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Comment by giantg2 | Hacker News Reader

"That’s countered, or partially, with the ability to not get in an accident being higher due to lower mass though."

I'm not sure that's really true. There are tons of variables that can affect performance. Like tire size/type, center of gravity, brakes, etc.

Driver attention, knowledge, and skill are much more important. I believe 90% of driving is mental and the majority of accidents are due to poor choices, which seem from things like not understanding vehicle capability and limits, not knowing the law, or not paying attention.

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It's kind of useless to blame drivers as there is little that can be done to resolve that problem. It would be much better to take a long hard look at road layouts. Engineer them for safety rather than traffic throughput.

"It's kind of useless to blame drivers as there is little that can be done to resolve that problem."

What makes you say that? Most accidents are driver error. The stats show that CDL drivers, who undergo more stringent testing, have a lower accident rate than others.

"Engineer them for safety rather than traffic throughput."

What would that look like? Even if you replace stop signs with roundabouts, the drivers still need knowledge of how to safely navigate them. If you're talking about reducing speed (technically the most effect if enforced systematically), how do we ensure enforcement?

Roads in the US are too straight and too wide to force drivers to be more deliberate in how they drive. They should have curves, speed bumps, etc. In general anything to force drivers to drive slower around pedestrians, and to reduce the number of times traffic streams cross each other perpendicularly.

"Roads in the US are too straight and too wide to force drivers to be more deliberate in how they drive."

I guess it depends. Most pedestrians are in cities or towns. The roads there may be straight, but not necessarily wide.

I'm also not sure how a road being straight and wide is a negative. Making them more narrow and winding is arguably less safe. Even if people reduce their speed, you present new issues of reduced line of sight, decreasing available reaction time. You also have reduced performance (braking on a turn vs straight).

Many areas do have some speed bumps. Mostly these are residential or near crosswalks.

It's not about making the roads more narrow or winding per se. It's about deliberately slowing cars down where they need to, through the road design. See this video for example: https://youtu.be/bglWCuCMSWc

Besides that, roads in the US are generally poorly classified. They're often trying to both function as both high throughput roads and destination serving streets. Such hybrid roads are known as "stroads" and they're bad for everyone involved. Stroads are bad for moving cars fast due to the many conflict points (driveways, intersections, etc.) that force drivers to constantly slow down. They are also bad at serving destinations because the many conflict points make stroads very dangerous, especially if you're not in a car. See this video for example: https://youtu.be/ORzNZUeUHAM

> In general anything to force drivers to drive slower

But never, ever force the handful of car manufacturers to electronically limit the top speed of their products?

Note: for the top-end German marques, this is just a configuration file change: they are already limited to 250km/h.

It depends on how that limiting will work. Ideally you still want relatively fast speeds on interstate type roads while much lower speeds on city streets. So it's not as simple as using the existing limiting feature and dropping it to 20mph (unless we want that to be the max speed everywhere). We would need a different, flexible framework.

Engineering for safety has been known since the industrial revolution brought heavy objects and assembly lines to the workplace and greatly increased the monetary benefit of avoiding accidents. Nobody wants to stop a whole line because someone got turned into a pancake.

The answer is basically to segregate traffic by speed, tightly control the interactions between different speeds of traffic and to generally have lighter traffic yield to heavier traffic. This is pretty much standard in every industrial workplace worldwide at this point. Look at what's going on on the tarmac next time you go to the airport.

Of course nobody wants to push for this in 2021 because it conflicts with a lot of the priors and ancillary goals that are floating around the ideological camp that most of the people who care strongly about traffic safety come from.

Look at the stopping distances, it's affected by mass F = ma here. The a part is affected by the quality of the tires/breaks/suspension... but that's getting into specifics that don't really fit the generality of the fleet of vehicles getting larger and heavier and their variety in qualities will more time to avoid an accident that they may not have.

I've never seen stopping distance noted that way. Looks more like force?

If you aren't changing other characteristics, then yes increasing mass will increase stopping distance. The problem with this assumption is that things like friction coefficient usually change when you are changing mass (tire size is an obvious one).

Most new vehicles stop 60-0 between 120-140 feet. There are heavier vehicles that stop shorter than lighter vehicles. I'm just saying it's not always that vehicles are heavy. The primary variable here (in applied stopping distance) is speed due to the simple fact that reaction time is the same and you are covering distance during that lag, plus velocity is an exponential effect.

Here's a good resource.

https://byjus.com/stopping-distance-formula/

Heavier car doesn’t mean it can’t stop well.

If the larger car also has a larger tire contact patch and larger brakes, it can stop just as fast as the smaller vehicle. This shown by many performance SUVs and various other vehicles that weigh in 5000lb+ but somehow come to a stop about as fast as their 3000lb counterparts. Consider the Tesla model s plaid - it has a super fast acceleration rate yet is also stupid heavy. If it can accelerate super fast - it can also stop super fast because the tires work well in either direction.

I’ve watched enough brake tests of cars to see this pan out. It’s all about the tires and brakes. Weight doesn’t matter that much when the manufacturer accounts for it.

Larger vehicles have larger blind spots too

Not really. It depends on the mirror size and geometry. Not to mention many are starting to use an array of video cameras.

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