You’re assuming that the demand for travel remains constant, which is a flawed assumption. Why do you need to travel today? You go to work. You travel in your job. You visit friends. You go to restaurants or cafes. You go shopping. Communication technology will eliminate some of your professional travel needs. Millenials socialise differently from you and I, and their habits will stick.
Conversely, delivery through rolling drones/AVs will admittedly increase the number of Vehicle Miles Traveled, but these miles can be traveled in a much lighter and smaller vehicle using more environmentally friendly fuels.
Also, ride sharing in AVs is a pricing issue. Taxation and subsidies of ride sharing solutions can move the market towards the goal of reducing the amount of vehicle miles traveled. Why do AVs need to be car shaped? Why not a type of bus along frequently travelled routes nearly for free and then you can either walk from your stop along a main transport route where you change to an electrical bike for the last 2 km? How much more are you willing to pay to be alone in your AV to work every day? €5? €10?