Beware unfinished bridges

America's response to covid seems like one example of this.

If I'm remembering correctly from Zvi's blog posts, he criticized the US's policy for being a sort of worst of both worlds middle ground. A strong, decisive requirement to enforce things like masking and distancing might have actually eradicated the virus and thus been worthwhile. But if you're not going to take an aggressive enough stance, you should just forget it: half-hearted mitigation policies don't do enough to "complete the bridge" and so aren't worth the economic and social costs.

It's not a perfect example. The "unfinished bridge" here provides positive value, not zero value. But I think the amount of positive value is low enough that it would be useful to round it down to zero. The important thing is that you get a big jump in value once you cross some threshold of progress.

I think a lot of philanthropic causes are probably in a similar boat.

When there are lots of small groups spread around making very marginal progress on a bunch of different goals, it's as if they're building a bunch of unfinished bridges. This too isn't a perfect example because the "unfinished bridges" provide some value, but like the covid example, I think the amount of value is small enough that we can just round it to zero.

On the other hand, when people get a little barbaric [LW · GW] and rally around a single cause, there might be enough concentration of force [LW · GW] to complete the bridge.

Perhaps more generally: The effectiveness of energy put into an action can easily be a non-linear function. Most gain in value may be achieved at a certain energy level, such that energy differences significantly below or above that level hardly change anything.

In some cases the function may even be non-monotonic, where spending some larger amount of energy is actually worse than spending some smaller amount.

This combines well with Robin Hanson's theory that signaling explains most public choice oddities.  Showing that we care about bike riders doesn't require that we actually make the city work for bike riders.  

Well, this is really just networking effects. Also why it's really hard to break out with your new hot dating app or social media website, no matter how much Tinder or Twitter suck. For your app to provide utility to users, it needs... users. Good luck breaking that stalemate.

Roads, or bike lanes, are a very literal network. Usefulness suddenly undergone a phase transition only when you hit the percolation point.

Sort of a tangent, but when I ride I technically fall into the "strong & fearless" group, but don't feel like it.

I'd much prefer protected bike infrastructure, but for a variety of reasons it's often unavailable. In those cases, at least in an urban setting, I generally prefer to ride in the lane with cars over using an unprotected bike lane. To me this is obvious:

• in the lane the cars will definitely see you
• if you ride far enough into the lane cars can't pass you by "squeezing by", getting dangerously close
• less likely to put yourself in precarious situations at intersections

Unprotected bike lanes seem like the worse possible option, and find it strange that anyone falls into the "enthused & confident" category.

Bike lanes don't only exist to get people from point A to point B. They also exist to provide an outlet for biking as a recreational activity. 

I would trust decisions based on empiric measurements of usage of the bike lanes a lot over your analysis when it comes to justifying decisions by cities. 

So, sure, there is a threshold effect in whether you get value from bike lanes on your complex journey from point A to point G.  But other people throughout the city have different threshold effects:

• Other people are starting and ending their trips from other points; some people are even starting and ending their trip entirely on Naito Parkway.
• People have a variety of different tolerances for how much they are willing to bike in streets, as you mention.
• Even people who don't like biking in streets often have some flexibility.  You say that you personally are flexible, "but for the sake of argument, let's just assume that there is no flexibility".  But in real life, even many people who absolutely refuse to bike in traffic might be happy to walk their bike on the sidewalk (or whatever) for a single block, in order to connect two long stretches of beautiful bike path.

When you add together a million different possible journeys across thousands of different people, each with their own threshold effects, the sum of the utility provided by each new bike lane probably ends up looking much more like a smooth continuum of incremental benefits per each new bike lane that is added to a city's network, with no killer threshold effects.  This is very different from a bridge, where indeed half a bridge is not useful to any portion of the city's residents.

Therefore, I don't think "if you're going to start building [a bike lane network], you better m ake sure you have plans to finish it".  Rather, I think adding random pieces of the network piecemeal (as random roads undergo construction work for other reasons, perhaps) is a totally reasonable thing for cities to do.

Another example of individual threshold effects adding up to continuous benefit from the provider's perspective:  suppose I only like listening to thrash-metal songs on Spotify.  Whenever Spotify adds a song from a genre I don't care for -- pop, classical, doom-metal, whatever -- it provides literally ZERO value to me!  There's a huge threshold effect, where I only care when spotify adds thrash-metal songs!  But of course, since everyone has different preferences, the overall effect of adding songs from Spotify's perspective is to provide an incremental benefit to the quality of their product each time they add a song.  (Disclaimer: I am not actually a thrash-metal fanatic.)

Well I understand that you are talking about how people in the interested but concerned group are affected by the "unfinished bridge", we should note that there are still 13% of people who would use an unprotected bike lane. 

Further, the unfinished bridge helps build up to addressing the network problem, with less investment than a protected bike lane, we can move from 7% of cyclists using the system to 13%. 

Finally, this is a chicken and egg sort of problem. People need to cycle to make the bike lanes worth it, but no one will start cycling without any bike lanes. If society deems more cyclists to be a social good, we need finished bridges, but unfinished bridges are still better than no bridges.