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?

## 7 Comments

Two thumbs up on the blurb. Using your baseline of 15km/h, machine blockages and antique city design are (at best) doubling my travel times by bicycle (for the current distances).

Using a ruler and a map it becomes apparent how much more accessible city facilities would be without the hindrances. I could easily travel at least twice the distance (thus four times the area) than I’d normally be bothered to (Melbourne machinery boxes one in) but probably feel compelled to go further afield in a welcoming environment (Velotopia).

Thanks Prof. Crank! I’m been neck deep in transport geography papers lately, phew! But one of had to I guess 🙂

From what I remember the Dutch commute times are marginally longer than the DFW times. One article that I read recently was practically gloating about being faster by a minute or two. It’s a damn shame that the Dutch are taller, fitter, healthier and more relaxed than the drivers in DFW.

Now think, think very hard: what was that article? 🙂

Honest question – is it possible for Manhattan densities to exist if everybody rides bikes? Will there be enough room for the bikes (both storage, and in use), or will the city have to sprawl a little to accommodate them, just as it does in a much more extreme way for the spacial demands of cars.

Let’s think about this. The basic unit of Manhattan’s density is that pre-war 4-5 storey walk-up block. On each level two small flats face the street and 2 small flats face the long narrow courtyard behind all the blocks. Making room for bike parking in flats, making galleries wide enough to ride a bike on, and widening the courtyard to get some better sun access would all necessitate an increase in height. Making flats big enough to entice average families, with all of their prejudices, in from the burbs: well there’s a death knell as well! Basically, I don’t think you can build so densely today, at least not in spoilt nations.

But your main interest is the capacity of the ground plane to handle the trips of 30,000 people per square km if they all rode instead of walking, driving, or using PT. I’m pretty confident this will be fine. Remember, the North/South routes in manhattan (the avenues) would be as quiet as the east/west routes (the streets) if there were more of them. But the De Witt plan deliberately limited the number of avenues to funnel pedestrians down a few routes and ensure the merchants had good passing trade. A bicycle city would be far more permeable (like Barcelona, or better) to diffuse traffic, not squeeze it through the least number of routes under pressure.

The other problem with New York for cycling is it relies on packed trains bringing people to work on Manhattan via a relatively small number of bridges and tunnels. Put all those train riders on bikes, and the bridges mightn’t cope even if you did get rid of the cars.

Thanks for that! What do you think?

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