Overview of NGC Rating
What is the NGC Rating?
The NGC Rating expresses a vehicle's environmental impact as a score ranging fromto .
Environmental impact is assessed over a model's whole life cycle including fuel production and vehicle manufacture – not just from the exhaust or 'tailpipe'. Next Green Car's database includes ratings for all new cars and older models in the UK registered since 2001.
The NGC Rating was developed by Next Green Car and is a unique method of assessing and comparing the environmental impact of a vehicle. Over 60,000 ratings are available for all models including petrol, diesel, hybrid, electric, biofuel, LPG and natural gas vehicles.
As well as the tailpipe emissions produced during a vehicle's use, life cycle emissions include 'upstream' pollutants produced during fuel production (including primary production, extraction, transportation, and refining) and vehicle production (manufacture and assembly).
It is widely accepted that the official data for emissions and fuel economy are far from accurate, measured as they are in the laboratory. The NGC Rating therefore uses Real Driving Emissions (RDE) where available to provide an accurate indicator of environmental impact.
Real world emissions and MPG are estimated using the EQUA Indices for Air Quality (NOx) , Carbon Monoxide, Carbon Dioxide and Fuel Economy as provided by Emissions Analytics.
Next Green Car has partnered with Emissions Analytics to improve the NGC Rating through the use of model specific Real Driving Emissions (RDE) data for NOx, CO and CO2 and MPG. This data is measured using portable testing equipment during real-world driving.
In cases where RDE data is available, the NGC Rating uses a vehicle’s EQUA Indices (banded) as measured in real world driving conditions by Emissions Analytics. In cases where no RDE data is available, the NGC Rating is based on official test data which is multiplied by a ‘conformity factor’ which estimates real world emissions.
To find out more about Emissions Analytics’ EQUA database, or to view the EQUA Indices for a specific UK model, visit the Emissions Analytics website.
How is the NGC Rating calculated?
The NGC Rating analysis first quantifies the extent of life cycle air emissions arising from the fuel and vehicle cycles. The air emissions assessed include: carbon monoxide (CO), oxides of nitrogen (NOx), non-methane organic gases (NMOG) and particulates (PM) and sulphur dioxide (SO2). In addition, the three main greenhouse gases associated with road transport are assessed: carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4).
The method then conducts an impact assessment, which as its name suggests, quantifies the impacts of the emissions rather than just quantifying the amount of emissions produced. The advantage of this approach is that the varying levels of all the emissions assessed can be combined to produce an overall environmental impact. This enables (for example) a comparison of a car with high CO2 and low NOx, with a second vehicle that has low CO2 and high NOx.
The impact assessment uses recognized 'external costs' to establish the relative weight to attach to different emissions; the external costs are values expressed in monetary terms that reflect the overall damage to the environment and to human health. The total impact is then calculated by summing the external costs associated with each of the eight emissions assessed.
The final stage of the calculation is to normalise the impact costs to a simplified scale, the final NGC Rating being expressed as a score between 0 and 100 – the lower the score, the less the environmental impact, with 100 representing a highly polluting vehicle.
Input data for the NGC Rating methodology comes from number of reference sources including: Emissions Analytics (for RDE data), Vehicle Certification Agency (for official tailpipe emissions), and a number of academic papers that estimate the emissions produced during the production of materials used for vehicle manufacture.
For more details of the methodology used to calculate the NGC Rating, download the PDF document: NGC Rating Methodology 2016 (United Kingdom)