Comparing cost-effectiveness of investment in public transport in London vs out of London for reducing carbon emissions

[Author: Pratyusha Singh, Year 13 Student.

Project via Leaf Maths of Morality Fellowship.

This report is based on ten hours of preliminary research.]

Main Takeaway:

Investment in public transport infrastructure over the last decade has been slightly more cost-effective in London than outside of London, but only just. This could be for a variety of reasons, including methodological issues in my research, so should be investigated further. However, this analysis has implications for investment decisions for the UK government, since if there is a concrete reason for the difference in cost-effectiveness, measures can be taken to make investment out of London more cost-effective in the long-term future, helping to reduce more CO2 emissions in the long-term. I will explore and consider these implications below.

Why care about public transport?

Climate change is arguably one of the most important issues our generation is facing.

Within the UK, domestic transport is the largest emitting sector of greenhouse gas emissions, accounting for 27.0% of all emissions in 2019 (pre-pandemic levels). Although the government has implemented new policies since 2019 such as a ULEZ expansion and a ban on new petrol and diesel cars by 2030, this percentage has actually increased by 2.1 percentage points to 29.1% in 2023. This indicates that current policies are failing to cap emissions substantially enough in the short-term for the UK to reach its net-zero target, as this will involve directly removing 100 million tonnes of CO2 from the atmosphere each year by 2050.

It is estimated that, compared with driving, public transport reduces CO2 emissions by 42% if travelling by bus and 73% if travelling by train. This makes it an excellent way of minimising our impact on the environment, since CO2 accounts for about 76% of total greenhouse gas emissions. However, in most areas of the UK outside big cities like London, taking public transport over driving is simply not a feasible option due to a lack of consistency of services when compared to TfL (Transport for London). In fact since 2008, bus services have decreased by 48% in urban areas (excluding London) and 52% in rural areas.

I will attempt to evaluate the historical cost-effectiveness of government expenditure on public transport services both in and out of London over the last decade. I am simplifying and assuming that the only public transport outside of London is the National Rail and Local buses, and the only public transport in London is the London Underground and London buses. I will first calculate the average amount of CO2 saved per year by using various types of public transport. I will then multiply this by ten to get the average for ten years, and divide the government spending over the last ten years by this figure to calculate the cost per tonne of CO2 saved. I will then compare cost-effectiveness in and out of London and explore possible reasons for the difference (although it is not very large), and what the government could potentially do with this information (upon further exploration and research).

Historical Cost-effectiveness Calculations:

All of the statistics being used in this section are from the Domestic Transport Statistics released by the ONS for 2022, and thus are quite reliable.

No. of train journeys per person per year (in vs out of London):

In Great Britain, of the 6.5 billion passenger journeys completed by public transport, 2.5 billion journeys were completed by rail.
Of the 2.5 billion rail journeys:
44% were completed using the London Underground (1.1 billion)
56% were completed by the National Rail (1.4 billion).
Number of journeys travelled by London Underground per person living in London:
1.1*10^9 / (8.982*10^6 )= 122 journeys per person
Number of journeys travelled by National Rail per person living outside of London:
1.4*10^9 / (66.97*10^6 − 8.982*10^6 ) = 24 journeys per person

No. of bus journeys per person per year (in vs out of London):

In Great Britain, of the 6.5 billion passenger journeys completed by public transport in a year, 3.7 billion journeys were completed by bus.
Of the 3.7 billion bus journeys:
46% completed using London buses (1.7 billion)
54% completed using British buses outside of London (2.0 billion).
Number of journeys travelled by London bus per person living in London:
1.7*10^9 / 8.982*10^6 = 189 journeys per person
Number of journeys travelled by Local bus per person living in Great Britain (excluding London):
2.0*10^9 / (66.97*10^6 − 8.982*10^6 ) = 34 journeys per person

Government investment in public transport:

In the last decade, total government investment in:
TfL = over £20 billion
National Rail and local buses outside of London = approximately £88 billion

CO2 saved per person per year by using London Underground:

Avg length of London Underground Tube Journey = 9 km.
Assuming an average speed of 30mph with a diesel car in London, accounting for heavy traffic, this would take approximately 20 minutes, which is roughly 2.55kg of CO2 emitted.
Taking the train instead of a car reduces CO2 emissions by 73%:
CO2 saved per London Underground journey: 2.55kg * 0.73 = 1.86kg of CO2
CO2 saved per person per year by using London Underground: 122 journeys * 1.86kg = 227 kg of CO2

CO2 saved per person per year by using London Buses:

Avg length of London bus journey = 4km.
With similar assumptions as above, this would take approximately 11 minutes by car, which is roughly 1.4kg of CO2 emitted.
Taking the bus instead of car reduces CO2 emissions by 42%:
CO2 saved per London bus journey: 0.42 * 1.4kg = 0.59kg of CO2
CO2 saved per person per year by using London Buses: 189 journeys * 0.59kg = 111.5kg of CO2

Total Cost-effectiveness of government investment in public transport in London over last decade:

CO2 saved per person per year by overall using public transport in London:
227 + 111.5 = 338.5 kg = 0.338 tonnes
CO2 saved in total per year by public transport in London:
0.338* 8.982 * 10^6 (London population) = 3.0 million tonnes
CO2 saved in the last decade:
3.0 * 10^6 * 10 = 30 million tonnes
Cost effectiveness of investment in London public transport over last decade:
£20 billion / 30 million tonnes of CO2 saved = £667 per tonne of Co2 saved.

CO2 saved per person by using National Rail:

Avg length of National Rail journey = 34.4km.
Assuming an average speed of 50mph with a diesel car outside of London, this would take approximately 30 minutes, which is roughly 7kg of CO2 emitted.
Taking the train instead of a car reduces CO2 emissions by 73%:
CO2 saved per National Rail journey: 0.73 * 7kg = 5.11kg of CO2
CO2 saved by using the National Rail per person per year: 24 journeys x 5.11kg = 123kg of CO2

CO2 saved per person by using buses out of London:

Avg length of a bus journey out of London = 6km
With similar assumptions as above, this would take approximately 5 minutes by car, which is roughly 1.68kg of CO2.
Taking the bus instead of car reduces CO2 emissions by 42%:
CO2 saved per Local bus journey: 0.42 * 1.68kg = 0.71kg of CO2
CO2 saved by using Local buses outside of London per person per year: 34 journeys x 0.71kg = 24kg

Total Cost-effectiveness of government investment in public transport out of London over last decade:

CO2 saved per person per year by using overall public transport outside of London:
123 + 24 = 147kg = 0.147 tonnes
CO2 saved in total per year by National Rail + buses out of London:
0.147 * 58.74 * 10^6 = 8.63 million tonnes
CO2 saved in the last decade:
8.63 * 10^6 * 10 = 86.3 million tonnes
Cost effectiveness of investment in National Rail + local buses:
£88 billion / 86.3 million tonnes of CO2 saved = £1019 per tonne of CO2 saved

Recommendation: The UK Government could further investigate the reason for this extra historical cost-effectiveness in London, and use this information to strategically invest in order to increase future cost-effectiveness of investment out of London (in the long-term)

As seen in the calculations above, investment in public transport in London has been £352 per tonne more cost-effective in the last decade than investment outside of London- a percentage difference of 35%. That is if we take the number of people utilising the different types of public transport per year and the amount of CO2 saved as a result as the main measure of effectiveness of investment.

Firstly, I would like to highlight that a difference of just £352 per tonne is fairly small, and this could possibly just be a reflection of methodological issues, indicating that perhaps the two options are similarly cost-effective. However, the fact that nearly half of the rail journeys completed in Great Britain in 2022 were completed in London, despite only 14.4% of the UK population living there, suggests that there may be a stark difference in quality of transport in and out of London. This is highly speculative though, since there could be other contributing factors such as a difference in environmental attitudes and culture. Therefore, the reasons for this difference should be investigated further.

However, I will assume the extra cost-effectiveness of investment in London is due to the overall better quality of public transport infrastructure, causing it to be utilised more on average and therefore more CO2 being saved per pound of investment. If this is the case, the calculations show that historically, investment in London has been more cost-effective, but only just. This suggests that there may be a threshold quality of service for people to start regularly using public transport (ie. for travelling to work etc), and whilst London may have exceeded that threshold, other areas haven’t. Therefore, it might be more cost-effective to invest in public transport outside of London to bring services in these areas up to the same standard, even though this hasn’t been quite as cost-effective in the past. This is because an increase in the quality of services will encourage more people to utilise it in the long-term, saving more CO2 per marginal pound invested. Although in the short-term, high initial costs of investment will make this venture seem highly cost-ineffective, I predict that in the long-term the cost-effectiveness will increase as more and more people start to choose public over private transport, saving more and more CO2. This will eventually make investment outside of London just as cost-effective as it currently has been in London. However, I reiterate that this is highly speculative and reasons for the slightly higher historical cost-effectiveness in London vs out of London should be investigated further.

Weaknesses of this calculation:

Not everyone using the London Underground will be residents of London, since it is a big city so has tourist visitors who use public transport as well as local residents. Therefore, my calculation for number of journeys per capita is likely to be an overestimate, since I only divided the total figure by the London population (excluding tourists)

In my cost-effectiveness calculation, I have taken the use of public transport in 2022 as the average and multiplied this by 10 to get the total utilisation over the last decade. However, this is likely to be an overestimate as new policies such as ULEZ being implemented have probably caused public transport to be used much more in recent years than, say, in 2012.

I have also used the statistics for Great Britain and the UK almost interchangeably, so this is likely to lead to some inaccuracies when using population figures for example, however I expect these will more or less cancel eachother out since this is only an estimation. I have also tried to be uniform when looking at different types of statistics, e.g. only looking at GB figures when looking at stats for transport , whereas only looking at UK figures when looking at stats for populations.

I have tried to keep most figures from the year 2022-23, however some of them are from 2023-24. I do not expect this to be a huge issue though, since these statistics do not change much year on year and both years were relatively unaffected by the pandemic.

When looking at government spending on public transport in the last decade, this includes the additional funding during the pandemic to support workers (ie. the extra £200 million in emergency funding provided in Feb 2022 as part of the Fourth Funding Package). However, since this additional funding is included in investment both in and out of London, this will have negligible effect on comparisons made between the two.

I have also assumed that the most popular type of car used in London is a diesel car, which is likely to change in the future as more and more people will be switching to electric vehicles given the 2030 diesel and petrol car sales ban, indicating cost-effectiveness may decrease in the future both in and out of London.

Furthermore, typical car speeds and journey length are highly approximated due to the extreme volatility of these quantities depending on various factors such as location, traffic and road type.

Lastly, I have failed to mention the significant energy and finite non-renewable resources, as well as land, required to improve public transport infrastructure in the first place. Of course, all of these factors will also have a significant impact on the environment in many different ways, but for simplicity, I am only analysing the environmental impact in terms of CO2 emissions saved once any improvements have been fully implemented (assuming a car would have been used instead). Another point is that in the future, travelling habits of the UK population may change significantly, though I cannot accurately predict how.