There were some fundamental incorrect assumptions with the classes of new locomotives ordered under the Modernisation Plan. Steam locomotives were replaced by diesel types on a 'like-for-like' basis with BR ordering, for example, large numbers of light-duty diesels intended for local mixed-goods services (such as the Class 20 and Class 24), which failed to take into account the decline in local and branch line goods services which was largely switching to the roads. In conjunction with the new marshalling yards, large numbers of diesel shunters were ordered which would soon be rendered virtually obsolete by the rise of container freight and, like the yards they worked in, often only served a few years before being scrapped.