“The bicycle is the most efficient machine ever created for converting human energy into motion.” — Vaclav Smil
Every mode of transport has a measurable energy cost — the amount of energy required to move one person (or one kilogram of cargo) one kilometer. Comparing these numbers reveals a world that is very different from what intuition might suggest.
Smil’s energy efficiency rankings for passenger transport (in megajoules per passenger-kilometer):
The bicycle is approximately 50 times more energy-efficient than a single-occupant car. A fully loaded train is roughly 10 times more efficient than the average car. These ratios have profound implications for urban planning, climate policy, and the future of transport.
The global passenger car fleet now exceeds 1.2 billion vehicles, most of which are occupied by a single person for most of their trips. The average car weighs about 1,500 kg to transport an 80 kg person — a weight ratio of nearly 20:1. This is spectacularly inefficient by any engineering standard.
Electric vehicles improve the situation significantly by using energy more efficiently (electric motors convert 85-90% of energy to motion vs. 25-40% for gasoline engines) and by enabling the use of renewable electricity. But an electric SUV carrying one person is still dramatically less efficient than a bus, a train, or a bicycle.
Commercial aviation is one of the great engineering achievements of the 20th century. It has also been one of the fastest-growing sources of greenhouse gas emissions.
Between 2000 and 2019 (pre-pandemic), global air passenger numbers grew from approximately 1.7 billion to 4.5 billion per year — nearly tripling in 20 years. Aviation fuel consumption grew proportionally, making aviation roughly 2-3% of global CO2 emissions, and potentially 5-8% of total climate forcing when the warming effects of contrails and high-altitude water vapor are included.
Modern aircraft are dramatically more fuel-efficient than their predecessors. A Boeing 787 uses about half the fuel per seat-mile of the 707 it effectively replaced. Yet total aviation emissions have grown because the number of flights has grown even faster.
This is the Jevons Paradox operating at altitude: making aviation more efficient and more affordable has dramatically increased its use, more than offsetting the efficiency gains. The same dynamic has played out with automobiles, air conditioning, and computing.
There is no renewable fuel for aviation at commercial scale. Green hydrogen and synthetic aviation fuels exist in demonstration projects but are nowhere near the volume, cost, or maturity needed to decarbonize global aviation.
The global shipping fleet — container ships, bulk carriers, tankers — moves approximately 90% of international trade by volume. It is also one of the most energy-efficient forms of transport that exists.
A modern container ship carrying 20,000 TEU (twenty-foot equivalent units) at sea can move approximately:
The shipping container itself is perhaps the most underappreciated innovation of the 20th century. Standardizing cargo containers reduced port handling costs by approximately 90%, enabling the global supply chains that underpin modern manufacturing and retail.
Electric vehicles (EVs) represent a genuine improvement in transport efficiency and emissions — when powered by clean electricity. The numbers:
But EVs are not a complete solution: they still require enormous material resources (lithium, cobalt, nickel, copper), still create urban congestion, and still consume far more energy than mass transit per passenger-km.
If you designed a city from scratch to minimize energy use in transport, what would it look like? What does that tell you about the design choices embedded in the cities most people actually live in?