Here is my hypothesis: Most GPS systems and most online driving directions guides (such as Google Maps) use similar (or the same) algorithms to provide people with directions, which means that more and more people are using the same routes resulting in increased traffic along those routes.
OK, I admit that is a bit of a mouthful. Not too long ago, if you needed to figure out how to get from A to B you basically had two options: you could look at a map and figure it out by yourself or, you could ask someone for directions.
If you figured it out by yourself, you may have picked the same route that a GPS system would predict, but you may have made some adjustments if you knew the area you would be travelling in, or if you had a preference for one kind of road over another. For example, some people don’t like to drive on highways.
Asking directions from someone who (supposedly) knows more than you would also result in a similar situation. It may be the same route that a GPS system would pick, but, most likely, it probably had a lot of personal preferences built into it.
Time of day is probably the factor that would alter the route the most. People familiar with the local traffic patterns of their town adjust their driving accordingly. For example, they may choose a highway that would give them a faster drive if they drove the route on a weekend, but they would never take that same highway during rush hour.
Of course, if all GPS systems accounted just for time of day, they would all be making the same recommendations, and we would be back where we started. If they could account for current traffic conditions, then they should help the overall traffic situation.
I believe that my hypothesis can be proven or disproven. The first step would be to pick a route. Then, pick a certain group of drivers and ask them how they would travel that route. Compare the results of those who used a GPS system and those who don’t. Ultimately, for any road, you would have to know how many drivers chose that road because of a GPS and how many didn’t. A little more challenging, but still doable. A computer simulation is also possible.
Finally, yes I did think about all this while I was stuck in traffic. And, I don’t have a GPS.