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[HighwayMaster]

This is odd. The M25 motorway from J4 to J5 is multiplexed with the A21 road. Is this the only place in the UK that has such a multiplex (excluding Ax and Ax(M) M.P.'s)?

[english si]

There's lots of them.

In numerical order and keeping to one- and two-digit A roads, here's what I have off the top of my head:

A5: M1 J4-9; M54 J5-7
A8: M9 J1-M8 J8
A10: M11 J11-14 (and from there along the A14 briefly)
A11: M11 J4-9A (beginning at the A12. you could consider these two separate roads called A11 that were once linked with a middle section)
A15: M180 J4-5
A20: M20 J9-10; M20 J12-13
A21: M25 J4-5
A30: M5 J29-31
A31: M3 J10-M27 J1
A33: M3 J9-14
A34: M40 J9-M42 J4 (could consider two roads that were once linked with a middle section)
A38: M5 J27-31
A41: M40 J9-M42 J5
A43: M1 J15-15A (from J15 concurrent with A45)
A45: M1 J15-16
A46: M69 (whole road) M1 J21-21A, M5 possibly
A48: M4 J42-44
A50: M1 J22-24
A61: M621 J5-7
A63: M1 J45-46
A66: A1(M) J56-57 (leaves as A66(M). also concurrent with the A1 south of there)
A90: M90 J1-11
A91: M90 J7-8

[HighwayMaster]

Whoa! I guess so! I guess that's the most notable one in Greater London that I could find.

[Road Hog]

I've learned (in reverse fashion, actually) that A-roads correspond roughly with U.S. highways here and often parallel and multiplex with M-roads, which of course are equivalents of our I-roads.

The fact that some A-roads are built to motorway standards and get an M-suffix adds to the confusion. I suppose by those standards, we would have U.S. 75 (I) from downtown Dallas to the Red River. Actually, that's not a horrible idea.

[Bickendan]

US 26 (I) in Portland. Hmm.

[on_wisconsin]

US-41(I) in Wisconsin, I wish it where legal...

[english si]

I've learned (in reverse fashion, actually) that A-roads correspond roughly with U.S. highways here and often parallel and multiplex with M-roads, which of course are equivalents of our I-roads.

No - nearly, but not quite. A roads are a far more dense network than US Highways, and even most states' State Highway system. And Motorways aren't directly equivalent to Interstates either.

The fact that some A-roads are built to motorway standards and get an M-suffix adds to the confusion. I suppose by those standards, we would have U.S. 75 (I) from downtown Dallas to the Red River. Actually, that's not a horrible idea.

Motorway Standards don't exist - Motorway Regulations do. Ax(M) roads are sections of A roads with motorway regulations (ie a special road limited to Class I and Class II traffic only).

CA238(I) is about the only time you use it, because Interstate is a subset of freeways that form part of a system and meet certain standards - rather than regulations. US41(I), etc would work though - as would any up-to-standard route that forms a logical part of the network.

[agentsteel53]

CA238(I) is about the only time you use it, because Interstate is a subset of freeways that form part of a system and meet certain standards - rather than regulations. US41(I), etc would work though - as would any up-to-standard route that forms a logical part of the network.

many other freeways are built to interstate standard.  some are even in the interstate system, albeit with a hidden number, like I-595 in Maryland, which could be US-50(I).

[english si]

Not to mention the other US-50(I) in Sacramento.

However there's surely a difference between unsigned motorways with a proper motorway number (not that I can think of any in the UK) and motorway sections of other routes that don't gain an M-number.

So US-50(I) (either one) would only be a USx(I) if there wasn't a secret number.

[mukade]

Using something like US 41(I) would tell the motorist the class of highway (if they care), but in the US the Interstate shield has become a brand. Like it or not some companies use the presence of an Interstate as one criterion for locating a new facility. I would say what we need more is allowing certain well engineered non-freeways in less densely populated areas to be able to use the Interstate brand. For example, does all of future I-11 really need to be a full freeway? Maybe it does - I haven't driven that route, but I remember driving from Bullhead City, AZ to Las Vegas on US 95 - a pretty empty road. Is US 93 a lot busier?