Leonardo Da Vinci's self-propelled "car"
is not news to me.
Da Vinci's toy "car" may have run by coiled-springs,
but he narrowly missed an opportunity to develop
a useful power-source for self-propelled land-vehicles.

Leonardo Da Vinci knew about the potential power
of STEAM...Da Vinci's notes also contain drawings for a STEAM-CANNON.
It's not much of a stretch to go from a steam-cannon to a crude
piston & cylinder steam-engine with just enough horse-power
to power either a primitive self-propelled wagon [that could hit the
'fantastic' top-speed of maybe 4.0 mph; it would have been
a 'fantastic' top-speed for the year 1500]] or a paddlewheel boat....

Put it another way! Da Vinci would have had no problem figuring out how
James Watt's steam-engine worked.

What if?...What if?...that man from Tuscany had designed, invented
and actually built a functioning, useful steam-engine in [say] 1500?...

But then the ancient Romans ALSO knew about the potential power
of steam, and they also had pistons and cylinders not much different
from those used in the first 'crude' water-pumping steam-engine
built for English coal-mines in 1712.
What if? What if?...

Jacob