There are the laws of men, and the laws of nature. The latter cannot be broken. Dura lex, sed lex! At human scale, a few parameters dominate almost everything.

I - Mass matters everywhere

Weight drives almost everything: the resources needed to build a vehicle, the energy required for every acceleration, climb, or stop.
It increases rolling resistance, amplifies non-exhaust pollution, and multiplies the energy involved in crashes.

Reducing mass is one of the most effective ways to reduce environmental and safety impact across the system.
Higher mass requires heavier tires, often with worse rolling resistance and more particle generation, which compounds the inefficiency.

II -Speed is expensive

Aerodynamic drag grows with the square of speed, and the power required to overcome it grows with the cube. Some automakers historically ignored aerodynamics, hoping to brute-force physics with bigger engines. As Enzo Ferrari famously quipped:

“Aerodynamics are for people who can’t build engines.”

We can now gently remind Signor Ferrari that drag grows with the square of speed, engine power grows linearly at best, and thus, horsepower cannot escape air resistance. Shape and frontal area matters more.

III - Aerodynamics matter sooner than intuition suggests

At 20–30 km/h, drag already dominates rolling resistance.
Frontal area, flow separation, and shape are just as important as drivetrain efficiency.
Lightweight, slender designs reduce energy use before even touching the question of energy storage.

IV - Powertrain efficiency

Thermal engines are inherently limited: rarely above 40% at their single best operating point, and closer to 20% averaged over a real drive cycle.
Electric motors can exceed 80% efficiency, dramatically reducing the energy cost per kilometre. But as we saw with EVs, powertrain efficiency alone does not solve the issue. The embodied energy of a now heavier and more resource-intensive vehicle cancels out a significant share of the benefit.

V - Safety

Imagine driving a tank: you may feel invincible inside, but everyone around you is in danger.
A heavier car may protect its occupants, but collisions with lighter vehicles or users transfer enormous energy.
If you need an illustration of the phenomenon, click here.

Designing for safety is therefore an ethical as well as technical problem:
we cannot optimize only for occupants without considering others.

VI - Range and energy storage

Batteries are not perfect, they are like chemotherapy: not harmless, but necessary in some context.
The “poison” is proportional to how much you carry. Massive batteries increase critical-mineral extraction, weight penalties, and inefficiency.

Range should be treated realistically. Most daily trips are 20 to 50 km.
We can design batteries for that reality, smaller, lighter, more repairable, because our vehicle efficiency drastically reduces energy needs.

Furthermore, the removal of conflict minerals from the equationn like cobalt can also help with the human rights aspect. Such chemistry are commercialy available aldready like Lithium Iron Phosphate (LFP).

Other storage ideas deserve exploration too, such as compressed air or other clever way of storing the required energy.

“Newton’s third law – the only way humans have ever figured out of getting somewhere is to leave something behind.” - TARS, Interstellar Whether it’s a horse on a military campaign or a spaceship in orbit, the further one wants to go, the more fuel or food must be carried, which in turn increases consumption to carry it in the first place. It’s not rocket science… though in rocketry, it’s formalized as the Tsiolkovsky rocket equation.

V - compound effect

This plot illustrates how energy consumption varies with speed across a range of vehicles. Modern petrol cars, like a typical hatchback, and historical models, such as the Citroën 2CV, show high energy use at even moderate speeds. In the decades between the 2CV and the modern petrol car, little to no progress was made in efficiency terms. Electric cars, such as a Tesla Model 3 or a Prius in electric mode, achieve lower energy per kilometer, but the gains are relatively modest, on the order of 3–5 times. Light vehicles, on the other hand — like the CityEL or the Twike, both designed almost 50 years ago — sit far below conventional and electric cars in energy use, especially at urban speeds (20–50 km/h). This shows that efficiency is not a matter of technology but of thoughtful design. Trains also show strong efficiency at higher speeds, thanks to low rolling resistance and to aerodynamic drag being shared across a very large number of passengers, though this varies wildly with train occupancy.

This plot highlights a fundamental insight: vehicle mass and aerodynamics dominate energy consumption, and lighter, streamlined designs achieve massive efficiency gains before even considering the type of powertrain. It emphasizes why reducing weight and frontal area is critical for sustainable mobility, particularly for city travel where conventional cars are extremely overpowered for the task.

If you want a more in-depth overview, the first chapters of this document might interest you

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