The A599 did not exist in 1922 but it was upgraded from the B5208 in the 1920s, explaining why the road is out-of-area. A few years later the road was bypassed by the A580.
Blackbrook - Haydock Park Racecourse
The road starts at a roundabout on the A58 Stanley Bank Way (aka. The Blackbrook Bypass) just outside Blackbrook and not too far from the centre of St Helens. The A599 runs along its new alignment for a few hundred yards, then it turns sharply to the right on meeting Vicarage Road, the pre-bypass A58.
The A599 continues south-eastwards for another few hundred yards, and reaches a mini-roundabout outside a Tesco Express, formerly a pub. The old A58 turned right here marking the original western end of the A599, which carries on straight ahead into Haydock, a large residential area near St Helens. The road passes a large high school, shortly after which there is a signal-controlled T-Junction. The road rises slightly uphill as it enters Haydock proper, then it curves left past some small supermarkets. The A599 then passes a Tesco supermarket, which opened in November 2007. Here the A599 reaches a roundabout with Bellerophon Way (the road is called this after the locomotive Bellerophon, which was built on the site of the Tesco store back in the 1800s), the access road to Tesco and a Conservative Club.
Church Road, Haydock
After the roundabout, the A599 becomes Church Road. There is then a traffic-signal-controlled T-Junction with Piele Road, one of the main routes to the A580, and a large industrial area just outside of Haydock. The A599 carries on straight ahead through the 'New Boston' area of Haydock, after which it reaches a mini-roundabout with the B5209. The A599 carries on straight ahead, soon passing underneath the A580. After this is where the 'Old Boston' industrial area begins. The A599 then curves to the left (just to the North of the old A599 alignment, which was abandoned when the M6 was built - this alignment has since been built over and is now part of a Travelodge car park), and dips slightly to pass underneath the M6, immediately after which it ends with a T-Junction on the A49 outside Haydock Park Racecourse. M6J23, which also provides access to the A580, is just to the right.