Thursday, August 27, 2015

Population densities and traffic jams: a tale of three cities

After reading so many complaints about the awful traffic Metro Manila has, I decided to look at some statistics. Since we love using Singapore as an example, I looked for Singapore data and used it as a baseline for estimating how many cars there are per square km. One of my expectations is the larger the number of cars per square km, the larger the probability of traffic jams. 

Let's look at population densities, with units of people per square km: Metro Manila 19000; Singapore's 8000; New York City 11000.

These numbers should help us get an estimate of the number of cars per square km. If we assume that we have the same rates of cars per person  as Singapore(9 per 100), this would still mean about 2000 vehicles per square km. If we assume New York City rates (20 cars per hundred people), this would give us about 4000 cars per square km.

Another estimate would be the following: as of 2012, the total number of registered motor vehicles is around 8 Million. The population of Metro Manila is around 12 percent of the Philippine population. This leads to 900,000 vehicles. Divide this by the area of Metro Manila (640 sq km), to get 1500 vehicles per square km. To one significant figure, this gives about 2000 vehicles per square km.

My own guess is around 3000 motor vehicles per square km, or somewhere in between Singapore and New York levels.

How does this compare with other cities? If we know the population density, and the number of cars per hundred people for each city, then we can estimate the number of cars per square km. For Singapore, this leads to a measly 700 vehicles per square km. New York has about 2000 cars per square km. Among US cities, New York belongs to the list of top ten cities with the worst traffic jams. So even if we reduce car ownership levels to the same rates as Singapore, we'll still have it, since we're trying to fit too many people-- and by extension, too many cars-- into the same itty-bitty space.

[Note: This analysis, of course, ignores a lot of things: Road discipline (some of my pet peeves: (1) outermost lanes, contrary to what most people believe, are not parking spaces! (2) misuse of U-turn slots :three lanes of vehicles using the same u-turn slot!) and a  lack of coaches and railways.]