Also see Downs–Thomson paradox (https://en.wikipedia.org/wiki/Downs%E2%80%93Thomson_paradox) - improvements in a road network will not reduce traffic congestion, but rather can make it worse.
In either case it's often overstated, expanding the road network (especially intelligently) usually results in less congestion. It's just a poor investment compared to other means of transportation investment in large cities.
If you meant adding capacity to existing roads (by adding lanes) it certainly can drop congestion as well. Expanding roads blindly CAN also make congestion worse but that's a possible outcome not a guarantee.
The point of the original "paradox" is that if you want the least amount of road congestion by private vehicles the best investment is to grow public transport but many places dump more money into roads and lower the percentage of users using public transport because "roads are where the congestion is". Hence the paradox, increasing road spending increases road congestion (in places with existing public transport).
The point of the second paradox is there exist ways to add more paths to a network that result in less flow than the network had before regardless of other conditions like public transport being available. The paradox is NOT that adding additional capacity to a network ALWAYS or NORMALLY results in less flow. In fact most of the time it does help flow (marginally) it's just a poor investment compared to the same amount spent on public transport.
Sure. An increase in supply--or a change in its nature--can increase demand.
>Wouldn't that be a good thing, economically speaking?
Not necessarily, in my estimation.
Yes, because it means people can live in places they couldn't before, or could get to jobs they couldn't before. Of course, people who already used the road won't perceive these benefits; they are in the same situation as before.
The page speeds that either have or have not gotten slower are generally understood to be purely a phenomenon of larger/bloated pages -- not a result of constricted internet "pipes".
If the paradox applied to the internet, then what you'd be seeing is that if pages loaded twice as fast, people would visit twice as many pages. But that's not at all how it works.
It is in fact a similar phenomenon. The cars are the bytes that developers are stuffing into what they build. It's not people visiting twice as many pages, it's developers continuously expanding the size of what they can stuff into sites to fill the capabilities of servers, end user systems and bandwidth today.
Some of it is unnecessary byte expansion because they can get away with it. The Web was very slow when everyone was on a 56k modem as well. The network pipes were smaller, the servers were drastically weaker, the consumer systems were weaker, everything was obnoxiously slow. It sucked to wait five to ten seconds or more to load a very simple website in 1996. It sucked to watch little real media files and wait a long time to load a couple mb file.
Developers are expanding their byte footprint to fill the available limits of patience, and often going over that line, exactly as they always will.