The A and B designate the 'Alpha' and 'Bravo' carriageway. (North and South). Easiest way to remember is A- away from the origin and B-back to the origin. (Hope that clears it up :) )
what if the carriageway connects two origins and there is an accident half way along?
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what if the carriageway connects two origins and there is an accident half way along?
The motorways only flow one way. ie/ from junction 1 to the end. Junc 1 onwards is the Alpha carriageway. Travelling towards junc 1 is the Bravo carriageway. Pretty irrelevant for the ordinary motorist....but it might come up in Trivial Pursuit one day. :)
Edited by midlifecrisis on 10/05/2008 at 18:33
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The number is the distance in kms from the datum point, or start, of the road (except the M6 which uses the M1s). The A denotes the carriageway going away from the datum point, B the converse.
The number is on the small white and blue marker posts which are placed every 100m. These posts don't have the A or B on them.
These marker boards / posts are essential for finding exact locations on the roads for anyone who works on them. The boards have recently been introduced to be help in finding locations in the dark (try reading the numbers on one of the small marker posts from the nearside lane at 50mph at night) and to make it easier for Joe Public to tell breakdown agencies, for example, where they are.
Getting the wrong carriageway is a real problem, (not helped by the fact that the marker posts don't have this information), to the extent that if the Fire Brigade are called to an incident on a Motrway, they will always dispatch at least 2 tenders, one in each direction.
Getting the number wrong by just 1 digit can cause real problems sending the emergency services to completely the wrong junction. And just a couple of hundred metres difference in marker post can make the difference between getting to a location from a particular junction or having to go up or down to the next junction to turn which can sometimes be a considerable distance and take tens of minutes even on blues and twos.
The Emergency Roadside Telephones (ERTs) have a number on them which relates to their location + an arbitrary number. For example an ERTs on the M1 at marker post 64.5 A is numbered 2645A (2000 + 645).
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