M23 motorway

History

The motorway was constructed between 1972 and 1975, at the same time as the southern section of the M25 from Godstone to Reigate (M25 junctions 6 to 8). The current northern terminus at junction 7 runs along most of what would have been its own sliproads for a broad northern continuation. In so doing, these splayed roads split to offer access to the more urban road which the M23 bypasses, the A23, and a flyover above the splayed fledgling motorway still exists for the onward northern continuation which remains unused, between these briefly, but widely, splayed carriageways of the motorway.

The cancellation of the unbuilt northern section from the M25 in towards Central London has resulted in the A23 carrying the majority of traffic through South London to the motorway. This is largely a single carriageway route, with many level junctions, traffic lights and awkward interchanges. It travels largely through residential areas and means south London reliance on the A22 (hence the Caterham Bypass), running SSE, and A3/A3M running SW (southwest).

A new junction (J10a) was opened in 1997, between J10 and J11, for access to the new Crawley neighbourhood of Maidenbower. It was financed as part of the development of Maidenbower by the construction consortium. It has only a northbound slip road, no southbound access.

Unbuilt sections

The M23 was planned to relieve congestion on the A23 through Streatham, Thornton Heath, Purley and Coulsdon in south London and was originally intended to terminate in Streatham Vale at a junction with the controversial London Ringways Plan's Ringway 2 (the intended replacement of the South Circular Road (A205)).

In an earlier version of the Ringways Plan it would have continued into central London where it would have met the Balham Loop spur from Ringway 1 (the London Motorway Box) at Tooting. This was dropped in 1967 when the northern terminus was changed to Ringway 2. While a definite route had not been chosen at that time for the northern section, approval was met for the route south of the Greater London boundary at Hooley.

By 1972 the southern section of Ringway 2 had been dropped from the plan, with an alternative proposal that the M23 continue further into London to end on Ringway 1. This was immediately countered in the same year by the GLC, who announced they would not be building that Ringway, which meant that had the M23 continued into inner London it would not have had the arteries required at its northern end to distribute traffic to the east and west. The plan was again scaled back to scrap any reaching to Mitcham Common but which would see an unsuitable terminus on Croydon Road (A232). and Minister for Transport "postponed indefinitely" the plan. By the late 1970s, this proposed northern corridor earmarked for significant demolition saw urban blight, and while the proposals were finally dropped in the mid-1980s, pockets of land that had been acquired were not released by the Department for Transport until the mid-1990s.

The unbuilt six-junctions motorway north of Hooley was due to the refusal of the GLC to finance the project, understanding the ultimately decisive, large-scale opposition to the construction of London Ringways, any network of high speed roads within London. However, the scale of the four-tier junction between the M23 and the M25, one of only three stack interchanges in the UK at the time, is indicative of the importance attached to the M23 at that time.

The motorway and its road continuations mirror its secondary importance to London in the original system of road numbering zones 1 to 4; the A23/M23 running due south from London, is as the original axes suggest, less arterial for London traffic than Central London's eight main routes the M1/A41, the A1 (as far in as Finchley), M11/A205, A2/M2, A3 and M3/A316, M4 and A40/M40. To these can be added, much expanded, three roads running far into Essex which are at least doubled, just as they are deep into London.

Smart motorway

Between July 2018 and July 2020 works took place to upgrade the M23 between junctions 8 and 10 to an all-lane-running motorway. The upgrades took place mostly for more reliable journeys to Gatwick Airport and increase the overall capacity of the route. The upgrades include an all-lane-running motorway, 12 new emergency areas, a new concrete central barrier replacing the current steel one, new roadside sound barriers, variable speed limits and two new emergency access slip roads. Changes were also implemented on the M23 junction 9 spurs: the hard shoulder westbound now a running lane; and for 50 mph speed limits in both directions.

In January 2020 all smart motorway projects were put under review due to concerns about their safety, during this period no new smart motorways could open. The review was published on 12 March 2020 and required no immediate amendments to the design or construction, however new technology to detect static vehicles is required to be fitted within three years, and a review on spacing of emergency refuge areas was to be carried out.

The fourth lanes were opened to traffic on 2 April 2020 with a temporary 50 mph speed limit. Works ran into the late summer to install more equipment, followed by testing and commissioning, before the project could complete and run at the national speed limit.

Junctions

Data from driver location signs are used to provide distance and carriageway identifier information. Traffic England Live Traffic Condition Map Highways Agency – Locations extracted from Traffic Camera Popup identifier text Where a junction spans several hundred metres (yards) and start and end points are available, both are cited.

References

1. (8 July 1975). "Construction Contracts". [[Hansard.
2. "1:50 000 Landranger map". [[Ordnance Survey]].
3. "The M23 Motorway (Balcombe Road Interchange) Connecting Roads Scheme 1996".
4. (23 February 1987). "M23, Crawley". [[Hansard.
5. Fred Mulley. (9 December 1969). "M23 Northern terminals Inquiry". [[Hansard.
6. "Balham Loop".
7. William Shelton. (12 November 1974). "M23 (London)". [[Hansard.
8. Geoffrey Ripon. (19 February 1973). "Greater London Development Plan". [[Hansard.
9. William Shelton. (26 July 1978). "Motorway (London)". [[Hansard.
10. "A Highways England road project {{!}} M23 junctions 8 to 10: smart motorway".
11. "Smart Motorway All Lane Running Overarching Safety Report 2019". gov.uk.
12. "New moves in M23 'smart motorway' upgrade".
13. "M23 Smart Motorway Progress March 2020".
14. (8 January 2018). "Five things you may not know about the M23 derby between Brighton and Crystal Palace".
15. Mills, Richard. (2021-02-22). "Brighton and Crystal Palace fans furious at Sky Sports over derby comments".