8 ms·

I think people are letting their personal biases (e.g. SUV=bad) get the better of them. With the rise of EVs, even small vehicles will weigh a lot. For instance

by zibby8 4y ago

I think people are letting their personal biases (e.g. SUV=bad) get the better of them. With the rise of EVs, even small vehicles will weigh a lot. For instance, the curb weight of a Tesla Model 3 is between 3,648 and 4,250 lbs, which is about the same as a Toyota Highlander.

someguydave 4y ago
rationally the speed limits should be lowered accordingly
- nemo44x 4y ago
  I agree that momentum should be the prime consideration. Especially as it relates to heavy trucks. Those guys shouldn’t be allowed to go over 55.
  - tzs 4y ago
    Is momentum what actually matters? A Ford F-150 at 45 MPH has less momentum than a typical locomotive has at 1 MPH, but I'd sure rather be hit by the latter.
    - nemo44x 4y ago
      Velocity is squared so yes that part matters more. Your extreme example is an edge case, sure, but not realistic. But overall, momentum is the force applied.
      - yibg 4y ago
        That doesn’t sound right. A 1mph train hitting you won’t kill you, it’ll just push you along. The sudden acceleration of all or parts of your body is important.
        nemo44x 4y ago
        Stand there for a few seconds or minutes. It’s what glaciers did. They travelled far slower than 1mph and took out mountains. I don’t make the physics, I just live with them.
        paulryanrogers 4y ago
        Right but you assume the person would be stupid enough to plant their feet and get slowly dragged under the train. Reaction time drops sharply as MPH increases.
        yibg 4y ago
        Unlike mountains, people are not nailed to the ground waiting to be carved out, they move when they get pushed by a slow but massive object. Only a tiny amount of the train's momentum will get transferred to the person, roughly 1mph x mass of the person worth.
      - ironmagma 4y ago
        p = mv, so in momentum velocity is simply linear. It's in KE = 1/2 * m * v^2 that has the square (kinetic energy).
  - dreamcompiler 4y ago
    Part of the reason I like driving on the Autostrada in Italy is that trucks are speed-restricted. Their speed limit is posted on the back of the truck itself so it's easy for anybody to see if the truck is speeding, and I'm led to believe that the penalty for speeding trucks is pretty severe. This may also be true in other countries; I don't know. It's not the case in the US and I wish it were.
  - FabHK 4y ago
    Why momentum and not energy? I'd say the latter. It is energy that deforms your body. So, reduce the speed by 15%, reduce energy by 28% (2*15% to first order, or 1-(1-15%)^2 exactly). Or, to put it differently, if the vehicle has twice the mass, speed should be reduced by 30%.
- plandis 4y ago
  Seattle changed a bunch of speed limits to 25MPH but the problem is that the roads were designed for faster speeds so now instead of everyone predictably going similar faster speeds, you get an unpredictable mix of some people going the speed limit and some people going closer to the old speed limits. In reality I think you need to redesign roads for lower speeds if you truly want a large percentage of drivers to follow the limits.
  - paulryanrogers 4y ago
    - coryrc 4y ago
      Of course they can, but: 1 it's America, cars matter, people don't 2 Seattle doesn't have police to be setting speed traps; it's also racist (I assume, since enforcing fares on transit and stopping cars with outdated vehicle tabs is considered racist here)
    - californical 4y ago
      > Can drivers used to the higher speed not read the updated signage? I live near a road that looks like a highway, and is 55 mph through a quieter area between towns. As you approach the business-heavy area, it drops down to 45, 35 mph, but the design is the exact same. It’s impossible to feel how fast you should be going because the entire road still feels like a highway, so you’ll just naturally go fast. Most people don’t look down at their speedometer very often. I have to keep looking down and correcting because your speed just naturally creeps up when a road feels like a highway. And this is as someone who lives near there and drives it regularly! Imagine the people who don’t go that way as often and aren’t aware that they should be making adjustments all the time because of the terrible road design.
    - occz 4y ago
      People don't follow speed limits, regardless of how literate they are. Relevant Not Just Bikes-video on the subject: https://youtu.be/bglWCuCMSWc https://youtu.be/bglWCuCMSWc
    - 4y ago
- Spivak 4y ago
  It'll never happen because speed limits aren't. Nobody actually follows the speed limit, people on average drive at speeds that match the safety conditions of the roads. It's not a coincidence that that speed roughly matches the speed limit. If the speed people actually drive differs from the limit and cops start actually start enforcing it the signs will eventually be set to that speed - 5 after people complain to their city council (or if they cant because fed money the cops will just be directed to not enforce it). The only real instance where speed limits differ form "the speed drivers feel safe driving" is school zones. But outside these situations speed limits are a waste of time because the roads are designed for specific speeds and people are naturally really good at feeling that speed. They exist because cops need some objective justification for pulling over people who drive faster than the norm.
  - occz 4y ago
    This is true, and the reason why most roads should be heavily narrowed to have their design speed match their speed limit. Speed limits get automatically complied with when it feels unsafe for the driver to exceed them, and all places where automobiles are permitted should be adapted to that reality.
foobazgt 4y ago
To be fair, the model 3 is middle of the road in weight compared to all of the cars in its class, i.e. high performance sports sedan. This is quite commendable given the extra weight for a 75kwh battery pack and has lots of room for improvement as the battery tech gets better.
morepork 4y ago
Bizarre that a Tesla Model 3 is called a small vehicle
- zibby8 4y ago
  Ok... a Chevy Bolt has a curb weight of 3,600 pounds as well. That's comparable in size to a Honda Fit at 163", but the Fit weighs 1,000 pounds less.
Andys 4y ago
The Toyota Camry and entry-level model 3 are both about 3500lbs these days. Electric cars look likely to keep dropping in weight as the designs improve (ie. battery pack becomes more structural and less of just an additional load)
tayistay 4y ago
SUV=bad isn’t just a personal bias. They’re more likely to kill a pedestrian because of their height. Weight isn’t the whole story.
morsch 4y ago
That is also terrible and we shouldn't let it happen.
PartiallyTyped 4y ago
In contrast, your Highlander has a higher centre of gravity, and kids can be standing next to it without you being able to see them.

by zibby8 4y ago

someguydave 4y ago

rationally the speed limits should be lowered accordingly

nemo44x 4y ago
I agree that momentum should be the prime consideration. Especially as it relates to heavy trucks. Those guys shouldn’t be allowed to go over 55.
- tzs 4y ago
  Is momentum what actually matters? A Ford F-150 at 45 MPH has less momentum than a typical locomotive has at 1 MPH, but I'd sure rather be hit by the latter.
  - nemo44x 4y ago
    Velocity is squared so yes that part matters more. Your extreme example is an edge case, sure, but not realistic. But overall, momentum is the force applied.
    - yibg 4y ago
      That doesn’t sound right. A 1mph train hitting you won’t kill you, it’ll just push you along. The sudden acceleration of all or parts of your body is important.
      - nemo44x 4y ago
        Stand there for a few seconds or minutes. It’s what glaciers did. They travelled far slower than 1mph and took out mountains. I don’t make the physics, I just live with them.
        paulryanrogers 4y ago
        Right but you assume the person would be stupid enough to plant their feet and get slowly dragged under the train. Reaction time drops sharply as MPH increases.
        yibg 4y ago
        Unlike mountains, people are not nailed to the ground waiting to be carved out, they move when they get pushed by a slow but massive object. Only a tiny amount of the train's momentum will get transferred to the person, roughly 1mph x mass of the person worth.
    - ironmagma 4y ago
      p = mv, so in momentum velocity is simply linear. It's in KE = 1/2 * m * v^2 that has the square (kinetic energy).
- dreamcompiler 4y ago
  Part of the reason I like driving on the Autostrada in Italy is that trucks are speed-restricted. Their speed limit is posted on the back of the truck itself so it's easy for anybody to see if the truck is speeding, and I'm led to believe that the penalty for speeding trucks is pretty severe. This may also be true in other countries; I don't know. It's not the case in the US and I wish it were.
- FabHK 4y ago
  Why momentum and not energy? I'd say the latter. It is energy that deforms your body. So, reduce the speed by 15%, reduce energy by 28% (2*15% to first order, or 1-(1-15%)^2 exactly). Or, to put it differently, if the vehicle has twice the mass, speed should be reduced by 30%.
plandis 4y ago
Seattle changed a bunch of speed limits to 25MPH but the problem is that the roads were designed for faster speeds so now instead of everyone predictably going similar faster speeds, you get an unpredictable mix of some people going the speed limit and some people going closer to the old speed limits. In reality I think you need to redesign roads for lower speeds if you truly want a large percentage of drivers to follow the limits.
- paulryanrogers 4y ago
  - coryrc 4y ago
    Of course they can, but: 1 it's America, cars matter, people don't 2 Seattle doesn't have police to be setting speed traps; it's also racist (I assume, since enforcing fares on transit and stopping cars with outdated vehicle tabs is considered racist here)
  - californical 4y ago
    > Can drivers used to the higher speed not read the updated signage? I live near a road that looks like a highway, and is 55 mph through a quieter area between towns. As you approach the business-heavy area, it drops down to 45, 35 mph, but the design is the exact same. It’s impossible to feel how fast you should be going because the entire road still feels like a highway, so you’ll just naturally go fast. Most people don’t look down at their speedometer very often. I have to keep looking down and correcting because your speed just naturally creeps up when a road feels like a highway. And this is as someone who lives near there and drives it regularly! Imagine the people who don’t go that way as often and aren’t aware that they should be making adjustments all the time because of the terrible road design.
  - occz 4y ago
    People don't follow speed limits, regardless of how literate they are. Relevant Not Just Bikes-video on the subject: https://youtu.be/bglWCuCMSWc https://youtu.be/bglWCuCMSWc
  - 4y ago
Spivak 4y ago
It'll never happen because speed limits aren't. Nobody actually follows the speed limit, people on average drive at speeds that match the safety conditions of the roads. It's not a coincidence that that speed roughly matches the speed limit. If the speed people actually drive differs from the limit and cops start actually start enforcing it the signs will eventually be set to that speed - 5 after people complain to their city council (or if they cant because fed money the cops will just be directed to not enforce it). The only real instance where speed limits differ form "the speed drivers feel safe driving" is school zones. But outside these situations speed limits are a waste of time because the roads are designed for specific speeds and people are naturally really good at feeling that speed. They exist because cops need some objective justification for pulling over people who drive faster than the norm.
- occz 4y ago
  This is true, and the reason why most roads should be heavily narrowed to have their design speed match their speed limit. Speed limits get automatically complied with when it feels unsafe for the driver to exceed them, and all places where automobiles are permitted should be adapted to that reality.

foobazgt 4y ago

To be fair, the model 3 is middle of the road in weight compared to all of the cars in its class, i.e. high performance sports sedan. This is quite commendable given the extra weight for a 75kwh battery pack and has lots of room for improvement as the battery tech gets better.

morepork 4y ago

Bizarre that a Tesla Model 3 is called a small vehicle

zibby8 4y ago
Ok... a Chevy Bolt has a curb weight of 3,600 pounds as well. That's comparable in size to a Honda Fit at 163", but the Fit weighs 1,000 pounds less.

Andys 4y ago

The Toyota Camry and entry-level model 3 are both about 3500lbs these days. Electric cars look likely to keep dropping in weight as the designs improve (ie. battery pack becomes more structural and less of just an additional load)

tayistay 4y ago

SUV=bad isn’t just a personal bias. They’re more likely to kill a pedestrian because of their height. Weight isn’t the whole story.

morsch 4y ago

That is also terrible and we shouldn't let it happen.

PartiallyTyped 4y ago

In contrast, your Highlander has a higher centre of gravity, and kids can be standing next to it without you being able to see them.