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posted by martyb on Thursday October 12 2017, @09:36PM   Printer-friendly
from the who-is-behind-whom? dept.

Confusion over what is a "safe following distance" has QUT [(Queensland University of Technology)] road safety researchers calling for a standardised definition to prevent tailgating.

  • Tailgating conclusively linked to rear-end crashes
  • Most drivers leave less than a 2 second gap between them and the vehicle in front
  • Rear-enders account for one in five Queensland crashes

Dr Sebastien Demmel, from QUT's Centre for Accident Research & Road Safety -- Queensland (CARRS-Q), said the results of the study which found 50 per cent of drivers tailgate, was being presented at the 2017 Australasian Road Safety Conference in Perth today.

"This study, for the first time conclusively linked tailgating with rear-end crashes, but we also identified confusion among drivers over what is deemed to be a safe following distance," he said.

"Despite drivers perceiving they are following at a safe distance, our on-road data showed that in reality most don't leave the recommended two to three second gap," he said.

"At some locations 55 per cent of drivers were found to leave less than a two second gap between them and the vehicle in front, and 44 per cent less than a one second [gap]."

A safe following distance is 5 feet. While looking at a smartphone.


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  • (Score: 2) by Arik on Friday October 13 2017, @02:04AM (6 children)

    by Arik (4543) on Friday October 13 2017, @02:04AM (#581501) Journal
    It's not that hard to check your speedometer, and get it calibrated if it's off.
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  • (Score: 0) by Anonymous Coward on Friday October 13 2017, @03:30AM

    by Anonymous Coward on Friday October 13 2017, @03:30AM (#581532)

    uh, it doesn't work that way. If you're really worried about it, get a GPS speedometer app for your phone. Chances are, at ~50-70 mph, your speedo reads about 1-3 MPH higher than GPS speedo will read.

    The car mags periodically do stories about just this, as does Consumer Reports.

    At least in the US, potential liability for having a speedometer indicating less than actual speed is...huge.

  • (Score: 1, Offtopic) by tangomargarine on Friday October 13 2017, @03:52PM (3 children)

    by tangomargarine (667) on Friday October 13 2017, @03:52PM (#581823)

    Speedometer readout isn't reliable 100% of the time. For example, my car gets rather bad traction in the winter, even with my winter tires on, and when I'm spinning my wheels on ice/snow at an intersection to get going, I've had the speedometer climb to 20mph before I actually start moving. So presumably it measures wheel rotation or something rather than actual velocity. Plus, can't your speedometer readout be off if you have the wrong size of tires mounted? Because the diameter is screwed up so the measurement is based on an assumption with drift from expected values.

    I've never looked it up but I imagine the problem of how to precisely measure your speed without GPS is a pretty interesting one mathematically. Differentials must be involved somehow? I really sucked at advanced math :P

    (2009 manual Toyota Corolla)

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    "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
    • (Score: 2) by Arik on Friday October 13 2017, @06:07PM (2 children)

      by Arik (4543) on Friday October 13 2017, @06:07PM (#581915) Journal
      "So presumably it measures wheel rotation or something rather than actual velocity."

      That's exactly correct. Which means that the only time it's inherently inaccurate is when, as you described, you lose traction.

      Other than that, it's a matter of calibration. As someone else already mentioned, it's actually illegal for it to be calibrated too low (i.e. to show 49 when you're actually doing 50) but it's not illegal for it to be somewhat too high (if it says you're doing 52 when you're doing 50, that's just fine, legally.) This means that when you buy a car it's expected to be calibrated too high. Test it with a stopwatch on a nice flat stretch of road and you can get a pretty accurate picture of exactly how high it is. Radar signs and GPS are other instruments that can be used to compare. The effective calibration changes slowly as your tires wear and of course quite quickly and drastically if you put on new tires of a different size, so it's necessary for the adjustment to exist.

      "I've never looked it up but I imagine the problem of how to precisely measure your speed without GPS is a pretty interesting one mathematically."

      Nah, it's dead easy, simple. Velocity=Distance/Time

      You need a relatively straight flat bit of road with known marked lengths. These are widely available. You get up to a given steady speed per your speedometer, click the stopwatch as you pass one marker, click again as you pass the second. If it's a one mile section, and it took 60 seconds, that's 60 miles per hour. (Sub kilometres if that's what you use, it works out just exactly the same regardless of unit.)

      1m/60s=Xmps

      but we don't actually want to know miles per second, we're looking for miles per hour, and it's going to be easier to do the conversion here than later, so it's 3600 seconds/hour of course. I'm using miles but if you prefer k just substitute it consistently and the formula works exactly the same. For that matter you can use it for inches per week or parsecs per season, it's the same formula. Anyhow.

      1m/(60/3600)h simplify to
      1m/(1/60)h
      60mph

      Of course that's the easiest case, what if it isn't 60 seconds, but something odd, like 57?

      x=1m/(57/3600)h simplify to
      x=1m/(63r9/57)h
      x=63+(9/57)mph

      or alternatively simplify to

      x=1m/(.95/60)h
      x=63.1578947368... (the same dang thing.)

      --
      If laughter is the best medicine, who are the best doctors?
      • (Score: 2) by tangomargarine on Friday October 13 2017, @06:22PM (1 child)

        by tangomargarine (667) on Friday October 13 2017, @06:22PM (#581921)

        "I've never looked it up but I imagine the problem of how to precisely measure your speed without GPS is a pretty interesting one mathematically."

        Nah, it's dead easy, simple. Velocity=Distance/Time

        No, I mean difficult for the engineers who design the car. The car has to measure speed without using visual cues or the outside world at all beyond the tires.

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        "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
        • (Score: 1) by Arik on Friday October 13 2017, @06:36PM

          by Arik (4543) on Friday October 13 2017, @06:36PM (#581929) Journal
          Ok, so again, that's the same math, you just have a little ways to get there.

          What internal sensor that drives the speedometer actually measures is effectively the rate of rotation of the wheels. Multiply that by the circumference of the tires to get your actual velocity. (And this is why whether it's the old-fashioned cable-driven speedometer or some new digital sensor there still has to be a way to calibrate it for the actual circumference of the tires in use.)

          Velocity = Rotations_per_time_unit multiplied by Tire_circumference. So 60rpm with tires 2m circumference means 120m/m or 2m/s.
          --
          If laughter is the best medicine, who are the best doctors?
  • (Score: 2) by NewNic on Friday October 13 2017, @05:45PM

    by NewNic (6420) on Friday October 13 2017, @05:45PM (#581895) Journal

    Not hard, correct.

    How many people actually do it? Very few.

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