Uber's freeze on self-driving car tests following the Arizona crash was very short-lived. The Arizona and Pittsburgh cars are still idle as of this writing, but they're expected to go back into service soon.
The company hasn't said exactly why it's resuming so quickly. We've reached out and will let you know if it can provide more details. However, the initial reports surrounding the crash suggest that there wasn't much Uber could have done. The company's Volvo XC90 test mule was knocked on its side after another driver failed to yield -- autonomous vehicles are certainly supposed to react to human drivers, but there's no guarantee that they can always respond to someone ignoring the rules.