We make cost-benefit tradeoffs on regulation all the time. The EPA uses a value of 7.2 million dollars (2006 dollars) for a life saved [1]: So if adding guard

We make cost-benefit tradeoffs on regulation all the time. The EPA uses a value of 7.2 million dollars (2006 dollars) for a life saved [1]: So if adding guards to trucks would save, say, 50% of the lives lost in underride crashes, that would give you a benefit of 200 * 7.2 million * (inflation adjustment). You'd also want to add in the benefits of reduced non-fatal injuries. But for the purposes of argument, let's imagine the benefits of imposing this regulation are roughly 1 billion dollars a year. All the costs you're talking about are measurable. It's not that hard to then figure out the costs of imposing the regulation and see whether the benefits outweigh the costs. And this is one of the simpler cases where there aren't complicating factors like privacy or liberty at stake. You're not requiring truck drivers or trucking companies to change their behaviour. All you're asking them to do is fit a couple of extra pieces of steel to their trailers. [1] https://www.epa.gov/environmental-economics/mortality-risk-valuation#whatisvsl https://www.epa.gov/environmental-economics/mortality-risk-v...