Making London’s buses cleaner

Not so old, as buses go, but definitely a polluting offender!
Not so old, as buses go, but definitely a polluting offender!

Public attention is now firmly focussed on the need to reduce diesel emissions. But whilst this has so far been aimed mainly at cars, the pollution contribution of public transport is now coming under increasing scrutiny, particularly in London where pollution levels regularly exceed permitted limits. This scrutiny is entirely justified: taxis alone contribute some 16% of all road transport NOx emissions according to London Transport data.

Given the sheer volume of buses and taxis in London, reducing their emissions creates a significant challenge, for there really is no remotely cost-effective alternative to diesel power for these essential vehicles, nor is there likely to be in the foreseeable future.

However, much can be done to reduce emissions from current diesel-powered public transport, and a couple of key manufacturers have recently announced ground-breaking plans which should make a huge difference. Firstly, a new, hybrid-powered London taxi has been announced, which is capable of running for short periods on electric power only. This initiative is being given a major boost by legislation introduced by London’s Mayor which effectively bans the sale of new diesel-only taxis from 1st January 2018.

Just as significant is a recent announcement from engine manufacturer Cummins that they have developed a clean diesel repower package to replace the engine and exhaust after-treatment equipment in older buses with a fully certified, very low emissions Euro 6 system. The repower will enable pre-Euro 6 legacy buses in London fleets to continue operating within the new Ultra Low Emission Zones (ULEZ) as they come into force, improving the air quality of the capital and lowering the carbon footprint of the 10,000-strong London bus fleet.

London has bought thousands of hybrid buses over the last few years, including several hundered of these "Borismasters", however they have not reduced pollution levels as much as had been hoped.

London has bought thousands of hybrid buses over the last few years, including several hundred of these “Borismasters”, however they have not reduced pollution levels as much as had been hoped.

Previously, London and many other cities have bought large numbers of hybrid buses in the expectation that this would achieve the necessary reduction in emissions. Unfortunately, this massive expenditure has been less than entirely successful, partly because some of those hybrid systems have not performed particularly well, notably those in the now-familiar “Borismaster” double-deckers, and also because the Euro 4 and 5 engines fitted to most of these buses did not perform at their best. This was not through any fault of their own, but simply because ultra-low speed operation in London’s traffic-clogged streets resulted in emissions levels being significantly higher in operation than during the flawed European test standard to which those engines were legally obliged to comply.

Euro 6 buses are cleaner than many cars

Only with the technology changes embodied in the latest, Euro 6, generation of engines have real-world emissions levels been reduced to more acceptable levels. This has been demonstrated in initial testing by Transport for London (TfL), which has indicated a Euro 6 bus to have 98 percent lower NOx emissions than Euro 5 (down from 9 g/km to 0.2 g/km). This indicates, significantly, that Euro 6 engined buses and HGVs will have NOx emissions better than many Euro 5 diesel passenger cars.

However attractive the idea may be in principle, simply getting rid of every pre-Euro 6 bus in London overnight is an impossibility. Even if the output of every British bus manufacturer was devoted to producing new buses just for London, it would still take several years to replace the fleet, not to mention the need to massively raise fares to cover the cost – just one double-deck bus alone can cost around £300,000!

Fuel savings are significant

The Cummins repower has additional benefits, featuring an integral Stop/Start system to eliminate fuel used during idling by automatically switching the engine off when passengers are boarding or alighting. This can reduce the daily fuel consumption of a double-deck London bus by up to 8 percent, saving up to £2,500 a year for each bus whilst reducing the vehicle’s annual Carbon Dioxide (CO2) emissions by an incredible 4 to 6 tonnes!

Routemaster Euro 6

Sir Peter Hendy with his RouteMaster bus equipped with a Cummins Euro VI clean diesel engine outside Charing Cross station, London. The vintage bus owned by the Network Rail chairman has been repowered to meet ultra-low emission zone standards and sports a new clean diesel engine and exhaust system supported with the latest diagnostic technology.
Photo: Professional Images/@ProfImages

Proof of the repower concept was established by a Cummins repower of a London Routemaster bus RM1005 which first entered service in 1962 and, post-repower, is now fully certified to meet Euro 6 emissions. This particular bus is in fact owned by the highly respected Sir Peter Hendy, formerly the Commissioner of Transport for London and presently Chairman of Network Rail.

The Routemaster is considered the most challenging bus to repower due to very restricted space under the bonnet, and the success of this project now enables Cummins with confidence to begin undertaking projects for any type of bus.

First production repower already under way

A 2009 London double-decker similar to this one has been repowered with a Cummins Euro 6 engine and is being tested.

A 2009 London double-decker similar to this one has been repowered with a Cummins Euro 6 engine and is being tested.

One of the first repower projects is nearing completion at Millbrook Special Vehicles in Bedfordshire, with a 2009-built Euro 5 London double-deck receiving the latest Cummins B6.7 Euro 6 system. Testing of the bus is now underway at Millbrook Proving Ground with the initial results confirming the expected fuel and emissions benefits.

Kirsty Andrew, General Manager of Millbrook Special Vehicles said “This project has great potential to help to improve air quality and to reduce greenhouse gas emissions. At the same time, it will enable the bus fleet market to benefit from fuel saving benefits over the extended life of their vehicles. We are delighted to be working with Cummins to deliver a product to their high quality standards.”

With a very high percentage of buses already powered by earlier Cummins engines in operation both in London and around the country, their emerging Euro 6 repower opportunity is adaptable to many different models and emissions levels. Depending on the age and condition of the bus, each repower project will be individually evaluated, with some requiring only a simple engine and after-treatment replacement, while others may need a complete powertrain refurbishment and fabrication work – with various levels of upgrade in-between.


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