this post was submitted on 06 Jan 2024
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Why highways are worse than city streets? Highway doesn't have traffic jams, frequent stops when you just burn fuel\electricity to move a little further. It's just supporting the momentum of a car. With more than one gear it's trivial.
Maybe I don't understand something about e-cars, but from my experience I have wasted like 30% less of fuel just driving on highways from city to city for the same distance I drove in town.
In traffic, the largest reduction of efficiency comes from accelerating and the braking. You use energy to start moving (proportional to m V^2) and then you dump that energy into heat in your brakes to stop. The second comes from idling where you use energy to keep the engine rotating. As others have mentioned, EVs use regenerative braking so a substantial portion of the energy used to slow and stop the car is used to recharge the battery. EVs have no need to keep an engine running so unless you’re running the a/c there are minimal demands on a stopped/idling EV.
On the highway, you have the internal friction in the drivetrain to overcome, the constant deformation of the tires, and - most importantly - wind resistance, which is proportional to cd x rho x V2.
Cd (drag) and rho (air density) are low, but that V (speed) squared means driving at 75mph incurs 25x the energy use as driving at 15 mph. An EV gets no sage harbor here - plowing through a fluid (air) is essentially the same work.
To give you a sense of numbers, my vehicle (F150) gets less than 10mpg the 5 miles to my local pool/gym. The speed limit is 25 mph but there are stop signs every block or two. Lots of braking loss. On back roads with gentle curves and a 45 mph limit I get close to 30 mpg. That’s the sweet spot between overcoming transmission friction and air resistance. On the highway at 60 mph I get 22-23 mpg. At 78-79 mph I get 19 mpg. These are all generally on flat stretches using the 6 min average on my dashboard.
(Sorry for the long post…I’m an engineer and mechanical efficiency and aerodynamics are my happy place)
So, in other words, the only things EVs are good at are things that public transit would be even better at.
Not quite. EVs can still do door to door transport, are faster portal to portal, and have a vastly more diverse infrastructure, including the ability to (at least in a limited extent) traverse areas without track or road infrastructure. Public transit is still better, especially for rail, in reducing energy losses due to wheel deformation, reduction of human fatigue and dependence on attentiveness, and in some cases station to station speed and net air resistance per passenger mile. Since this is technology instead of fuckcars, it seems reasonable not to circlejerk too much.