The Modernisation Plan called for the large-scale introduction of diesel locomotives: a total of 2,500 locomotives for mainline service to be procured in 10 years at a cost of £125 million (£3 billion in 2020), plus the replacement of much of the existing pre-war passenger rolling stock with over 5,000 diesel or electric multiple units or new carriages at a further estimated cost of £285 million (£6.8 billion in 2020). The longer-term plan was to electrify all the major trunk routes, the important secondary lines and the remaining suburban systems, but the Plan initially called for the acquisition of 1,100 electric locomotives for £60 million (£1.4 billion in 2020) plus £125 million (£2.8 billion in 2020) for electric infrastructure. Diesel traction would therefore serve mainly as a stop-gap between steam and electric traction, remaining only for more minor routes, shunting and certain freight movements.