tyre wear on tight curves, and they quickly had to be replaced by the old DMUs. The solution lay elsewhere, although, after much modification, the Pacers eventually proved themselves in traffic. Sprinters BR needed something midway between the Pacers and the Class 210s. In 1984/1985, two experimental DMU designs were put into service: the British Rail Engineering Limited built Class 150 and Metro-Cammell built Class 151. Both of these used hydraulic transmission and were less bus-like than the Pacers. After trials, Class 150 was selected for production, entering service from 1987. Reliability was much improved by the new units, with depot visits being reduced from two or three times a week to fortnightly. The late 1980s and early 1990s also saw the development of secondary express services that complemented the mainline Intercity routes. Class 155 and Class 156 Sprinters were developed to replace locomotive-hauled trains on these services, their interiors being designed with longer distance journeys in mind. Key Scottish and Trans-Pennine routes were upgraded with new Class 158 Express Sprinters, while a network of 'Alphaline' services was introduced elsewhere in the country. By the end of the 1980s, passenger numbers had increased and costs had been reduced to two-and-a-half times revenue. Electrification The British Rail Class 323 electric multiple units were built by Hunslet Transportation Projects between 1992 and 1995, although mock-ups and prototypes were built and tested in 1990 and 1991. Forty-three 3-car units were built for inner-suburban services in and around Birmingham and Manchester, including the Cross-City Line in the Birmingham area and services to the new Manchester Airport railway station. Rolling Stock Livery Initially, many vehicles carried standard British Rail blue livery. From 1986, Provincial adopted a version of the prototype Class 150 livery: aircraft blue over white, with a light blue stripe at waist level. All new units, plus a few existing ones, such as selected Class 304 EMUs, received it. Some units and coaches received the livery with either ScotRail or Regional Railways branding. The Class 158s, introduced in 1989, appeared in Express livery: dark grey window surrounds over light grey, with light and dark blue stripes at waist level. This colour scheme was also applied to some Class 156 units around privatisation. The Class 323 EMUs introduced in 1994 appeared in the West Midlands Passenger Transport Executive (Centro) livery for the West Midlands based sets, and the Greater Manchester Passenger Transport Executive (GMPTE)