Facts sheet 5(a) Emissions: Like for like comparisons for rail and road transport

May 2006: Wp Ref. emit01

Summary

This analysis compares the emissions per passenger-km and per tonne-km from the UK 's national rail network with the emissions that would arise if that function were discharged by express coaches and lorries using roads occupying rail's right of way and managed to avoid congestion. The data is for the year 2002/3 and t he road vehicle emissions assume Euro II standards . The reason for the year base is Network Rail's inability, or refusal, to divulge later fuel consumptions.

For passenger rail we assumed replacement express coaches would return 10 miles per (imperial) gallon with an average occupancy of 20 passengers. On that basis the replacement coaches would reduce carbon emissions attributable to rail passengers by 28%, CO by 55%: NOx, by 26% and SOx, by close to 100%. (The latter arises because sulphur has been virtually eliminated from the fuels used by road vehicles but not from that used by trains and power stations).

For freight we assumed lorries return 8 miles per gallon with an average load of 15 tonnes (30 tonnes out back empty). On that basis the replacement lorries would emit the same carbon as the trains, 23% less CO, 32 % more NOx and close to 100% less SOx.

We also provide the emissions per passenger-km by diesel car assuming 1.5 passengers per vehicle and a fuel consumption of 45-50 miles per gallon. Under that assumption the carbon emission per passenger-km by car is double that of rail and 3 times that of the express coach cited above. However:

1. The average journey by car is 8.7 miles, compared with 25 on the line haul element of a rail journey.
2. Where the main mode is rail the average distance traveled is 7.5 miles more that the line haul element.

Hence, if half the 7.5 miles at (b) is by car and the rest by tube (here taken as equivalent to rail in terms of emission) then the carbon emission from the rail journey as a whole will be the same as a line haul by rail of 36 miles (i.e. 25 + 7.5 x 1.5 = 36.25). It follows that the carbon emissions per passenger journey by car are likely to be less than half those where the main mode is rail -
i.e. 8.7 x 2/36 = 0.48.

Comment

The carbon comparisons presented by the rail industry and by the DfT always show rail with a significantly lower carbon emission than bus, coach or lorry. In contrast we show the reverse of that for express coach and equality for the lorry. The reason will lie in the vehicle occupancy and fuel consumptions assumed. For example, a bus on a city street may return only 5 miles per gallon and carry an average of only 9 passengers. Hence those buses yield less than one quarter the passenger-miles per gallon of an express coach returning10 miles per gallon with 20 passengers aboard. Similarly (a) a lorry suffering congestion may return perhaps 4-5 miles per gallon overall, rather than the 8 that we have used and (b) 70% of rail freight is bulk freight, leading to heavier loads than typical road freight.

Further, the official comparisons have little practical application since (a) there is little or no possibility of people in buses on city streets and cars or lorry freight transferring to trains or vice-versa and (b) the conditions that road vehicles suffer are not comparable to those enjoyed by trains. In contrast our comparisons are like for like. They are useful in that they show the reduction, or change, in emissions that paving the railways would enable.

Separately from that we note that 20% of electricity is from nuclear sources. Hence, the comparisons we, and others, present understate the environmental impact of rail by omitting (a) the effect of nuclear waste and (b) the substantial amounts of CO2 required to mine and refine uranium.

Summary procedures

We already have from Network Rail the electricity and fuel consumptions along with passenger and tonne-km for 2002/3, see Facts Sheet 5. Melanie Hobson of AEA Technology provided the emissions from diesel trains, Appendix 1. We calculated the emissions from electric traction by multiplying the emissions from all ( UK ) power stations by the ratio of electricity used by the trains to total electricity supplied. The CO2 emissions from power stations are available from special features Table 1 of the DTI's Energy Trends. Other emissions from power stations are from Defra's e-digest of air quality statistics.

The carbon, CO and NOx emissions from burning a litre of diesel in a road vehicle are calculated using data from the NAEI warehouse (AEA Technology) using a speed of 100 kph as input. The SOx emission is from Melanie Hobson of AEA Technology citing 0.072 gms of SO2 per Kg. That data, together with fuel economy and vehicle occupancy assumptions, enabled emissions per passenger or tonne-km to be calculated.

(We here note the fuel consumptions for artics operating at 100 kph estimated by the NAEI data is 4.3 miles per gallon. That is unrealistically low according to industry sources. E.g. www.tnn.co.uk/RoadTests

The following table summarises the results of calculations

Table 1. Emissions: Grams per passenger-km or tonne-km for the year 2002/3

* Carbon may be converted to CO2: by multiplying by 44/12 = 3.67. Also note the carbon is total carbon

Further and referring to rail – the annual carbon emissions from table 2 total 890,156 tonnes.

Electricity generation and emissions from power stations :

Table 5.2 of Energy Trends provides a total of 395,000 GWh in 2002 of which 9,182 was imported, 17,126 used by the power stations themselves plus 3,463 in pumped storage with 29,980 lost in transmission. Hence a control total for use in factoring emissions is (395,000 - 17,126 - 3,463 - 29,980) = 344,431 GWh . There is then the option, not here adopted, of factoring emissions up by 2.5% to take account of imports. The source for that is .: Energy Trends Table 5.2 www.dti.gov.uk/files/file17410.xls .

Total emissions from power stations in 2002/3 were:

Carbon: 44 million tonnes
see Energy Trends Special Topics Table 1 in www.dti.gov.uk/files/file27084.pdf

To access Defra Air Q uality T ables se e : http://www.defra.gov.uk/environment/statistics/airqual/alltables.htm

Rail

In Table 2 Passenger and tonne-km along with rail's fuel consumption are from Network Rail, see facts sheet 5, and the diesel emissions are from Appendix 1 provided by AEA Technology. The emissions due to electricity used in traction are calculated by multiplying the total emissions from all electricity generation cited above by the ratio of the electricity used to the total supply, namely the 343,431 GWh, also cited above. The emboldened data in the table was taken forward to Table 1

Table 2. Data and emissions for rail.

(a) typical calculation: Intercity: 44 x 1,000,000 x 591/343,341 = 75,718 tonnes
(b) typical calculation: Intercity: (75,718 + 142,546) x 1,000,000 /(12.9 x 1,000,000,000) = 16.92 gms

Road vehicles

Given the emissions per litre of diesel when burnt it a modern vehicle, plus fuel economy and occupancy data, it is a simple matter to calculate emissions per passenger or tonne-km. Here is the detail.

Item 3 within the NAEI warehouse http://www.naei.org.uk/data_warehouse.php provides data on fuel consumptions and emissions in grams per km for a range of vehicles and speeds. We have used 100 kph. However, as noted above , the fuel consumptions for artics appear suspect in that the system gives the fuel consumption for such a vehicle as 546 grams per km, equivalent to only 4.3 miles per gallon. In reality an artic will cruise at 8 miles per gallon. For that reason we have (a) used the NAEI warehouse data to calculate the emissions per gram burnt and (b) applied those values to our own estimates of fuel consumptions for vehicles cruising on railway alignments. The detail is summarised in Table 34 below. Data from the last 4 rows was taken forward to Table 1.

Table 3 Emissions in Gms/Kg, miles per gallon, and gms/passenger-km assuming Euro II

Typical calculation

Bus coach: carbon:
UK Gallons per passenger-mile = 1/10 x 20 = 1/200
Hence Kg diesel per km = Gallons per Litre, 4.54 x Specific Gravity diesel, 0.84 x Km/miles, 0.625/200
Hence carbon grams per km = 860 x 4.54 x 0.84 x 0.625/200 = 10.249

Table 4 cites the NAEI warehouse emissions, fuel consumptions and corresponding percentages of emissions to fuel. The values taken forward to Table 3 are emboldened. The rest are available for reference.

Separately from that Table 4 data shows lower fuel consumptions and higher carbon emissions as emissions standards for NOx, SOx and CO tighten. That is the penalty of both the higher standards and heavier vehicles (or at least heavier cars) due to safety requirements.

(In the absence of fuel consumptions beyond Euro II in the source we have set those at the Euro II levels).

Table 4 Emissions detail

Typical c alculation of MPG .

Invert grams per km, multiply by 1000 and be 0.84 , the specific gravity of diesel. That yi elds km per litre. Multi p ly by 4.54 a nd by 0.625 to convert to miles per gallon .

E .g. for th e fi r st row in the table : Miles per gallon = 840 x 4.54 x 0.625/4 3 .23 = 55.13 5 .

Appendix 1 Emissions in tonnes from the railway sector (diesel trains only)

Data provided by AEA Technology, May 2006.

Note:
Regional Trains include Network South East. We have divided those emissions between the two sectors according to the diesel consumptions for those sectors available to us for 1990.

It is the emboldened data for 2002 that has been taken forward to calculations. Note that the emissions for 2004 are substantially lower. That is because diesel traction is being phased out and implies a corresponding increase in electricity use. 

Also, the total carbon emission from rail in 2002 from above, namely 552,563 Kg is substantially higher than implied by the total diesel consumption of 530 million litres from Table 2 and provided to us by Network Rail.  Multiplying that by the specific gravity of 0.84 and by the carbon per Kg of 0.86kg yields 382,872 Kg. Hence either Network Rail’s numbers are light or AEAs are heavy.

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