It is based on travel time surveys that we “know” people commute 27 minutes each way in Dallas-Fort Worth, 37 minutes in London, and 42 minutes in the big Asian cities like Tokyo, Hong Kong and now Singapore (a chart and stats here). Those are all cities in the 6-8million category where you can’t cycle uninterrupted because of all the transport machines in your way. I would like to know what the average commute time would be in a city of 6 million people, without the machines in our way. If all of us were on bikes, and the ground plane was very permeable (chamfered corners, short blocks, some piloti) I’m assuming we could make virtual beelines to our destinations without ever touching our brakes. That just leaves the question of distance.
You may have heard me say this before, but a 15 km diameter circular city with the same number of people per square kilometre as Manhattan (30K) would have 6 million people. So let’s say this imaginary circular Manhattan had a permeable ground plane and no cars. What would be the average commute time for people on bikes making near-beelines and cruising at a constant speed of 15kph?
This leads us to a maths question that I am able to answer because my brother-in-law is a physicist. We want to know the average distance between any two randomly chosen points on a 15 km diameter disc. The technical term is “disc line picking“. If you are my brother-in-law you will be able to work it out this way and even generate some sweet drawings:
Or if you are more like my lazy mate who I went to school with, or Edward from Bike Adelaide who helped out as well, you would just plug the r (radius) value into this formula you found on the web:
d = 128r/45π
Either way the average distance between any two points (people, jobs, schools, shops etc) in this imaginary city of 6 million people is 6.79km. Beelining bikes doing 15kph will cover that distance in 27 minutes and 9 seconds (you gotta be precise once you start playing with maths).
Oh boy! That’s the exact time residents of Dallas-Fort Worth are claiming to average when they complete their travel time surveys.
You may say bikes can’t go as the crow flies, even in a permeable city, so let’s round 6.79 up to 9km. But that figure needs rounding down by a third. Transport geographers talk about the need for two thirds of a city’s jobs to be within striking distance of each resident’s home—not the whole lot. And you know yourself that, given a choice, few would take the job on the opposite side of town in preference to one that is nearby.
So our average commute distance is 6km, which 15kph would take 24 minutes. At 20kph (the speed Copenhagen’s cyclists are encouraged to maintain to catch all the green lights rolling into the city) it would take 18minutes—substantially less than Americans commute on their kazillion dollar road networks. Am I wrong that the fastest city imaginable is permeable, as dense as Manhattan, and completely car free?
So I have just drafted a cover blurb for this book I am now preparing to send off to the editors. What do you think?