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London's busiest road junction

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dr.bob
1319810.  Fri Apr 19, 2019 8:28 am Reply with quote

What's the definition of "busiest junction"?

If it's just based on the amount of traffic that passes through it, then I'd imagine you're looking for a major road with a very minor road joining it. Assuming the lights stay green for the major road 99% of the time and only ever change on the rare occasion that something comes along the minor road, then I think there'd be lots of traffic flow thanks to the lights hardly ever changing.

 
crissdee
1319811.  Fri Apr 19, 2019 8:35 am Reply with quote

I think this might be a contender. Just down the road from me (see blue pointer for details) it has the A12 and the A406/M11 feeding on to it and is never less than busy, day or night.

 
Jenny
1319815.  Fri Apr 19, 2019 9:57 am Reply with quote

Hanger Lane gyratory sounds like a good contender.

 
GuyBarry
1319863.  Sat Apr 20, 2019 3:52 am Reply with quote

dr.bob wrote:
What's the definition of "busiest junction"?


The one with the most vehicles passing through it per hour (or per day), I would assume.

Quote:
If it's just based on the amount of traffic that passes through it, then I'd imagine you're looking for a major road with a very minor road joining it. Assuming the lights stay green for the major road 99% of the time and only ever change on the rare occasion that something comes along the minor road, then I think there'd be lots of traffic flow thanks to the lights hardly ever changing.


I don't follow you. Not all junctions are signal-controlled, and not all junctions are "at-grade" (i.e. with the roads at the same level). The busiest junctions are likely to be "grade-separated", where roads cross at different levels. One candidate might be Brent Cross, which is at three levels, with the A41 passing over the top of the central roundabout and the A406 North Circular passing beneath it.

Were it not just outside the Greater London boundary, the busiest junction would probably be the four-level Colnbrook Interchange, where the M4 meets the M25 near Heathrow Airport.

 
GuyBarry
1319864.  Sat Apr 20, 2019 4:02 am Reply with quote

Quote:
Historically I think it was Hyde Park Corner


I've found a reference for this - it's from Hansard for December 1957, when MPs were debating the Park Lane improvement bill:

Harold Watkinson, Minister for Transport and Aviation wrote:
If hon. Members doubt the necessity for the Bill, they might bear in mind that the traffic passing through Hyde Park Corner, as shown by the Metropolitan Police census of 1956, is about 91,000 vehicles in a 12-hour day. That makes it the busiest junction in the whole country. Everyone knows that at peak hours it is overloaded, as is also the length of Park Lane and Marble Arch. Marble Arch carries 65,000 vehicles in the same period, which makes it the third busiest junction in London.


Of course, traffic flows and traffic levels will have changed significantly since then.

 
GuyBarry
1319865.  Sat Apr 20, 2019 4:21 am Reply with quote

Jenny wrote:
Hanger Lane gyratory sounds like a good contender.


It's certainly one of the most congested, but I'm wondering now whether it's likely to be the busiest, because congestion restricts the amount of traffic that can move through the junction. The busiest junctions are presumably going to be ones with little or no congestion.

crissdee wrote:
I think this might be a contender. Just down the road from me (see blue pointer for details) it has the A12 and the A406/M11 feeding on to it and is never less than busy, day or night.


Known as Redbridge Roundabout, and could certainly be a contender. (At first I thought it was called "Charlie Brown's Roundabout", but that's about a mile further north.)

EDIT: For the curious, here's a page on how London's road junctions got their names.

 
bobwilson
1319913.  Sat Apr 20, 2019 4:27 pm Reply with quote

Quote:
The busiest junctions are presumably going to be ones with little or no congestion.


I would say the definition of "busiest" is flawed if we're just going to measure number of vehicles per day.

Surely, busiest should at least factor in average length of time taken to traverse the junction

 
crissdee
1319926.  Sat Apr 20, 2019 5:28 pm Reply with quote

GuyBarry wrote:
Known as Redbridge Roundabout, and could certainly be a contender. (At first I thought it was called "Charlie Brown's Roundabout", but that's about a mile further north.)


Having lived hereabouts for something over half a century, I was well aware of this, but I appreciate most of the posters on this forum (with the exception of PWUM and possibly suze) might like it explained.

 
GuyBarry
1319966.  Sun Apr 21, 2019 5:13 am Reply with quote

bobwilson wrote:

I would say the definition of "busiest" is flawed if we're just going to measure number of vehicles per day.

Surely, busiest should at least factor in average length of time taken to traverse the junction


The measure used by the Department for Transport is called Annual Average Daily Flow (AADF), defined as the average over a full year of the number of vehicles passing a point in the road network each day.

However, AADFs are calculated for stretches of roads between junctions, not for the junctions themselves. So I don't know if there's any official way of calculating how "busy" a given junction is.

Maybe it's just an ill-defined question.

EDIT: All the relevant data for individual stretches of road appears to be available at https://www.dft.gov.uk/traffic-counts/. I'll see if I can use it to estimate how many vehicles pass through all of the junctions mentioned so far. This could take some time!

 
dr.bob
1320123.  Tue Apr 23, 2019 6:11 am Reply with quote

GuyBarry wrote:
It's certainly one of the most congested, but I'm wondering now whether it's likely to be the busiest, because congestion restricts the amount of traffic that can move through the junction.


That was the point I was trying to make. In order to increase the amount of traffic passing through a junction, you want the traffic to be travelling well, hence no congestion. You also want the traffic to be travelling fast, so you're probably looking at a motorway junction.

Google maps tells me that Junctions 25, 28 & 29 of the M25 are both just within the Greater London boundary. Given they all intersect with major roads heading into London, I would imagine the numbers of vehicles passing through these junctions must be pretty substantial.

 
GuyBarry
1320129.  Tue Apr 23, 2019 7:30 am Reply with quote

dr.bob wrote:

Google maps tells me that Junctions 25, 28 & 29 of the M25 are [all] just within the Greater London boundary.


I think you're right on all three counts!
https://www.roads.org.uk/motorway/m25/290
https://www.roads.org.uk/motorway/m25/340
https://www.roads.org.uk/motorway/m25/350

Quote:
Given they all intersect with major roads heading into London, I would imagine the numbers of vehicles passing through these junctions must be pretty substantial.


Out of those three it's got to be either junction 28 or junction 29, because the capacity is higher - they're both "three-level stacks", with the A12 and A127 respectively carried over the top of the roundabout on a flyover. (A10 through traffic at junction 25 has to go round the roundabout.)

I would guess that the A12 is likely to be busier than the A127 because it's the main road to the container port at Felixstowe. Also, at junction 28 you've got the additional complication of another road, the A1023, joining the roundabout. So on those two counts I reckon that Brook Street Interchange (M25 J28) is likely to be the busiest road junction within the Greater London boundary. I'll see if I can confirm it with some figures.

 
tetsabb
1320294.  Wed Apr 24, 2019 1:27 pm Reply with quote

I think 28 and 29 are actually in Essex, so I will check on Sunday when next back at work.

 
GuyBarry
1320298.  Wed Apr 24, 2019 1:47 pm Reply with quote

Thanks! Highways England says that junction 28 is in Essex, so I'm really not sure now.

 
suze
1320307.  Wed Apr 24, 2019 5:08 pm Reply with quote

I have it on very good authority that OpenStreetMap is more accurate than any other online mapping service for local government boundaries.

Using that as our source and going clockwise around the M25 from Dartford:

Kent: J2 Darenth A2, J3 Swanley A20, J4 Hewitt's Spur to A21, J5 Chevening M26
Surrey: J6 Godstone A22, J7 Merstham M23, J8 Reigate Hill A217, J9 Leatherhead A243, J10 Wisley A3, J11 Addlestone A317, J12 Thorpe M3, J13 Runnymede A30
Hillingdon LB: J14 Poyle Heathrow Spur
Slough and Buckinghamshire (boundary goes through junction): J15 Thorney M4
Buckinghamshire: J16 Denham M40
Hertfordshire: J17 Maple Cross A412, J18 Loudwater A404, J19 Chandlers Cross Spur A41, J20 Kings Langley A41, J21 Chiswell M1, J22 The Bell A1081, J23 Bignell's Corner A1(M), J24 Potters Bar A111
Enfield LB: J25 Waltham Cross A10
Essex: J26 Honey Lane A121, J27 Theydon M11
Havering LB: J28 Bell Lane A12, J29 Codham Hall A127
Thurrock: J30 Mardyke A13

As is reasonably well known, there is no J1. The section through Dartford is the A282, not the M25.

 
tetsabb
1320739.  Mon Apr 29, 2019 9:30 am Reply with quote

I have just checked our system at work, which is good to 100 metres -- J29 and 28 of M25 appear indeed to be part of the Met area for our purposes.

 

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