the middle door (was never carried out) Changes in Series 3 IBIS equipment delivered ex-factory, retrofit to Series 1 and 2 vehicles until 1987 Mandatory selection of "steps high" and "steps low" setting before doors can be opened, retrofit to all prior vehicles Changes in Series 4 Skylight windows on one side only GTO chopper control with 8085 microprocessor Fire protection (tested on 6147 from January 1987): new sheet metal roof in the passenger compartment plastic light covers replaced by steel lamellas roof and side handles in joint area replaced with cast plastic handle Additional tail lights Changes in Series 5 Adjusted size of door windows Wider door seals Changes in Series 6 Double doors without handrail in the midsection, new lock mechanism (tested on 6083, partly retrofit to older vehicles) Refurbishment An invitation of tenders for a refurbishment programme began in 2018. About 40 sets are slated for refurbishment, which includes LED lighting and repainting. The first refurbished set was presented in 2019. TW 6000 in Budapest After Hanover had upgraded its fleet with TW 2000s on the occasion of the Expo 2000 World's Fair, Üstra offered part of its used TW 6000 rolling stock for sale. Hungarian company BKV, operator of the tram network in the capital of Budapest, bought the majority of it. In 2000 Budapest had an aging tram fleet including more than 300 UV and UV trailer cars, 40–60 years old, still in operation. The last mass purchase had been the Tatra T5C5 cars in 1980-84. The TW6000 would arrive in good condition and had a highly favorable price compared to new trams. Nevertheless, it was often disputed if Budapest really had to rely on used trams, and the contradictory feelings were so strong that the leading party of the Budapest council (SZDSZ), including mayor Gábor Demszky, voted against the purchase. Preceded by lengthy political debates, the city council of Budapest provided 7 billion forints for the purchase of 68 units altogether. The first cars (6061 and 6070) arrived at BKV in 2001 to begin their test run. The first run in passenger operation on the tramline number 3 was in October 2001. The cars got new numbers in Budapest, beginning with 1500. The BKV soon decided to buy 8 additional trams. The cars got an overhaul in Hanover and were repainted into the orange yellow livery used on the BKV trams (earning the nickname