And here is her brother with a car.

She is asking more highway questions.

She beams at him. "Hello! Thank you for shuttling us resources! I'm Maitimë, this is Fëanáre, we're so excited to meet you."

She'll ask car questions now.

"Wow, Bella wasn't kidding about the quick language learning thing. Hi. I'm Alex. ...Uh, this is a Ford, that's all I know."

Isabella laughs and hugs him and hops in the car and answers car questions.

What's the range on a car, what materials go into cars, what's the per-capita car density -

Cars can go more or less as far as they are driven with regular stops for fuel every few hundred miles. Gas stations like that one over there make it easier. Car bodies are made of steel mostly, the dashboard is plastic the tires are rubber the windows are glass the upholstery is fake leather. Most adults in the United States have a car but it has higher car ownership rates than most countries.

How much of that infrastructure is necessary for cars to be a good method of transit - are they even a good one or just a local optimum -

They're not that great; what they are is a compromise between a bunch of desiderata. Trains and planes are faster but they suck at last-mile problems because they're only used when many people want to make the same trip (and planes require particularly specialized training to operate; she's not sure how much that's true of trains), buses have many of those problems and are also slow, bicycles are safe and autonomous but slow and bad for hauling things and exposed to weather, motorcycles are really dangerous and not much better at hauling or weather but they're as fast as cars (better, if you lanesplit in traffic). You kind of need fuel stations to use cars for long distance trips but you could also just put extra gas in the trunk.

So if you were a dictator and starting from scratch -

If you're a dictator and starting from scratch you probably want subways, way more densely stationed than most cities (not starting from scratch) can manage so you never have to walk more than a block or two, bullet trains between cities, and then you want some system for getting inconvenient-to-haul objects to places - streets wide enough that they can accommodate trucks even if they normally don't would suffice if the need for that isn't constant.

Nod. "Elves might not mind transit being slow as much, but that's good to have in mind for city planning."

"Time spent on trains or whatever is still an opportunity cost even if it's not also really annoying."

"Now that there are mortals around, I guess. When everything'll last forever opportunity cost is less of a pressure."

"I suppose."

Road signs! The sky! The sun!

"Wait, you don't have a sun?"

"I mentioned they don't have a sun. They have magic trees instead of a sun."

"Must not have been paying attention. Is there some way having magic trees instead of a sun isn't really stupid?"

"Well, having your light source be a giant on-fire ball of gas eighty million miles away doesn't seem like the most efficient lighting solution, but there's something to be said for not requiring any magic? I'm working on gems that output arbitrary light, personally. Then I could put them eighty million miles away if that seemed the thing to do or I could have them closer if there turns out to be no good reason to have them so far off."

"If the sun were closer it would be too hot."

"Arbitrary light. I can have it output less if it's useful to have closer."

"If you just keep making something that can do sun stuff closer and smaller then eventually you just kinda have a lightbulb, don't you?"

"Yes! Or, really, whatever on the sun-lightbulb spectrum is most convenient for lighting a nation."