M1 - M25

Chiswell Interchange

Where is it?

M1 junction 6a, M25 junction 21. The country's principal north-south motorway meets the M25, London's ring road.

What's wrong with it?

It's a nice three-level free flowing interchange, except for the minor gripe that the M1 to the south is totally ignored. It may as well end here. For M25 traffic to reach the M1 into London, or vice versa, requires leaving a junction or two earlier and tootling along the A41 or A405 through houses and shops.

Why is it wrong?

This is what's so annoying. There is no real reason why this is the case. There's no shortage of land to the south for the rest of the movements to be built on, which is often the reason for a silly layout. One reason that seemed plausible was that when the M25 was built the M1 south of here was still two lanes wide and it would have been thought better to prevent any more traffic from using the road. But in fact the M1 widening was carried out before this section of M25 was built, so that's not it. It seems that to save a few pennies, whoever planned the junction was perfectly happy to allow the streets of Watford to be used as rat-runs.

What would be better?

A couple of left-turn slip roads in the southern half of the interchange would be a simple and quick start. Adding the other movements in is harder — it would probably involve demolishing what's there already.


Right to reply

Martin Whelton 28 February 2005

The reason that no southbound slips were built is if sliproads had been constructed they would have had to go through an area of special scientific interest which was seen to be unacceptable.

Stephen Murphy 25 March 2006

To be honest, I don't see what on earth everyone is rattling on about. The A41 provides a perfect route from the M1 northbound to the M25 anticlockwise (and vice versa), and is much faster than using the M1 to go all the way to Junct. 6A before turning onto the M25. Also, it is the same with the A405 - this road is a fast route for anyone wishing to travel from the M1 northbound onto the M25 clockwise (and vice versa). Anyway, travellers from London going on the M25 clockwise would just take the A1 instead.

Mikey C in response to Stephen Murphy 29 March 2018

In reply to by Stephen Murphy

Due to the A1 between the A406 and M25 being significantly inferior to the M1, it's much nicer to use the M1 instead, even when then going clockwise on the M25. Apart from going through two "Bad Junctions"!

Jon Hubert 21 November 2006

Look at CBRD.co.uk every week, having driven all over our green and pleasant land. Normally let others' comments on the site just wash over, but the general attitude to the miserable design of the M1-M25 junction really wound me up. I drive Aylesbury-London regularly, having to transport tools and equipment: anyone who thinks the A41 through Watford (M1 North to M25 West, or vice versa), or the A405 (M1 East to M25 South) is better should drive it in rush hour! All the worst examples of drivers' bad behaviour manifest themselves as a result of the 10-to-20 minutes extra journey time added to the trip. Re-designing this into a "proper" motorway junction would definitely be a Good Thing.

Anonymous 24 November 2009

I do not know how much traffic joins or leaves M1 at J6, but if the remaining movements were to be added, would not that cause weaving problems, similar to Almondsbury? Though honestly, in my opinion the whole set of junctions should be improved.

Patrick 30 December 2009

I see why the M1/M25 interchange isn't the best junction in England, but I don't see why it has to be listed as a 'Bad Junction'. There could be an addition to allow access for M25 West-bound for M1 traffic going northbound (for those on heading north-bound on the A405), but for those coming further south, there isn't much that needs to be changed. If the A41 (M1-M25) and the A405 (M1-M25), were improved, traffic could quickly access west and east-bound M25.

Jacqui 27 July 2010

It wouldn't be so bad if the route to the M25/M1 junction was sign posted more clearly.

Anonymous 29 December 2014

Couldn't this easily become a four-level stack? Look, it just looks like a four-level stack missing just one of it sides. Another junction, Waterdale Interchange, is south from here and can be demolished if this happened.

Shabirlondon 27 December 2015

It's ridiculous driving through Watford to get onto the M1 and vice versa to get onto the M25. Must be a rational reason a junction wasn't built there and I bet it wasn't about finance. It would be interesting to find out who owns the land there. Maybe it's the Queen's or somebody really high profile with a lot of clout and connections.

Nik 19 November 2017

Yes, this one has always puzzled me. It does feels like it was meant to be a 4-level stack, what with the 3 tiers of traffic, but then something went awry and the southern connection was never built. Someone mentioned a nearby SSSI may be to blame but the closest is Bricken Wood Common and that's on the other side of houses 3/4 of a mile south. Nor does there seem to be any listed buildings, schelduled monuments etc. that would have caused a problem either. I suspect one of the older comments is right - it was simply too close to Junction 6 on the M1 and DoT didn't want to spend money on the reconfiguration/weaving lanes that would have so surely been needed.

I also feel that the problem is compounded by the signage provided for motorists - particularly those unfamiliar to the area - approaching on the clockwise M25. You've very much given the impression that you *must* turn off onto the A41 and trundle through Watford in order to reach the M1. In reality, you're far better off leaving at 21a and using the A405 to join the M1 at junction 6. This certainly caught me out the first time.

Craig 28 February 2018

Coming from St Albans or from the M25 J21 roundabout is ridiculous. It all bottlenecks at set of traffic lights where everyone has to turn left to get on the M1 slip road. This small traffic light junction is the only access onto the M1 for all traffic coming from; St Albans, M25 and North Watford. It is gridlocked every day and this morning took 45mins to get from the M25 roundabout onto the M1 which was absolutely clear.
Is there a government petition that can be signed up to?

Sally Sherman 12 March 2019

If there were a petition I would sign it . The poor residents of Brickett Wood would definitely benefit from a southbound slip road for traffic travelling from the westbound M25 onto the M1 southbound . Waze always tells me to use ‘rat runs’ through Brickett Wood to avoid the dreadful jam on the A405 , along Mount Pleasant Lane (nothing Pleasant about it !) which takes a huge volume of traffic past Mount Pleasant Junior school .. this is a ridiculous junction . There appears to be no valid reason for the lack of southbound slip roads . Apart from the removal of a couple of trees .

CK 10 August 2019

This probably have something to do with this section’s Ringway 4 legacy. Ringway 4 would have been designed to be the long distance road, and as a consequence wasn’t designed to facilitate traffic into London (that was up to the other ringways). When Ringways 3 and 4 were amalgamated to form the M25 they probably took most of the existing plans without modifying them (costing a lot of money), considering the now-contemporary situation ‘good enough’.

Sadly not. This section of M25 was designed from scratch in the late 1970s and early 1980s, and is not on the line of any Ringways-era proposal.

The North Orbital Road (aka Ringway 4) in this part of London would have followed the existing A405, meeting the M1 at J6, and was not going to be a motorway.

Floyd 24 August 2019

As has been noted, the two left slips- N-bound to West and W-bound to South would be quite easy to put in. As for the E-bound to South right turn, I don't think that would also be too much of a problem considering the space here. (A cloverleaf could even be used coming off the existing E-bound to North left slip) The only other right turn needed is N-bound to East and that could be done using the existing junction(s) to the East (maybe with some lane widening and a flowing slip to bypass the roundabout with the M25-again there's plenty of room for this). There is even enough room to get rid of the cloverleaf in the NW quadrant, and have a bridge crossing over the M1 and dropping down along side the 405. Right turning traffic to M25 East can then stay in the left lane as it will soon be peeling off again to join the 25.

Ba 25 August 2019

This is ridiculous! Just realised that's the case indeed after traveling a couple of times with Waze tinking it's being too clever for its own good.

This is probably one of the most important junctions in the whole country connecting to the most important metropolitan area... WTF?

Incredible. Incredible also that traffic is diverted through Watford. Simplest solution would have been to uturn at tge next M1 junction or use A1M had I known...but no warning and Google maps flummoxed

Emmett Murphy 8 August 2021

When did the racetrack-sized roundabout (M1-M25, junction 21) get replaced with a cloverleaf variant? Across the pond, we're playing Englishmen & replacing corners all over the country with circles. Your example suggests we need to rethink this one.

There’s never been a roundabout here - this is the only junction that has ever existed at this site. Are you thinking of the A1/M25 junction?

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