs, as the Class 172 units then in service were unable to handle the passenger demand, causing overcrowding throughout the day. TfL issued a tender for manufacturers to supply eight three- or four-car trains.^[3] However, this proposal was subsequently shelved when the Government announced in June 2013 that the Gospel Oak to Barking line would be electrified,^[4] with proposals instead to purchase a fleet of new EMUs. ^[5]

TfL invited expressions of interest for a total of 39 four-car EMUs in April 2014, with 30 required for the Lea Valley Lines, eight for the Gospel Oak to Barking line, and one for the Romford–Upminster line - all of which have replaced Class 315 and Class 317 trains dating from the 1980s, and Class 172 trains dating from 2010.^[6] Since then the planned procurement was increased to 45 four-car EMUs, with the additional six units intended for the Watford DC Line. The intention is that the five-car Class 378 trains currently used on the Watford DC line will be cascaded back to the North London line and East London Lines to allow for strengthened services. TfL issued an Invitation to Tender (ITT) in early 2015.^[5]

Contract award and construction

In July 2015, TfL announced that it had placed a £260m order for 45 four-car Bombardier Aventra EMUs, with an option for 24 more four-car units plus further options to extend some or all units including option units to five cars.^[5] These are similar to the Class 345 and Class 720 trains that are currently used on the Elizabeth line and Greater Anglia services.^[7]

The units were delivered in two subclasses; an AC-only version – subclass /1 – for use on the Lea Valley lines and Romford–Upminster services, and a dual-voltage version – subclass /2 – for the Watford DC and Gospel Oak to Barking line services. These carry pantographs on their PMS(W) vehicles^[1] and are maintained at Willesden TMD, while the subclass /1 units are maintained at Ilford EMU Depot.^{[8][full citation needed]} Both versions have all-longitudinal seating, after the plan to fit some transverse seats to the AC units was dropped.

In 2017, Transport for London put forward a proposal to procure nine additional Class 710 units for the purpose of capacity enhancement, using 42 of the 249 additional vehicles for which TfL held options. Of the nine units, three would be four-car units (one for the Watford DC line and two for the extension of the Gospel Oak – Barking line to Barking Riverside), while the other six would be five-car units for the North London line and West London line, allowing a cascade of Class 378 units from those lines to the East London line.^[9] Following delivery, the six five-car units were renumbered from subclass /2 to subclass /3.^[10]

Delays in introduction

In April 2018, the Islington Gazette reported that the trains would be introduced three months later than scheduled due to delays in their testing.^[11]

In June 2018, the Barking & Dagenham Post reported that the trains would be in service by November 2018, "almost 18 months later than planned".^[12]

In November 2018, TfL said that they hoped the units would be in service by December 2018;^[13] however, further delays prevented this.^[14]

In January 2019, TfL announced that three Class 378 trains would temporarily be deployed on the Gospel Oak to Barking line while continued problems with the Class 710 units were resolved,^[15] since leases on the existing Class 172 stock running on this line would come to an end before the 710's likely introduction into passenger service. In April 2019, the Office of Rail and Road approved the use of the Class 710, with restrictions.^[16]

Illustration