London new buses' green credentials revealed by TfL

New Bus Image copyright TFL
Image caption The new buses have been in use on London's 38 route for a few months

Today I have received figures on the new bus for London's fuel economy and emissions from Transport for London (TfL).

The Routemaster-inspired bus, which runs on diesel and electricity, has been touted by the mayor as "the greenest double decker hybrid in the world", and is being used to argue for more investment in London transport.

Before receiving these statistics, it was difficult to scrutinise the new vehicle's green credentials.

TfL's figures, which are drawn from the eight prototype new buses already being used on route 38, show the buses have achieved a fleet average of 6.74 miles-per-gallon (mpg) in recent weeks.

Prototypes 'heavier'

However by TfL's own admission the figures are not definitive.

A spokesperson for Tfl said: "The prototypes are heavier than the production vehicles and have only operated on route 38 during the day so the fuel consumption data is not representative."

They added the new bus was "significantly better" than the standard diesel buses operating on the route 38.

TfL is comparing the new hybrid bus with old hybrids on a different route.

"For comparison purposes, double deck hybrid buses operating on route 73 are achieving 6.1 mpg and diesel buses are achieving 5.3 mpg," a spokesperson said.

Improvements 'expected'

"We estimate the production vehicles will deliver approximately 1 mpg improvement on the prototype vehicles.

"We also expect improvements to result from the buses operating over longer distances and over longer periods of time."

This means TfL is claiming that the new buses could eventually have a fuel efficiency of 7.7 mpg.

From 22 June, another 27 production models will begin operating on route 24, during peak hours.

TfL said: "We intend to make fuel economy data for the New Bus for London available next year when the production vehicles have been operating in passenger service for at least six months on route 24.

"This data will allow meaningful comparison with conventional diesel buses currently operating on the same route in the same conditions and with similar passenger demand."

Reduced emissions

I've also been given the following figures for a new bus emissions, taken from a prototype measured at the Millbrook testing centre that has been in service for eight months. This is the breakdown from TfL:

  • 2.048g/km of nitrogen oxide (NOx) - this is a quarter of the emissions from the fleet average for standard hybrid buses (7.7g/km) and diesel buses (9.3g/km).
  • 690.23g/km of carbon dioxide (CO2) - which is better than the fleet average for standard hybrids (864g/km) and is almost half the fleet average for diesel buses (1295g/km).
  • 0.012g/km of particulate matter (PM) - this is a quarter of the emissions from the fleet average for standard hybrids and diesel buses - which emit 0.048g/km of PM.

All these figures - if we take them at face value - certainly look encouraging.

Of course, some will argue the new buses are still not worth the £50k-per-bus premium over an off-the-shelf hybrid, or the £11m which has been spent on developing them.

The real test will be when the figures from the production vehicles are compared to similar hybrids on the same route six months down the line.

Better results

At Mayor's Question Time this morning, Green Party Assembly Member Jenny Jones asked Boris Johnson about the fuel efficiency of the New Bus.

The mayor replied that in tests for the New Bus at Millbrook testing centre the bus was getting 11.7 mpg compared to 6.7 mpg on the road. Testing centres run vehicles in lab conditions and so get better results.

Given the pollutant readings were also taken at Millbrook - some will expect those to be similarly affected too - i.e. the benefits will not be as great.

Green party assembly member Darren Johnson told me: "There is a huge gap between the Mayor's claims for this being the greenest bus in Europe and the reality of how it performs on the road, in real life conditions.

"The prototype new bus for London is consuming almost twice the amount of fuel on the road, as it was on the Mayor's press releases.

"That means all the other figures for emissions could be twice those advertised."

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