The British Rail Class 142 Pacer was an attempt to produce a cost effective train to replace the worn-out and elderly first generation BR Diesel Multiple Unit fleet that had been introduced in the late 1950s. The Class 142 concept was a marriage of proven bus technology and traditional railway chassis and powertrain by utilizing modular Leyland National Bus Bodies mounted on a substantial steel underframe and powered by conventional underfloor diesel engines. They came at a time when the network was lacking in investment, and when first introduced from 1985 onwards, they presented a fresh, bright & clean image, breathing new life into many suburban and rural services. Unfortunately, soon after introduction, there were serious reliability problems, which necessitated much re-engineering, since when they have become a familiar sight across the network. With the remaining ninety-four trains now all past their thirtieth birthday, the fleet is due to be retired by 2020.