Which is fuel efficient, roadways transport vs waterways transport?

Question

Which will be more efficient in term of fuel price:

1. Transport via roadways, say truck or motor vehicle.
2. Transport via waterways, say via ship or motor boat.

Assumptions:

Same caliber engines (same power) are used in either ways. Fuel is same. The distance is same for both water ways and land ways. The aim is to find which would be needing lesser Fuel, if both are travelling with same speed:

Considering real life scenarios, like considering friction on land and turbulence in water.

Answer 1

Unfortunately, this question shares multiple similarties to the phrase "How long is a fish?"; meaning that the answer is very dependent on the assumptions, limitations and scope of your question. I will for this reason not aim to give you an explicit answer to your question, but rather inspire you to narrow it down and hence hopefully bringing you closer to what you are seeking.

• In your question, you mention details such as "turbulence" and "friction", suggesting to me that you are thinking of a hypothetical race between a car and a vessel over an equal distance. However, this introduces follow-up questions such as; what tires are the car using, what is the hull shape of the vessel or what is the weather at the time of this race?
• You also mention in your question that "same caliber engines are used", but in what regard, seeing as marine engines are not built to be used in the same way as car engines? E.g., should they have the same power output, the same fuel efficiency, or...? Should they both use the same type of fuel?
• What are you transporting, and why are you transporting it? Is the objective to get from $A$ to $B$ as fast as possible, or does it matter how comfortable the journey is? Are you transporting people, bananas, oil or simply yourself?
• ...

The list goes on and on, but hopefully these initial thoughts will encourage you to come up with more follow-up questions yourself.

When you have a clear understanding of what you really are asking, then you may start searching for the correct answers. For example:

• The European Environment Agency stated in 2020 that "Rail is the most energy-efficient mode of passenger transport [...] For freight transport, trucks consume significantly more energy per tonne-km than rail or ship transport"
• The Intergovernmental Panel on Climate Change of 2018 gives in Fig. 8.6 (see p. 610) an indication of "Typical ranges of direct CO2 emissions per passenger kilometre and per tonne-kilometre for freight, for the main transport modes when fuelled by fossil fuels including thermal electricity generation for rail."

Best of luck!

Answer 2

From the European Environment Agency - Rail and Waterborne cited in Jon Arnt's answer:

Chart shows gm CO2 / tonne km.

For my preceived interpretation of the question. The best way to ship cargo on land would be rail at 24 gm, then Inland WaterWays at 33gm, which are significantly better than heavy goods vehicles at 137gm.

But for shear mass of cargo the best way is via ships. 7gm would correspond to container ships.

From EEDI Explained

Even generic cargo vessels >400 gt produce less than 30 gm CO2 / tonne nautical mi. 1 nautical mi = 1.852 kms. Larger the vessel the less polution is produced per tonne of cargo.

Carbon Calculator Emission Factors from CN (Canadian National) railway report: 2.5-6 gm CO2e/tonne-km for bulk carriers; 8.3 gm CO2e/tonne-km for containerships; 12.1 gm CO2e/tonne-km for rail; and 63.4 gm CO2e/tonne-km for trucks.

If there is a water path, cargo transport consumes significantly less fuel than a road path.