4 ms·

A hundred years? I feel like 90% of what happens is done because of election cycles and quarterly reports

londons_explore 3y ago
People build bridges today that are expected to still be standing in 100 years. They could have made it a bit weaker, not bothered with paint or inspection hatches, and saved a little money, and had it only last 25 years... The time-value of money says that any benefit 25+ years from now is almost worthless, so it probably wasn't worth spending anything on those things to make the bridge last longer. Yet in most cases we still tend to build it to last 100 years, despite the economist saying it isn't worth it.
- moffkalast 3y ago
  Probably not the best example since once a bridge is built you can immediately use it, the benefits don't only start rolling in after a 100 years. Making sure something lasts is correlated with natural disaster safety margins anyway so if it has to be built to survive near term extremes it'll generally also survive a while as a side effect. Older constructions also seemingly last longer through survivorship bias and the lack of computer modelling at the time meant that safety margins had to be higher. A better example are maybe tree avenues that take decades to grow into anything useful, or maybe long term river redirection projects or reactors. ITER's still in construction after 16 years. But there's just about nothing we do that would take more than a few decades to start showing returns.
- elliotto 3y ago
  I'm not sure what the rules are in the US but in Australia the infrastructure service life is set by regulation. It's not an economic / financial argument or even a benevolence / moral argument that causes this, it's a legal requirement. There are significant real world advantages of having a bridge last more than 25 years that are not reflected by a financial return on investment.
- ozim 3y ago
  I don’t think we really have most bridges built to last 100 years. What I see most is built to last 50 years and then usually it is stretched by patching/fixes or ignoring the issues as those will be passed on to whoever is in charge politically when a bridge finally fails.

People build bridges today that are expected to still be standing in 100 years. They could have made it a bit weaker, not bothered with paint or inspection hatches, and saved a little money, and had it only last 25 years... The time-value of money says that any benefit 25+ years from now is almost worthless, so it probably wasn't worth spending anything on those things to make the bridge last longer. Yet in most cases we still tend to build it to last 100 years, despite the economist saying it isn't worth it.

moffkalast 3y ago
Probably not the best example since once a bridge is built you can immediately use it, the benefits don't only start rolling in after a 100 years. Making sure something lasts is correlated with natural disaster safety margins anyway so if it has to be built to survive near term extremes it'll generally also survive a while as a side effect. Older constructions also seemingly last longer through survivorship bias and the lack of computer modelling at the time meant that safety margins had to be higher. A better example are maybe tree avenues that take decades to grow into anything useful, or maybe long term river redirection projects or reactors. ITER's still in construction after 16 years. But there's just about nothing we do that would take more than a few decades to start showing returns.
elliotto 3y ago
I'm not sure what the rules are in the US but in Australia the infrastructure service life is set by regulation. It's not an economic / financial argument or even a benevolence / moral argument that causes this, it's a legal requirement. There are significant real world advantages of having a bridge last more than 25 years that are not reflected by a financial return on investment.
ozim 3y ago
I don’t think we really have most bridges built to last 100 years. What I see most is built to last 50 years and then usually it is stretched by patching/fixes or ignoring the issues as those will be passed on to whoever is in charge politically when a bridge finally fails.