Two interchanges along its length--at Brown and McKellips Roads--will be of the dumbbell type, with a roundabout at the ramp termini on each side of the freeway. As suggested by Weber et al. in a paper presented at the TRB-sponsored roundabouts conference in May 2005, the guide signing for these roundabouts is designed according to guidelines given in Chapter 7 ("Design of Traffic Signs") of the British Traffic Signs Manual. Some changes have been made to accommodate American differences--such as the use of route markers and a different set of traffic signing typefaces--to yield the following signs:
Where diagrammatic signs ("map-type signs" in British traffic sign designer's parlance) are concerned, perhaps the most eye-catching difference between the Chapter 7 design idiom and the one that has evolved in the USA (see the Oregon example below) is the use of right-angle chamfers rather than filled-barb arrowheads on the arms indicating exits from the roundabout. Arms with these chamfers are called "stub arms." However, Chapter 7 rules also provide for the more important arms (generally the ones carrying more traffic) to be thicker, as is the case in the examples shown above.
The chevron-ended signs ("flag signs") follow Chapter 7 guidance to the extent that a wider chevron is used for taller signs, but in Britain the sign border would have a point, with a background-color gap of uniform width between the chevron and the inner edge of the border. The sign panel itself would also have a point unless, of coure, the sign were mounted on an aircraft gray backing board, as in this instance:
The lane assignment signs closely follow British designs except for the filled-barb American arrowhead.
Chapter 7 design rules for direction signs have their ultimate origin in Traffic Signs for All-Purpose Roads, the 1963 report of a committee chaired by Sir Walter Worboys which gave rise to the modern British traffic signing system. Unlike the United States in the 1950's, which opted to bolt several slightly different systems for signing freeways onto an existing system for signing surface roads which has received only incremental modifications over the years, the British opted to replan their traffic signing system from the bottom up. Map-type and flag signs were introduced in the Worboys report; lane assignment signs were introduced later, though I am not sure when (I hope to research their history in the future).
Loop 202 will probably be the first trial of Chapter 7 design rules on a freeway, although industry Deep Throats have told me privately of one or two roundabout projects on surface roads where signs are being designed to adapted Chapter 7 rules with Clearview typefaces. It remains to be seen whether the British idiom will come into general use; as matters now stand, American designers have already abandoned some of the most fussy aspects of Chapter 7, such as the requirement to radius out all inward-pointing corners in the roundabout symbol (this is done automatically in British sign design packages such as KeySIGN, but it would be unrealistic to expect American sign design software to have this capability yet). There have also been problems with chamfer angles other than 90° being used, apparently as a result of pre-chamfered arms being horizontally shrunk or stretched to a desired new width.
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