Today's unsigned piece in the Economist "Democracy in America" blog picks up on Tom Vanderbilt's Slate item reviewing my book.  I'm certainly grateful for the publicity, though for the record, I do believe in pleasure!

But the Economist's writer ends his piece with a commonplace of old-inner-city thinking that can do real harm when taken outside those bounds:

Ultimately, what makes public transit work is massive redundancy: lots of different systems layered on top of each other, all running at high frequencies, providing you clear information on when the next one arrives. The world's best cities, New York, Paris, London, Hong Kong, Berlin, all do this pretty well. For cities that aspire to greatness, the road map doesn't seem so hard to follow.

"Lots of different systems layered on top of each other" begs the question of whether these systems are working together -- for example by encouraging connections from one to the other -- or simply duplicating each other.  That is the distinction that matters.  

Yes, if you're in "New York, Paris, London, Hong Kong and Berlin" you may perceive a layering of "redundant" services, but one of two very different things is happening:

1. The services are truly redundant in the sense of duplicating (or even competing) but the demand is so intense that they're all full, so the duplication isn't much of a waste.  This is the case with many big-city commute markets, but often not with all-day patterns.
2. The services are actually fitting together into an integrated network, through some mix of planned connectivity and complementarity.  An example of complementarity is the simultaneous presence of services in one corridor that differ in the speed/access tradeoff.  A major Manhattan avenue, for example, may have an "express" train stopping only every mile or less, a "local" train stopping less than every half-mile, and a bus on the surface stopping even more frequently.  That isn't redundancy unless the market isn't strong enough to support all three.

Praising these super-dense cities for "massive redundancy" sends exactly the wrong message to less-dense and smaller cities.  Tell them to plan for redundancy, when their markets are insufficiently developed, and they'll spread their resources out in tangles of overlapping services none of which are frequent or attractive enough to be worth waiting for.  This is the lesson of inner Sydney, discussed in Chapter 12 of my book.

You need massive agglomeration for true redundancy to work.  Without that, you dissipate service quality too much.  This was a key failing of the privatization of the British bus industry, which gave private companies control over transit planning and prohibited them from working together to create rational connective networks, by declaring that to be collusion.  The result was a generation of frustrated riders who had to let Jim's bus go by because they had a ticket for Joe's bus, even though the two bus lines together might add up to enough frequency to actually be useful.  The last Labour government finally removed this prohibition on "collusion," allowing simple, obvious, and mutually beneficial plans to go forward, like this one in Oxford.

"Massive redundancy" may be fine if you're a megacity, though even there, its effectiveness may be a feature of the peak that doesn't translate to the rest of the day.  Anywhere else, services need to work together as a network.  Even in London, New York, Paris, Hong Kong and Berlin, that's really what's happening.