Are there any objective resources to estimate the ecological impact of various travel alternatives? Sites like Bahn.de offer to calculate it, but they obviously favour trains. I've asked a question on ferries on Travel SE, but didn't get a complete answer taking everything into account. For electrical trains it obviously depends on the mode the electricity is produced. Are there any canonical resources to decide about the trade-off between ecology and other factors when planning travel?
Long question, short answer: No.
There is nothing like an universal database on carbon footprints or similar. Of course there are a lot of websites which allow you to calculate the impact of - for example - travelling by plane or by car. But the actual calculation of such values is very complex and always comes along with a lot of research.
You mentioned the example of trains (Deutsche Bahn). Let's dig into it. What do we need to know for an objective estimation of your ecological impact?
- Model and size of train (ICE, IC, EC, RE, RB, S-Bahn, Tram, ...)
- Type of energy used (diesel, electricity, ...)
- Quantity of energy used
- Average speed, number of stops
- Number of passengers (occupancy)
With these accurate numbers you could calculate your ecological impact (carbon footprint) for traveling by train. I doubt that the Deutsche Bahn for instance is able to provide you with all these data. And even if they could, it's getting more complex. For example - if a train uses electricity - how do you know how the electricity was produced? It's a huge difference on the ecological impact if the train is powered by coal power plants or by renewable energy sources.
All you get is always some vague estimations. Let's have a look at flights. This is a very hot topic and a lot of sites on the internet offer some sort of calculators. Let's compare some.
One-way-flight Berlin (TXL) to Tel Aviv (TLV) - ca. 3,000km
- Carbon Footprint: 280kg CO2
- Terra Pass: 315kg CO2
- Carbon Neutral: 340kg CO2
- Travel Nav: 372kg CO2
- Atmosfair: 820kg CO2
The numbers above already tell you a lot about the "objective" nature of this issue.
Have a look at this one. This one allows you to adjust more parameters, for example type of plane and overall occupancy of the plane. Maybe a better resource. But still no full objective resource to estimate your travel impacts.
Well, I hope this is enough to answer your question and explained why I said "No" in the beginning. Calculating carbon footprints takes a lot of time for research or else you will only get very rough - sometimes unusable - estimates.
While this doesn't fully answer the question in terms of ecological impact, David MacKay provides a good chart of the energy use of various modes of transport, here.
I'll extract some figures from it (they're approximate, from me reading off the vertical axis). They refer to typical occupancy unless otherwise stated.
Note that, as pointed out by a commenter here, the first two figures are far too high - this may be a problem with reading off the very bottom of a linear y-axis scale. The others should be considered as approximate (but useful) estimates, rather than accurate results.
- Cycling: 2 kWh per 100 passenger km
- Walking: 4 kWh per 100 passenger km
- Tram: 10 kWh per 100 passenger km
- Electric train: 15 kWh per 100 passenger km (2 if full)
- Bus: 31 kWh per 100 passenger km (6 if full)
- Turboprop aircraft (full): 39 kWh per 100 passenger km
- Boeing 747: 52 kWh per 100 passenger km (42 if full)
- Car (single occupant): 80 kWh per 100 passenger km (20 if full)
- Range Rover: 112 kWh per 100 passenger km
- Helicopter or private jet: 150 kWh per 100 passenger km
Yes, there are such databases. These are Lifecycle Cost Assessment (LCA) databases.
They are very difficult and expensive to build, and expensive to maintain. And they exist. You'll need to do a web search for LCA database and your region, but they are out there.
The EU has several, for different purposes. Here's the LCA database from the EU Joint Research Centre. And this is a US one from NREL.
Note that it's rather difficult for air travel, because of the high uncertainties around the multipliers that should be applied to aviation emissions.
And for public transport generally, there's the rather vexing question of whether you should use short-run marginal cost, or long-run average cost. If it's a journey you are going to make frequently, then it's definitely average cost. If it's a one-off trip, and the provider has historically shown very few changes in supply in response to changes in demand, then maybe, just maybe, short-run marginal cost is relevant (but there are plenty of experts who'd disagree with me on that point, so take it with a large pinch of salt).