Jarrett Walker has been designing bus networks for thirty years. From his consulting practice in Portland, Oregon, he’s built a specialism in helping cash-strapped local authorities optimise their networks through his business Jarrett Walker Associates.

And you can’t optimise if you don’t know what public transport is actually for and how you’re measuring whether or not it’s achieving those goals.

Eventually he’d done so much thinking on this topic that he wrote it all down in his book Human Transit.

In our conversation, he talks me through why it’s important to understand whether a transport network is seeking to optimise for coverage or patronage and how ‘access analysis’ can provide everyone with their own personal measure of public transport freedom.