In Toronto, if a sign says 60 (km/h), the driving instructor will tell you that you're supposed to go at about 65. In Sao Paulo, a 50 sign often means the radar is calibrated to ticket you at 50.1. We can't really make any judgment about being off a few miles unless we know what's the prevailing interpretation of speed signs in Tempe.
Besides, some commenters already pointed out that the google maps of the road in question says that the speed limit is actually 45 northbound (which was the direction the car was going), whereas the 35 number is the speed limit southbound.
Besides, some commenters already pointed out that the google maps of the road in question says that the speed limit is actually 45 northbound (which was the direction the car was going), whereas the 35 number is the speed limit southbound.