Should ref=* for Texas State Highways begin with "TX" or "SH"?

Minh_Nguyen · May 5, 2024, 10:44pm

Here’s some background as to why “TX” is so commonplace in OSM:

Originally, the U.S. community tended to format ref=* on roadways according to the DOT’s preferred abbreviation, such as on signs, except that hyphens were replaced by spaces to match British tagging norms. State routes in Utah were tagged ref=SR *. However, some mappers preferred a uniform national format of ref=XY *, where XY is the state’s USPS abbreviation. Traditional GPS vendors such as Garmin and TomTom had long used the “XY-123” format. Some in the roadgeek community also prefer this format in writing, for consistency and to avoid having to clarify the state separately when remarking on new road construction or bragging about the roads they’ve traveled.

After the OSM-based MapQuest Open map was released in 2010, there was a push to institute postal abbreviations nationwide. At the time, MapQuest was the most prominent commercial user of OSM data in the U.S. Their renderer was the first to display realistic state route shields in each state, but to do so, it required each way ref=* to begin with the state’s postal abbreviation. By contrast, other data consumers such as Mapbox geocoded roads to distinguish between different states’ route networks.

Mappers in most states went along with the postal abbreviation format, but there were a few holdouts in some states with active local communities, especially Michigan and Ohio, based on real-world usage. (Indiana later went back to the “SR” format.) Tennessee and Virginia also distinguished their primary and secondary state route systems using the postal abbreviation and “SR”, respectively, but out-of-staters usually missed this nuance.

MapQuest Open was discontinued in 2016. By then, the U.S. community had reached a clear consensus that route relations are the preferred representation of a highway route, since the network=* tag on a route relation allows us to encode the route network without any ambiguity. Unfortunately, it wasn’t until 2022 that the OSM Americana project released the first viable reference implementation of realistic state route shields based on route relations. In the meantime, the MapQuest-influenced format has become entrenched in the database. Out-of-state mappers sometimes haphazardly insert postal abbreviations in states that don’t use them, thinking there was an oversight.

Ignoring the states that held out against the convention of state postal abbreviations, Texas was one of the last states to get moved over to that convention. In 2014, it was still pretty easy to find “SH” on Texas roadways.

That would be incorrect. TxDOT has standardized on “SH” as the only acceptable abbreviation for “State Highway” on signs. I’m unaware of any source in the media or the software industry that reserves “SH” for toll roads only. The main parties that consistently use “TX” are OSM, TomTom (in navigation guidance data), and roadgeek websites.

Internally, TxDOT uses an elaborate system of two-letter abbreviations for various highway designations. Some of them are quite obscure, like “SL” for State Highway Loops. I don’t think we need to conform to what TxDOT uses internally, but “SH” (and to a much lesser extent “IH”) have been adopted by the public because of signage and frequent mentions in the media. Waze has similarly standardized on the “common speech” approach to tagging numbered routes. We’re almost there, except for this “TX” prefix.

These street name signs’ red color is a telltale indication that a county or local agency put them up. Small towns across the country often generically refer to “Highway” because they only have to worry about a single highway within their jurisdiction. Noncompliant red street name signs also seem to be a favorite of rural small towns in some states (Indiana being another).

Texas regulations allow 13 different designs for street name signs, none of which are red. The department doesn’t always follow the TMUTCD to a tee, but they normally wouldn’t go out of their way to violate it by procuring a custom rectangular red sign blank.