Short trips in cars
April 9, 2014
Discussions about replacing car trips with bicycle trips often focus on commutes, and whether those are too long or too unpleasant/unsafe. However, it turns out that commuting trips are only about a quarter of all trips, and also disproportionately not-short, so this makes cycling look less practical than it actually can be. Here are bar charts, taken from data from ORNL about vehicle use in 2009, where the heights of the charts were chosen to (1) be roughly in proportion and (2) split evenly into four parts on the cumulative-amount scale. Each pair of bars shows the number of trips of a particular length in miles (blueish bar), together with the sum of all trips that long or shorter (reddish bar). The first chart, with height to scale, shows how this is distributed for commuting vehicle trips only, the second chart shows how this is distributed for all vehicle trips.
Thus, it’s easy to see that half of all vehicle trips are five miles or less long, versus commuting, where the median trip distance appears to be closer to 8 miles (extrapolating on the 5-9 scale). Note also that there are more “all trips” that are three or fewer miles long and not commutes (76.5 billion total, comprising 11.4 billion commuting trips and 64.1 non-commuting trips) than all commuting trips combined (60.8 billion).
Short trips, however, don’t amount to that many road miles. Putting people on bikes may make cities quieter, cleaner, and safer, and their riders healthier, but it won’t put that big a dent in fuel use.
The charts were produced in Numbers, exported as PDF (which is a vector PDF), then imported into OmniGraffle (Pro), with the irrelevant bits of the PDF quickly pruned out as objects. The four charts were then exported as SVG (which is what the “Pro” gets you).