On Texas freeways, what does the circled "HC" mean?

Question

On Texas freeways, what does the circled "HC" mean?

Answer 1

It is the Hazardous Cargo route.  If a truck is carrying hazardous cargo, it must follow the route to avoid potential problems.  For instance, if a truck was carrying toxic chemicals, you wouldn't want  it driving near a watershed or in a densely populated area.  Most beltways are HC routes to keep trucks out of downtown unless they're making deliveries.

Answer 2

HC stands for "Hazardous Cargo".

The sign means that anytime a vehicle is carrying Hazardous Cargo (typically semi's), then they have to take that route, when available.

Answer 3

Hazardous Chemicals -