Keeping an Eye on Traffic

The US Department of Transportation's Federal Highway Administration maintains a traffic monitoring program. Based on a network of some 4000 sensors on roads, streets and highways across the nation they can esimate the total number of vehicle miles driven in a given hour, day or month. Vehicle miles is a way of measuring a combination of how many vehicles were moving and how far they moved. One vehicle mile could mean a single car drove a mile or that 4 cars each covered a quarter mile. The graph to the side shows the traffic volume for the entire US averaged over a 12 month window. This is interesting, because the amount of fuel used by the nation principally depends on two things. One is how many vehicle miles we are driving and the second is how much gas it takes on average to move a vehicle a mile. This graph shows that vehicle miles traveled goes in one direction - up. Until the summer of 2008 that is. You can see how the $4.00 gasoline we had at that time caused an unprecedented crash in the amount of driving.