Ever wanted to know precisely how great you are for taking the train instead of flying? Well now you can! The newest addition to the Loco2 booking tool estimates how much carbon you’ll save by travelling by train versus an equivalent flight.

When it comes to sustainable travel, going by train is much greener than flying. Not only is fuel used more efficiently, but electric trains can run on green electricity, reducing CO2 emissions even more. Celebrating low carbon travel is at the heart of what we do, and even our name is a nod to the fact that trains are “low CO2″ compared to planes.

The green travel debate

There are lots of fantastic green travel initiatives. For example, we love the Travel Foundation, whose mission statement, that holidays should be “good for local communities, the environment, holidaymakers and tourism businesses”, hits the nail on the head. Despite great projects like this, we often feel there’s something missing from the debate.

A lot of sustainable travel companies focus on carbon offsetting or “eco-accommodation” instead of where the majority of emissions come from – flights! We think that true green travel should look at the bigger picture, and admit that offsetting doesn’t really work (it’s a bit like paying someone else to be monogamous while you have an affair).

Most carbon calculators focus on the negatives; calculating a carbon footprint which can seem a little daunting. We wanted to do something different, so instead of telling you how much CO2 your train journey produces, ours displays the savings you’ll make by switching from a plane to the train. And if you want to put your travel habits in context, there are lots of easy-to-use carbon calculators out there, such as the Guardian’s quick carbon calculator or the UK Government Act on CO2 calculator (which is powered by AMEE).

How we calculate the carbon saving

To calculate the carbon saving, the first thing we do is estimate the distance between the departure and arrival points for the train and the plane.

For trains, we haven’t yet found reliable data to plot the exact routes, so we draw a straight line between each connecting station on our train maps. For example, for London-Barcelona we calculate the distance between London and Paris, and between Paris and Barcelona. The sum of the two legs gives us an estimate for the entire journey.

For planes we use a ‘great circle distance’ calculation (the algorithm we use is called the Haversine Formula). This takes into account the curvature of the earth and is a good way to approximate the distance between two points.

Once we have the two distances, we apply standard conversion factors. For planes, we use the short-haul international average factor of  0.09429 kg CO2 per km, and for trains the International rail (Eurostar) factor of 0.01502 kg CO2 per km. The difference between these two is your saving.

It’s only an estimate

Calculating carbon footprints can be tricky, and our estimates should be taken with a pinch of salt. For more accurate calculations we *should* consider:

• The model of train or plane, including fuel consumption
• For electric trains, the method of electricity generation (since most journeys booked on Loco2 are in France we use the French grid electricity factor)
• The exact distance travelled by train, including its bends and curves
• The exact plane route, plus time spent taxiing before take off and after landing
• Occupancy: the fuller the vehicle, the more people to share the CO2
• Class of travel: First Class uses more space and therefore more CO2