The M80 interchanges with the M73 at Junction 4 via east facing slip roads. These act as free flow links for traffic travelling to or from the north and south. The motorway temporarily increases in width to three lanes, returning to dual two lanes at Junction 4A.

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Limited access to the motorway is provided at Junction 4A, where only south facing slip roads were constructed. South of here the motorway is connected to Traffic Scotland’s network of overhead sign gantries, although variable message signs and CCTV cameras are place along the entire length of the route.

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At Junction 5 (Auchenkilns), the M80 interchanges with the A73 dual carriageway, a former trunk road constructed as part of the development of Cumbernauld. This junction, which is a full access 'dumbbell' type, was constructed in 2005, ahead of the main motorway contract.

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The motorway climbs steeply between Junctions 5 and 6, acting as a boundary between the newer and older parts of Cumbernauld new town. At Junction 6, a service area is signed, though there is no direct access from the main carriageways. The site is currently operated by Shell. Much of this stretch is affected by peak time congestion, in line with predictions made when it was decided to remove a third traffic lane from the design.

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After passing below the main Glasgow to Edinburgh railway line at Castlecary, the motorway turns northwards, crossing the Forth and Clyde Canal. The canal underbridge was constructed in 2000 as part of a project to reopen it to navigation. Junction 6A is located immediately south of the canal and has north facing slip roads only. Junction 7, with connections to the A803, is full access and has seen little modification since 1974.

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The motorway gains a running lane in each direction as it approaches the M876 at Junction 8. The routes are linked via east facing slip roads, allowing for north to south movements only. 

 

The motorway continues through predominantly agricultural land for a further five miles before reaching the M9 at Junction 9. The southern section of this stretch, which was upgraded from an all-purpose dual carriageway, features discontinuous hard shoulders at some bridges.

 

Junction 9 is a large roundabout interchange with connections to the M9 southbound and the A91 and A872 towards Stirling. Stirling Services, operated by Moto and constructed in the mid-1980s, is also accessed from this part of the junction.

 

The M80 becomes the M9 a short distance later, with traffic wishing to continue towards Edinburgh forced to 'turn off to stay on'. Similarly, traffic travelling north on the M9 must merge with the M80 via a long slip road.