During his closing keynote at South by Southwest, Google X director Astro Teller provided a bit of insight into exactly why the company ditched the steering wheel and pedals in its autonomous car (but kept some other human aides like windshield wipers and mirrors).

After logging thousands of hours behind the wheel, Google’s autonomous driving team recruited other employees outside of the division to test their vehicle. At the time, the self-driving feature only worked during highway driving meaning a human had to drive the car to the highway before relinquishing control.

Part of the agreement was that these new testers would need to focus all of their attention on the road when the car was driving unassisted, just as they would be expected to do in any other vehicle. Knowing this and also being aware of the fact that they were being recorded, drivers’ poor human habits kicked in almost immediately.

Considering that people already do stupid things like texting while driving a car they are 100 percent in control of, it goes without saying that things got even worse when they weren’t actually driving. Teller didn’t give any specific examples although he did say it wasn’t pretty.

The experiment led them to the painful conclusion that humans simply wouldn’t be a reliable backup and that the car needed to be in control at all times. The best way to express this, Teller said, was to eliminate the pedals and wheel completely.

The windshield wipers and mirrors, however, were left on the car for legal reasons. As it turns out, cars are required by law to have such accessories, even if humans aren’t at the helm.