Contrary to popular opinion, London isn't a elliptical city. It isn't circular-ish, it isn't approximately round, and it isn't egg-shaped. London would be roughly ovallish were it not for that long wiggly river snaking across the middle. The Thames splits the capital into two geographically distinct halves, and getting from one side to the other is often a lot harder than it looks. Not in very-central London, where crossing the river is a doddle, and not so much out west, where bridges are relatively regularly-spaced. But head out east, especially beyond Greenwich, and traversing the Thames is nigh impossible.
Oh no, London isn't elliptical, it's C-shaped. And heaven help you if you want to cross from one eastern arm to the other.
Tower Bridge is the easternmost point at which crossing the Thames is easy. Beyond that, much harder. There's the East London Line at Rotherhithe (sorry, closed until next summer, look elsewhere). There's the Rotherhithe Tunnel, which is OK if you have four wheels, a bit ropey on two, and possible (but highly unwise) on foot. Are there any buses through the Rotherhithe Tunnel? No there aren't, not any more, so public transport's not an option. The Jubilee line crosses the Thames a magnificent three times, so its contribution to linking London is excellent, but all that disappears when TfL schedule yet another weekend closure. At Greenwich there's a choice of DLR or foot tunnel, at least for the time being (although the council are planning a year-long closure of the foot tunnel in advance of the Olympics, which is very bad news for cyclists who aren't allowed on the DLR). The twin bore Blackwall Tunnel allows road traffic through, plus the 108 - east London's only Thames-crossing bus. Then there's a crossing bonanza at Woolwich (ferry, foot tunnel and DLR), but after that nothing until Dartford, and that's outside the capital's boundaries. Between Bexley on the south bank and Barking and Dagenham and Havering on the north, none shall pass.
I tried getting across the Thames yesterday, from the Leamouth end of Tower Hamlets to the Dome. Mistake. One lane each way of the Blackwall Tunnel was closed, creating lengthy tailbacks for road traffic. I couldn't get the Jubilee line because it was closed, and any DLR crossing would have required a ridiculously lengthy detour. So I thought I'd avail myself of the rail replacement ferry service. When the tube's buggered, folk at The O2 pay Thames Clippers to run a boat across from East India Pier every 10 minutes - which sounded like a good option. But, in a triumph of bad planning, East India DLR station was also scheduled to be closed, so the gate from the quayside to the pier was locked, and I had to take a badly-signed 15 minute diversion to find my way round to the pier from the Blackwall side. That was two boats missed. And, in an even bigger triumph of bad planning, East India station wasn't actually closed after all, so the locked gate was totally unnecessary (and annoying a heck of a lot of other people too). Whatever the O2's website may claim, North Greenwich is most definitely not "So Easy To Get To". Half an hour it took, to get from one bank of the Thames to the other. I could have walked it in five, if only there hadn't been a heck of a lot of water (and centuries of non-investment) inbetween.
It's a bit rubbish, really. Radial traffic in London works fine, but orbital connections go all pear-shaped when they reach the eastern Thames. Permanent river crossings out east have never been a priority, first because of the engineering skill required, and then because of the expense. More recently the environmental costs of any new crossing have come to the fore - a bridge would be cheaper but more damaging, a tunnel would be less damaging more more expensive. We may be getting a new Crossrail link within the next decade, but (several) otherplans remain on the drawing board mired in controversy. All of which leaves certain neighbouring London boroughs anything but neighbours. Because London is actually C-shaped, with a watery divide preventing millions of inhabitants from coming together.