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Construction Timeline

When the various parts of the M4 were built, listed in chronological order.

Open Jct Section
1959 J1 Chiswick Flyover
1961 J7-9 Maidenhead Bypass
1963 J5-7 Slough → Maidenhead Bypass
1965 J1-5 Chiswick → Slough
1966 J18-20 Tormarton → Almondsbury
1966 J20-21 Almondsbury → Aust
1966 J39-41* Port Talbot Bypass
1967 J23*-24 Crick → Newport Bypass
1967 J24-28 Newport Bypass
1971 J10-14 Winnersh → Wickham
1971 J14-18 Wickham → Tormarton
1971 J9-10 Holyport → Winnersh
1972 J44-46 Morriston Bypass
1977 J28-29 Tredegar Park → Castleton
1977 J32-35 Coryton → Pencoed
1977 J37*-39 Pyle Bypass
1977 J46-49 Pontardulais Bypass
1980 J29-32 Castleton → Coryton
1980 J35-37* Bridgend Bypass
1994 J41*-44 Baglan → Lon Las
1996 J21-23 Second Severn Crossing