Last reviewed 28 June 2019

On 8 April 2019, the London Ultra-Low Emission Zone (ULEZ) came into effect covering the same area as the Congestion Charge and with stricter emissions standards for heavy vehicles than the existing Low Emission Zone (LEZ).

In other towns and cities, Clean Air Zones (CAZs) with differing restrictions are supposed to be introduced by the end of this year.

Meanwhile, the London Borough of Hackney has separately introduced two zones that it calls “ultra-low emission streets” or “ULEV streets” with completely different standards and Oxford City Council has plans for what it calls a “zero emission zone”. In addition, it is proposed that conventionally-powered vehicles should be banned from sale by 2040 or even sooner.

Richard Smith looks at ultra-low and zero emission technology and the likely issues for PSV operators.

Ultra-Low and Zero Emission Vehicles

While conventional vehicles continue to be defined in terms of their type approval emission standards, these new classes of vehicles are defined not in terms of their output of the conventional pollutants (CO, HC, NOx and PM) but in terms of carbon dioxide (CO2) output.

  • Ultra-Low Emission Vehicles (ULEVs) are vehicles that produce tailpipe CO2 emissions of 75g or less per kilometre.

  • Zero Emission Vehicles (ZEVs) produce zero tailpipe CO2 emissions.

As the definition suggests, a ULEV still has an internal combustion (IC) engine but this is typically married with an electric motor to produce a hybrid vehicle. Hybrid vehicle may be of different types according to the way in which the IC engine and electric motor work together.

  • Parallel Hybrid Vehicle — a hybrid vehicle in which the IC engine and electric motor both work together to provide the power that drives the wheels.

  • Series Hybrid Vehicle — a hybrid vehicle in which the electric motor is the only means of providing power to the wheels. The motor receives electric power from either the battery pack or from a generator run by a gasoline engine.

  • Series/parallel Hybrid Vehicle — a hybrid vehicle that combines the principles of both series and parallel hybrid, ie the vehicle can be powered by the IC engine and electric motor combined or by the electric motor alone.

In addition, any of these types may be a “self-charging” hybrid vehicle, where a relatively small-capacity battery is charged by the engine under light load conditions and by regenerative braking, or a “plug-in” hybrid electric vehicle (PHEV) with a larger battery that can be also charged when the vehicle is static through a connection to the mains supply. In either case, the addition of the electric motor means that a smaller IC engine can be used, with lower fuel consumption and CO2 output, and some battery-only running.

True ZEVs have no IC engine and are powered entirely by an electric motor.

  • A Battery Electric Vehicle (BEV) derives the energy to drive the electric motor from an on-board storage battery and the range is therefore limited to the capacity of that battery and any contribution from regenerative braking. Regular static recharging is therefore required.

  • A Fuel Cell Electric Vehicle (FCEV) also uses an electric motor as its sole power source, but the electricity supply comes not from a storage battery but from the electrolysis of hydrogen gas. The gas is stored in a tank on the vehicle and converted to electricity in the fuel cell. This electricity then powers the electric motor directly. When the hydrogen tank is empty, it is refilled exactly as with a conventional fuel tank.

Hybrid vehicles — disadvantages

While hybrid vehicles were once a must-have for any environmentally-conscious celebrity, they have recently fallen out of favour with environmentalists, with suggestions that some of them should be included in any ban on the sale of conventional vehicles. As they use an IC engine for at least some of the time (possibly most of the time in real life) they still produce the same range of emissions as conventional vehicles and are still subject to Euro 6/VI regulations. Real Driving Emissions (RDE) testing since late 2018 has resulted in some being recategorised in terms of CO2 emissions to the extent that they are no longer eligible for subsidy in Europe. In fact, the RDE test probably still does not replicate real long-distance use where the electric range will be a tiny proportion of the whole.

Zero emission vehicles — disadvantages

Battery-powered cars and vans have developed a great deal, to the extent where some can operate for two hours with a 20-minute recharge time. This is an entirely acceptable cycle, but the problem remains the recharging infrastructure. For present numbers, there are sufficient fast charging points but as the number of vehicles in service grows, these will need to increase to the point that, for example, every public parking space will need its own charging point. The idea of rapid swapping of a discharged battery for a fully charged one at a service station seems unattainable given the size and weight of battery necessary (around 2m2 and half a tonne for a Tesla) and the fact that the demands of styling dictate the need for bespoke installations.

FCEVs can be refuelled as quickly as filling a tank with diesel if the refuelling infrastructure is provided. This is not yet the case, though it could be, and these vehicles look like the answer at the moment.

However, there is a more fundamental problem with both BEVs and FCEVs in that while both offer zero emissions at the tailpipe that simply moves the emissions problem further back down the line since both technologies rely on the generation of electricity in the first place, either to charge the battery or to produce the hydrogen. With the decommissioning of hydrocarbon-fuelled power stations, the hope is that all our electricity needs, including this huge new demand, will be generated by so-called “renewable energy” sources (wind and solar) that are notoriously uncertain with regard to the amount available at any given time. It is fair to say that reliance on such unreliable sources will lead to the almost certainty that at some stage demand will outstrip supply and large-scale blackouts will occur.

What does it mean for PSV operators?

As things stand at the moment, the suggested ban on sales of conventional vehicles (including some hybrids) does not affect operators of buses and coaches because there are (yet) no suggestions that they should be included in the ban.

Clean Air Zones may be implemented at different levels but the lowest level includes buses, coaches, taxis and private hire vehicles so operators of these vehicles will always be affected by any CAZ.

Most operators already include at least some hybrid vehicles in their fleet, though some regard them as an expensive developmental dead-end and have moved back (or on) to conventional engines powered by compressed natural gas (CNG). These require only a small reduction catalyst for NOx in order to reach the Euro VI standard, avoid the complexity of hybrid power units and thus satisfy the CAZ requirements. Operators of hybrids with a diesel engine must make sure that the engine is rated Euro VI.

However, when dealing with zero emission zones defined in terms of CO2 output rather than Euro standards neither hybrid nor CNG power units will be sufficient. The amount of CO2 produced in a combustion engine is directly proportional to the cylinder capacity and no IC engine capable of providing the power needed to propel a large bus or coach is likely to be small enough — even with electric assistance — to get below a 75g/km CO2 threshold.

Hydrogen provides one answer, either as a combustible fuel in an ic engine or as the energy source in a fuel cell, since the only exhaust product is water. While the lack of an extensive refueling network will be a barrier to adoption for many potential users, bus operators with their central depots are ideally placed to provide their own dedicated bunkering facilities, albeit at much greater cost than diesel bunkering though perhaps in the same order of magnitude as CNG.

The latest battery electric vehicles may well be suitable for local bus operations, with limited mileage especially where fewer vehicles are required to operate off-peak services and some can therefore recharge after the morning peak to be available later in the day. Local bus services running on fixed routes with pre-determined stopping points are also ideal candidates for flash-charging, as supplied by ABB in Geneva and Nantes, since the necessary fixed infrastructure can be installed at bus stops. In less than one second the bus connects to the charging point and the battery is recharged in a further 20 seconds, while the passengers alight and board. An alternative is induction charging which requires no physical connection with the battery being charged wirelessly from a plate in the road surface or on an overhead gantry.

The background to these latest initiatives

The reasons for these initiatives outlined above are both straightforward and complex. Straightforward because the adverse effect of combustion products on air quality and health has been well understood and tackled for a very long time (even before the advent of the IC engine) and exhaust emissions have been regulated in the USA since the beginning of the 1960s and in Europe since 1970.

Having got a firm control of the toxic emissions, particularly after 1991 with the introduction of the Euro 1 and subsequent regulations, governments got distracted by the spectre of anthropogenic global warming, caused by CO2 and focused on policies to reduce CO2, including tax incentives to switch to diesel engines for cars on the grounds that higher-efficiency diesel engines tend to produce less CO2. What seems to have been forgotten was that diesel engines by their nature also produce NOx and PM, neither of which features much from the petrol engine.

Thus, policies to combat global warming have encouraged a huge increase in light-duty diesel vehicles in use and subsequently, urban air quality took a steep decline. The response to this has been to swing back abruptly in the other direction, with tax incentives abruptly replaced by tax penalties and international commitments to “de-carbonise” the economy by 2050. In support of this, governments have announced a ban on sales of conventional vehicles by 2040, with some suggesting this needs to be sooner, maybe by 2030. Such vehicles would be replaced by ULEVs and ZEVs.