GPS could be more accurate if companies wanted it to be. The main limitation is a more accurate time source. There are chip scale atomic clocks: a couple years ago when Apple bought a small California fab from Maxim used for making MEMS and similar devices, some speculated they'd use it to develop custom devices to make iPhone's positioning a lot more accurate.
An atomic clock combined with higher precision MEMS devices able to manage accurate dead reckoning travel are what would be needed. If they made a quarter billion such devices a year they could probably make them pretty cheap - maybe not quite as cheap as the MEMS they buy now (from NXP I think?) but making them themselves would give them an advantage very difficult for others to match.
Anyway, phone based GPS and MEMS may not be as accurate the sensors in a car that know its exact speed but it is more than good enough to tell whether a car has hit a traffic jam. You don't need to know where you are to the foot, and traffic jams are indicated by a prolonged slowdown, not a blip. If it senses slowing and other phones around it sense the same thing, what other conclusion could there be?
I use a GPS based app on my iPhone to track my bike, and it works quite well. Granted I'm never traveling more than about 35 mph, and averaging 15 mph, so much slower than a car, but it does a pretty good job of tracking speed and even elevation pretty well - I see pretty consistent results of similar speeds on similar hills, similar elevations indicated. WIthin 10% or so, which is plenty accurate for figuring out a car has hit a traffic jam.
Biting the hand that feeds IT
