Hi @txemt and @Minh_Nguyen,
I’ll try to clarify how we decide which roads to tag as truck routes and why Texas looks different.
We began our U.S. work by mapping truck restrictions (height, weight, no trucks, etc.) in cities of interest to our clients. We then expanded to long‑haul designated truck routes, starting with the federally defined National Truck Network which we also discussed here.
After working on the National Network, we added state‑designated truck routes for some states. For each state we used the relevant DOT source and recorded it in source:hgv. Examples of sources we relied on include:
These maps and documents do not list every road in a state. We also cross‑check designations with feedback from clients whose truck drivers operate statewide and nationwide.
Why Texas looks different?
Texas law allows all state‑maintained highways to be used by trucks by default unless a municipality, through ordinance and with TxDOT approval, reroutes trucks onto an alternate state highway. TxDOT explains this in the already mentioned manual (see the section that says TxDOT cannot prohibit the use of any highway by a class of vehicle).
Before bulk tagging, we confirmed on‑the‑ground designated truck‑route signage on representative examples of TxDOT‑maintained highways - Interstate (I‑xx), U.S. (US‑xx), State (SH/TX‑xx), Farm‑to‑Market (FM), and Ranch‑to‑Market (RM). We then added the appropriate hgv tags to those routes, without overwriting any existing truck restrictions.
The goal of our project is improvement of truck information in OSM. While discussing National Truck Network topic, some mappers noted that interstates are “commonly understood” to be truck-designated roads. In that thread I mentioned that there are exceptions, and there are federal and state laws defining those truck routes. But even taking that argument of “common understanding”, we believe such information not tagged in OSM is effectively missing data for data consumers. Texas default truck routes might be another type of this “common understanding” case, but we believe TxDOT source we referenced as official government based source notes what is considered as truck routes.
Explicit tagging avoids gaps. Otherwise, truck‑route maps generated from OSM would abruptly drop off at the Texas state line. Having a lot of hgv=designated tags in Texas is just a reflection of what the rules in Texas are, compared to other states.
Marko
OptimoRoute team