Lack of clarity over emissions from hybrids, says TRL scientist

Hybrid vehicles may not be as environmentally friendly as they appear, a senior scientist at the consultancy TRL has warned.

The main area of contention revolves around whether a plug-in hybrid is operating in electric mode or engine mode, said Dr Helen Viner, TRL’s chief scientist, infrastructure.

Speaking at the TRL Academy’s annual symposium, Viner said: “If in electric mode, there will be zero exhaust emissions from the vehicle while in engine mode there will be exhaust emissions. There is very little information at the moment about how these vehicles are actually used.”

There is an urgent need for further investigation into the dual function of hybrids, “especially once zero-emissions capable taxis start appearing in London from 2018”, said Viner. “It also gives a problem to anyone trying to implement a zero emissions zone – it will be possible to tell from DVLA data that a vehicle is zero emission capable, but how will they be able to tell what mode it is operating in?”

Viner also questioned the benefits to air quality of ‘smart motorways’, designed to allow smoother traffic flow through variable speed limits and hard shoulder running during busy times. She acknowledged that enabling vehicles to move at constant speeds would lower exhaust emissions and also reduce brake, tyre and road abrasion particulate matter emissions. 

“Driving that contains lots of accelerations and decelerations and stop/start driving will result in high emissions.”

But she added: “Smart motorways aim to smooth the flow, hence improving emissions and improving local air quality. The only concern is that if the motorway is freer flowing it might attract more vehicles, causing emissions to increase. It is, therefore, important that suitable monitoring is put in place, so that if a detrimental effect is observed additional measures can be put in place such as lowering speed limits.”

Referring to the latest figures from the Department for Environment Food & Rural Affairs, Viner pointed out that transport is a large contributor to the problem of Nitrogen Dioide (NO2) emissions (see graph above).

Viner also told delegates that around 90% of city dwellers in Europe are exposed to pollutants at levels deemed harmful to health, based on the latest figures from the European Environment Agency.

“For example, fine particulate matter (PM2.5) in the air has been estimated to reduce life expectancy in the EU by more than eight months,” she said. “Benzo(a)pyrene is a carcinogenic pollutant of increasing concern, with concentrations being above the threshold set to protect human health in several urban areas, especially in central and eastern Europe.”