Pollution is a major contributor to chronic human sickness, not just environmental damage, according to the 2017 annual report of England’s Chief Medical Officer, Professor Dame Sally Davies, released on 2 March 2018. The report made 22 policy recommendations, many of which related to monitoring and ameliorating pollutant emissions. Emissions Analytics is pleased to have had its EQUA Index real-world emissions rating system (www.equaindex.com) cited in the report.Cutting-pollution-and-improving-public-health
The relevance of official fuel economy figures is still a perennial topic across the automotive industry, and one of the hardest to answer directly takes into account the human factor. Some claim that the official figures are in fact perfectly valid, if only the average driver wasn’t so lead-footed. But is there any truth in this train of thought?
Thinking laterally, one way to assess this question is to consider a scenario where the UK parc features a high penetration of connected and autonomous vehicles (CAVs). By taking the driver out of the loop an autonomous vehicle could deliver a more “responsible” and consistent driving style. This would in turn consume less fuel and so deliver significant reductions in nitrogen oxide (NOx) and carbon dioxide (CO2) emissions, then perhaps the driving style hypothesis is true.
To look at this very question Emissions Analytics and Imperial College London collaborated on the “Optimised Vehicle Autonomy for Ride and Emissions” feasibility project, supported by the Centre for Connected and Autonomous Vehicles and Innovate UK.
The research methodology started with Emissions Analytics performing on-road PEMS tests of 21 vehicles to its standard EQUA Index protocol across the UK and Germany. This provided second-by-second driving characteristics and the simultaneous emissions, allowing an emissions map for each car to be created.
These were then integrated with VISSIM traffic simulation software to model the effects of traffic flow and driving behaviour on the emissions. The simulation covered three main factors: vehicle driving strategy, communication between vehicles and infrastructure, and the penetration of CAVs. This included scenarios were a CAV followed a normal vehicle, a non-CAV followed a CAV, and CAV following another CAV.
We also factored in the ability for CAVs to communicate with traffic lights allowing them to approach a junction knowing when they were going to change, and so avoid coming to a complete stop.
In essence, the virtual CAVs were configured to mimic a more cautious and gentle driver with better anticipation of the road ahead and smoother style of driving. The benefit of the approach was we could model a world of 100% CAV penetration, but also the transition to that point via a mixed fleet of CAVs and non-CAVs.
The headline results are that, with 100% CAV penetration with congested traffic, NOX and CO2 could be reduced by approximately 20%. The preliminary analysis assumes a simplified scenario with only diesel cars, so the results are not yet reflective of the current UK fleet. It is plausible that petrol vehicles would show a similar CO2 reduction, while NOX emissions are typically low NOX whatever. Overall, the results show that smoother traffic flow could have significant benefits in urban areas.
This suggests that optimised driving styles can deliver lower vehicle emissions. However, according to our EQUA Index (www.equaindex.com), on average diesel NOx emissions are approximately five times the regulated limit on average (399 mg/km), and CO2 emissions are 40% above official values (based on the New European Driving Cycle). This means that even if driven more responsibly the average vehicle will only reduce its NOx exceedances to about a factor of four, and the CO2 exceedances to 30%. While this is an improvement, and underlines the benefits of driver training initiatives, it strongly suggests that the driver is not responsible for the majority of the emissions exceedances observed.
The chart below shows the reduction in NOx, as the penetration of CAVs increases from 0% to 100%. The benefits are seen is a broadly linear way as penetration increases, although the majority of NOx emissions still come from non-CAV vehicles even when CAV penetration passes 60%.
In summary, even if the driver and all associated “bad” driving habits are eliminated, the current fleet of vehicles will still well exceed official CO2 values, and diesel vehicles will exceed the NOX limits. Modifying driver behaviour can offer a valuable mitigation to these exceedances, but real-world emissions are still primarily determined by vehicle selection.
Emissions Analytics’ EQUA Index (www.equaindex.com) has been revealing the cleanest and most efficient cars since it launched in 2016. Since then, technology and vehicle performance have improved to a point that a new class of even cleaner vehicles can now be revealed.
On 17 October, the Mayor of London, in collaboration with Emissions Analytics, launched an online Cleaner Vehicle Checker (www.london.gov.uk/cleaner-vehicle-checker) with a new EQUA Aq A+ rating for those vehicles with the very lowest emissions of nitrogen oxides (NOx). This identifies 105 Euro 6 petrols meeting this more stretching standard and 11 diesel engines from four manufacturers.
To achieve the A+ rating a vehicle must emit no more than 0.060 grams per kilometre of NOx across the real, on-road EQUA Index test, made up of equal proportions of urban, rural and motorway driving. This is 25% more stringent than the A rating of no more than 0.080 grams per kilometre. It is also significantly tougher than emissions required under the new, official Real Driving Emissions (RDE) regulation, under which 0.168 g/km (180% higher) are allowed until 2021.
A recent study, conducted by Imperial College London on behalf of the campaign group Allow Independent Road-testing (AIR, www.allowair.org), concluded that RDE and the EQUA Index tests are broadly similar in how demanding they are on the vehicle.
The new A+ rating illustrates dramatically the challenge that diesel engines face, but also shows that they shouldn’t be automatically consigned to the history books. Not that many years ago, governments encouraged car buyers to opt for diesel cars in order to reduce carbon dioxide (CO2) emissions. However, the NOx emissions were much higher (often five times higher, and more than the petrol cars they replaced), and even the CO2 emissions were higher than the official figures suggested (often 40% or more adrift).
With the progress in standard “full” hybrid technology – ignoring for a moment plug-in hybrids – the newest models now delivers Mpg comparable with diesels. This in-turn means that on average CO2 as well as NOx emissions are lower too – the best of both worlds.
Does this spell the end for diesel passenger cars? Maybe. The loss of confidence in the automotive industry combined with the political narrative, nationally and locally, may be hard to correct. Consider the new Volkswagen Passat 1.6 litre diesel, with an EQUA Aq rating of A+, an EQUA CO2 rating of B and EQUA Mpg of 52.6 mpg. Compared to the latest Hyundai Ioniq petrol hybrid with EQUA Aq of A+, EQUA CO2 of A and EQUA Mpg of 58.1 mpg. The diesel has impressively low NOx emissions, but the hybrid is beating it on fuel economy and CO2 emissions.
So, the battle between diesels and hybrids is on. Can diesels shrug off the legacy of those Euro 6 diesels still on the market with EQUA Aq H ratings (12 or more times the regulatory NOx limit)? Does the current performance of hybrids obviate the need for alternative powertrains to meet urban air quality goals? Whatever happens, the EQUA Index will be tracking through its independent, real-world test programme.
The EQUA Index data can be accessed for free at www.equaindex.com. There are four ratings for each vehicle: EQUA Aq rating for NOx; EQUA CO2 for carbon dioxide; EQUA CO for carbon monoxide; and EQUA Mpg for fuel economy. In publishing the EQUA Aq A+ ratings, the boundaries for categories B to H have not been changed.
AIR – Allow Independent Roadtesting -has been launched and is a new global alliance promoting the voluntary adoption of an independent on-road vehicle emissions test and rating system.AIR_UK_INFO_250917
The latest analysis of the EQUA Index data shows that the average daily distance driven in passenger cars is not sufficient for a vehicle’s pollution control system to warm up and become fully functional. The resultant high levels of cold start NOx emissions, from both gasoline and diesel engines, could provide an additional challenge for urban air quality initiatives such as the proposed Clean Air Zones in the UK.
According to the Department for Transport more than half of car driver trips nationally are under 5 miles. In Inner London, the average journey distance by car per-person-per-day is just 1.5 miles. For the majority of vehicles tested by Emissions Analytics, it can take more than five minutes for after-treatment systems to reach operating temperature.
The table below shows the uplift in NOx for cold starts tested at 1 minute and 5 minutes from key-on, compared to when fully warm, across the combined EQUA Index cycle.
|Absolute NOx emissions
|Ratio to official limit
|Uplift on warm||Absolute NOx emissions
|Ratio to official limit
|Uplift on warm|
Gasoline has lower NOx in absolute terms but proportionally has much higher NOx in the first minute, but which then falls more rapidly than for diesel cars. This is typically as the three-way catalyst reaches effective operating temperature.
More generally, the thermal management of exhaust systems for engines where the exhaust frequently cools, such as with stop-start technology or hybridisation, is of growing importance in limiting NOx emissions.
By looking at the average NOx emissions of 5% of the data with lowest instantaneous exhaust temperatures from each Euro 5 and 6 passenger car test (excluding data points where the engine is off), and comparing it to the average NOx emissions when the engine is warm, it shows a very similar picture to the cold start data.
|Absolute NOx emissions
|Absolute NOx emissions
|Lowest 5% exhaust temperature||0.719||0.098|
Gasoline engines suffer proportionally much more from cooler exhausts although produce less NOx in absolute terms, whereas the diesel engines have a 29% uplift in NOx when the exhaust temperature is lower. In terms of total emissions, the average uplift is 0.160g/km for diesels and 0.067g/km for gasoline vehicles.
The potential introduction of Clean Air Zones in UK cities is a cornerstone of the government’s strategy to reduce air pollution. However, driver behaviour in cities (short trips, the use of stop-start technology and/or choice of hybrid vehicles), when combined with exhaust after-treatment technologies which are sensitive to exhaust temperature, means that other measures will be necessary if NOx emissions are to be reduced.
Encouragingly, the EU has acknowledged the importance of cold start emissions by including their measurement in the new Real Driving Emissions regulations that start in September 2017. However, there is a danger that the effects are under-measured compared to real-world journeys of short length.
Vans weigh in on the EQUA Index
Light commercial vehicles (LCVs) travelled 48.5 billion miles last year according to the Department for Transport. In its tests, Emissions Analytics has seen similar levels of variability from official fuel economy and emissions figures in vans as in cars. With van mileage growing by an average of 4.1% each year this is bad news for air quality and for van driver’s wallets. Launched today, drivers can now use the EQUA Index to check the on-road performance of light commercial vehicles.
The table below shows a sample of the vans tested. All give fewer miles per gallon than advertised. The average is 17.1% below but the range is from -5.3% to -38.8%. However, the mpg gap is smaller than for passenger cars which was 29% in 2016, perhaps because light commercial vehicles are not being hyper-optimised to the NEDC.
Similarly, all of these vehicles were homologated to either the Euro 5 or Euro 6 standard and yet there are seven Euro 5s and three Euro 6 vehicles which have been rated ‘H’ on the EQUA Aq Index, meaning they emit 12 times or more the current Euro 6 limit when they are out of laboratory conditions.
The best performing diesel van is the Euro 6 VW Transporter, scoring an B-rating on-the-road, meaning it is just 1.5 times the legal limit. This is mirrored in the passenger cars tested, where only 15 of the 131 Euro 6 diesel cars tested meet the standard, of which 10 are from the Volkswagen group.
|Make||Model||Regulatory stage||Variance to official MPG||EQUA Aq rating|
|FORD||Transit Connect||Euro 5||-16.7%||E|
|FORD||Transit Custom||Euro 5||-22.7%||H|
|FORD||Transit Custom||Euro 6||-16.1%||C|
The effect of load
Tested on the same EQUA cycle as passenger cars, vans additionally run parts of the route ballasted to fifty per cent of their maximum payload. The effect of load on fuel economy is an average of -11.2% for a fully loaded van. A quick calculation based on average diesel price (122.12p/l) shows that for every 100 miles driven with a fully loaded van, refuelling costs on average £1.91 more than empty. Multiply this by the average yearly mileage travelled per van  and this is approximately £450 per year.
With around 30 to 50 vans added yearly, the EQUA Index is available for everyone to use free of charge and enables drivers and fleets to pick the most economical as well as the least polluting vehicles. Find out more by looking at the EQUA Index online.
This year’s round up of EQUA fuel economy data shows a five percentage point increase in the gap between official and real-world mpg, reaching 29% in 2016.
Official mpg figures averaged 60.7mpg in the year, the highest we have seen since we started recording in 2011. This is an increase of 9% on 2015’s figures, which stood at 55.7mpg; however, real-world mpg reached just 42.3mpg. On a like-for-like basis, this represents a 3% increase on 2015.
With air conditioning now widely available in cars, in 2016 Emissions Analytics updated all its mpg results to include the effect of air conditioning on fuel economy. Results are now expressed to reflect manually adjusted air conditioning (not automatic climate control) switched on at 50% of maximum throughout the test. This increases fuel consumption typically by 4%.
Incorporating the use of air conditioning, the gap between official mpg figures and real-world EQUA Index Mpg has risen to 29% on average, with the largest gaps well exceeding 40%. This increases to 75% below the official figures for hybrid vehicles that have not had their battery charged and are running purely on the ICE.
Can regulatory change reduce the gap?
From 1 September this year the World harmonised Light duty vehicle Test Procedure (WLTP) will be introduced to certify the carbon dioxide and fuel economy of cars. Work started on this around 2008 and was originally intended to be a worldwide certification standard. However, with the passing of significant time and the withdrawal of North America from the process, it has become less relevant.
It will still be an improvement on the existing type approval process, which incorporates the New European Driving Cycle (NEDC), largely due to the removal or restriction of loopholes in the procedure. However, the test cycle itself is not much more representative of real-world driving, as it remains in the laboratory with no changes in elevation and still modest acceleration rates. Our prediction, also consistent with modelling from the International Council on Clean Transportation, is that the current mpg gap of 29% and the CO2 gap between official and real-world of around 40% will approximately halve. So, a significant gap will still remain.
Crucially, it has yet to be agreed when and in what way the WLTP results will be made available to consumers. In the meantime the EQUA Index is available for anyone wishing to find out the on-road fuel economy of both Euro 5 and Euro 6 vehicles.
We looked at our data on over 750 EU cars tested, to see how much of an influence vehicle class was on variance between the NEDC-derived official MPG and our cycle and found:
- Petrol sports cars come closest to their official figures
- The MPG gap is worse for small cars, whatever the fuel
- Overall the gap is almost always bigger for diesel engines.