ZiU-9

ZiU-9, or ZIU-9 (Cyrillic: ЗиУ-9) is a Soviet (and later Russian) trolleybus vehicle. Other names and indexes for the same vehicle include ZiU-682 and HTI-682 (Cyrillic: ЗиУ-682 and ХТИ-682). The ZiU acronym stands for Zavod imeni Uritskogo, which is a plant named after Moisei Uritsky, the Russian revolutionary. Before 1996 this acronym was also a trademark of the vehicle manufacturer. It has been changed to Trolza. The ZiU-9 was put in mass production in 1971 and it is still assembled along with other more advanced trolleybus vehicles in the Trolza (former ZiU) factory. The total number of produced ZiU-9s exceeds 42,000 vehicles. In addition, many copies of ZiU-9 were made in other factories of the former Soviet bloc. This model is the most numerous trolleybus vehicle in the world.

The explosion-like development of trolleybus systems in the Soviet Union in the 1960s required a large number of trolleybus vehicles. The mainstay of the contemporary Soviet trolley fleet, the ZiU-5, was not sufficient for huge urban passenger transfers. It was more suited for medium-size cities rather than large megapolises such as Moscow or Saint Petersburg. In addition the ZiU-5 had an aluminium hull, which was expensive and complicated from a technological point of view. The two doors in the ZiU-5 hull ends did not work well in overcrowded situations which were quite common in Soviet public transportation.

The ZiU-9 was a quite successful attempt to solve these problems. It has one extra door compared to the ZiU-5. Two doors are wide and placed in the middle and rear end of the vehicle hull. One small door in the front end of the vehicle was/is comfortable for the driver and for outgoing passengers. The hull of the ZiU-9 is a welded steel one and it is significantly cheaper and simpler in production than the hull of the ZiU-5. The external appearance of the ZiU-9 was influenced by contemporary German-made MAN trolleybuses.

The electrical equipment of the ZiU-9 had some minor differences from the ZiU-5. The power of the main motor was increased. The indirect resistor-based control system of electric current was slightly modified to deal with the increased power of the main motor. While western designers developed new semiconductor-based control devices, Soviet engineers decided to leave the old resistor-based system for service simplicity. The first prototype vehicles were tested in Moscow in 1971 and were approved for mass production after some minor design adjustments.

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