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