TThe line graph illustrates the amount of nitrogen oxide emissions produced by four types of vehicles (buses, lorries, petrol cars, and diesel cars) at different speeds, measured in kilometres per hour (kph).
Overall, buses and lorries emitted significantly more nitrogen oxide than petrol and diesel cars at all speeds. In addition, emissions from heavy vehicles generally decreased as speed increased to a certain point before rising again, whereas emissions from cars remained relatively low and stable.
At 10 kph, buses produced the highest level of emissions, at approximately 40 g/km, followed by lorries at 32 g/km. The figures for both vehicle types then fell steadily, reaching their lowest points at around 60-80 kph, with buses emitting 28-30 g/km and lorries about 21-22 g/km. After that, emissions increased again, peaking at roughly 41 g/km for buses and 28 g/km for lorries at 130 kph.
In contrast, petrol and diesel cars generated much lower emissions throughout the period. Petrol car emissions decreased slightly from 11 g/km at 10 kph to 9 g/km between 40 and 80 kph, before rising gradually to 12 g/km at 130 kph. Diesel cars showed the lowest figures overall, falling from 7 g/km to around 5 g/km at medium speeds and ending at approximately 6 g/km
