Why the Euro VI bus is essential to the success of Clean Air Zones

Prior to carrying out research on vehicle emissions earlier this year I subscribed to the view that all diesel vehicles should be banned from Clean Air Zones. I now see the latest Euro VI Diesel bus as a crucial part of the solution to our air quality challenge.

If diesel buses are banned from Clean Air Zones bus passengers will experience a reduction in service levels of at least 80%. A reduction of service of this magnitude will not only be disastrous for bus passengers it will also have severe consequences for city economies, road congestion and social inclusion, causing levels of social deprivation to rise by nearly a third.

What surprised me in my research was just how clean Euro VI buses are and the extent to which diesel bus technology has progressed. It's a pity that car manufactures have not made the same progress nor inspired the same level of confidence in their vehicles when it comes to emission standards. This has been recognised by Government. In the UK Plan for Tackling Roadside Nitrogen Dioxide (NO2) Concentrations, published in July 2017, it states:

"Standards on vehicle engines (known as Euro Standards) which should have led to a major reduction in emission of NO2 from vehicles failed to deliver, particularly for diesel vehicles, whose "real world" emissions have proven to be many times higher than laboratory tests—the Volkswagen scandal showed that deliberate cheating of the emission tests was built into some vehicles".

The above statement would have been even more accurate, however, if it had clarified that Euro standards have delivered when it comes to bus manufacturing, and that there is much that the car manufactures can learn from UK bus manufacturers. The rigorous on road testing requirements for bus manufacturing means that an equivalent of the Volkswagen emissions testing scandal would be inconceivable in the bus sector.

The role of the Euro VI bus in the implementation of Clean Air Zones

The Government's plan for tackling roadside emissions makes clear that a local plan (CAZ) will only be approved by Government, and thus be considered for appropriate funding if:

a) It is likely to cause NO2 levels in the area to reach compliance within the shortest time possible.
b) The effects and impacts on local residents and businesses have been assessed, including on disadvantaged groups, and there are no unintended consequences.
c) Proposals that require central government funding demonstrate value for money.

The Euro VI diesel bus meets these criteria. Let's look at each in turn:

a) Compliance in the shortest time possible

Modern Euro VI diesel buses, and buses retrofitted to Euro VI standard, can deliver the seismic reduction in NOx required, and in the timeframe available. Retrofits for buses are reliable and proven to deliver Euro VI emission performance.
Whilst the aspiration to move from diesel to electric/hydrogen is widely shared, it is not logistically possible for the entire fleet to be electric/hydrogen by 2020. It couldn't be done without reducing the number of buses in operation, resulting in many more cars on the road, with the rise in congestion creating severe adverse consequences for city economies and their environment.

It will take time to replace older buses with new Euro VI vehicles based on bus company's fleet replacement strategies. However older buses can be retrofitted to Euro VI standard quickly and cost effectively at relatively modest cost (around £15K per vehicle). The Government has recognized this by allocating £100 million towards low emission buses and retrofitting older buses, and £40 million from the Clean Bus Technology Fund to retrofit older buses. This is a good start but the case for retrofitting is so compelling that even more could be done.

The Mayor of London recognizes the importance of retrofitting. 5000 London buses are to be retrofitted to the latest ultra-low Euro VI emissions standard. By 2020 the entire London bus fleet will be at least Euro VI standard.

Progress in clean bus technology has far exceeded car technology. A Euro 6 diesel car emits 10 times more per passenger NOx compared to a Euro VI diesel bus.

Since 2004, NOx emissions from diesel buses have been reduced by a factor of 20, but emissions for diesel cars have reduced by less than a third. It's astonishing to think that a new Euro VI bus emits less NOx than a new diesel 6 car given the discrepancy in size and the fact that a bus has 15-20 times the carrying capacity of a car. Real world testing of the latest Euro VI diesel engines demonstrates a 95% reduction in NOx emissions compared with their older Euro V counterparts. This is transformational!

b) Avoiding unintended consequences

While no Local Authority designing a CAZ would set out deliberately to undermine the bus sector, they need to be aware of unintended consequences.

If diesel buses are banned from Clean Air Zones bus passengers will experience a reduction in service levels of at least 80%. This figure is based on the number of electric, hydrogen and hybrid vehicles in use now plus an assessment of how many new vehicles could realistically be procured in the next couple of years based on fleet replacement.

A reduction of service of this magnitude will not only be disastrous for bus passengers it will be also have severe consequences for city economies, road congestion, social inclusion and actually have the unintended consequence of increasing harmful pollution levels. These are the unintended consequences that the Government have said they are keen to avoid in their consultation document.

Economic implications of an 80% reduction in bus services:

 • 21.6% reduction in employment.
 • 22.4 % fall in incomes.
 • 11.2% reduction in adult skills.
 • 5.6% reduction in people in posts -16 education.

Equity implications:

 • 28.8% increase in social deprivation.

With one bus having the potential to replace 75 cars an 80% reduction in bus service levels will dramatically increase the number of cars on the road.

A ban on diesel buses from CAZ's will have devastating consequences for parts of the UK bus manufacturing sector. The two largest UK bus manufacturers (ADL and Wrights) are geared up towards manufacturing the latest certified clean buses: Euro VI. Their R+D investment, assembly plant and supply chain will need time to adjust to a big increase in orders for zero emission vehicles. It will result in orders for certified clean Euro VI buses drying up which will lead to the closure of at least one of our domestic manufacturers.

ADL and Wrights each have around 2000 employees with around another 1500 in the supply chain. Wrights have manufacturing plants in Falkirk, Scarborough and Guildford. Their supply base is diverse including BAE, Cummins, ZF and Voith. The Wrights manufacturing plant is in Ballymena in Northern Ireland.

c) Delivering value for money

Investing in clean buses delivers the best value for money. Retrofits for buses are proven to deliver Euro VI emission performance and are reliable with direct monitoring already in place. Few retrofits exist for cars, they are unproven in the real world and very difficult to monitor in service. And if a scrappage scheme is justified for diesel cars the case is even more compelling for diesel buses and offers better value for money.

Government financial support for bus retrofitting provides more than 15 times as much value as scrappage allowances for diesel cars to convert to Euro 6 or electric, and 11 times as much value from a bus scrappage scheme compared with diesel car scrappage. The bus options of retrofit and scrappage allowance offer much better value for money than a diesel car scrappage scheme or grants for electric cars.


Clean certified diesel buses (Euro VI) must be an integral part of the solution in CAZs, if they are to be successful in dramatically cutting harmful emissions, reducing congestion and stimulating economic growth. If Clean Euro VI buses are seen as a problem, and not part of the solution, CAZs will be less successful in tackling harmful emissions and congestion will rise to even more intolerable levels in our urban conurbations with an adverse impact on the economy, the environment and society as a whole.

Buses are becoming incredibly clean. Since 2004, NOx emissions from diesel buses have been reduced by a factor of 20, but emissions for diesel cars have only reduced by less than a third. The Treasury would get 15 times more value from investing in bus retrofitting than they would from a diesel car scrappage scheme (measure in kg of NOx saved).

If all diesel buses are banned from CAZ's we face the prospect of bus service cuts of at least 80%. To ensure the success of CAZs in our cities decisions at national and local levels must be based on evidence rather than political expediency. The key to improving urban air quality is to make clean certified Euro VI buses, running on less congested roads, a central part of the solution and to avoid labelling them as the problem.