# This is the USA interstate system (how does the UK system work?)

This is the USA interstate system (how does the UK system work?)
In the USA, the two-digit interstate highways start at even numbers
of the 10 in the south, then 20 further north, then 30, 40.... 80, and finally 90 when you get to the northernmost route (not all of which actually exist but all that do exist are unique).
Notice all interstate mile markers increment similarly south-to-north on odd-numbered two-digit interstates (and the exit numbers follow suit).
Likewise, the odd two-digit interstates start at the 5 on the west coast, and move to 15, 25, 35 ... to 95 (not all of which exist but all that do exist are unique) as you move east.
Similarly, all Interstate mile markers increment in the same direction, west-to-east, on the even-numbered two-digit interstates (and the exit numbers follow suit).
When it comes to three-digit interstates, a *different* numbering system is used, which makes them not always unique and which makes the general direction not always clear.
Also, the three-digit (secondary) interstate system is vastly less complete than the two-digit (primary) interstate system.
Essentially, the second two digits of the three-digit secondary interstate indicates which primary two-digit interstate it connects to; hence, 280, 380, 480, 580, 680, 780, 880, & 980 all connect to "80" in some way, fashion or form (or, will connect to, someday, or, were planned to connect, at one point, etc.).
Given that, there could be, say, a 280 in every state, because all it has to do to comply with the number system is connect to 80.
The significance of the first digit in the three-digit system varies, and I forget the details, but the lower the number, the closer it is to the city center. So, for example, a 480 would be a circle that is closer around a city than an 880, and a 280 would be a spur that is closer to a city center than a 980 spur (although, all bets are off when plans change).
Everyone gets confused because they don't understand this system; once you know the system, about 80 to 90% of the roads follow it faithfully (although there are always exceptions that people love to call out).
The beauty is that, without GPS, in just one mile, you always know what direction you're going if you know the road number (in the east coast, you know what direction you're going usually in 1/10th of a mile because of the closer-spaced mile-marker culture compared to the west, which just barely started numbering the exits just a few years ago).
BTW, you also know the exit number, because they have (mostly) been correlated with the mile markers (with a, b, c, etc. used with closely spaced exits).
This is the USA interstate system (how does the UK system work?)
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On 09/03/2015 23:57, Adair Bordon wrote:

[ snip USA Interstate explanation ]

The basic Great Britain (not UK) all-purpose road-numbering system (originating during the 1920s) works on the basis of six routes radiating from London plus three in Scotland. The original routing was:
A1 London-Edinburgh via Newcastle A2 London-Dover via Canterbury A3 London-Portsmouth via Guildford A4 London-Avonmouth via Reading, Bath and Bristol A5 London-Holyhead via St Albans, Luton, Tamworth and Shrewsbury A6 London-Carlisle via a branch of the A1 at Barnet then St Albans, Luton, Leicester, Derby, Buxton, Stockport, Manchester, Preston and Lancaster. A7 Carlisle-Edinburgh A8 Greenock-Glasgow-Edinburgh A9 Edinburgh-John O'Groats.
[This applies only to Great Britain including the isle of Wight, Anglesey, etc. Ireland, north and south, has two more numbering systems.]
The routes divide up the island into zones and other roads take their numbers from the zone in which they start.
Between A1/A2 - Zone 1 Between A2/A3 - Zone 2 etc...
Many of the above routes and other important roads have become moth-eaten by the addition of motorways or other high-quality roads which have supplanted part of their line(s). For that reason, there are numerous examples of roads which are now discontinuous. One such would be A5, which is no longer numbered as such as it passes through St Albans (where it is A5183). The signed route takes traffic via the M1 from south of St Albans to some way north of it. The same is true of the A6, also passing through St Albans as A1081. Both A5183 and A1081 are now regarded and treated as minor routes. But they used to be the major routes from London to the West Midlands and the North West of England, right through the middle of St Albans.
Similarly, the A34 - a major long-distance route from Winchester to North Lancashire via Newbury, Oxford, Stratford, Birmingham, Stafford, Stoke, Manchester and Bury) has missing stretches where the route is superseded by the M40 motorway.
Motorways are numbered largely on the basis of the all-purpose routes, but with a few significant departures.
M1 = London Edinburgh via Leeds and a connection to the A1 for the NE and eastern Scotland M2 = London-Dover (more strictly, a motorway-standard bypass functioning as a part of the A2 route) M3 = London Southampton (duplicating the AP route A30) M4 = London South Wales via Bristol M5 = Birmingham - Exeter (a departure - it neither starts nor finishes in Zone 5) M6 - London-Carlisle via M1 to Northamptonshire then via Birmingham, Stoke, Warrington, Preston, lancaster. M7 = there is no M7 M8 = duplication of parts of route A8 M9 = Edinburgh to Dunblane, bypassing part of A9 M10 = was a short spur off M1 to St Albans, but now downgraded into part of an all-purpose route.
Other motorways tend to follow the normal zone-based numbering criteria, with the obvious exception, for instance, of M62, which whilst it did follow that convention when the first stretch was opened in the early 1960s (and was a short route near Manchester in the "6" zone), was subsequently extended west to Liverpool (in the "5" zone). As a result, the M62 neither starts nor ends in the "6" zone.
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JNugent wrote:

> >[snip explanation]
An important difference - I've seen many roads signed with two numbers in the USA, but none in the UK. I believe that's because in the USA they number routes, rather than roads, and two routes can share the same road.
--
Mike Barnes
Cheshire, England
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On 10/03/2015 19:08, Mike Barnes wrote:

It happens in the UK occasionally; possibly Watford Way is A1 and A41.
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On Tuesday, March 10, 2015 at 4:03:55 PM UTC-5, Nick Finnigan wrote:

Former U.S. President Dwight David Eisenhower saw the German Autobahn when he was over there in World War Two. That is how America's Interstates began.
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On 3/10/2015 4:18 PM, JR wrote:

That's true. But also, as a Lt Col in 1919, he led a convoy of Army vehicles form Washington DC to San Francisco on the dismal roads of that era. That's why he felt the Interstate System was a defense priority, not just another public works project. I bet he also read Clausewitz regarding the importance of interior lines.
--
Andrew Muzi
<www.yellowjersey.org/>
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Does this really happen? More likely is that the A41 joins the A1, and a short distance further on, leaves the A1 (or vice versa). The bit between the joining and the leaving will be officially be one or the other - but not both. This can be confusing if the signs appear to indicate that you're on the wrong road.
There is certainly such a situation if you leave the M40 at the Warwick junction, and head north-eastwards for the M1 at the Leicester Forest junction. You first travel from Warwick to Coventry on the A46 - intending to continue around the east side of Coventry on the A46, which then becomes the M69 until you reach the M1. However, at Coventry the A46 intersects with the A45, and you suddenly find that you're unexpectedly on the A45 for a mile or so. I think that the only reassurance that you're still on the right road is that one of the signs - if you spot it - includes "(M69 M1)".
--
Ian

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On 10/03/2015 23:17, Ian Jackson wrote:

Yes, but Streetview suggests that is signed as A1 (A41).
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Which would be the correct way of signing it. It indicates that you're on the A1, which will take you to (or towards) the A41. It's not that you're on the A1 merged with the A41.
--
Ian

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On 10/03/2015 23:17, Ian Jackson wrote:

You may be right, but it's a distinction without much of a practical difference.
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Ian Jackson wrote:

Not that confusing when you consider that the "right" road number appears on the road signs, albeit in parentheses.
--
Mike Barnes
Cheshire, England
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I'm pretty sure that the bracketed road number indicates either that the one road is really two, or that it is heading towards - or will become - that road. If so, it could be confusing if you had been on the A41, and didn't realise you had effectively left it and were now on the A1. Of course you shouldn't worry, because if you keep on going, you will eventually be able to regain the A41. However, my first reaction would probably be "How on earth did I get off the A41?".
--
Ian

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On Wednesday, March 11, 2015 at 2:29:32 PM UTC-5, Ian Jackson wrote:

In America, Rand McNally Road Atlas is allways very handy to have, when traveling. In Europe, Stadtplan 'Road Atlas'. I have two of them I once bought years ago at a Goodwill thrift store.
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Ian Jackson wrote:

no

yes

possibly

If you find that confusing, fair enough, but I don't think most people would bother about it as long as the road signs indicate that they're going in the right direction.
--
Mike Barnes
Cheshire, England
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I don't really find it all that confusing - but if you're on an unfamiliar bit of road, surely it's only natural to sometimes have a brief flash of suspicion that you might have gone astray!
--
Ian

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Nick Finnigan wrote:

Tempting to think that, but I don't think so. Driving E on the A41, approaching the roundabout at the N end of Watford Way, where the A1 joins from the N, the sign says...
C. London A1 (A41)
(On UK signs a road number in parentheses means that that road can be reached by driving in the indicated direction.)
Similarly proceeding N on the A41 the sign says
The North Hatfield Mill Hill A1 (M25) Aylesbury (A41)
So the A41 leads to the A1 and then the A41 resumes. In the USA the signs would (I think) indicate A1 *and* A41.
--
Mike Barnes
Cheshire, England
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On 10/03/2015 23:44, Mike Barnes wrote:

I think I also recall continental roads carrying two E numbers.
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On Tue, 10 Mar 2015 19:08:08 +0000, Mike Barnes

I think what you are seeing is a reflection of how the UK road system was always pretty much a national system since the entirely of the UK isn't really all the big. In the US by comparison, the land area is much larger AND almost all the highways originally were State Highways, not "federal" highways. So the states created their own numbering systems within the state. Then the feds started getting involved and created the US highway system which mostly overlaid the existing state highway systems. That allowed there to be a continuous US 60 that went from the east to the west coast and be "named" the same, US60, all along the way even though in one state it might be State Highway 12 and in the next state it would be State Highway 54. Because the US route might cover more then one State Highway, even within a single state, it was usually not possible to simply renumber the state highway in the state to simply match the Federal number. The interstate, while more organized in it's numbering system (North-south routes are always odd numbers, etc) still often overlaid existing state highways and multiple state highways so the same issues remained.
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Ashton Crusher wrote:

I get that - thanks - and much the same situation exists in Europe with the "E" road numbers which are largely superimposed on national networks. In the UK there are some "E" road numbers but they don't appear on signs.
But what I actually had in mind was two numbers from the same authority (e.g. two state route numbers) on the same stretch of road.
--
Mike Barnes
Cheshire, England
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On Tuesday, March 17, 2015 at 12:34:40 PM UTC-5, Mike Barnes wrote:

Road signs in Ireland. Gaelic spelling and also English spelling.
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