A quick look at SMC’s Parex project and the concept of “induced demand”

San Miguel Corporation (SMC) projects the Pasig River Expressway (Parex) to be able to move up to 120,000 cars a day and has labeled it the “ultimate solution to traffic.” How true is this proposal?

“Induced Demand” is a well-known and supported engineering concept. The concept is straightforward: a street is congested because the number of drivers exceeds its capacity. If you enlarge the street, you will eliminate congestion. (This is what SMC is proposing via Parex.) What actually happens, according to seventy-five years of evidence, is that the number of drivers quickly increases to match the increased capacity and congestion returns in full force.

Conversely, “Reduced demand” is the idea that “if road capacity is reduced, people will also change their behavior: people may stop making certain trips, condense multiple trips into one, use alternative transportation options like walking, biking, transit, or travel at different times of the day.” (via CNU)

Reduced demand explains why “Carmageddon” never occurred in numerous historical instances where traffic capacity was suddenly eliminated. For example, a 60-foot section of the West Side Highway in Manhattan collapsed in 1973. The highway carried 80,000 vehicles a day. A city traffic engineer at the time, Sam Schwartz, was tasked with measuring the impact on the vehicles on nearby city streets. To his amazement, about half of the traffic could not be found at all on nearby streets, and the rest was absorbed without major impact on the city’s grid.” (via CNU)

Reduced demand is not unique to New York. You can find links to more studies on the concept here.

Based on the evidence behind these two theories alone, one could infer that the solution to congestion that Parex offers is unlikely to deliver. It will likely meet its quota of 120,000 cars a day but whether it solves any of our traffic woes is another thing entirely.

SOURCE(s): Walkable City Rules, Manila Times, CNU, Wikipedia