induced demand and transit

[mindstalk]

So, there's induced demand, the observation since the 1930s that widening a congested road to fix congestion never works. It does do something: it increases bandwidth, allowing more drivers to crawl through congestion. But it doesn't increase speed. Because when demand is high, congestion is the only 'price' that discourages drivers from using the road. Lower the price, and more of them show up until it's high again.

People who learn of this sometimes ask how transit factors in, and I've always said, pessimistically, that it's the same: expanding transit allows more people to bypass congestion -- which is good! -- but won't solve the congestion. Any drivers who take the train will be replaced by more drivers. So the only way to reduce congestion is with actual congestion charges, charging people money to use the road and charging more until you have the levels you want.

But, despite my enthusiasms, I'm an American with American experiences, and I now think I was wrong. At least some of the time. You can watch this Not Just Bikes video or read Wikipedia about the Downs-Thomson paradox or read on:

Imagine that we start with congested roads, and add a subway system that is on average *faster* door to door than driving. As the video says, most people aren't mode bigots (I am! I hate being in cars) and will do whatever is faster (or some mix of faster and cheaper). So if driving is 40 minutes and transit is 25 minutes, lots of people will take the subway. And a good subway system doesn't slow down when heavily used, so it'll keep being 25 minutes even if unpleasantly crowded. Drivers leave the road... and *don't* get replaced, until congestion comes down so much that driving takes less than 25 minutes.

That's the "paradox": "the equilibrium speed of car traffic on a road network is determined by the average door-to-door speed of equivalent journeys taken by public transport." Or by other alternatives, such as bicycling in Amsterdam. If biking were faster than driving, and safe, would you drive most of the time? Probably not. Certainly the Dutch don't. The video guy has said elsewhere that Amsterdam traffic is fairly decent, and this would be why: driving is competing with good bicycling and transit systems, and there's no point to driving to the point that it takes more time than those.

So if you provide good, high-capacity, alternatives to drive, you can reduce congestion!

Now, is this practical? Downs says it's valid in

"regions in which the vast majority of peak-hour commuting is done on rapid transit systems with separate rights of way. Central London is an example, since in 2001 around 85 percent of all morning peak-period commuters into that area used public transport (including 77 percent on separate rights of way) and only 11 percent used private cars. When peak-hour travel equilibrium has been reached between the subway system and the major commuting roads, then the travel time required for any given trip is roughly equal on both modes."

Even for this American, it's hard to imagine such a fast and high capacity transit network. (I was not paying attention to what rush hour driving is like in Osaka.) And it's not like NYC or pre-congestion charge London traffic are/were good, though since NYC transit speeds aren't that high, that might not be a refutation. And of course there are complications: taxis, trucks, and through traffic might contribute traffic that isn't divertible by the alternatives. Conversely, high parking or gas costs could drive people to transit even when slower: what we'd really expect is that people would take the mode that has the lowest cost to them, where the travel cost is a function of time, money, aggravation (overcrowding, weather exposure, being stuck behind a wheel), need to carry things, and maybe more. And as an application of the Law of One Price, people should shuffle between the various modes until the modes have the same average cost.

And this is the problem being an American: we've gone in for cars so much, and scanted the alternative so much, that even with multi-hour rush hours, driving is typically still the fastest and lowest 'cost' mode of getting to work, or anything else. Especially when buses or bicycles get stuck in, or endangered by, cars -- no matter how bad things get, the car is still least bad. This is what killed off streetcars. Subways and bus lanes bypass traffic, as do Dutch (bike paths) or Japanese (wide sidewalks) bicycles.

But as a practical thing... taking a lane of road for bus lanes might actually improve congestion for the cars as well as the buses, by diverting drivers into the buses. If you run enough buses to absorb demand, then the driving speed should come to match the bus rapid transit speed.

Comments

[elusiveat]

I feel like there has to be more to it than just speed. In a lot of parts of the Boston Area, bicycling is already faster than driving, once you account for time required for parking, but people (and not just people with disabilities that keep them from biking) drive anyway. I don't think safety is really the issue either. Last time I saw statistics on bicycling, biking was safer per mile than driving, which means a lot safer overall.

[mindstalk]

I've never seen US stats where biking is safer. Of course it's regional, but biking on Boston streets hasn't sounded obviously safer. And it sure doesn't *feel* safe IMO.

[elusiveat]

I've done some poking around and I might be incorrect about the accidents per mile numbers, although it's a bit hard to tell because there seems to be a lot of focus on injuries and fatalities, which is a bit different. Automobiles have become safer for passengers over the years, largely due to technologies protecting riders in the event of a crash.

This webpage is old (from the late 1990s) but pulls together a number of different safety metrics, and puts bicycle travel in the U.S. at a bit over twice as fatal as driving on a per-mile basis: http://www.bellboycott.com/cached/www.kenkifer.com/bikepages/health/risks.htm. I think that's still a lot safer in terms of lived experience. Almost no one commutes 50 miles by bicycle on a daily basis. In terms of exposure hours, the same site puts bicycling at a bit over *half* as dangerous as driving. And it puts the fatality rate per population (population of bicyclists and population of car-riders) as *much* lower for bicycle rider than for motor vehicle passengers.

I agree that Boston streets can *feel* dangerous, and I do think it's important to make roads feel safe for bicyclists, but I also think it's important to separate the feeling of safety from actual safety. There is a strong cultural aura of danger around bicycling that I don't think is particularly founded on evidence, and reinforcing that narrative makes people even more reluctant to ride. I kind of cringe every time a non-bicyclist says "bike safe" because it reinforces this narrative.

I'm sure you're aware of the "shared space" model (https://en.wikipedia.org/wiki/Shared_space), which proposes that unmarked streets are safer for everyone precisely because they cause people to feel *less* safe and therefore result in higher levels of caution and of intentional communication among road users. In practice, the situation isn't really that clear-cut, and there are definite problems with that approach, but I do think it's an important exploration of the fact that actual safety and feelings of safety are not the same thing.

Overall, I do think that it's worthwhile to make streets feel safer for cyclists and pedestrians, simply because more people will walk and bicycle if it feels safer. That fact alone can also directly impact real safety because motorists become more skilled at sharing roads with bikes and pedestrians when there are more bikes and pedestrians out there.

But your original claim wasn't that people would bicycle more if biking *felt* safer, your claim was that people would bicycle more if it *were* safer (and faster), and I don't think there's evidence to support that view at all.

[elusiveat]

I think your suggestion on dedicated bus lanes reducing congestion is interesting. I do think that it's important, though, to do this carefully so that increased bus traffic doesn't contribute patterns of bicyclists needing to continually "leap-frog" buses, which isn't good for either the speed or safety of bicycling. Separated bike lanes up on the sidewalk might do the job, but I'm not sure.

[contrarianarchon]

"induced demand" or "we didn't do enough to fix the problem so the problem is only a little bit fixed"; there are a finite number of people with a finite desire to go places so *eventually* you'll exhaust the people who were holding off from the awful commute but who will do a slightly less awful commute and like maybe that's not viable but this doesn't seem like a special case of supply and demand? Public transport is only solving this problem by being higher-capacity and therefore eating demand more efficiently. (Which, yes, public transport good.)