[revelation]

Sure, lets do all of that. But there is plenty of low-hanging fruit. Maximum of 20 mph everywhere you have pedestrians, certainly in any city or city center - the simple reasoning being that higher speed only reduces time to travel some distance linearly, but the forces at work in a potential collision increase quadratically. So this is a complete no-brainer tradeoff that is directly reflected in survival rates for pedestrians in ped-car crashes:

http://www.streetsblog.org/wp-content/uploads/2008/11_10/Fat...

(There need to be legal repercussions regardless. If you are involved in a collision as a car driver, you can not be allowed to be driving again the very next day, regardless of fault. People that operate multi-ton machinery producing enough kW to provide power for a whole block take on a massive gamble at the cost of other people, and so that in and of itself needs to be remedied legally.)

[freehunter]

I think the premise of the 20mph speed limit is good, but the way car transmissions are geared, doing a sustained slow speed could actually be dangerous as well. Doing 15mph through the parking lot at my office means I'm feathering the throttle quite a bit, and paying close attention to my speedometer and less attention to the things in front of me. I've never driven a car that "wants" to do 15mph or 20mph. I can't just keep the throttle at one position and stay at 20mph, the pedal, the foot controlling it, and the sense of speed related by the brain just aren't designed for fine adjustments.

The point being, I believe that setting low and strict speed limits could be counter productive and could lead to drivers being more distracted and less prepared to stop. If my hunch is right, there would be an increase in car-pedestrian accidents at exactly 20mph, and fewer at 10mph or below due to people being less likely to get their foot on the brake because of the effort required to keep the car moving at 20mph and watching the speedometer.

I've actually hit a pedestrian once. My light turned green as the person stepped into the crosswalk, and I hit them less than a second after I was stopped at 0mph. The pedestrian and the car were both fine with no injuries. Perhaps rather than dropping the city speed limit from the 25mph it already is down to 20mph, we should be focusing on getting pedestrians to cross in locations where cars are naturally going very slowly to begin with. I don't want to shift the blame of an accident from the perpetrator to the victim, but for pedestrian safety, crossing at a light (and following crosswalk signals) is worlds safer because the cars there will already be either stopped or going very slowly.

[sp332]

This sounds like an argument for introducing a separate class of "city car" to the USA. On a highway, I want a big comfy car that can be efficient at 55-65 MPH, and protect me in a collision at those speeds. In a city, I don't really need that.

[graylights]

That big comfy car that protects you from highway collisions accomplishes that by shifting the impact toward the smaller car. It doesn't increase overall highway safety, just steals it from others in your favor.

[kahirsch]

Large cars are also safer in single-vehicle collisions, which account for 65% of traffic deaths. There is some adverse effect on occupants of other vehicles, but this is much smaller than the advantage in safety from the large vehicle.

It is definitely not true that it "just steals it from others".

[SixSigma]

It definitely is true. In a collision the vehicles absorb the energy of the collision inversely proportional to their relative masses i.e. the lighter car takes the brunt of the crash.

Safety researchers are responding by using active protection systems: in vehicles equippped with v2v transcievers will stiffen or soften their crash protection systems based upon the relative masses of the vehicles.

[thaumasiotes]

Imagine the following:

- two people driving paper-thin cars crash into each other head-on at 60 mph. The cars divide the energy of the collision evenly, disintegrate, and pass on a lot of energy to their passengers.

- two people driving huge voluminous and massive SUVs crash into each other head-on at 60 mph. The SUVs divide the energy of the collision evenly, warping into unrecognizable crumply wads of steel. The passengers take less damage than in the earlier scenario.

This is impossible?

[SixSigma]

Sounds like you're restating my premise.

[Dylan16807]

You're ignoring the word 'just'.

[malandrew]

Of that 65% that is single vehicle collisions, what causes are responsible for most of those and where do most of those collisions take place? suburbs, rural, city?

I would imagine that the overwhelming majority of single vehicle collisions are in low density suburbs.

I would also imagine that the overwhelming majority of those deaths involved colliding with a stationary, immovable object, such as a tree or traffic pole. In such a case, smaller vehicles will much less kinetic energy, but still as much thought given to their safety designs, should be much safer.

[Dylan16807]

Big doesn't have to mean particularly heavy, and it's ridiculous of you to suggest that a couple extra feet of crumple zone isn't going to make impacts less forceful.

[Gracana]

What about all the safety features found in larger cars? What about single-vehicle accidents? I don't need to drive a logging truck to feel safe, but I'd much rather drive a new corolla than an 80s model. Solid pillars and increased crumple zones and multiple airbags make a car bulkier, but the safety improvement is much greater than a simple function of weight.

[collyw]

I would feel far safer on my bike being hit by one of these larger cars and their safety features.

[mikeash]

I don't think that's true. Consider the two extremes.

1. You somehow manage to get a cardboard box up to 70MPH. You strike another fellow pulling the same trick. How badly are the two of you hurt? I believe the chances are excellent that you both die immediately.

2. You somehow manage to get a container ship up to 70MPH. You strike another fellow pulling the same trick. How badly are you hurt? If you're strapped in and not near the front, I believe chances are excellent that you'll both walk (swim) away.

[seanmcdirmid]

Sounds like a tuktuk, many cities in Asia have them, but they mix with car traffic.