Perhaps a library vs a commercial book store might have worked as a better analogy. The queue theory part of it I think breaks down a lot. Induced demand is not only about queue theory, but also choosing between options.
In short though, induced demand is somewhat simple. If it takes 10 minutes to drive and 30 minutes to take a bus, then I drive. If it takes 30 minutes to drive and 10 minutes to take a bus, then I take the bus. Eventually enough people choose to drive, or take a bus, that that mode becomes congested/inconvenient enough that people start making other choices. In other words, there are some people who avoid highways during rush hour because the traffic jams are bad. If the highway is widened, then they would join the rush hour once again and be part of the traffic jams. Induced demand is about taking away the reason why people avoid something, and thereby doing so they change their behavior to start doing that thing.
Yea but really the choice here is "go somewhere vs stay home", not "car vs bus". Highway expansion leads to more people travelling because bus service is non existent in the vast majority of the country. Of course some people need to go where theyre going, but on the margins more people will go to the city or what not if traffic is lower.
Good points. Yeah, as the cost of travel goes up, people make various decisions: bite-the-bullet, find alternatives, delay, consolidate, and/or go without. As the cost decreases, the incentives to find alternatives, delay or consolidate trips goes down (which means roads are then used for less important reasons and less efficiently - why go to the grocery store once a week if you can go every day in half the travel time?)
I would agree, at some point when all alternatives are equally unattractive (or non-existent), then going without is a more attractive option.
Though, the "consolidate" option is a big one to consider. Rather than going to the city every day, perhaps people could do so every other day for the same benefit. If traffic is bad, then people will go less often (frequency of travel is a function of cost). Thus, in some cases, highway expansion is filled by people that want to go to the grocery store every day rather than going once a week. Meanwhile, those that commute to work, are still going to do so because they have to. If the commute gets too bad, then some people will decide to move.
On the other side of the spectrum, at some point there are so many people that want to go into the city every day - you can't do it with single occupancy vehicles and roads. It's a scaling problem. For example, someone did an analysis of parking decks in Seattle and whether there were not enough of them. They found if there were all filled and everyone then tried to leave - it would take 2 days for all the vehicles to exit the city.
In short though, induced demand is somewhat simple. If it takes 10 minutes to drive and 30 minutes to take a bus, then I drive. If it takes 30 minutes to drive and 10 minutes to take a bus, then I take the bus. Eventually enough people choose to drive, or take a bus, that that mode becomes congested/inconvenient enough that people start making other choices. In other words, there are some people who avoid highways during rush hour because the traffic jams are bad. If the highway is widened, then they would join the rush hour once again and be part of the traffic jams. Induced demand is about taking away the reason why people avoid something, and thereby doing so they change their behavior to start doing that thing.