The argument that I usually hear against more lanes is induced demand, but when I looked at some of the data this problem was very overblown. Going from 2 -> 3 or 3 -> 4. This is quite different from increasing 5 lanes to 6 though, then I can imagine it becomes chaotic and other problems such as the ones mentioned start to dominate.
Well, the fixed parameter is people's tolerance for driving time. Everything else (including number of users) will scale up practically indefinitely.
So if you give people more capacity, they will use it until they're back to their trip time tolerance, which is roughly at the same level of congestion.
Price is an extremely effective means of restoring flow to a congested system. Usually, how this works out is that a toll is placed on, say, an existing bridge to finance a parallel or upgraded replacement, and then magically traffic tends to disappear to the point where the new span is no longer needed.
Of course, tolling untolled roads is extremely unpopular.
>Price is an extremely effective means of restoring flow to a congested system.
That's like saying famine is a great way of dealing with overpopulation.
You're fundamentally taking a small subgroup (the trips that are justified despite the increased cost) and saying "look how good things are for them" while completely ignoring everything not in that subgroup. By that same (asinine) logic the SF housing market is great for homeowners.
At best toll roads function as fuzzy rationing (and that isn't great either) where the masses only take the most critical trips.
No, because the limit isn't driving time, it is things they wany to do. Induced demand is people who can finally do something better. The only time you are right is when you are so far behind that people who used to stay home pick a second best thing because what they really want still isn't in their time tolerance.
Note that building roads is in general not the rigjt answer, build good transit so they don't drive is much cheaper in the long run.
Induced demand happens in all types of transportation, but cars are so space inefficient relative to other modes that it does not take a whole lot to get back to where you started, whereas the same cannot really be said of say a subway.
People are not finite. They change addresses, have kids, get different jobs, etc. The flows of people shift around over time, and the transportation infrastructure is one factor that influences those flow patterns.
I don't take issue with the concept of induced demand but when people trot it out like it's a bad thing and is a reason not to build something it makes me want to buy a bulldozer and a welder and pay them a house call.
Trips are a good thing. They're economic activity. They're people going to visit friends/family. Each trip is a case where the benefit outweighed the cost of the trip.
The really infuriating part is that 99.999% (yes, 5 9s) of people who complain about induced demand on roads talk about it like it's a good thing when the context is literally any other form of infrastructure. You can induce demand for parks and subways by carpet bombing a city with them too or making the existing ones more attractive. The concept isn't just for public infrastructure. All sorts of business can induce a lot of demand if you plop it down in the right spot where a lot of potential customers were letting the need go unfilled because the opportunity cost of the next existing best option was too high.
> Trips are a good thing. They're economic activity.
Spoken like a true capitalist. Not all "economic activity" is good.
Sitting in traffic driving to an out-of-town shopping centre to buy groceries because there are no local shops in walking distance may be economic activity, but I'd struggle to call these boring, wasteful trips I'm forced to make a good thing. More like an irritating waste of time and gas.
If people's local options didn't suck they wouldn't travel. Time isn't free, nobody gets more of it and people love convenience.
The fact that the local grocer has to compete with the out of town grocer may be derided by the whole foods crowd but it's a boon for the price sensitive masses.
If the local grocer doesn't exist then why? It's either going to boil down to the population density not supporting it or local regulatory oddities making the business economically non-viable.
You can model traffic as something resembling a network flow problem. You have many individual drivers choosing routes, often using a greedy algorithm without full awareness of traffic conditions. If you add more capacity somewhere, some drivers will start making different choices. That could make existing bottlenecks worse, reducing overall throughput.
On the other hand, if you have a good central traffic planner that gives everyone a route, adding more capacity will never reduce throughput. Some drivers may just get routes that are suboptimal from their perspective.
This is the expected outcome of any system where people make individual choices.
I meant educational degree. What educational degree covers traffic analysis as part of the curriculum. I think civil engineering comes close but i am not sure.
If you'd like to see similarly counterintuitive behavior in computer-land, check out Bélády's anomaly (increasing the number of pages in memory results in more page faults, not less for the FIFO page replacement strategy): https://en.wikipedia.org/wiki/B%C3%A9l%C3%A1dy%27s_anomaly
