5 ms·

Speeding in a residential area is a lot worse, for the reason you described. New York City's speed limit of 30 is way too high (should be 20, without the 10mph

Speeding in a residential area is a lot worse, for the reason you described. New York City's speed limit of 30 is way too high (should be 20, without the 10mph tolerance). Most highways are underposted and should be 70-90. Bizarrely, 40mph in a residential zone is a minor offense while 100mph on the freeway (which isn't exactly good, but not as dangerous as it sounds with a good car) with zero traffic can cost you your license in almost any state, and put you in jail in some.

bluedino 13y ago
>> Most highways are underposted and should be 70-90. Maybe in the middle of Montana or Texas where it's 50 miles between towns, but not anywhere with off/onramps. People are very bad at merging and it'd be very difficult for many vehicles, especially trucks to get up to speed if 90 was the limit.
- rmc 13y ago
  Don't trying going on the German Autobahns (motorways). Unlimited speed limit, and unlike USA bendy roads, and lotsa on/off slip roads.
- michaelochurch 13y ago
  You make a good point when it comes to merging. Speeds of 90-120 mph are reasonably safe on German autobahns, because people have a regimented driving style (absolutely no passing on right, but the left lane really is the fast lane) and follow it to a T. Most Americans aren't trained to drive those speeds, though, nor do they follow lane discipline.
- drcube 13y ago
  That's what on-ramps are for. If traffic is congested enough to demand merging (rather than just making sure the road is clear), you shouldn't be driving at 90mph. On the other hand, you probably shouldn't be driving at 60 either. Speed limits should be limits, not averages, or worst-case.
sliverstorm 13y ago
Potential energy goes up as a square function of speed. 25mph => 45mph : 1400 "units" increase 65mph => 100mph : 5775 "units" increase So at least in terms of kinetic energy and therefore destructive potential, 100mph on the freeway is more dramatic than 40mph in a residential zone.
- lfuller 13y ago
  The point is that there is a lot less to destroy on a barren freeway than a residential area filled with pedestrians and property.
- michaelochurch 13y ago
  45 vs. 25 mph in residential zone: child runs out in front of you, hit the brakes but you can't stop in time, hit him still going 30mph and kill him... vs. you stop and don't hit him. 100 vs. 65 mph on freeway: you certainly die vs. you probably die, depending on the accident. Freeway accidents are very bad at either speed. Luckily, there shouldn't be any pedestrians, children running into the street, or bicyclists. The danger of freeway speed has more to do with differentials. Accident risk goes up 2x every 15-20mph of raw speed but 2x every 3 mph of speed differential (in either direction). If you're in traffic and driving 100 mph, you're probably an asshole because most people won't be, but it's the speed variance (and weaving, tailgating, and other asshole behaviors) that makes it dangerous.
  - dragontamer 13y ago
    At 65mph, it is realistic to drop your speed to 50mph or 40mph before a collision. (Delta-V of 20mph or so seems reasonable). The survival rate of a 40mph collision is around 50%. The survival rate of a 80mph collision is 0%. There is a _big_ difference between a 60mph cruising speed and 100mph cruising speed.
- harshreality 13y ago
  If I weigh 200 pounds am I more likely to be fatally injured in a car crash than if I way 150? A car that weighs more is safer because its velocity changes are slower (barring collision with an immovable object) and because it will usually have better crumple zones that absorb more energy before turning the passenger compartment into a compactor. If higher kinetic energy or momentum caused higher lethality, heavier people would die more often and/or heavier cars would be more lethal (for its own occupants) in wrecks at the same speed. Since it's not always possible to know what speed a car was going when it crashed, and since I haven't found any tables or graphs of either speed or KE [or momentum for that matter] vs lethality, I doubt there's enough data to draw any conclusions about KE being better at predicting lethality. I don't understand what the focus on collision energy is for.
dragontamer 13y ago
http://youtu.be/XFkn37BDvTw?t=1m27s http://youtu.be/XFkn37BDvTw?t=1m27s The difference between a 60mph collision and a 100mph collision is significantly larger than the difference between a 20mph collision and 30mph collision. In fact, with a lot of today's technology, a 20mph collision can be avoided by collision detection systems... and 30mph collisions are effectively transformed into 5mph collisions automatically. But nothing is going to save your life from a 100mph collision.
- sukuriant 13y ago
  Well designed cars can. Formula One drivers are going those speeds when they crash, or faster.
  - dragontamer 13y ago
    Formula One drivers have HANS to prevent their necks from snapping in half in those crashes. Beyond just roll cages and crumple zones... Formula One drivers have far more restrictive seatbelts and safety measures than the typical driver. The fatality rate for the typical on-the-road driver reaches ~100% at 65mph collisions. With racing-level safety equipment and car design... sure, it can get better. But that sort of stuff is irrelevant from a public safety perspective.
    - bagels 13y ago
      What is your citation for 65mph collisions being nearly 100% fatal? I find it hard to believe that two cars rubbing when travelling the same direction would be fatal.
      - sukuriant 13y ago
        it would also imply that a collision with someone where both of you are going 32.5 miles per hour and hit each other head on would end in near 100% fatality. That said, I would believe that a head-on collision at around those speeds has a high chance of fatality being that it's a 130mph collision.
jimmaswell 13y ago
Driving around at 20mph sounds barely worth it. There has to be a better solution.
- michaelochurch 13y ago
  Public transportation, biking, and dense, walkable cities. Obviously I'm not saying that the speed should be 20mph everywhere. I'm talking about dense, residential areas, such as New York City.
  - jimmaswell 13y ago
    None of those will exceed 20mph - public transportation and biking (presumably) follow the speed limit and the average human running speed is 5 to 8 mph. Unless it's a subway or a train.
    - vostrocity 13y ago
      Public transportation and biking both reduce congestion. That said, drones.
    - michaelochurch 13y ago
      In a city center, your average speed will be substantially less than 20mph anyway no matter how fast you drive (unless you violate laws, running through lights and speeding) due to congestion, traffic lights, etc. A 20mph isn't going to make much of a change to average travel speeds. Most likely, however, you're not going to be driving 20 miles in a city center. If you're driving more than 10 miles, you'll probably want to use a highway, and the US highway system is extensive enough that you can. As for biking, I have less of a problem with people biking over 20mph in the city. (However, you're correct that, in practice, there's no way someone's going to average 20mph for a city bike commute. Most people aren't in good enough shape to sustain 20mph on the flat.) I regularly hit 30-35mph on downhills (say, Central Park at the north end) because I know what I and the bike can handle. Bikes are small and agile (it's easy to swerve and avoid hitting someone) and much less massive than a car.
vostrocity 13y ago
Don't know if it's just me, but for the three months that I lived in NYC, I did not see a single speed trap or cop that batted an eye at speeders (and there are many who drive way too fast).

bluedino 13y ago

>> Most highways are underposted and should be 70-90. Maybe in the middle of Montana or Texas where it's 50 miles between towns, but not anywhere with off/onramps. People are very bad at merging and it'd be very difficult for many vehicles, especially trucks to get up to speed if 90 was the limit.

rmc 13y ago
Don't trying going on the German Autobahns (motorways). Unlimited speed limit, and unlike USA bendy roads, and lotsa on/off slip roads.
michaelochurch 13y ago
You make a good point when it comes to merging. Speeds of 90-120 mph are reasonably safe on German autobahns, because people have a regimented driving style (absolutely no passing on right, but the left lane really is the fast lane) and follow it to a T. Most Americans aren't trained to drive those speeds, though, nor do they follow lane discipline.
drcube 13y ago
That's what on-ramps are for. If traffic is congested enough to demand merging (rather than just making sure the road is clear), you shouldn't be driving at 90mph. On the other hand, you probably shouldn't be driving at 60 either. Speed limits should be limits, not averages, or worst-case.

sliverstorm 13y ago

Potential energy goes up as a square function of speed. 25mph => 45mph : 1400 "units" increase 65mph => 100mph : 5775 "units" increase So at least in terms of kinetic energy and therefore destructive potential, 100mph on the freeway is more dramatic than 40mph in a residential zone.

lfuller 13y ago
The point is that there is a lot less to destroy on a barren freeway than a residential area filled with pedestrians and property.
michaelochurch 13y ago
45 vs. 25 mph in residential zone: child runs out in front of you, hit the brakes but you can't stop in time, hit him still going 30mph and kill him... vs. you stop and don't hit him. 100 vs. 65 mph on freeway: you certainly die vs. you probably die, depending on the accident. Freeway accidents are very bad at either speed. Luckily, there shouldn't be any pedestrians, children running into the street, or bicyclists. The danger of freeway speed has more to do with differentials. Accident risk goes up 2x every 15-20mph of raw speed but 2x every 3 mph of speed differential (in either direction). If you're in traffic and driving 100 mph, you're probably an asshole because most people won't be, but it's the speed variance (and weaving, tailgating, and other asshole behaviors) that makes it dangerous.
- dragontamer 13y ago
  At 65mph, it is realistic to drop your speed to 50mph or 40mph before a collision. (Delta-V of 20mph or so seems reasonable). The survival rate of a 40mph collision is around 50%. The survival rate of a 80mph collision is 0%. There is a _big_ difference between a 60mph cruising speed and 100mph cruising speed.
harshreality 13y ago
If I weigh 200 pounds am I more likely to be fatally injured in a car crash than if I way 150? A car that weighs more is safer because its velocity changes are slower (barring collision with an immovable object) and because it will usually have better crumple zones that absorb more energy before turning the passenger compartment into a compactor. If higher kinetic energy or momentum caused higher lethality, heavier people would die more often and/or heavier cars would be more lethal (for its own occupants) in wrecks at the same speed. Since it's not always possible to know what speed a car was going when it crashed, and since I haven't found any tables or graphs of either speed or KE [or momentum for that matter] vs lethality, I doubt there's enough data to draw any conclusions about KE being better at predicting lethality. I don't understand what the focus on collision energy is for.

dragontamer 13y ago

http://youtu.be/XFkn37BDvTw?t=1m27s http://youtu.be/XFkn37BDvTw?t=1m27s The difference between a 60mph collision and a 100mph collision is significantly larger than the difference between a 20mph collision and 30mph collision. In fact, with a lot of today's technology, a 20mph collision can be avoided by collision detection systems... and 30mph collisions are effectively transformed into 5mph collisions automatically. But nothing is going to save your life from a 100mph collision.

sukuriant 13y ago
Well designed cars can. Formula One drivers are going those speeds when they crash, or faster.
- dragontamer 13y ago
  Formula One drivers have HANS to prevent their necks from snapping in half in those crashes. Beyond just roll cages and crumple zones... Formula One drivers have far more restrictive seatbelts and safety measures than the typical driver. The fatality rate for the typical on-the-road driver reaches ~100% at 65mph collisions. With racing-level safety equipment and car design... sure, it can get better. But that sort of stuff is irrelevant from a public safety perspective.
  - bagels 13y ago
    What is your citation for 65mph collisions being nearly 100% fatal? I find it hard to believe that two cars rubbing when travelling the same direction would be fatal.
    - sukuriant 13y ago
      it would also imply that a collision with someone where both of you are going 32.5 miles per hour and hit each other head on would end in near 100% fatality. That said, I would believe that a head-on collision at around those speeds has a high chance of fatality being that it's a 130mph collision.

jimmaswell 13y ago

Driving around at 20mph sounds barely worth it. There has to be a better solution.

michaelochurch 13y ago
Public transportation, biking, and dense, walkable cities. Obviously I'm not saying that the speed should be 20mph everywhere. I'm talking about dense, residential areas, such as New York City.
- jimmaswell 13y ago
  None of those will exceed 20mph - public transportation and biking (presumably) follow the speed limit and the average human running speed is 5 to 8 mph. Unless it's a subway or a train.
  - vostrocity 13y ago
    Public transportation and biking both reduce congestion. That said, drones.
  - michaelochurch 13y ago
    In a city center, your average speed will be substantially less than 20mph anyway no matter how fast you drive (unless you violate laws, running through lights and speeding) due to congestion, traffic lights, etc. A 20mph isn't going to make much of a change to average travel speeds. Most likely, however, you're not going to be driving 20 miles in a city center. If you're driving more than 10 miles, you'll probably want to use a highway, and the US highway system is extensive enough that you can. As for biking, I have less of a problem with people biking over 20mph in the city. (However, you're correct that, in practice, there's no way someone's going to average 20mph for a city bike commute. Most people aren't in good enough shape to sustain 20mph on the flat.) I regularly hit 30-35mph on downhills (say, Central Park at the north end) because I know what I and the bike can handle. Bikes are small and agile (it's easy to swerve and avoid hitting someone) and much less massive than a car.

vostrocity 13y ago

Don't know if it's just me, but for the three months that I lived in NYC, I did not see a single speed trap or cop that batted an eye at speeders (and there are many who drive way too fast).