M4 corridor bridge, serving Chepstow, being renumbered the M48, although the area is still generally considered as falling within the M4 corridor. Since the start of the 21st Century there has been evidence of more investment west of Cardiff, such as: M4 corridor The M4 corridor is an area in the United Kingdom adjacent to the M4 motorway, which runs from London to South Wales. It is a major high-technology hub. Important cities and towns linked by the M4 include (from east to west) London, Slough, Bracknell, Maidenhead, Reading, Newbury, Swindon, Bath, Bristol, Newport, Cardiff, and Swansea. The area is also served
M4 (Istanbul Metro) M4 (Istanbul Metro) The M4, officially referred to as the M4 Kadıköy–Tavşantepe metro line (), is a , 19-station rapid transit line of the Istanbul Metro. Running between Kadıköy and Tavsantepe, it is currently the only rapid transit line operating on the Asian side of Istanbul. The M4 mostly runs under State road D100, parallel to the Istanbul-Ankara railway and is entirely underground. The M4 opened on 17 August 2012 with a large ceremony in Kadıköy, in which Prime Minister Recep Tayyip Erdoğan personally took part in. On 29 October 2013, with the opening of Marmaray rail service under the