the m45 motorway was constructed in 1959 parallel to part of the old a45 in the midlands. it opened on the same day as the m1 motorway and was soon one of the busiest sections of motorway. the m6 opened in the late 1960s and early 1970s, after which more traffic to the ports used the route from junction 1 of the m6 via the a427 to market harborough followed by a short section of the a6 to kettering and then the a604 to cambridge before joining the old a45 to the ports as above. the m45 now carries little traffic.