God. East London river crossings. You wait decades for one, and then five come along at once. They're like buses, aren't they?

The Thames has a very different character in the two halves of London. To the west of Tower Bridge, where the river is relatively narrow, you're never more than a mile or two from the nearest bridge: west and south west London are relatively tightly connected.

East of Tower Bridge, though, getting across the Thames is, if not impossible, then certainly not easy, and east of Blackwall it becomes certainly not easier still. It's around 16 miles from the Blackwall Tunnel to the Dartford Crossing, just outside Greater London. Between those two points, there are precisely four river crossings. Three of them (a ferry, a foot tunnel and a branch of the DLR) are all at pretty much the same place. To be precise: Woolwich.

Consequently, there's almost no intercourse between east and south east London. Which, any urban theorist will tell you, is probably a bit rubbish for both of them.

So ways of making it easier to get across the Thames have been discussed for decades, and today London's mayor Sadiq Khan made his contribution to the lip-service. (Reports say he's "given the go-ahead" to the projects, but... we'll see.)

Image: Transport for London.

The big one first. Khan has approved the Silvertown Tunnel, a new four-lane road crossing, very slightly to the east of Blackwall, intended largely to relieve the existing tunnels. This one's a bit controversial: its opponents include anti-air pollution campaigners, south east Londoners worried about an increase in traffic, and the boroughs of Lewisham and Hackney.

So in a transparent attempt to fob them off, Khan's “improved” version of the tunnel will include, in the words of the Evening Standard:

These included new green bus routes through the tunnel, a bespoke “bike bus” to carry cyclists on demand, and improvements for pedestrians and bikes on both sides.

I'm guessing Khan had similar motivations for approving a new pedestrian bridge linking Rotherhithe to Canary Wharf.

Then there are plans for two new cross-river rail links: a DLR extension from Gallions Reach to Thamesmead, and a London Overground one from Barking, to Abbey Wood via Barking Riverside and, yes, Thamesmead again.

These ones are basically housing policy in disguise: there are big opportunity areas on both sides of the river at that point, but not a lot has happened because they're a right pain to get to. New transport links would make those new homes much more likely to happen.

The selection of new crossings is rounded out by a new ferry link between Canary Wharf and North Greenwich. This one feels a bit of a cheat – there are already plenty of boats on that part of the river, and it's not that difficult to do that journey by tube. In fact, I’m pretty sure what's being proposed here is actually just a new pier at Wood Wharf, something that’s been on the table for ages. But hey, if you're trying to get to a round number, I guess it counts.

Two notable absences from today's announcement are the other two road crossings Transport for London were proposing under Khan's predecessor, Boris Johnson (one at Gallions Reach, the other between Rainham and Belvedere). Whether this means they're off, or just being de-emphasised for a bit, remains to be seen.

I'm not entirely convinced all these crossings will ever come off. It's easy to announce things; much harder to actually get them built. There are still umpteen planning meetings to get through, and a lot of people really don’t want the Silvertown Tunnel.

But ambition is good, and knitting the two halves of east London together better is a good thing for a mayor to be ambitious about. So, huzzah.

Jonn Elledge is the editor of CityMetric. He is on Twitter, far too much, as @jonnelledge.

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