What-if 0061: "Speed Bump"

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elasto
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Re: What-if 0061: "Speed Bump"

Postby elasto » Wed Sep 04, 2013 3:37 am UTC

dalcde wrote:Terminology I use:
    Road: anything cars drive on
    Highway: Road where you can drive very fast (no traffic lights/pedestrian crossings etc.)

But apparently WIkipedia says that
Traditionally highways were used by people on foot


Think "highwayman" and "highway robbery".

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Eshru
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Re: What-if 0061: "Speed Bump"

Postby Eshru » Wed Sep 04, 2013 3:51 am UTC

Diadem wrote:Isn't something, by definition, not a highway if it has pedestrian crossings, or any other kind of crossings for that matter? I'm not exactly sure how most people define a highway, but my definition would be "A road with no at-grade intersections or traffic lights".

Under those rules, the state of Missouri likely has no highways. I would make those distinctions for something like a freeway, which in my mind has more lanes and all that other stuff , compared to highways.

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Re: What-if 0061: "Speed Bump"

Postby bondsbw » Wed Sep 04, 2013 5:02 am UTC

Theory aside, here's my experience. My neighborhood has 12 of those rubber speed humps. Yes, 12, within about 1.5 miles of road. I absolutely despise them, mainly because a piece of metal that got stuck in one slashed my tire one day, and the underside of my wife's car had to be repaired recently.

Anyway, I go faster now than before. I try to get up to at least 35 MPH. For these particular speed humps, it is actually a lot smoother to go 40-50 MPH over them than to go less than 20.

(It ultimately depends on the installation. One got replaced because the road got worn underneath it. The new pavement had just the slightest angle itself... it seriously couldn't be more than a degree or two... but added to the speed hump angle now it is unbearable at anything over 15 MPH.)

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Re: What-if 0061: "Speed Bump"

Postby Istaro » Wed Sep 04, 2013 5:37 am UTC

lgw wrote:"High street" was the common term before highway, and remains the most common street name in America.


Wait, really? America as in the U.S.? I thought "high street" was the BrE equivalent of the AmE term "main street". I've definitely never heard of a street named "High Street" in the U.S. (in California, at least).

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Re: What-if 0061: "Speed Bump"

Postby ve_ » Wed Sep 04, 2013 6:10 am UTC

what if we used a motorcylce?^^

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keithl
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Re: What-if 0061: "Speed Bump"

Postby keithl » Wed Sep 04, 2013 7:07 am UTC

bondsbw wrote:My neighborhood has 12 of those rubber speed humps. Yes, 12, within about 1.5 miles of road. I absolutely despise them
Rubber. Hmm. I wonder how flammable they are ...

Decades ago, my high school added some asphalt/gravel speed bumps. Nocturnal experiments demonstrated that gasoline softens asphalt, and rolling over softened speed bumps a few dozen times with a heavy vehicle flattens them out. And contrary to the assertions of the disciplinary vice principal, I was home sick, out of town, or washing my hair.

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Re: What-if 0061: "Speed Bump"

Postby niauropsaka » Wed Sep 04, 2013 7:26 am UTC

This one sort of lost focus and petered out.

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Re: What-if 0061: "Speed Bump"

Postby dalcde » Wed Sep 04, 2013 11:26 am UTC

Sidenote: Cititation 13 used to point to the video in Citation 12. Now fixed

(or is it just me?)

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PM 2Ring
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Re: What-if 0061: "Speed Bump"

Postby PM 2Ring » Wed Sep 04, 2013 11:49 am UTC

adavies42 wrote:
What-if 0061 wrote:Therefore, if you drove a car over a Philadelphia speed bump at 90% of the speed of light, in addition to destroying the city ...

... you could expect a speeding ticket of $1.14 billion.


Amusingly, someone I know was using this as the punchline to the "But officer, the stoplight looked green to me!" blue-shift joke just this past weekend.


As we discussed in an earlier What-if, the speed required to blue-shift a red light to green is the more leisurely pace of 0.27c.

...

FWIW, in Australia there are pedestrian crossings in some places on our major highways, eg the Pacific Highway.

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Re: What-if 0061: "Speed Bump"

Postby cream wobbly » Wed Sep 04, 2013 6:57 pm UTC

There are way too many bad assumptions in the analysis.

Speed bumps are designed to make drivers to slow down.

Not all speed bumps are. Some are designed to make car drivers slow down, while allowing larger vehicles to pass over them unmolested. The intention is that large emergency vehicles which have a wider track, such as fire engines, shouldn't have to slow down, while cars with a narrower track, do. Still others are designed to ensure drivers are travelling at or slower than a particular speed, but not necessarily slow them down.

Going over a typical speed bump at 5 miles per hour results in a gentle bounce, while hitting one at 20 delivers a sizable jolt.

Not so, either by design (see below) or by accident. There are two speed humps in particular that I can call to mind that are perfectly fine for driving over at the speed limit of 25 mph. Different makes of car show the same response. I see other drivers choosing not to slow down too, so it's not just me.

If you hit a larger speed bump—like a speed hump or speed table—your car might not fare so well.

A speed table is one of the type I mentioned above: they are designed to deliver an uncomfortable bounce at, say, 35 mph, while traveling over them at 25 mph is perfectly fine.

This is nothing at all to do with size. In my experience, it's the smaller speed bumps, and back in the UK, "sleeping policemen", that deliver the most uncomfortable jolt, even at very low speeds, with unconcealed tyre traps at parking lot exits being the most uncomfortable of all, at any speed. The approach and departure angle determine how much horizontal energy is converted to vertical motion, not the size.

There's also the horrible assumption throughout that we're talking about a "typical sedan". Even though I read the US motor press almost daily, I still think of sedan chairs when I see that word. The answer there is "What speed bump, commoner?" But what about an emergency vehicle? These have provision for poor road conditions. What about a luxury car or an SUV? These aren't always as great as they're sold to be, but some like the Land Cruiser and Range Rover definitely are. Unimog or other military vehicle? Baja, rallycross, or rally car? These are all designed to go over rough terrain at speed. What about a hovercraft?

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Re: What-if 0061: "Speed Bump"

Postby Viltris » Wed Sep 04, 2013 8:51 pm UTC

dalcde wrote:Terminology I use:
    Road: anything cars drive on
    Highway: Road where you can drive very fast (no traffic lights/pedestrian crossings etc.)


Same, except highways for me also have higher speed limits.

cream wobbly wrote:There are way too many bad assumptions in the analysis.

Speed bumps are designed to make drivers to slow down.

Not all speed bumps are. Some are designed to make car drivers slow down, while allowing larger vehicles to pass over them unmolested. The intention is that large emergency vehicles which have a wider track, such as fire engines, shouldn't have to slow down, while cars with a narrower track, do. Still others are designed to ensure drivers are travelling at or slower than a particular speed, but not necessarily slow them down.

Going over a typical speed bump at 5 miles per hour results in a gentle bounce, while hitting one at 20 delivers a sizable jolt.

Not so, either by design (see below) or by accident. There are two speed humps in particular that I can call to mind that are perfectly fine for driving over at the speed limit of 25 mph. Different makes of car show the same response. I see other drivers choosing not to slow down too, so it's not just me.


Are people really expected to slow down drastically for a speed bump? In San Jose, driving over speed bumps at speed is the norm. (Note that "at speed" means anything from 15 mph to 30 mph, since that's the usual speed of roads where speed bumps show up.)

On the other hand, in Seattle, coming to an almost complete stop in front of the speed bump is the norm. Which really annoys me.

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Re: What-if 0061: "Speed Bump"

Postby eigenvictor » Thu Sep 05, 2013 3:50 am UTC

I have to say I am disappointed at how little Randall delved into the physics of suspension systems this week. As bondsbw points out, there is a neat effect where going faster actually reduces the jolt. This is the same reason that driving faster on washboard roads results in a smoother ride [1].

The car body combined with the suspension system acts as a single degree of freedom oscillator. As with any SDOF oscillator, it has a resonant frequency beyond which the amplitude response decreases, i.e. it acts as a low pass filter. This is why it smooths out your ride, because low pass filters smooths things. Basically displacements applied with low frequencies are passed to the car body while displacements at high frequencies are absorbed by the suspension system. The faster you go the more the energy in the jolt is spread out to higher frequencies. For a given jolt of fixed amplitude, the acceleration delivered is going to be linearly proportional to velocity. However the spectrum of the jolt also scales linearly in frequency with respect to velocity, and for a this type of low pass filter the amplitude response falls off exponentially past the resonant frequency.

Now here's where things get interesting. For the washboard example, the spectrum of the jolt is concentrated at non-zero frequencies. Once you go fast enough, all of the energy has basically been shifted to high enough frequencies that the oscillations get damped out (it's still probably really bad for your suspension system). However for the speed bump, there is a significant amount of energy at or near zero frequency, which will not get filtered out even at high speeds. This means that the amount of acceleration passed to the car can continue to grow with speed (albeit not neccessarily monotonically).

Now there's probably a point at which too much sudden acceleration is bad for your health. I don't know how fast you need to go for that to happen, and it may well be that aerodynamic forces tear your car apart well before that, but I would have loved to see a graph or some numbers like that. Perhaps I'll try to code up a simple model later.

[1] I'm new here so I can't post any links, but Mythbusters proved this one. Google it.

drewder
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Re: What-if 0061: "Speed Bump"

Postby drewder » Thu Sep 05, 2013 4:49 am UTC

He didn't seem to answer the question he teased at the end. What happens to the earth if a whole car gets accelerated to .9c or higher.

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Re: What-if 0061: "Speed Bump"

Postby niky » Thu Sep 05, 2013 7:13 am UTC

One thing bothered me about this article... While I agree that there are no road speeds at which a bump would kill the driver (because the suspension and wheels will tear themselves to shred absorbing the force of the impact), most modern cars have very low aerodynamic lift. Some have zero lift and even marginal downforce in some cases (even without wings).

It should be perfectly possible to push something like a Prius to 300 mph and then run it over a hump. Not that it would be pretty.

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Re: What-if 0061: "Speed Bump"

Postby Diadem » Thu Sep 05, 2013 7:34 am UTC

niky wrote:It should be perfectly possible to push something like a Prius to 300 mph and then run it over a hump. Not that it would be pretty.

Very few things are pretty when done in a Prius, though "utterly wrecking it" is certainly one.
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Re: What-if 0061: "Speed Bump"

Postby speising » Thu Sep 05, 2013 7:48 pm UTC

i have hit my head on the car roof sometimes from the jolt of a speed bump. i imagine this could be actually fatal, and doesn't depend so much on speed, but more on how you sit and how big you are.

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Re: What-if 0061: "Speed Bump"

Postby bmonk » Thu Sep 05, 2013 10:48 pm UTC

jpvlsmv wrote:
Diadem wrote:Perhaps it's a US thing. You guys are rather weird when it comes to naming roads.
You park on a driveway.
You drive on a parkway.
You do your high-speed driving on a freeway, which may or may not be free-access
You do your free-access driving on a highway, which may or may not be high-speed.

There are Interstate Highways in Hawaii, Puerto Rico (neither of which are accessible by car from any other state) and Alaska.
Turnpikes are no longer access-limited by actual pikes needing to be turned.
People drive right by the "NO PASSING" sign. And they don't wait for the one that says "STOP" to change.
And of course, there's the rediculous sign "END CONSTRUCTION"... I never know if it's put there as a protest, or if the guys running the machinery would keep fixing the road past that point. (Hey Bob, we passed the sign. Oh s***, back up the steamroller)

--Joe

The "END CONSTRUCTION" sign does serve a legal purpose--it spells the end of the higher fines for speeding imposed in work zones.
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Re: What-if 0061: "Speed Bump"

Postby Himself » Fri Sep 06, 2013 3:30 am UTC

niky wrote:One thing bothered me about this article... While I agree that there are no road speeds at which a bump would kill the driver (because the suspension and wheels will tear themselves to shred absorbing the force of the impact), most modern cars have very low aerodynamic lift. Some have zero lift and even marginal downforce in some cases (even without wings).

It should be perfectly possible to push something like a Prius to 300 mph and then run it over a hump. Not that it would be pretty.

Couldn't the speed bump bump the car up enough that the car could lift and flip, as shown in the linked videos?
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Lazy Tommy
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Re: What-if 0061: "Speed Bump"

Postby Lazy Tommy » Fri Sep 06, 2013 7:17 pm UTC

lgw wrote:In a lot of US neighborhoods these days, the association will give you a ticket if you park in your driveway


Why?

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Re: What-if 0061: "Speed Bump"

Postby jpvlsmv » Fri Sep 06, 2013 8:17 pm UTC

bmonk wrote:
jpvlsmv wrote:And of course, there's the rediculous sign "END CONSTRUCTION"... I never know if it's put there as a protest, or if the guys running the machinery would keep fixing the road past that point. (Hey Bob, we passed the sign. Oh s***, back up the steamroller)

The "END CONSTRUCTION" sign does serve a legal purpose--it spells the end of the higher fines for speeding imposed in work zones.

Yes, in jurisdictions where fines are elevated in those zones, that makes some sense. But they're everywhere.

And of course, even in those jurisdictions, you'd be able to argue that you were beyond the work zone, regardless of the presence or absence of the sign. Just like the reduced work-zone speed limit (and increased fine) applies regardless of the presence/absence of an explicit posted limit sign.

--Joe

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Re: What-if 0061: "Speed Bump"

Postby Mikeski » Sat Sep 07, 2013 9:29 am UTC

Lazy Tommy wrote:
lgw wrote:In a lot of US neighborhoods these days, the association will give you a ticket if you park in your driveway

Why?

1) Safety. Cars parked outdoors at 3AM invite crime. It's one thing if random visitors park outdoors overnight in few spots; it's another if half the neighborhood routinely has petty-theft targets sitting there in every driveway... volume of targets plus ability to "case the joint".

2) Aesthetics. Though nobody cares if your shiny new BMW is parked in your upper-middle-class McMansion zone, a lot of people care if your up-on-blocks rusty restoration project is. So since it's very difficult to draw a legal line between "acceptable car" and "eyesore" (how's the twice-rear-ended 1998 minivan looking?), the rule is a blanket "thou shalt not".

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Re: What-if 0061: "Speed Bump"

Postby Diadem » Sat Sep 07, 2013 10:22 am UTC

Then where do you park your car? Lots of people use their garage for other purposes than parking cars (at least over here), plus, quite a few people have a 2nd car.
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Re: What-if 0061: "Speed Bump"

Postby dalcde » Sat Sep 07, 2013 10:39 am UTC

Diadem wrote:Then where do you park your car? Lots of people use their garage for other purposes than parking cars (at least over here), plus, quite a few people have a 2nd car.


A car park

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Re: What-if 0061: "Speed Bump"

Postby Klear » Sat Sep 07, 2013 10:52 am UTC

Mikeski wrote:2) Aesthetics. Though nobody cares if your shiny new BMW is parked in your upper-middle-class McMansion zone, a lot of people care if your up-on-blocks rusty restoration project is. So since it's very difficult to draw a legal line between "acceptable car" and "eyesore" (how's the twice-rear-ended 1998 minivan looking?), the rule is a blanket "thou shalt not".


Really? Wow...

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Re: What-if 0061: "Speed Bump"

Postby PM 2Ring » Sat Sep 07, 2013 12:01 pm UTC

lgw wrote:In a lot of US neighborhoods these days, the association will give you a ticket if you park in your driveway

What is "the association"?
I presume you don't mean these people. :)
It's not exactly an easy thing to Google...

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Re: What-if 0061: "Speed Bump"

Postby waidh » Sat Sep 07, 2013 12:54 pm UTC

PM 2Ring wrote:
lgw wrote:In a lot of US neighborhoods these days, the association will give you a ticket if you park in your driveway

What is "the association"?
I presume you don't mean these people. :)
It's not exactly an easy thing to Google...

It might be this: Homeowner association
But I could be mistaken; only heard about it in a movie.

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Re: What-if 0061: "Speed Bump"

Postby rmsgrey » Sat Sep 07, 2013 2:22 pm UTC

Yeah, apparently it's a big thing in parts of the US where your neighbours get to impose rules about how to live on you above and beyond the usual laws about not making loud noises at night or shining search-lights in other people's windows after dark - so you can get entire stretches of suburbia where all the houses and gardens look identical because the local committee of self-appointed busybodies have decreed when and how often lawns are to be mown, what shrubs are acceptable around the borders, and so on.

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Re: What-if 0061: "Speed Bump"

Postby mathmannix » Mon Sep 09, 2013 3:26 pm UTC

Yes, we just moved to a neighborhood with an HOA. Around here, if you want to live in a neighborhood (= within city limits), you will have to live under an HOA's rules. There is a monthly fee to the association (required to live in the neighborhood). In "return" for the fee, the HOA "helps" by making rules that are designed to keep property values high. (If my neighbor were allowed to paint his house pink, keep a junker automobile in his yard, not mow his grass for two weeks at a time, or heaven forbid, install any but one of the four approved styles of front doors, then it would lower the value of my own home by association.)

The fee in our current neighborhood is around $30 a month. As far as I can tell, the fees are used mostly for (1) landscaping and snow removal (about 35% of the budget) and (2) administrative expenses internal to the HOA (about 60% of the budget). Where we lived before, the fee was about $75 a month, but that included use of a community pool in the summer.

P.S. - not kidding about the front door policy.
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Re: What-if 0061: "Speed Bump"

Postby Mikeski » Mon Sep 09, 2013 6:40 pm UTC

Yup, some of them are crazier than others. We're "allowed" cars in the driveway, and the architectural rules basically come down to "no two adjacent houses in the same color and style" (which prevents the builders from coming through and making rows of clone houses, but doesn't really affect the homeowners), and "run all the changes past the architecture committee" (which prevents the criminally insane from living in four-tone-pink houses*). Our fees are $40 a year, for signs and flowers at the entrances to the neighborhood.

* - one of which I used to live down the street from, when I lived in a place without a HOA. It made giving directions easy... "turn left at the pink gingerbread house and I'm on the next block". Even had a pink-painted driveway and red shingles.

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Re: What-if 0061: "Speed Bump"

Postby ve_ » Mon Sep 09, 2013 9:51 pm UTC

Typical speeds resulting from speed humps are 10–20 mph (15–30 km/h). Studies show an average 18% reduction in traffic volume and an average 13% reduction in collisions.

https://en.wikipedia.org/wiki/Speed_hump


soo while 18% of vehicles will avoid that road, the per vehicle collision increases?
lets get these everywhere to support the repair workshops and hospitals!

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Re: What-if 0061: "Speed Bump"

Postby ve_ » Mon Sep 09, 2013 10:08 pm UTC

cream wobbly wrote:[...] But what about an emergency vehicle? These have provision for poor road conditions.[...]


here in europe most Ambulance cars are just VW transporters with modified interior (much added weight). Some got stiffer suspension some don't. In any case it is far worse on speed bumps. if anything a few have suspended beds for the patients (work great for them but add even more weight to the car).

source: I'm a medic.

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Re: What-if 0061: "Speed Bump"

Postby Nnelg » Thu Sep 12, 2013 12:56 am UTC

PolakoVoador wrote:
keithl wrote:As a rule of thumb, it is imprudent to pass over speed bumps faster than orbital velocity.

I'll totally sig this

Me too. :)
keithl wrote:As a rule of thumb, it is imprudent to pass over speed bumps faster than orbital velocity.

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Re: What-if 0061: "Speed Bump"

Postby Viltris » Fri Sep 13, 2013 2:40 am UTC

Diadem wrote:Then where do you park your car? Lots of people use their garage for other purposes than parking cars (at least over here), plus, quite a few people have a 2nd car.


I never understood why people would have a car and a garage and not use the garage for its intended purpose. Then again, I'm an anti-pack-rat, and I'd rather leave my 2-car garage half empty than to use any of it for long-term storage.


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