[Talk-us] US Trunk road tagging

[Roff, Thomas (FHWA)]

On the point of definition of an Expressway. We usually refer the Highway Capacity Manual for their definition. However, I am not sure if there is a legal definition in the US.


From: Joseph Eisenberg <joseph.eisenberg at gmail.com>
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To: Adam Franco <adamfranco at gmail.com>
Cc: OpenStreetMap talk-us list <talk-us at openstreetmap.org>
Subject: Re: [Talk-us] US Trunk road tagging

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I agree, this is a very good point.

The Trunk/Primary/Secondary/Tertiary system is based on the UK roads classification, where Trunks are the most important "A" roads - often they are dual carriageway (divided roads) but not always, and there is no particular "expressway" meaning to them. Primary roads are mostly 1 lane in each direction and mostly undivided - but in cities they can be divided, and connect small towns. Secondary roads are quite minor.

In the Western USA, where distances between towns are high and traffic volumes are low, it's sensible that many of the most important roads are just one lane each way (except perhaps when going up steep hills or in towns). But as long as they are maintained in winter and used by trucks and as the main route between two large towns or small cities, they are important enough to be highway=trunk.

Another issue with using highway=trunk to mean "expressway" is that there is not a clear definition of what an expressway means which can be used consistently across the USA, let alone in other countries. The meaning of "motorway" (freeway) is well defined, but "expressway" is not.

- Joseph Eisenberg
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