A line on a map connecting points of equal elapsed time; especially, travel time to or from a given location.
Esri’s GIS Dictionary
What a fun word.
Living in Cambridge with a car, a bike, and a T pass, my intuition is that a lot of the time, biking is the easiest way to get around.
The car has a certain appeal, especially when it’s sleeting, but the bike usually wins.1 Isochrones can (approximately) prove this is a good decision.2
Side by side isochrones of biking and driving, centered around Cabridge’s town hall, show that 15 minutes of biking literally covers more ground than the same time in a car – and that’s without accounting for parking.
How much of this depends on daily traffic patterns? Change the time from 5pm to 5am, and a car can get you a lot further. Biking still gets further into Somerville and Fenway, but now driving can get you to East Cambridge and Back Bay, even to a little island of Newton if you get on 90.
How much of it depends on this area being fairly flat? It does appear the isochrone API takes elevation into account, at least for biking: looking at where you can get in five minutes from Coolidge Corner, part of the answer is “not very far up Summit Ave.”
Fifteen minutes appears to be a sweet spot for biking. As travel time increases to twenty or twenty-five minutes, the highways give the car a greater advantage, again with little islands around highway exits. With thirty minutes, a car can cover all of Cambridge/Boston/Somerville and most of a dozen or neighboring towns, although North Waltham is an odd little less-accessible zone.
Is Cambridge special? Compared to what? It does appear to favor biking more than Boston – at least if you start downtown, near the nexus of several highways.
What about my much less dense, suburban-maybe-even-rural hometown? A bike can cover most of town in fifteen minutes, although not the outskirts. Low density – traffic is not really a thing, unless the lift bridge in the middle of town is up – and high-speed roads mean you can get all the way out of town in a car pretty quickly.
A more extreme version of this characterizes much more rural Sundance, Wyoming: a smallish, roundish bike area and a way bigger driving area for the car, kind of octpus-shaped since the road network is so sparse.
How about the American cyclist’s fever dream, Amsterdam? I’ve never been, so I can’t speculate on why its isochrones look odd. Cyclists can cross the bridge going north, but they don’t seem to get vary far. And cars don’t seem to want to go towards the northwest. No idea what’s going on here.
Is there anywhere bikes more consistently come out on top? Unscientifically traipsing around the world, I land on Delhi, although I haven’t either driven myself around3 or biked4 there . Picking Connaught Place as a fairly arbitrary center, biking gets you noticeably further in 15 minutes than driving. This holds for 20, 25, even 30 minutes. Even at an hour, driving doesn’t win out by much.
Obviously, nothing works for everyone. Biking takes a certain type of physical ability. Driving takes a fair amount of money. Biking gets you outside, often a positive, although less great when it’s pouring, you’re somewhere you don’t feel safe, etc. Driving makes it easy to cart much more stuff, including other people, although you then need a place to store the big metal box at home and while out doing whatever you’re doing. But it’s satisfying to be able to defend biking as a practical choice, not just a weird bicycling evangelist thing.
- The T almost never wins. In theory I appreciate the T, but in practice I mostly use it when with other people who won’t/can’t bike. ↩︎
- There are a handful of publicly accessible ways to create isochrones. The one I’ve been playing with is TravelTime’s playground. ↩︎
- And haven’t really wanted to, especially after getting into two car accidents, in two separate taxis, on the same day. ↩︎
- Not yearning to do this, either. Air quality is no joke. ↩︎
North on Quincy 
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