The line graph illustrates the nitrogen oxide emissions in grams per kilometre (g/km) for four vehicle types—diesel cars, petrol cars, lorries, and buses—across a speed range of 10 to 130 kph.
Overall, diesel and petrol cars maintain the lowest emission levels, showing minimal variation regardless of speed. In contrast, lorries and buses exhibit much higher and more volatile emission patterns, with buses consistently producing the most nitrogen oxide.
Diesel cars start at 7 g/km at 10 kph and gradually decline to 5 g/km, remaining stable from 70 kph onwards. Petrol cars follow a similar trend, fluctuating slightly between 9 g/km and 11.5 g/km throughout the speed range.
Conversely, lorries show a downward trend until reaching a minimum of 17 g/km at 90 kph, before rising again to 24 g/km at 130 kph. Buses display a distinct U-shaped curve; emissions drop from 40 g/km at 10 kph to a low of 26 g/km at 60 kph, before climbing steadily to reach a peak of 42 g/km at 130 kph. Consequently, buses are the most polluting vehicles at both the lowest and highest speeds recorded.