A412

Route

The A412 shadows the northwest section of the M25, between Slough and Watford. The road is technically incorrectly numbered as it starts in the 3-zone rather than the 4-zone: our start point is on the A332 (Windsor Road) in the middle of Slough, halfway between the M4 and the A4.

Slough - Watford

The A412 on the outskirts of Slough

In the best tradition of road numbering, our route (which essentially runs from south to north) begins by heading east-south-east from the A332 past the Upton hospital, to a roundabout with the B376 to Dachet. At this point, we turn north, towards the A4. We pick up the name Uxbridge Road, then cross the A4 at what the maps indicate to be a Hamburger junction, where the A4 forms the meat in the burger.

The A412 becomes dual-carriageway here, and runs past Black Park country park, to the south of Pinewood Studios (famous for James Bond and the Carry Ons, amongst other films). At another roundabout, just outside Iver Heath, we bear left along a very straight alignment, crossing the M25 just south of its junction with the M40. The A412 then crosses under the M40 eastern terminus by means of a magic roundabout - a group of mini roundabouts arranged in a circle. We take the clockwise route here, passing the westbound on-slip to the M40, but turning onto a short multiplex with the A40. After less than a mile has passed, we turn right, back onto the A412, then pass through Denham.

We then run alongside a reservoir in the Colne Valley - one of many to the west of London. After passing the village of Maple Cross, we reach another roundabout, where a dual carriageway spur also numbered A412 leads to M25 junction 17. This spur was part of the A405 Rickmansworth bypass - planned to become part of the M25 when the bit from J16 to J17 was built, and forming a bypass for the A412 (which performed the function of the North Orbital Road) through Rickmansworth and Watford.

Rickmansworth

The main line of the A412 continues as a single-carriageway road into Rickmansworth. There is a short dual carriageway multiplex in the town centre with the A404, where we pass under one of the branches of the Metropolitan Line. At the end of the multiplex section, the A404 heads up the hill towards Chorleywood and the M25, whereas the A412 runs on to Watford town centre. We cross the Metropolitan Line at Croxley Green, then reach a short dual carriageway section as we cross the River Colne.

Another short length of single carriageway follows. The road is surrounded by a mix of old and new housing together with industrial units, though many of these are being redeveloped for housing. We reach a somewhat complex junction with the A4178 Cassio Road, then the now-dual-carriageway A412 passes under a grade-separated roundabout with the A411 at Watford Town Hall. We now reach the section known as St Albans Road, which starts as dual carriageway, but becomes single carriageway after crossing the West Coast Main Line near Watford Junction railway station.

The St Albans Road was one of the first roads in the area to be comprehensively remodelled as a bus priority route. This happened once the new link from Watford Town Centre to the M1 was opened in the early 1990s, with the consequential reduction in traffic on St Albans Road.

In north Watford, we reach the Dome Roundabout, where we cross the A41. At the roundabout, supermarket competition extends to the level of signage given to each store. One is signed as a Supermarket and the one on the opposite side of the road is signed as a hypermarket! In the interest of diplomacy, I forget which store is which! After we pass a McDonald's on the left hand side, we reach the northern terminus of the A412 at a traffic-signal-controlled junction with the A405 North Orbital Road.

History

The A412 originally began at the A40 at Denham. In the late 1920s it was extended along the B471 to meet the A4007 (which took over the A332 between Uxbridge and Slough at the same time) at Five Points. In 1935 it was extended along the A4007 to the point (then on the A4) where Uxbridge Road sets out northeastward from Slough High Street. The Upton section south of here, taking the road out of zone, and the start of today's route – the 1.2 km between the A332 (Windsor Road) and Slough High Street, following Albert Street, Mere Road, and Yew Tree Road – is mostly new construction along roads first built in around 1970.

The route forms part of the North Orbital Road, which consisted of a mixture of new build, upgrades and realignments in the 1930s. It used to continue north of Garston, multiplexing with the A405 (since it was built; in 1922 it just went straight!), under the M1 at junction 6, across the line of the M25 at junction 21A, then turning left (leaving the A405) at the next roundabout (Chiswell Green) along the present B4630. After crossing the M10 (now A414), the A412 terminated at the King Harry public house on the A5 (now A5183) on its way into St Albans. When the St Albans area was renumbered, once the M25 opened, this section was downgraded.

Named Junctions List

Image	Name	Classified Road(s)	Grid Reference	More Info	Map
	Five Points	A4007	TQ019828		SABRE • Google • geo
	Denham Roundabout	M40 / A40 / A4020	TQ043858		SABRE • Google • geo
	Maple Cross Interchange	M25	TQ030942		SABRE • Google • geo
	Ebury Roundabout	A404	TQ055943		SABRE • Google • geo
	Station Roundabout	A404	TQ057947		SABRE • Google • geo
	The Dome	A41	TQ111993		SABRE • Google • geo