From the abstract of the paper cited, "vehicle-kilometers traveled increases proportionately to roadway lane kilometers for interstate highways and probably slightly less rapidly for other types of roads." Congestion may not decrease but building more roadway lets more people get to travel where and when they want.

Cities are powerful because of ease and variety of people and businesses you can interact with. A fast point-to-point transportation system where one can travel with up to 40 tons stuff seems to me to be a great system. Cars and trucks have large external costs that we should vigorously try to reduce (physical pollution, noise pollution, land use for roads and parking, energy use, time wasted driving, etc.) but forcing people to use less desirable modes of transport by having the desired mode suck more due to traffic seems quite regressive. If we had instant teleportation from point to point, but the machine took up a city block and belched sulfur dioxide, I would hope the impulse for society would be to research decreasing the size and pollution of the machine and not to just restrict by law that there is to be only one machine per city.