Academic Writing Task 1 · line graph

Nitrogen oxide emissions produced by four different types of vehicles

The given graph shows the nitrogen oxide emissions produced by four vehicles.

Summarise the information by selecting and reporting the main features, and make comparisons where relevant. Write at least 150 words.

Nitrogen oxide emissions by four types of vehicles (g/km)

Diesel car
Petrol car
Lorries
Buses

View the data

	10	20	30	40	50	60	70	80	90	100	110	120	130
Diesel car	7	6.5	6	6	5.5	5.5	5	5	5	5	5	5	5
Petrol car	11	11	10.5	10	10	9.5	9.5	9	9	9	9.5	10.5	11.5
Lorries	33	31	29	27	25	23	20	18	17	18	20	22	24
Buses	40	37	34	32	29	26	29	32	34	36	38	40	42

Chart redrawn by BandLadder from the data in the original IELTS practice task. Many IELTS practice tasks come from the Cambridge IELTS series (Cambridge University Press & Assessment); all rights in the original tasks remain with their owners.

Band 8 sample answer

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.

183 words. Every figure in the answer comes from the chart above.

How to write about line graphs

Overview first: the overall direction of each line and which was highest.
Group lines that move together instead of describing each one in turn.
Give the start and end figures plus the peak or low point, not every value.

fluctuate: to change frequently and irregularly in amount
volatile: liable to change rapidly and unpredictably
minimal: of a minimum amount, quantity, or degree
consistently: in every case or on every occasion
distinct: recognizably different in nature from something else
climb: to increase in value or amount steadily

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Frequently asked questions

What should the overview say?

While emissions from diesel and petrol cars remain relatively stable across all speeds, lorries and buses show significant fluctuations, with buses being the highest polluters overall.

How long should an IELTS Task 1 answer be?

At least 150 words; 170 to 200 is the safe range. Spend about 20 minutes on it and leave 40 for Task 2, which carries twice the marks.

How do I describe line graphs?

Overview first: the overall direction of each line and which was highest. Group lines that move together instead of describing each one in turn. Give the start and end figures plus the peak or low point, not every value.