5 ms·

"by letting a gap grow in front of me that would absorb the wave" would cause the freeway to carry fewer cars if everyone does it. My oldest one used to argue w

"by letting a gap grow in front of me that would absorb the wave" would cause the freeway to carry fewer cars if everyone does it. My oldest one used to argue with me on this point when I asked him to keep a bigger gap from the car in the front for safety reasons.

mavhc 5y ago
Not if they all go faster. The human induced delay is the problem. Plus it causes accidents, which really slows down the system.
- hbarka 5y ago
  Ever since driving an electric car, I have come to believe that a gas-throttle car’s laggy response during stop and go traffic may be responsible for the elasticity of the delay propagation. From zero, a piston pumper goes through a complicated series of windups which seems like days compared to an electric motor.
  - grepfru_it 5y ago
    Throttles have only become drive by wire over the last 15 years, prior to that it was cable actuated and was instantaneous. Like a lawnmower. One could argue carburetor cars were even (a fraction of a second) more responsive. Also if you WOT a modern car you get the instant response without the ecu calculating pedal angle, comparing to accelerator history, humidity factors etc etc but kiss fuel efficiency bye bye. There are mods and tunes that reprogram the fuel map to cut out this processing time I also drive a big turbo family sedan and am used to saying 2 Mississippi before the engine pulls at full boar
    - lathiat 5y ago
      Though drive-by-wire throttles absolutely do modify and potentially hold back your throttle input for reasons of both economy, comfort and enforced driveline sympathy, there is also an inherent response difference between petrol and electric engines and also slop in the driveline system. That difference varies on the engine and transmission type. Unfortunately I cannot find an easy good reference on what exactly that difference is quantifiably. Also many of the Electric cars right now are higher end even sporty vehicles, and more likely to have a throttle mapping that is more direct.
sangnoir 5y ago
But it could arguably increase the throughput (easier to on and off). Which is better: more vehicles on the freeway at lower average speeds - or fewer, faster ones?
- ojosilva 5y ago
  According to analysis from engineers, or Esther from a guy I used to work with who studied break waves for the state transportation board, less cars with larger gaps is better. That's why you see semaphores on highway entering ramps sometimes, ie 101 around SV or certain European big city inner highways. This is a problem that can probably be solved someday with self driving cars collaborating to make highways huge coordinated conveyor belts.
  - mattmanser 5y ago
    Actually, this is a problem that is already solved by smart motorways in the UK (Europe too maybe?). They have a variable speed limit that dynamically changes according to traffic that stop brake waves happening. Do you not have them in the US?
    - Talanes 5y ago
      Not only do we not have them, but I don't think I've ever read a freeway speed limit sign at all.
      - jlkuester7 5y ago
        > I don't think I've ever read a freeway speed limit sign at all Lol, why adopt the UK's variable speed limit when we have already de-facto reinvented the Autobahn....
    - rand49an 5y ago
      If my experience with smart motorways is anything to go by they seem to increase brake waves because there are often times that speeds get reduced significantly for arbitrary reasons that not everyone chooses to follow. You then get larger closing speeds which causes people to slam on the brakes. Additionally the removal of hard shoulders is just dangerous.
Faaak 5y ago
You should read about the "Fundamental diagram of traffic flow" and it's corresponding diagram. It's very well explained and shows that throughput can increase when having fewer cars on the road

mavhc 5y ago

Not if they all go faster. The human induced delay is the problem. Plus it causes accidents, which really slows down the system.

hbarka 5y ago
Ever since driving an electric car, I have come to believe that a gas-throttle car’s laggy response during stop and go traffic may be responsible for the elasticity of the delay propagation. From zero, a piston pumper goes through a complicated series of windups which seems like days compared to an electric motor.
- grepfru_it 5y ago
  Throttles have only become drive by wire over the last 15 years, prior to that it was cable actuated and was instantaneous. Like a lawnmower. One could argue carburetor cars were even (a fraction of a second) more responsive. Also if you WOT a modern car you get the instant response without the ecu calculating pedal angle, comparing to accelerator history, humidity factors etc etc but kiss fuel efficiency bye bye. There are mods and tunes that reprogram the fuel map to cut out this processing time I also drive a big turbo family sedan and am used to saying 2 Mississippi before the engine pulls at full boar
  - lathiat 5y ago
    Though drive-by-wire throttles absolutely do modify and potentially hold back your throttle input for reasons of both economy, comfort and enforced driveline sympathy, there is also an inherent response difference between petrol and electric engines and also slop in the driveline system. That difference varies on the engine and transmission type. Unfortunately I cannot find an easy good reference on what exactly that difference is quantifiably. Also many of the Electric cars right now are higher end even sporty vehicles, and more likely to have a throttle mapping that is more direct.

sangnoir 5y ago

But it could arguably increase the throughput (easier to on and off). Which is better: more vehicles on the freeway at lower average speeds - or fewer, faster ones?

ojosilva 5y ago
According to analysis from engineers, or Esther from a guy I used to work with who studied break waves for the state transportation board, less cars with larger gaps is better. That's why you see semaphores on highway entering ramps sometimes, ie 101 around SV or certain European big city inner highways. This is a problem that can probably be solved someday with self driving cars collaborating to make highways huge coordinated conveyor belts.
- mattmanser 5y ago
  Actually, this is a problem that is already solved by smart motorways in the UK (Europe too maybe?). They have a variable speed limit that dynamically changes according to traffic that stop brake waves happening. Do you not have them in the US?
  - Talanes 5y ago
    Not only do we not have them, but I don't think I've ever read a freeway speed limit sign at all.
    - jlkuester7 5y ago
      > I don't think I've ever read a freeway speed limit sign at all Lol, why adopt the UK's variable speed limit when we have already de-facto reinvented the Autobahn....
  - rand49an 5y ago
    If my experience with smart motorways is anything to go by they seem to increase brake waves because there are often times that speeds get reduced significantly for arbitrary reasons that not everyone chooses to follow. You then get larger closing speeds which causes people to slam on the brakes. Additionally the removal of hard shoulders is just dangerous.

Faaak 5y ago

You should read about the "Fundamental diagram of traffic flow" and it's corresponding diagram. It's very well explained and shows that throughput can increase when having fewer cars on the road