Taxes are a terrible way to pay for highways. They put an unfair burden on local citizens and businesses, many of whom get relatively small benefit from the new facility. At the same time others who get huge benefits could pay relatively little. For example, tourists passing through the state and using the new roadway could avoid paying anything toward them. Even if Legislators hike fuel taxes, some of those motorists could tankup out of state and refuel on the other side.
Taxes also have a debilitating impact on the economy.
Tolls are fairest because those who use and benefit the most from the expensive new highway pay directly. And those who don't need to use the new highway won't be burdened. Modern or electronic tolling has another advantage. Toll rates can be varied by time of day, or level of congestion. This would encourage many motorists to reschedule their trips, or to carpool or ride the bus.