British Rail Class 799

British Rail Class 799 HydroFLEX
Class 799 unit 799201 at Long Marston Depot in 2026
Manufacturers	As Class 319: British Rail Engineering Limited Conversion to Class 799: Porterbrook, University of Birmingham CRRE
Family name	BR Second Generation (Mark 3)
Constructed	2019, 2021
Number built	2
Number scrapped	1
Formation	4 cars per unit
Fleet numbers	799001, 799201
Specifications
Car body construction	Steel
Car length	Outer vehicles: 19.830 m (65 ft 0.7 in) Intermediate vehicles: 19.920 m (65 ft 4.3 in)
Width	2.816 m (9 ft 2.9 in)
Height	3.774 m (12 ft 4.6 in)
Wheelbase	Over bogie centres: 14.17 m (46 ft 6 in)
Prime mover	Ballard FCveloCity
Engine type	Hydrogen fuel cell
HVAC	Electric heating
Electric systems	25 kV 50 Hz AC overhead 750 V DC third rail
Current collection	Pantograph (AC) Contact shoe (DC)
Braking system	Electro-pneumatic (disc)
Safety systems	AWS TPWS
Coupling system	Tightlock
Track gauge	1,435 mm (4 ft 8+1⁄2 in) standard gauge

Cab interior

The British Rail Class 799 HydroFLEX is a prototype class of bi-mode multiple unit adapted from Class 319 electric multiple units (319001/382). The existing 25 kV AC and 750 V DC equipment has been retained with a hydrogen fuel cell added, currently taking up one of the carriages.