system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How will self-driving cars be able to determine the amount of friction there is on the surface of roads?

How would it recognize ice/snow patches or wet surfaces that require the driver to compensate for?
gpt
Cars are already pretty good at this. Traction control and anti-lock brakes have been effective safety features for a long while
Basically, they'll calculate the difference between the amount of power being supplied to the wheel, and how much resistance the wheels are providing. 

If the car is putting 1000 lb/ft of torque on a 2000 lb car, it can expect the tires to move 0.5 ft (assuming absolutely no resistance). If the tires move an entire foot, then it's easy to establish that there isn't enough resistance between the tire and the surface.

Not exactly a LI5 answer, but it's difficult to explain effectively. 

Also, cameras and Doppler radar can determine the material on a road surface (light reflections, radar signal responses, moisture sensors, temperature guages) and the streets *should* be fitted with certain types of sensors that communicate with vehicles on the road to tell them upcoming conditions.