a test-bed unit and engaged Bombardier Transportation to rebuild it as a pre-series unit with new traction equipment. The DC motors, traction electronics and thyristors were removed, though the original transformer remained in place. The original bogies were modified to accept new AC motors, and three-phase converters fitted. Regenerative braking was also fitted. Because AC motors are more reliable than DC ones and require significantly less maintenance, this should potentially bring significant cost savings. The work has the potential to extend the life of the Class 317 by up to 20 years. Angel Trains and Bombardier will evaluate the performance of the unit compared to a conventional Class 317. At the same time, a £1 million interior refurbishment was carried out on two vehicles of the same unit - driving trailer standard open 77021 and motor standard open 62682. The interiors were refurbished in a Metro style layout and provided a direct contrast to the 3+2 and 2+2 seating in use on the remainder of the unit. Trials to test the reaction of passengers commenced with Greater Anglia in mid-2014. Trials were not particularly successful, and the unit was kept at Ilford for several years before being withdrawn in early 2019. Accidents On 17 September 2015, unit 317346 collided with the buffer stops at King's Cross at a speed of . Fourteen people were injured. Fleet details Named units A number of units carry or have carried names as follows: 317345: Driver John Webb 317348: Richard A Jenner 317363: The Hatfield Comet 317370: Harlow 50 Years 1947-1997 317371: Stevenage New Town 50 Years - 1946 - 1996 317372: Welwyn Garden City Seventy Five Years 317507: University of Cambridge 800 Years 1209-2009 317654: Richard Wells 317709: Len Camp 317723: The Tottenham Flyer 317892: Ilford Depot Preservation DTSO vehicle 77092 from unit 317345 is preserved at the East Anglian Railway Museum, and TCO vehicle 71621 from the same unit is at The Depot in Caxton. The static display will show the history of both the Class 317 fleet and that of electrification in Anglia. Notes References Further reading External links 317 317 Train-related introductions in 1983 25 kV AC multiple units