I have experienced this twice. So I know it wasn't just a "once in a lifetime" glitch. While driving along Florida Highway 20 between Panama City Beach and the Defuniak Springs Supercharger, I'm tooling along fat, dumb and happy on AP at about 60 mph. Suddenly, the speed drops to 20 mph. I glance at the Traffic Aware Cruise Control indication on the dash and it shows it is set to 20 mph! I'm scratching my head when I look at the speed limit indicator just to the left of the speed indication. It shows the speed limit is 20. It took a second for this to set in but apparently the camera caught the road sign indicating that I was on Route 20 and interpreted it as a speed limit 20 sign. I ran the exact same route a few days later and the experiment is repeatable!! Clearly, there is a need for some sort of software adjustment here. Makes me wonder what would happen in California while travelling down Route 1. Or how 'bout the Washington DC beltway, Highway 495? Does the Tesla interpret that as 1 mph or 495 mph speed limit? This could lead to some interesting situations . . .