Brad raises excellent points:
- The vehicles are not rated for certain weather conditions, like a certain amount of snow, and they all stop service when this happens
- Some major fault in the fleet management system makes it impossible to summon cars. (Airlines have shut down fairly often due to this.)
- A safety problem in the software is discovered that is so serious that the fleet manager decides to cease operations until it’s fixed.
from Tumblr http://doronelinav.tumblr.com/post/182600956829