28/11/2016 10:31 GMT | Updated 27/11/2017 05:12 GMT

With Diesel Usage Forecast To Continue To Grow For The Next 25 Years, Are We Focusing Enough On The Elephant In The Parking Lot?

After many false starts, electric car sales are finally pulling out into the fast lane. The global fleet doubled to 1.3 million last year, battery costs are falling, and mainstream manufacturers now scrambling to introduce new models. This good news comes not a moment too soon. But it is important to realise that EVs alone cannot fix the environmental damage caused by road transport. The International Energy Agency (IEA) forecasts that global demand for diesel will continue to rise for the next 25 years in spite of the growth of EVs - because of booming demand for road freight. So if we are serious about greening road transport, we have to get serious not just about cars but also heavy goods vehicles.

Because they haul heavy loads over long distances, HGVs need a fuel that is energy dense. While shorter distance delivery trucks that return to base can now run on batteries, for long-distance HGVs this remains utterly impractical. The lorry would neither carry much payload nor travel very far - and much of the battery's energy would be spent dragging itself around. Another alternative would be advanced biofuels, but these are taking far longer than expected to emerge, and many developers have gone bust. Another would be natural gas powered trucks, but the economics are challenging, particularly at current low oil prices.

The global freight fleet is expected to expand by over two thirds to almost 300 million by 2040, driven largely by rising population and living standards in the developing world. As a result, the IEA projects that although fuel consumption by passenger vehicles will flatline because of EVs and efficiency improvements, diesel consumption will grow 3.4 mb/d or 20% by 2040. This alone accounts for 30% of the total increase in oil demand to 2040 in the IEA's central scenario, and a proportionate increase in emissions.

For the next couple of decades at least it seems therefore we will not only have to live with diesel, but accept that consumption is set to rise. So rather than simply demonising the fuel but with no viable alternative for HGVs and massive growth in demand for HGVs - or worse, imagining that because of the EV, road transport is 'sorted' -  we should instead intensify our efforts to improve the fuel efficiency of commercial diesel HGVs through radical innovation.

Immediate wins can be achieved by policy. Refrigerated trucks and trailers, for example, usually have secondary diesel engines to power their cooling, which are highly polluting. In fact if we replace the TRU with a zero-emission unit the vehicle's combined engine emissions will fall by 73% for NOx and 93% for PM. One logical step therefore must be to regulate freight vehicles' total engine pollution rather than just that of the propulsion engine.

But the IEA's projections make clear that tackling diesel is at least a 25 year challenge, so we also need to find ways to deliver innovation to achieve major improvements in efficiency in the primary powertrain such as the work at Dearman or Ricardo around liquid air -diesel hybrids giving 30% improvement in fuel efficiency.

Battery research is clearly vital for electric cars. But diesel engines look set to dominate HGV propulsion for decades to come. Yes, we need to identify and develop the longer term energy carriers with adequate energy density to replace diesel in HGVs. But we should also be investing heavily to support innovations that significantly improve HGV diesel engine efficiency, accelerating their path to market to deliver major reductions in CO2, NOx and PM emissions for the critical next two decades.