Comment by Aurornis | Hacker News Reader

Comment by Aurornis | Hacker News Reader

Parent Full thread

> Honestly, there wouldn't be that much need for bollard is majority of cars would be city-car like the one in 4:39 min

A Smart car starts around 1500 lbs without driver. Something like a Smart fourtwo can be as much as 2300 lbs.

No person or bike is going to stand a chance against a vehicle weighing an order of magnitude more, even if they look visually smaller.

The idea that Smart car sized vehicles would remove the need for bollards is not realistic at all.

You also can’t judge vehicle safety by appearance. There are a lot of lightweight, small, low front end cars that actually have poor pedestrian crash ratings because the low front end takes people out at the knees. The Honda S2000 is a classic example.

A lot of the internet anti-car anger likes to idolize things like Smart Cars as solutions to everything, but the reality is that any time you have a vehicle weighing an order of magnitude more than a human capable of traveling at 40mph in a matter of seconds, humans don’t stand a chance against it in an impact. Smart cars are great for parking and fuel efficiency, but the idea that they would automatically solve pedestrian safety issues as well is just fantasy. Marginal improvement? Sure. Solution that removes the need for bollards? Definitely not.

A human isn't going to have much effect on the mass of a smart car, but something like a planter, another car, a curb, a tree, the front of a 7-elevn etc. is going to stand a much better chance of stopping a smart car than it is a 4,900 + lb. F-150 that carries its weight up high.

If there is a tree between me and a speeding car, I would much rather it be a Smart car than just about any other car.

I don't think I'd feel too safe no matter what. There are good odds that the smaller car is moving faster than the big clumsy pickup, and so the car is likely to have at least as much, and maybe more kinetic energy.

Also, bumpers on pickups are actually pretty low. Any normal bollard or concrete planter is going to be pretty effective. No pickup is going to drive over something like that.

Why are there good odds that a smaller car is traveling faster? Pickup trucks and SUVs don’t noticeably lag behind traffic or travel slowly in my experience.

The scenario I was discussing is when there isn’t a bollard but some other barrier specifically designed to stop a vehicle.

A higher center of gravity and larger wheels will certainly help get over many obstacles that would otherwise stop a smart car.

If you had to bet which car was more likely to be deflected by a curb strike and which would not, I have a hard time believing you would put your money on a truck vs a small car.

> but something like a planter, another car, a curb, a tree, the front of a 7-elevn etc. is going to stand a much better chance of stopping a smart car than it is a 4,900 + lb. F-150 that carries its weight up high.

This is another area where looks can be deceiving. Those large vehicles also have large frontal areas and large crumple zones to absorb impacts.

Those small smart cars have small frontal areas and relatively rigid frames because they can’t crumple on impact.

It’s not hard to imagine scenarios where a small, narrow smart car would literally slip between obstacles where a larger vehicle would get hung up on them. This is especially true for typical bollard spacing.

> If there is a tree between me and a speeding car, I would much rather it be a Smart car than just about any other car.

I think you’re overestimating the difference it would make. Like I said above, the smaller area of a smart car makes it less likely to actually catch the tree (by definition) and the relatively rigid frame isn’t doing much to dissipate the energy it’s carrying.

Looks can be deceiving. I know everyone wants to believe smart cars are super safe alternatives, but any of these thousand pound vehicles isn’t going to be good to go up against. The differences are more nuanced than your eyes would tell you.

Do you have any sources or reading about this?

I would love to see something more than conjecture about a VERY unintuitive idea.

Newton was pretty adamant that an object weighing 5k lbs (an F-150) would impart quite a bit more force than an object weighing 2k pounds (an economy car).

If all of the force is being imparted into a planter, a tree, or the front of a 7-eleven, I'm still inclined to believe that more force, higher off the ground, is going to matter a whole lot more than a few extra square feet. One way or another the energy is going somewhere, and there is A LOT more energy in a pickup truck.

Also, keep in mind, the crumple zone protects the passenger compartment, not the object being hit. The bumper of an f150 is right in front of a ladder frame to which several thousand pounds of iron machinery is bolted.

I'll still take the smaller, faster stopping, more maneuverable, less energetic battering ram.

Even if we assume smartcar--pedestrian collisions are just as dangerous for pedestrians as pickup--pedestrian collisions, a smartcar--smartcar collision is going to be a lot less dangerous for the occupants than a smartcar--pickup or pickup--pickup collision at equal speeds.

Not disagreeing with your overall point, but vehicle size and weight still contribute an awful lot to the >40000 vehicle fatalities in the US each year.

Statistically, the majority of pedestrian deaths each year occur on high speed roads, with cars doing 45-55 mph. The v^2 part of the equation is going to dominate. We should get average speed down in areas where pedestrians are, and take steps to ensure that pedestrians are nowhere near the places we allow cars to go highway speed.

About half of all pedestrian deaths are caused by drunk driving, so that's another relatively low hanging fruit we could aim for if we really had the political will to do so.

I used to be against speed limit like this, but when I realize it's MPH instead of KPH and starts converting, I realize that the speed is quite extreme from what I'm used to. My motorcycle-addled road already feels quite dangerous if the riders goes to 60 kph (<40 mph) and no car reach 50 mph. Now I understand some seemingly draconian suggestion that people here says to curb this behavior. People say that Asian roads are dangerous but our average speed is much lower to compensate.

But other comment suggesting to lower it to 20mph (or 10??) is egregious. It's standard for a pendulum to swing from an extreme to an extreme I guess.

I feel like any sane driver already drives 30 km/h (~20 mph) or under on residential streets. (Obviously higher-capacity roads are different.)

20mph on a residential street is perfectly reasonable. Urban roads on the other hand are usually more like 30-35mph where I live, which is also perfectly fine.

I guess this is using American convention where people are expected to go 1.2x or 1.3x the speed limit. Although funnily residential roads I know doesn't need speed limit for this, solely because of road quality.

No, it's in Europe and you're not "expected" to go over the limit at all.

If you want to step on it, leave the city. Most non-access roads in non-built-up areas are 50mph, and more for motorways. Some major urban thoroughfares are also 45mph.

I said "wouldn't be _THAT MUCH_ need for bollards". But I tend to lean towards less hostile spaces if possible.

Yes, colission with Smart would still be probably quite nasty but probably way less than with F-150.

Just for the kicks of it: https://www.carsized.com/en/cars/compare/smart-fortwo-2014-3...

In case of Ford it is like hitting vertical wall while in Smart case you have angle which limits impact surface.

(and last but not least: with city-cars (and not oversized bulky pseudo-suvs) you can actually see over the car, as they tend to be lower, to orient yourself better on the situation on the street)

Smart cars aren't that impressive mileage-wise. A regular Smart car gets ~40mpg Smart Fourtwo's get about 36mpg. A Kia Niro Hybrid gets >50mpg. A CR-V hybrid gets ~40mpg. Both while being much more car than any Smart car.

You'd think with the massive size compromises you'd get a lot better mileage tradeoff. Maybe they'll release a hybrid version and get some real impressive mileage.

Reply on news.ycombinator.com