The A23 forms a north-south radial route from London to Brighton. It serves many south London suburbs, along with Redhill, Horley, Crawley and Brighton. Haywards Heath and Burgess Hill also have fairly good connections to the A23 via the A272 and A2300 respectively. Within the M25 the A23 remains largely unimproved; however much work has been undertaken to bring the section from Crawley to Brighton up to modern high quality dual carriageway standard.
Section 1: London - Hooley (M23 J7)
Oddly for one of the "radial" roads, the London end of the A23 is in the 3-zone — one might logically expect it to start on the A3, but in fact it starts on the A302 opposite Lambeth North tube station. Some maps even show that the road starts at the eastern end of Westminster Bridge near what used to be County Hall (the A302/A3200/A3036 junction, in fact). This used to be a roundabout, but one side of it was closed a few years ago and now traffic flows in both directions round the remaining parts.
The A23 heads south along Kennington Park Road. Opposite Kennington Park it crosses the A3 (with the tiniest of multiplexes) and branches off along Brixton Road, crossing the A202 near Kennington Oval. In Stockwell it is joined by the A203 Stockwell Road, and near Brixton station there is a five-way junction with the A2217 and A204, from which the A23 progresses up Brixton Hill to cross the A205 South Circular Road.
The next stretch, Streatham Hill, is dual carriageway. Unfortunately, that's one of the few stretches of dual carriageway you'll find before reaching the Surrey countryside. Most of the main arterial roads out of London become dual carriageway or even motorway near their junction with the North or South Circular and continue that way, but the main route to Gatwick Airport and the south coast has many miles of single carriageway through the south London suburbs, making the journey agonizingly slow. This is partly because the South Circular runs closer to central London at its junction with the A23 than just about anywhere else, but mainly because the original plans to extend the M23 into central London were scrapped many years ago.
At Streatham station there's a one-way system providing connections with the A214 (west) and A216. There's a small section of dual carriageway at Streatham Common which meets the A214 (east), and the road forks right in Norbury. The next notable junction is at Thornton Heath Pond, a roundabout where the original road carries straight on into Croydon as the A235 and the A23 turns right along Thornton Road. It crosses the A236 Mitcham Road at the Lombard Roundabout, becoming Purley Way, a feeble attempt at a Croydon bypass. Another short section of dual carriageway heads over the Croydon Tramlink line and past an industrial estate before reverting to single carriageway towards Fiveways Corner, the junction with the A232. Yet another short dual carriageway runs between the playing fields at Roundshaw, from which the road continues into the centre of Purley.
Purley Cross is a five-way junction with the A22, A235 and A2022. From here the A23 runs parallel to the main London-Brighton railway line, now bypassing the centre of Coulsdon where it's then joined by the A237. At last we start to emerge from endless suburbia into Surrey proper, though the open area on the right turns out to be the entrance to the Cane Hill Forensic Mental Health Unit. As the road skirts the village of Hooley it once again becomes dual carriageway on the approach to the start of the M23 at junction 7.
Section 2: Hooley - Pease Pottage (M23 J11)
At Hooley, traffic tends to like to leave the A23 for its larger neighbour the M23. Traffic would probably have much rather made this change much earlier, but that's another story. For those who follow the green signs, they find themselves first heading under the dead-end of the M23 flyover and then a few miles south heading over the might of the M25 and into Merstham: once a sleepy village, now at the junction of two motorways and trapped between two railway lines.
Immediately after crossing the M25, the road takes a sharp bend to the left. At this point, the traffic often begins to jam as the single lane road weaves through the village and on to Redhill. In Redhill, the road briefly becomes dual carriageway as it runs around the eastern side of the town centre (the direct route now being pedestrianised). It is here that it meets the busy A25 route running east-west across Surrey.
From here, the road heads south again through Earlswood and Salfords (briefly gaining a 2nd lane for approximately ¼ mile) until it reaches Horley. At the apex of Horley town, the A23 heads slightly south-west, while heading south-east is the B2036 Balcombe Road. The route skirts along the western edge of Horley, and finally arrives at Povey Cross, where the route meets the A217 from Reigate, and the Sussex border. At this point, drivers must take a left-turn at the roundabout, and are rewarded with the a proper stretch of dual carriageway, which runs round the outskirts of London Gatwick Airport (the original line of the road being lost under the airport runway). In fact, from here onwards, the A23 remains dual-carriageway until Brighton.
Just north of the airport are the access roads allowing traffic to join the M23 spur to access the airport, or the M23 proper. From here to the Pease Pottage M23 junction (J11), the road acts as the Crawley bypass (built in 1938/9). There are no fewer than 5 roundabouts, 5 sets of traffic lights, and one gyratory on this 7-mile stretch of road. The junctions include those with the A2011, the A2220 (former A264) and finally the A264 (new route).
Section 3: Pease Pottage - Brighton
Upon reaching Pease Pottage, the road comes to M23 J11 of the M23. Here, the southern slip roads of M23 J11 descend to the three-lane dual carriageway which has continued immediately from the end of the M23. After much work in the 1990s, the road from here until the A27 at Brighton is modern high-quality dual carriageway. However, it was not until 2014 that the Handcross Hill section was re-aligned and widened to three lanes.
The road travels across the Sussex weald until it passes over the A272. Shortly after this, as the signs for the A2300 to Burgess Hill appear, the left-hand lane becomes the slip to join the A2300, and the main road reverts to just two lanes. Having passed the junction, the South Downs come into view. It is from here that you can sense you are almost reaching the coast, although until the last minute it really does appear that there is no way through the downs. At the last minute the roads turns to sneak through a gap in the hills and then onwards into Brighton. As the A273 joins on the left-hand side, the road once again becomes 3 lanes.
As you reach the outskirts of the city of Brighton and Hove, it is clear that the road has been widened considerably. The obelisks that once stood either side of the road at the city's edge now only just manage to stay either side of the Southbound carriageway.
Finally, we reach the junction with the A27. Southbound the road widens to 4 lanes at this point. Traffic wanting to join the A27 must join the 2 left-hand lanes, westbound traffic is swung through 270 degrees in a very small area, and Eastbound traffic must negotiate a dumbbell junction. Traffic continuing into Brighton first comes to the Mill Road roundabout, and then proceeds on the single carriageway route into the city.
From here on in, the road weaves between houses and offices (in increasing numbers the further south one travels) and an ever-more-complicated array of one-way systems, and lane arrangements before emerging at the Old Steine. It is here that the view of the Brighton Pavilion, and then the Palace Pier confirm that you have finally reached the coast itself. However, it is not until you use the roundabout at the very end of the A23 to join the A259 that sea-water comes in to view.