Focus on the environmental impact of domestic transport is intense, with public perception typically identifying public transport as better than private, both for health and the environment(1).
Department for Transport figures back this up, but don't factor in emissions generated by the transport method's overall infrastructure, which can more than double emissions generated by the vehicle's operation alone. What's more, many trips require multiple modes - plane and taxi, for example, or train and hire car.
So, what's the best way to travel once you compare the overall impact of real, on-the-ground journeys?
In 2009, UK car, light van and taxi emissions counted for 15% of the UK's CO2 output, with rail coming in at 0.37%2
. However, a complex American study carried out in the same year3
indicated that a transport method's lifecycle - vehicle production, maintenance, infrastructure construction, fuel production and delivery, for example - could add an extra 63% CO2 emissions to road journeys, and a surprising 155% to rail. With this factored in, and add a pinch of salt for the difference between American and British vehicles, the car/taxi/van CO2 contribution jumps to 24.9%, with rail still under 1% at 0.96%.
But how does this boil down when you look at emissions per journey?
Brits travelled a total of 680 billion kilometres by car, taxi or van in 2009, while we only travelled 61 billion kilometres by rail4
. That still works out as less than half the overall CO2 per passenger, per kilometre on train journeys in 2009, compared to passengers on the road - when you factor in the American "total infrastructure" study. On exhaust pipe emissions alone, one train p/km generates 77% less CO2 than one car p/km.
So it looks like rail is winning from an environmental perspective, but cars clearly remain more popular. There are dozens of reasons for this, from convenience to plain availability, with many journeys simply not possible by rail.
There must be a compromise, especially for long journeys. A fold-up bike/train combo might be an option for some intrepid commuters, but there's limited space in on commuter trains, and it certainly isn't practical if you're carrying much luggage, let alone travelling with kids, or anywhere far beyond the nearest railway station.
The best solution so far seems to be taking the train where you can, and using a hire car to fill in the detail at either end.
Even without the train aspect, hire car fleets are arguably more environmentally friendly than the average UK car. They're more likely to be new, with typically 12% lower exhaust CO2 emissions compared to cars UK-wide5
, and lower levels of other local pollutants, too. Compared to privately owned cars, they tend to be used more efficiently - hired out 70-80% of the time, and often with more passengers in them, reducing that emissions/passenger/kilometre ratio.
Let's compare the two methods - car only, and rail+hire - using a typical domestic UK journey for leisure purposes; London Paddington to the charming Cotswolds town of Broadway, with four passengers.
You can't get there directly by train. If you want to use public transport at all, you must travel by train to Moreton-in-Marsh, then jump in a car to finish the trip - bus services are scanty out here.
By car alone, using the AA Routefinder, that's 144.7km. The rail journey to Moreton is 147km, plus 15.4 once you're in the car. But even though the rail+hire journey is longer in total, it still emits less CO2 - whether you factor in the American study or not . And that's not even taking traffic jams into consideration.
This is, it must be admitted, not a peer reviewed scientific paper. These calculations have been made using data reported by the UK Department for Transport and the UK Transport Research Laboratory. However, they certainly point to a viable eco-friendly compromise - one that's well worth looking into.
1 http://www.dft.gov.uk/statistics/tables/att0206/ first accessed 24th July 2012
2 http://www.dft.gov.uk/statistics/tables/env0201/ first accessed 24th July 2012
3 http://iopscience.iop.org/1748-9326/4/2/024008/pdf/erl9_2_024008.pdf first accessed 24th July 2012
4 http://assets.dft.gov.uk/statistics/releases/transport-statistics-great-britain-2011/tsgb-2011-complete.pdf, "Passenger transport: by mode", first accessed 24th July 2012
report_vehicle_rental:_environmental_and_sustainability_implications.htm first accessed 24th July 2012
With US study: 144.7km x 4 people x 0.00021 tonnes of CO2 pp/km = 0.122 tonnes of CO2 pp/km
Without US study: 144.7km x 4 people x 0.00013 tonnes of CO2 pp/km = 0.075 tonnes of CO2 pp/km
Train + car:
with us (15.4km x 4 x 0.00021 = 0.013) + ( 147km x 4 x 0.00009 = 0.053) = 0.066 tonnes of CO2 pp/km
w/o us(15.4km x 4 x 0.00013 = 0.008) + (147km x 4 x 0.00003 = 0.018) = 0.026 tonnes of CO2 pp/km
So rail+car = 46% less than car (with US) or 65% less than car (w/o US)