Travel time and trip length

Last week, we were talking about doughnuts. Not the sweet type that makes one susceptible to diabetes, but the phenomenon of the urban population to move outwards from the city center and create residential suburbs in an effort to build homes in larger, more spacious, but cheaper land, albeit, farther and more expensive to travel to and from their places of work. This is the basic treatise of spatial economist von Thünen’s theory of rent which simply states that the farther you are from the city center, the cost of land is cheaper but your transport cost increases. Finding the balance, thus defines how a city develops and takes shape.

The doughnut effect caused the establishment of residential subdivisions outside of Cebu City in the last two decades because the cost of land is lower. As far as transportation cost is concerned, this is both distance-based and time-based. But the development of transport infrastructure (roads, bridges) decreased travel time to the farther places, making them “nearer” to Cebu City. Thus it’s now more fashionable to live in Naga and Compostela, compared to twenty years ago, because “anyway, it’s just less than an hour away.” The wider roads, north and south, also induced people to buy cars.

Everybody knows the time-distance relationship but let’s try to revisit it again to see how it works. If you’re travelling 10 kilometers per hour, you can travel 30 kilometers in three hours. If you increase your speed to 15 kph, you cover the 30 km. In 2 hours. If your speed is 20 kph, it will take 1.5 hours. For 30 kph, it would be just 1 hour, but for a speed of 60 kph, you cover the distance in 30 minutes. Now speed depends on the road infrastructure and the traffic congestion, so if a city develops wider roads or manages traffic more efficiently, people will start moving out and lives farther and farther away from the city.

Metro Manila is a classic example. Not only were corridors expanded (EDSA and C-5), but the expressways were built which made areas hundreds of kilometers away from the centers of Makati and Ortigas, among others, “near.” Thus, throngs of people, in-migrants from the provinces among them, decided to buy lots and build houses in Bulacan, Pampanga, and Cavite, since these are already “accessible” to Manila. There’s this current agony of increasing transport costs, owing to the increases in toll fees but that was expected. That’s another transport concern. What we are focusing here is “trip length.”

What people failed to understand, planners among them, is that trip length itself, contributes to traffic congestion! It’s not only the number of cars or vehicles which causes the congestion – longer trip lengths also do, sometimes even to a higher degree. When one transfers to Compostela, for example, but still works in Cebu City, he/she will be contributing to the traffic in Cebu City, but also Mandaue, Consolacion and Liloan. Transport economists use the parameter, total “vehicle-kilometers travelled” or VKT per capita as another benchmark in defining the transportation characteristics of a city. The higher the VKT per capita, the more difficult the transport problems in a city. But higher VKT per capita is a result of the doughnut effect AND building fast expressways outward.

Expressways may do some good if there are associated interventions also put in place – two specifically. First, is if land use plans are designed to make suburbs more self-contained – dispersion of employment and business opportunities and other non-work related trips (why do you have to travel to the city just to buy this good or service?). The second is if an efficient public mass transport is in place. The problem with expressways is they induce people to buy and use cars. Which will overrun the road sooner or later?

Building expressways to solve traffic jams is like buying bigger clothes to cure obesity!