math help ...

[Charlie Stone]

I know there have to be some serious math people lurking around.
In the past year, 3 houses, a street light, and a fire hydrant have been hit by cars along my block.
My wife and I figure it has to be our turn soon, so we want to put a bolder in as a barricade in our yard. How heavy of a rock would we need to stop a 5000 lb vehicle (average idiot not paying attention) traveling at 35 mph?

[John Coloccia]

Are you trying to kill somebody? Maybe petition the town for a guard rail. That will serve the same purpose without killing the driver of the car. I suspect if a car actually did hit your boulder that you might very well have a lawsuit on your hands.

For what it's worth, though, I have a very steep drop off at the end of my driveway (my property drops about 50 feet straight down onto the main part of the property). There are some boulders at the end that are about 1 ton. The old owner hit them with his pickup, albeit slowly, but they kept him from going over. A LOT of energy is dissipated into crushing the the crumple zones over a relatively long period of time. Still, I suspect you'll need a sizeable rock anyway, and after the car hits there's no telling where it will go. It can launch it, or very well send it into your own house.

[Charlie Stone]

I am trying to keep the cars out of my living room. The drunk drivers are trying to kill someone. In my mind, better them than my daughter playing tea party in the living room. I don't see them hitting a bolder in my yard vs. my brick house, or my neighbors retaining wall would set me up any more for a lawsuit any more than when someone drives in to a bolder left there by nature along the side of a highway.

[Brian Kent]

I'm glad you're not taking your safety for granite, Mr. Stone.

Is there landscaping you can do where the car hits bushes, then a split rail fence, then the boulder, as a crush zone to save their lives?

[Matt Meiser]

Nature didn't post on a public forum that it was intentionally placing the boulder in a spot where it could be hit, and that if it killed someone then so be it. Nature therefore doesn't have to worry about a lawyer finding the post and bring into court. ;)

In a quick google search, I think your target weight is about 20% high. Also I think any boulder big enough dimension-wise to provide an effective barrier will probably weigh more than enough. Guard rail might be cheaper than moving such a beast. Maybe you can disguise the guardrail with landscaping and/or fencing.

[John Coloccia]

i'm glad you're not taking your safety for granite, mr. Stone.

rofl. :D :D :D

[Charlie Stone]

there is a curb, a 10' blvd (with trees and a lamp post depending on the line of travel, sidewalk, and 10 feet of yard before they hit my house. The accident which happened last week across the street, the guy swerved though an empty corner lot, back on to the street, spun the van 90 degrees went up a 1-2' concrete porch, though the front door and corner of a house, across an alley and though the covered porch of another house until he hit the concrete stair case where he put a huge V in the front of his van.

[David Weaver]

You're looking at a physics question rather than math, but speaking from experience...

... when I was little, people clipped off our mailbox at regular intervals. usually drunk people, but sometimes in the winter people skidded into it, even though it was along a straight of road and there was a telephone pole a fair way beyond it which you would obviously want to avoid.

One year, my father had enough of people clipping off the mailboxes and put a 6x6 oak post in a very large concrete footer.

A drunk driver hit it later that year and almost killed himself. His car literally severed into two parts, and it made my dad sick (this was probably around 1980). We went back to tolerating that the mailbox was broken from time to time.

I can still remember being there at age 4 or 5 having no clue what was going on other than seeing a car in two parts in the middle of the night and standing in the yard with the flashing lights everywhere. I have pictures of that car in my picture album, taken with a 110 camera back then. Not something I'd want to be responsible for.

It sounds like a township issue, and I'd agree with matt, a guard rail would maybe not put you in a position where someone could at a minimum force you to go into court and fight off a frivolous suit.

[Charlie Stone]

f-150 (very common) is about 7000 GVW.

[Charlie Reals]

f-150 (very common) is about 7000 GVW.

2005 f-150 gvw 5396, goooood truck

[John Coloccia]

Just to give an idea of the energies involved, a 5000lb truck doing 35MPH has about the same energy as a loaded 18 wheeler doing 10MPH.

[Charlie Stone]

Ya know, you are all right about this. Maybe I am not taking the drunks safety into account.

Allow me to rephrase the question. In physics, How many tons of feathers would it take to stop a 18 wheeler doing 10 miles per hour.

[Dan Friedrichs]

I'm not sure you actually have any liability issue to worry about (IANAL) - our HOA has had its front entrance landscape/fence/sign hit several times by vehicles. This last time, the insurance company wouldn't pay to fix it UNLESS we installed several large boulders in front of it! I don't know what they weigh, but they're about 24" diameter granite. I believe the insurance co specified the size and they were installed by a professional landscaping company.

[David Weaver]

Ya know, you are all right about this. Maybe I am not taking the drunks safety into account.



You might feel a little different after the fact. Especially if the person has kids, went through hard times out of their control, etc. But you'd find that out after the fact - maybe by meeting their kids or their spouse.

What you should do if you want a boulder, though, is go at it with the overbuild philosophy, like 2 or 3 times what you think it'd actually take.

So that the same drunks don't find a bigger truck than you're thinking (like a loaded shop truck or something) and bulldoze the rock right through your house.

The guy at the corner in my neighborhood, and the lady at the other corner - both have rocks - like 10 of them, and probably on the order of about 1000 pounds each. I've never seen anyone in their yards, and they're in prime spots for someone to cut a corner short or miss a turn on our unlighted suburban streets.

[Eric DeSilva]

This isn't a math question. In physics, you see problems like this, but the solutions always rely on the collisions being inelastic. The problem here is that the collision between a car and a boulder is anything but inelastic. There are too many factors you just can't assess--how deep is boulder buried? How dense is the soil? What is the shape of the boulder? You might as well just take a wild guess.

That said, and in deference to some of the other comments, you might think about placing the boulders/guards such that any car that lost control might be redirected away from your house, as opposed to being stopped dead.

[John Pratt]

I got to go with Charlie on this one. I don't think I want to be planning my kids funeral but thinking "whew, at least the driver of that car is ok." In our area there was a family that lived at the end of a "T" intersection that had their house hit twice by people not seeing the turns at night. They installed the same pop-up security barriers you see at government facilities. They hit a button and they are down during the day, hit the button again and they are up at night when it is more likely someone will run the intersection. As long as you are placing this barrier on your private property and not on public property I don't see where the liability is. We're not talking about building man-traps, booby-traps, or something similar that would catch unsuspecting persons. We're not talking about a minefield, we're talking about a visable barrier that if you run into it, it is your fault and you assume responsibility for your actions.

[Brian Kent]

We had a similar crash spot a couple of blocks from our last home. In 7 years there were 4 major crashes in the same spot. 1 drunk driving - passenger killed. 1 driving high. 1 teenager fell asleep at the wheel (not drunk, but early in the morning), and 1 cause unknown but not dui.

[Charlie Stone]

I'm not sure you actually have any liability issue to worry about
In my city, you get a ticket for hitting a stationary object with a car. They also have the option of tacking on failure to maintain control of your vehicle. I have seen enough drunk driving accidents to not have much sympathy for the drunk drivers, who typically are unhurt after they kill someone. On Halloween a drunk killed a pregnant woman who was taking her older child trick or treating .. the woman died in front of her kid.

[Charlie Stone]

I haven't even tried to count or keep track of the car on car accidents at my corner. There is at least 1 per month. Going back more than a year, there has also been a tow truck that hit a tree, an SUV which rolled over (solo, very weird) a drunk who hit 3 cars and my tree then drove off, someone hit a no parking sign along the side of my house and ended up on the sidewalk. Most of these have happened when there was no snow or ice on the ground. Typically in the winter, since I am on a busy corner, all the snow gets piled from the intersections on my corner, and the plows create a nice 2' berm along the streets.

[alex grams]

Consider security planters (http://www.bohlmann.com/productcart/pc/General-Security-Planters-c9.htm). They are specific to what you are looking to achieve, though I don't know how they compare cost wise to large stones. They are more aestetic and probably a lot easier to mow/edge around.

In regards to stones:

I would not place a single larger boulder, but consider smaller ones (roughly 1 cubic meter). And place several in the line in which you are concerned the vehicles would come from, no further apart than the vehicle width at the indicant angle from which the vehicle would be traveling.

If the stone is granite, a cubic meter gives you about 6000lbs of stone. The only suggestion I can make as far as the stone is dont get a flat one, get one where you have at least a foot of height above an estimate impact from a vehicle (maybe 3' tall stone), that way a vehicle can't go over it.

Also, if you want to help prevent a vehicle from going over it, consider making a small mount along the line maybe 1-2 feet high and place the rocks on the apex, then the vehicle would come up into the boulder and have little chance of going over. Dig the dirt from in front of the mound that way you have a smaller depression in front of it to even further heighten the effect of the rocks/mound. The more you do this, the more comfortable you could feel with smaller rocks.

[Bryan Morgan]

In my city, you get a ticket for hitting a stationary object with a car. They also have the option of tacking on failure to maintain control of your vehicle. I have seen enough drunk driving accidents to not have much sympathy for the drunk drivers, who typically are unhurt after they kill someone. On Halloween a drunk killed a pregnant woman who was taking her older child trick or treating .. the woman died in front of her kid.


I'm with you. I have family who were killed by drunks. An F150 hopped into oncoming traffic and plowed head on into my cousin in his 3 series BMW. Killed him almost instantly and fractured the skull and almost killed his infant son. The driver of the truck was perfectly fine though, of course. To me, its the equivalent of murder, or worse. They make a conscious decision to drink, they accept %100 of the responsibility, even if it kills them. You must protect your family. I have no sympathy or empathy for anyone who gets killed while willfully doing something they know could easily kill them, especially drinking. I'd put whatever rocks and walls you need to protect your property and family from those losers.

[Kent A Bathurst]

Ya know, you are all right about this. Maybe I am not taking the drunks safety into account.

Allow me to rephrase the question. In physics, How many tons of feathers would it take to stop a 18 wheeler doing 10 miles per hour.

heh-heh-heh - very good, Charlie, very good. :D :D

Just put in some BDB [big doggone boulders]. See what the landscapers have. You don't have to stop 'em cold, you just have to deflect 'em, and let 'em ride up onto the reef. I'm with you. If the traffic is that dangerous - and it certainly sounds like it is - stop them from getting to your home + family. Rocks don't injure drunk drivers - drunk drivers injure drunk drivers. Give them a big body shop bill to go with the fine and the hoosegow - maybe they'll get the message.


As an alternative, you could go medieval or WW-II on your approach ;).

Good luck.

http://heraldry-armoury-and-more.com/picture_library/equip/abatis.jpg
http://www.tanksim.com/reviews/images/steelbeastspro/SS_00_10_32.jpg

[John Coloccia]

re: drunks
I guess I was thinking of the non-drunk mom in the minivan that got distracted for a second with her kids screaming in the back.

re: the legality
There's usually setbacks for structures. Not sure how large boulders or security devices would factor into that.

[Steve Friedman]

From someone who barely remembers high school physics and chemistry -

How about a mud pit situated to grab the wheels of any drivers who veer off the road? The mud needs to be thin enough to slow the car gently, thick enough to get the car stuck (so the driver needs to get towed out), and sticky enough to leave a permanent mark on the offending vehicle to warn everyone about their driving tendencies - kind of like a modern day scarlet letter!

Just a thought.

Steve

[Charlie Stone]

as far as I know, no minivan mothers have been involved in an accident near us. Just drunks and people talking on cell phones.

[John Coloccia]

From someone who barely remembers high school physics and chemistry -

How about a mud pit situated to grab the wheels of any drivers who veer off the road? The mud needs to be thin enough to slow the car gently, thick enough to get the car stuck (so the driver needs to get towed out), and sticky enough to leave a permanent mark on the offending vehicle to warn everyone about their driving tendencies - kind of like a modern day scarlet letter!

Just a thought.

Steve

Do you think you'd need a permit for the drawbridge? :p
:D

[Mike Cruz]

Charlie, to directly answer your question, I don't think it is so much a matter of the total mass of the boulder, more the height of it. A 20 to boulder that is only 5" high won't do the trick. A one ton that is 30" high, probably would. Even if it didn't stop it cold in its tracks, it would certainly slow it down enough to stop its momentum. What you probably want to avoid is a launch. So, look at guard rails. Measure their height. That is where I would start...

[Shawn Pixley]

I think you are over thinking this. How about large raised planters? Filled with dirt, a two to three foot high planter will stop a large truck. In commercial structures, these are often used to to stop the drive through (crash through?) robbery / burglary. Railroad tie, retaining wall CMU, or concrete planters will be both decerative and no one could accuse you of attempting to injure some one. Just trying to beautify your lot.

[Tim Boger]

Here is a suggested 20 ton boulder .... I figure it would stop an errant vehicle.

[Bryan Morgan]

re: drunks
I guess I was thinking of the non-drunk mom in the minivan that got distracted for a second with her kids screaming in the back.

If the mom is too distracted to be piloting a 5000lb+ lethal weapon she probably shouldn't be driving. These are lethal weapons, to be sure. Nobody accepts any excuses for accidentally popping off some rounds from an AK47 through your neighbors house while drunk, distracted, or otherwise. I don't mean to seem nasty or anything but vehicles are way too dangerous to be doing anything other than driving them. You can tell I drive So. Cal. freeways every day, and every day I'm dodging people doing anything other than driving. :) Heck, I've even seen guys reading the newspaper while eating a bowl of cereal, holding the bowl in one hand and the spoon in the other! No joke! :eek: I won't even go into the ladies driving land barges while yacking on the phone..... I pray to Darwin to make things right with the universe :D

[Don Alexander]

the really sad thing is that you have to worry about the irresponsible people harming your house / family in the first place
and even worse that protecting it/ them even has the possibility of landing you in legal trouble

just illustrates very graphically how screwed up things have gotten

[Colin Giersberg]

You could try several concrete barriers like you see on highway projects. They pin together, and are designed to deflect vehicles as long as they hit the barriers at a shallow angle. While not perfect, it might be helpful, and you might contact a road contractor about buying some of their older barriers. Maybe the damaged condition of them would get people to slow down.

[Joe Chritz]

5 accidents on one street over a year period is hardly an epidemic. Amazingly enough there are around 290 thousand accidents per year in Michigan alone. The vast majority are single motor vehicle accidents.

I would certainly run your scenario of a vehicle catch by an attorney or homeowners agent first, especially since the intent of said object is now public.

To answer your question, there isn't an easy answer. As part of my job duties I investigate serious and fatal accidents. There are way to many factors to count to figure what will work. Because the vehicle is moving it will always want to "glance" off and continue unless it hits at a 90 degree impact. Because an object at rest wants to stay that way it won't take as much weight as you may think to completely stop a vehicle. Any object big enough to reliably keep a vehicle from deflecting off will be plenty heavy.

You don't mention the speeds involved and that is the primary factor to consider. When speed increases the stopping distance increases at a much greater rate. So stopping an object, in this case a vehicle is largely weighted towards speed.

Joe

[alex grams]

Chritz,
Charlie mentioned in his first post the speeds of the vehicles:


How heavy of a rock would we need to stop a 5000 lb vehicle (average idiot not paying attention) traveling at 35 mph?

[Charlie Stone]

5 accidents on one street over a year period is hardly an epidemic.

Joe, on one block, an approximately 200 foot distance. 3 houses out of 9 were hit by cars in 1 year. That is pretty bad. 5 accidents isn't the grand total for the year, that is just the ones where stationary objects were hit on a single block.

This is a straightaway. There is no curve, there is no dead end, nothing special about the area. No visibility issues, the road going north/south, so sunrise/sunset isn't the issue. There is a college on one side and bars on the other. The only odd factor is the block in question is at the bottom of a 1000' long hill.

[Ted Calver]

Also consider creating an earth berm which incorporates a few large boulders, a couple of nice trees and an evergreen ground cover and some seasonal color. Couple of feet high, 2:1 slope on the edge and a nice natural undulating shape might fit into your yard and look more natural than just slapping down boulders. Can't tell without seeing your yard. Heck...go crazy and incorporate a water feature..your local landscapers will thank you.

[Dan Hintz]

Make it a shrubbery... with a path down the middle, giving it a two-level effect :D

[Charlie Stone]

Make it a shrubbery... with a path down the middle, giving it a two-level effect :D

hmm .. now I need to find a shrubber or they will say Ni again.

[Mike Cruz]

Charlie, the unfortunate truth about this forum is that (while I absolutely LOVE it, and it is the best thing since sliced bread) you are generally barking up the wrong tree when it comes to sympathy for situations like yours. I do not just sympathize with you, I empathize with you as well. But there are many here that don't. Unfortunately, you asked a direct question about math (or maybe it was more about physics, but what is physics but higher math?...) and got answers that were not digital, analog, computed or calculated. You got opinions as to whether or not you SHOULD put up a rock, what other bariers you could put up, what other methods you could use to stop vehicles, and the ever present total dismissal of your situation being a problem at all.

Personally, I love the rock idea. I love the idea of a bunch of them. Use them as hardscaping. Plant around them...or at least on the back side of them so when someone plows into them, it doesn't mess up your plants. ;)

But again, as I said in my previous post in response to your question, I would imagine that anything in the two ton range AS LONG AS IT IS TALL ENOUGH TO NOT LAUCH THE CAR OVER THE ROCK, would/ought to do a decent job. Of course, I don't know how far the rock(s) would be placed from the house and just how quickly they need to be stopped. But 2 tons, with the friction of the ground, and enough space between the rock and your house ought to keep them out of your living room. A line of large rocks would also make a nice sort of "fence"....

[Mike Cruz]

Classic, Dan! And kudos to you Charlie for catching it...;)

[Charlie Stone]

Mike, you are 100% correct. I knew of the "moral" issues around something like this, however, It was the math (in my mind, physics is math) I was after. If I were a less complicated person I would have simply thought, well, a parked car seems to do a pretty good job stopping most other vehicles when they are hit or when a car is broadsided. So, roughly the weight of a large car. Silly me for over thinking it.

[Dan Hintz]

I posted something about replacing the boulder with a metal spike, but it appears to have been removed... shades of a conversation started on one of my engineering forums discussing how to deal with bad drivers.

[Bill Cunningham]

a 5000lb vehicle traveling at 51.3333 fps (35mph) will have a impact of 204843.836 ft pounds of energy..
You need a bigger Rock :D

[Dan Hintz]

And just remember, you don't need to stop the vehicle dead in its tracks, you simply have to stop it within 10-15'... objects like a large rock take a lot of energy to keep moving...

[Charlie Stone]

we picked out a 1.25 ton boulder. about 2 feet tall and 3 wide and set it on top of a slight incline. It makes a wonder decoration and my wife will be looking for a shrubbery to plant near it.

[alex grams]

Good deal. I take it you have a pretty small window to cover if a single stone can do the job, that or it is at a pretty steep angle. Did you make the slight incline yourself, or was that already a natural feature of the terrain?

What the heck does a 1.25ton boulder cost to have delivered and 'installed'?

Plant some trees around it, in 5-8 years the trees will be big enough also to stop or sufficiently slow down a car.

Not sure how people could have a moral objection to a tree, but then again, you are probably dealing with a drunk who would think you put that tree there just to damage his car! I personally have no sympathy for any drunk who hits it. 9 houses and 3 have been hit by a drunk or distracted person, you are very well to be concerned and applauded to be proactive to protect your family. Thankfully though it sounds like no one was hurt on your street yet from the wrecklessness (pun/spelling typo intended!) of others.

[Charlie Stone]

Alex, The cost was totally dependant on the type of rock. In our case, the total cost was about $400, and that included the forklift putting it where we wanted it.
As far as the area to cover, our highest concern was the corner near the intersection. There is a tree to one side and a lamp post to the other. Over time, We may have other rocks put in spaced roughly 6 feet apart, but we got the area covered that we were the most concerned about. The incline was man made, but before we moved in. There is a small concrete curb around a flower bed, and behind that, there is an additional 6 inch rise of dirt. That foot on its own would only be a speed bump but with the boulder on top, it puts it high enough to help with the ramp effect.

I too have no sympathy for drunk drivers or people not paying attention.

[Charlie Stone]

Here are the pictures of the most recent accident which started the whole rock thing ... My wife just got a replacement adapter to get the pictures off her fancypants camera.

1 van managed to hit 2 houses, missed 1 car with a mother and kids (was stopped to make a left turn into the alley), 2 people on the sidewalk (literally 10 feet from where the van hit the small white house), and one of the people who lives where the van came to rest was about 3 seconds from standing on the porch when it hit ... she was grabbing her coat to walk out the door.

[Bryan Morgan]

Nice! That looks suspiciously like the van that wound up in my neighbors front room a couple months ago. Our street makes a right hand turn at the end and someone decided instead to just to straight and up across the lawn and right into their living room. All I saw was the tail end about flush with the side of the house.

[Mike Cruz]

I think it looks suspiciously like someone who NEEDED A ROCK OUTSIDE THEIR HOUSE!!!!!!!!!!!

[Bill Cunningham]

I have a bolder on my front lawn, that's about 3ft high, and 5' long. It was dropped there sometime during the last ice retreat, so don't know what delivery cost..:D I think things, and real estate were much cheaper then... ;) I've been temped to drill into it, and install a sword just to see how many would try to 'be the king'..:rolleyes:
I found another one about the same size while digging the foundation for my work shop.. It's still four feet down, but now part of the foundation..

[Dan Hintz]

It was dropped there sometime during the last ice retreat, so don't know what delivery cost..:D
Nothing too bad, just the cost of global warming :p

[Bill Cunningham]

Nothing too bad, just the cost of global warming :p

Well, that bout of global warming saved us all, or I would be living under a sheet of ice a mile thick about now, ha..
As for today? It's more like "Global Whining" :D

[Bryan Morgan]

..............

[David Weaver]

Uh oh...brian flatlined!

[Jim Koepke]

Maybe you can get together with your neighbors and get the police to hit the area hard with patrols to catch speeders.

Or start a campaign with the bars and call them at different days and times to tell the patrons that the police are set up in that area looking for intoxicated drivers.

Then there is the plywood police car that you could move around the neighborhood to coax people to slow down.

jtk

[daniel lane]

I would think a sign that reads, "DANGER: LARGE BOULDER AHEAD - DO NOT STRIKE WITH VEHICLE" would cover all legal issues. :D

[Bill Cunningham]

Maybe you can get together with your neighbors and get the police to hit the area hard with patrols to catch speeders.

Or start a campaign with the bars and call them at different days and times to tell the patrons that the police are set up in that area looking for intoxicated drivers.

Then there is the plywood police car that you could move around the neighborhood to coax people to slow down.

jtk

I can remember a few years ago, a few local cops got in a 'bit' of trouble for identifying possible drunks.. They would visit the local pub parking lot, and clean 1 headlight on every car, then wait down the street and start pulling over cars. Nothing they did stood up in court, because they had no probable cause to pull people over. Now, if they only had the brains to set up a R.I.D.E. check instead, and give a little more attention to the 1 lighters..

[Rod Upfold]

The accident which happened last week across the street, the guy swerved though an empty corner lot, back on to the street, spun the van 90 degrees went up a 1-2' concrete porch, though the front door and corner of a house, across an alley and though the covered porch of another house until he hit the concrete stair case where he put a huge V in the front of his van.


Holy cow - whats the speed limit on your street?


Rod

[jackie gates]

Charlie: If I lived in your situation, I think I would be contacting a realtor to find me a more pleasant place to live.

[Charlie Stone]

35 mph ... which I think is too high

[Charlie Stone]

naa .. I wont move,i have worked on this house so long and so hard its got enough of my blood, sweat and tears in it to be a relative.

[keith jensen]

I'd find a nice private road to live on I guess. I'm not an overly sentimental person though.