The fact is that in the state of Texas, the state gas tax is constitutionally dedicated to the state highway system (and schools) – meaning it cannot be spent on any roadway without a route shield (number) on it. For instance, I-35, US 183, RM 2222 – state highways; can get gas tax funding and usually do (with some local contributions thrown into the mix). While the federal gas tax has no such restriction, in practice in our area, the metropolitan planning group that disperses such money spends almost all of it on the state highway system as well.