Today was road-traffic day at Real-time Decision Making at Berkeley. Jane MacFarlane (LBNL) and Alexandre Bayen (Berkeley) gave great talks about road dynamics. In MacFarlane's talk I learned that provided (by providers) mobile-phone location information is posterior information not likelihood information. And the priors are outrageously informative (like that every phone is on the midline of a known road!). That is good for the user (the mobile-phone owner), who wants navigation information, but not good for anyone trying to do hierarchical inference over phones or people! This is very related to the issues that Alex Malz (NYU) is working on in cosmology.
Bayen focused on the influence of mobile phones on traffic, which has been immense! As mobile phones have gained traction with drivers, they have driven traffic patterns to a non-optimal Nash equilibrium, where all paths from point A to B take the same amount of time. But these same phones also create crazy new nonlinear dynamics, because all drivers get re-routed simultaneously to a small number of alternate routes when something goes wrong. And it is like a repeating multiplayer game, because each routing company is constantly learning the dynamics induced by all the other companies! But this game is played out in the parameters of a set of differential equations, so it is crazy.
Things would be better if we could find a way to cooperate; this led to great lunch discussions with Josh Bloom (Berkeley). We discussed ways to capitalize on the fact that different drivers have different objectives. No existing apps capture this at all: They all optimize for the triviality of minimum expected travel time!