M74 or A74(M)?

[Gef]

Why does this continuous road change its title?

[sft42]

It changes because some parts (the M74 part) is a Motorway with the restirctions that apply to those roads....the A74 is just an A class road but the M afterwards in brackets is to let roadusers see that the road becomes a Motorway at some point ahead and lets Mopeds and Bicyclists find an alternate route.

[sddsddean]

Afraid you are wrong there sft. If a road carries the suffix (M) it is a motorway with all the various extra rules etc. The reason a motorway has the suffix is that it substantially follows the route of an old A road ie it has been upgraded. To use the example in question, the A74 from Gretna to Abington was basically an upgrade of the , then, existing A74 dual carriageway. The section from Abington up to the Hamilton area was a completely new road which took over from the old single carriageway road and is thus deemed to be a new route, so does not need the suffix. I agree it would be easier to just call the whole thing the M74, but some bloke in Whitehall would probably lose his job if he didn't have to make these ludicrous red tape decisions!!

[Gef]

My thanks to both responders. I had just figured out the answer myself by visiting http://www.iht.org/motorway/page1.htm

[sddsddean]

I thought of another case when you would use the (M) suffix whilst driving today. If the route is a major one and has replaced another major route. eg The A1(M) is already known as the London - Edinburgh road, so to call the motorway bits something like the M15 (as M1 has already been used) may cause confusion.