The A1173 is a relatively new primary route which diverges from the A46 at Caistor and heads towards the oil refineries and docks of Immingham.
Southern section: Caistor – Stallingborough
The longer, southern section (formerly the B1361) runs northeastwards for 8.2 miles (13.2 km) from Caistor, intersecting the A18 at Riby Cross Roads before meeting the new alignment of the B1210 (also formerly the B1361) at Stallingborough. It turns to run northwestwards to another roundabout, then northeast again to meet the A180.
Northern section: Immingham
Queens Road, Immingham – part of the A1173's spur
The northern section, the main line of which is 3.6 miles (5.8 km) long, runs in an arc around the eastern and northern sides of Immingham town to terminate at a roundabout junction with the A160. This section is nearly all new-build apart from the last 1.2 miles (2 km) along Manby Road, most of which is now dual carriageway. From roughly the mid-point of this northern section a branch runs eastward for 1 mile (1.6 km) to the entrance to Immingham Docks; this was at one time the A1136.
For a while, the A1173 route was somewhat disjointed, consisting of two (only indirectly) connected sections plus a branch to Immingham Dock. From the B1210, the road was supposed to go straight up to the A180 at a grade separated junction just 0.8 miles (1.3 km) to the north – however, the road was believed to pass over an historical archaeological site, so it was postponed for several years. To drive from one end of the A1173 to the other required a trip of 3.4 miles (5.5 km), mostly along unclassified roads.
The "missing link" was eventually built further west, and opened on 30 June 2017.