Furthermore, Ubers like cabs drive around waiting for fares so they create traffic while not providing rides. Similarly with recent cases of Uber driver brigading to drive up surge prices, they also create surges of traffic.
Gas taxes only pay for up to 40% of road maintenance and that's in states with the highest gas taxes. The rest of the cost is made up from general funds and transportation budgets. There was a high profile case recently in Maryland where the governor redirected light rail funds to highway maintenance and construction. In fact gas taxes have never fully covered road construction and maintenance costs anywhere in the US, ever.