35 mph.
According to this article the speed limit is 45 and the car was going 40.
http://www.phoenixnewtimes.com/news/cops-uber-self-driving-car-didnt-brake-much-in-arizona-pedestrian-death-10247629
I think this is the artilce where the 35mph comes from and the source is the police chief who says it appears Uber is not at fault.
https://www.sfchronicle.com/business/article/Exclusive-Tempe-police-chief-says-early-probe-12765481.php?utm_campaign=twitter-premium&utm_source=CMS%20Sharing%20Button&utm_medium=social