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List of Single Carriageway Motorways

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Despite almost all motorways in Britain and Ireland being dual carriageways - ie having a central reservation between opposing traffic flows - there are a few that buck the trend and are single carriageways. Most of those listed below are sliproads, and so not fully-fledged motorways, but there are a few genuine mainlines that are single carriageway:


  • The A38(M) is a single carriageway, though a temporary central barrier is often installed during roadworks.
  • The M58 has a single carriageway section, running north from the eastern roundabout of its junction with the M6 at Orrell Interchange to meet the A577. This link is really more like a slip road, but as the M58 does not continue east on its formerly proposed alignment, the link can also be considered as the eastern end of the M58's current mainline. There is a proposal to build a single-carriageway road eastward from the roundabout; this may lead to the removal of motorway status from both the link in question and the roundabout.
  • The M12 (NI) in Northern Ireland is single carriageway at the southern end.

Former mainlines

  • The A6144(M) was a single carriageway motorway before it was downgraded to A6144.
  • The newer, southern part of the A601(M), east of the M6, was a single carriageway motorway until it was downgraded to B6254 in 2020.

Slip roads

Each of the junctions listed below has at least one stretch of slip road where one carriageway carries two-way traffic. The list is believed to be complete.

Former slip roads

  • M6 - J34 had two-way slips for 56 years, but replacement slips were opened in 2016 as part of the A683 Heysham to M6 Link scheme.
  • M40 - J12 had two-way slips until they were dualled in a pinch point scheme completed in 2016.
  • A1(M) - J2 (northbound off-slip) here there was a farm access, resulting in two way traffic along the northbound exit sliproad, however, in 2017/18 barriers were put in place to prevent access.

Extensions of slip roads

Junctions listed below have two-way traffic on a stretch of single carriageway road which is not under motorway regulations, and is usually also separated from the motorway mainline by a side-road junction or property access, and is for these reasons technically not a slip road, but is a smooth extension of a slip road and so might be thought of as a slip road.

  • M5 - J5 (southbound on-slip)
  • M8 - J5 (the positioning of start and end of motorway signs is inconsistent)
  • M74 - J11 (northbound on-slip; here the side road was a dual carriageway until 2016)
  • M80 - J7 (NE-bound side only; but this junction is also listed above on account of both sides)
  • M876 - J1 (westbound on-slip)
  • A1(M) - J38 (both sides) (the northern terminus of a stretch of motorway)
  • A74(M) - J22 (northbound on-slip, a surviving bit of the pre-dualling A74)

Extensions of former slip roads

  • M74 - Canderwater Interchange (both sides) (the former southern terminus of the M74)
  • M6 - Catthorpe Interchange (northbound) (the current southern terminus of the M6, but it has since changed in layout and the slip road in question no longer connects to the motorway)

This article started life as a discussion on the SABRE forums

List of Single Carriageway Motorways

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