Friday, April 29, 2011

Using agents to explore traffic: Part Two-Micro to Macro

Following on from a previous post on traffic modeling with agent-based models, I have been thinking of other work in this area and came across the following movies on Youtube. The first is a traffic simulator from Martin Treiber. What is interesting is the "coffeemeter" that gives an impression of the accelerations and jerks in the traffic. You can investigate this model further here: or watch the movie below.

The question you might be asking in yourselves is, do such models work in reality? The mathematical theory behind these so-called "shockwave" jams was developed more than 15 years ago using models that show jams appear from nowhere on roads carrying their maximum capacity of free-flowing traffic – typically triggered by a single driver slowing down. Below is a movie of the NetLogo Traffic Basic Model exploring this principle.

Hopefully the movie above helps add something to your question. But if not check out the next movie (make sure the sound is on). In which a team of Japanese researchers recreated the phenomenon on a test-track by putting 22 vehicles on a 230-meter single-lane circuit. Drivers were asked to cruise steadily at 30 kilometers per hour, and at first the traffic moved freely. But small fluctuations soon appeared in distances between cars, breaking down the free flow, until finally a cluster of several vehicles was forced to stop completely for a moment. That cluster spread backwards through the traffic like a shockwave. Every time a vehicle at the front of the cluster was able to escape at up to 40 km/h, another vehicle joined the back of the jam. The full article can be read in New Scientist (click here).

Moving away from traffic jams, as the previous post highlighted we can also use agent-based models to look at traffic intersections. The movie shows a more complicated intersection than in the last post and shows how different intersections can be visualized and modeled.

But while the above movie is rather simplistic, agent-based models can be developed from such simple situations to more complex one. For example, if you can model one type of intersection what is stopping you for modeling more? The movie below shows a more complex set of intersections using Paramics (however, this is noted to be a microsimulation model, if you are interested in finding out the difference between microsimulation and ABM see here).

From a local scene we can also turn to exploring more larger scenes such as entire metropolitan regions. The movie below is of that of TRANSIMS microsimulation-agent based model applied to downtown Chicago:

What I find so interesting about such traffic models is how one can go from basic models at the micro level and scale up such models (and of adding more complexity) to explore more macro phenomena such as traffic jams at metropolitan scales.