>That adds up to more than 600 million miles of motor-vehicle traffic in the past 3 years alone—reflecting not only the staggering growth in rides, but also a t

>That adds up to more than 600 million miles of motor-vehicle traffic in the past 3 years alone—reflecting not only the staggering growth in rides, but also a trend toward lengthier trips and more “deadheading,” or cars traveling without passengers. My 2 cents: If and when self-driving cars take off, and if this on-demand ride-hailing model persists, I predict that the streets will be clogged with empty self-driving Ubers and Lyfts, skirting parking fees and constantly circling around for fares.