One reason I voted Green for second preference in May was the Lib Dems apparent conversion to the some of the rituals of the bendy jihad movement, although to be fair they wanted to replace them with trams, which is at least sensible.

Now, in a welcome outbreak of ‘when the facts change, I change my opinion’ Caroline Pidgeon AM is hacking away at one of the few remaining struts of the policy – that scrapping bendies will magically decrease pollution, and is calling for the phase out to be delayed until son-of-RM is ready (or, more realistically, until greener buses are available).

Citing TfL figures the Mayor says a typical double-decker emits 1.25g of CO2 per kilometre whereas a bendy bus emits 1.69g over the same distance. London’s 351 bendy buses have a capacity of 140 passengers each giving a total capacity on the buses of 49,140. Double-decker buses typically only carry 91 passengers meaning there will need to be 540 buses on the streets of London to maintain capacity.

Boris’s answer to Caroline goes thus:

A typical double-deck bus emits 1,250g of CO2 for every kilometre it operates compared to 1,690g produced by an articulated bus.  These figures are based on tests undertaken in typical London conditions.  The levels of C02 emitted would not change significantly, based on these figures.

There’s something a bit odd here – my little Skoda emits 170g/km, so I think Caroline’s got her decimal points and commas mixed up.  The real figures are presumably 1250g/km and 1690g/km.  It’s also unnecessary to guess at replacement fleet sizes based on capacity when TfL have provided us with the real figures.

So we can refine the figures a bit here.  TfL’s own capacity studies for the initial debendifications show how many more buses are required of each type.  I’m going to assume that a 12m single decker is about the same emissions as a double decker – 1.25kg/km.  In practice it might be a bit less, but the 12m bus holds more people and is rather longer.

Let’s recap:

  • 38 – goes from 47 bendies to 66 double deckers.
  • 507 – goes from 9 bendies to 17 single deckers
  • 521 – goes from 19 bendies to 34 single deckers

Now, next we have to come to some estimate of how many km are travelled on each route currently and in the future.  Since the extra buses are being provided to keep the capacity the same, the distance travelled should scale with the number of vehicles, in order to get the same capacity past the bus stops.  Therefore we get:

  • 38 – 47*1.69 = 79.43 now, to be 66*1.25 = 82.5 = 4% more CO2
  • 507 – 9*1.69 = 15.21 now, to be 17*1.25 = 21.25 = 40% more CO2
  • 521 – 19*1.69 = 32.11 now, to be 34*1.25 = 42.5 = 32% more CO2

That’s a big old increase – we can certainly say that whatever you replace a bendy with *currently* is going to be worse for the environment, and a lot worse in the case of the Red Arrow routes, owing to the near 2 for 1 replacement rate.  Therefore, in order not to be even more hopelessly wrong on green issues, Boris *has* to wait until, as Caroline Pidgeon says, greener alternatives are available.  Strangely enough, this shouldn’t actually take that long, as we’ve seen.  Plenty of big manufacturers are going for hybrid drive, although there’s still about a 10% weight penalty (figures based on the 12m Citaro hybrid coming out in 2009).  Lugging batteries around will do that to you.

Engineering lesson – It’s usually the case that larger vehicles are more economical; think big container ships, heavy coal trains, Boeing 747s.  For example, a BMW X5 4×4 kicking out 280g/km has six passengers in fully loaded, so you’d need 25 of them to replace a single bendy.  Those 25 X5s kick out 6.95kg/km against 1.69kg of a bendy, so a bendy is four times better for the environment than a 4×4.  Obviously Boris wasn’t thinking of the environment when he relieved the X5 of the threat of a £25 daily congestion charge and signed the bendy’s death warrant, then.

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