Safety Equipment

The white panel between the wheels of this truck is called a "Lateral Protective Device", and its purpose is to prevent people, bicycles, motorcycles and small cars from getting sucked under the truck's rear wheels when it swerves into them:

This second safety device must serve a similar function, but I can't quite put my finger on it:

I pass this truck all the time. It seems to spend hours almost every day parked in front of the Flower Mart with its engine running the whole time.

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26 Responses:

  1. Defiance! says:

    I thought that was called a side skirt and is for improved aerodynamics. Whereas a side guard is made of steel bars, specifically for preventing injury

  2. oration says:

    That is not a Lateral Protective Device, that is a Side Skirt.

    The side skirt aerodynamically improves fuel efficiency by about 5%.

    It is possible to buy a side skirt that also acts as an LPD, but this. . . . is not that.  The side skirts that increase safety are flush with the full length of the trailer.

    • Duality K. says:


      Also, those dumb spikes are decorative covers/shin scrapers more than the roadgoing garbage disposers they look like they are.  At least some of the ones so nicely mismatched on that wheel are of the push-on variety (push on/kick off if you are so inclined.)

    • David K says:

      Whew. I thought my engineering spider sense was failing me.

  3. It's a pity SF doesn't have the idling truck bounty system NY has. Record a truck idling for more than 3 minutes and you get 25% of the $350 fine. $87.50

  4. Gabriel N says:

    the backend of the truck was cropped, and the truck nuts can’t be seen.

  5. Narr says:

    The spikes can also be used to tell if the wheel is rotating/brakes are locked up/wheel is missing by looking in the mirrors or looking out the window. Typically you would use or see a longer and brighter-coloured strap, but the owner of this vehicle chose something else.

    Typically, the lug nuts would also have triangular markers sticking out and arranged in a circle to tell if any had loosened, which this style does not indicate.

  6. The spikes in the second picture are for chariot races and drag races in the LA river.

  7. flikx says:

    Truckers use these spiky lug nut covers as a talisman to keep away cars and the occasional pedestrian from their lane. They work on the same principles as deer screamers.

    • bq Mackintosh says:

      I'm having a hard time envisioning a scenario in which a car driver, bicyclist, or pedestrian didn't notice the semi truck itself, but then spotted the lug nuts and was discouraged from approaching.

      • reboots says:

        Driving trucks has taught me that they are noticed, to the extent that other drivers intuit something reptilian along these lines: "I perceive a slow-moving vehicle with a trained operator which is therefore totally predictable, so I may cut it off or otherwise behave like a jackass with complete impunity."

        But in fact, coming anywhere near those wheels in motion is suicidal. There's an oft-cited comedy routine about improving driving by mounting a sharp spike in the center of everyone's steering wheel; I imagine wheel spikes are making the same point.

  8. SNS says:

    I don't know if this will be helpful, but at least in some cases, it's not legal for trucks to idle for long periods in California. The relevant code is here:

    ...but naturally, it's a rat's nest of GOTO statements, so it's not immediately clear whether it would apply here.

    When I was living in New York, complaints about idling were taken somewhat seriously; your mileage may vary. There's a complaint form here:

  9. thielges says:

    The hub spikes serve the same purpose as loud exhaust, spoilers, lift kits, or giant tires: they broadcast the driver’s insecurities.  

  10. narf says:

    DOT bars are a fun little safety feature on trailers as well... Until you get to thinking of why they are there.

  11. prefetch says:

    Good grief - at least put some effort in. The Japanese has much wisdom to impart, on both ends of the spectrum:

  12. david widel says:

    It's been a while since I was a truck mechanic, but all the lug nut covers I've seen are cheap plastic caps that just push on.   Not nearly as scary as they look.

    • jwz says:

      Even if truck nuts aren't made of real testicles, it's not going to improve my opinion of the driver.

    • Tyler says:

      While plastic is softer than any metal other than mercury, it's still harder than human flesh.

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