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[youtube]http://www.youtube.com/watch?v=h9VWF1DXQ8s[/youtube]

Stupid truck driver! hehe

Another reason to upgrade your brake system first..... . Oh, and if that driver hadn't have looked at the other driver he would have reacted faster.....Don't drive distracted

Replace one of those cars with a locomotive and see how well the truck does.

Get a Ferrari so you can go under the truck, movie style.

Well, unless the stupid truck has a barrier on the side. Who does that!

Just did some physics here...

If a 1000-kg car goes at a speed of 108 km/hr (=30m/s - physics!) it will take approximately 51 metres for the vehicle to stop completely (that is assuming that the coefficient of friction between the tires and the road is 0.9 - pulled out of the physics textbook).

If the same vehicle travels at a speed of 113 km/hr (or 31.4 m/s) it will take roughly 56 metres to come to a complete stop. In 51 m of braking (ie same distance), the speed of the vehicle will be approximately 33.4 km/hr.

E=(m*v^2)/2=F*d=µ*m*g, F = µ*m*g,

1-st equation is kinetic energy equation, the second is work, the 3-rd is rearrangement of force of friction doing work, the 4-th is the force of friction equation.

where:

m - mass (in kg)

v - velocity (in m/s, to convert from km/hr divide by 3.6)

µ - friction coefficient, denoted by Greek letter mu (looks like u with a long tail on the left side of u).

g - acceleration due to gravity, 9.81 m/s^2

If you rearrange, the stopping distance d = m*v^2/(2*µ*m*g), or d=speed^2/17.658, since m cancels out, µ is constant (dry tires on dry pavement), g is also constant. So mass of the vehicle doesn't matter o_O, a truck will take as long....

On the same note, a vehicle travelling at 35 km/hr will take only 5.4 metres to stop (about 16 feet). What's going 40 when the stopping distance is 6.3 metres???

So, it all depends on which 5 km/h it is...........

Yepper, 'cause the speed is squared...

Ya isn't that common sense though. So if driving 5 km/hr over is unsafe. Why don't we limit the highways to 50 km/h so the province can protect people from themselves?

People know this but they dont care. How do i know this. Cause when im on the 401 the guy in the left lane going 119 km/h with 10 cars on his bumper doesn't seem to care and nor do the people who are all trying to pass him.

Sure in the event of an accident lower speeds will do less harm. But what is to say they're will be an accident. What is to say that accidents and death have more to do with excessive speed as opposed to not paying attention. You can make things slower buts its hard to prove.

All we know is people drive these speeds everyday in many places around the world and they arent dying anymore or less than we do. Theyve done studies in the states and other European countries. They seemed to find the zones with higher or no limits didnt show they were any more dangerous then zones without speed limits.

The province never seems to understand cause and effect. With my example before. The province might decide to crack down on aggressive driving and tailgating or improper lane changes. So they cant spend a whole pile of our money trying to enforce laws. But they might fail to see the cause of the aggressive driving is because of improper lane usage that angers other drivers.

Sure you cant stop sooner but then why not limit all roads even lower? What is the best speed? Who knows how do we decide the right speed? Arent all traffic injuries speed related. The t-bone at a 50 km/hr zone at a city intersection has speed as a factor to.

Everyone drives to close. Just enter the 401 or the QEW in rush hour and Toronto. NO BODY travels 2 cars distance. Every car on the road is "tailgating." People don't seem to care.

Racer - think I understand the bottom line there....but what does not appear answered in that equation (please correct me if I am wrong) is the following:

But I guess I'm using the video as an example.....

if driver a = 108km and the other driver b = 113km/hr......and the transport blocks their path......driver b is obviously farther down the road, driver b reaction time will be the same, however the distance travelled during that reaction time is longer....., then the braking distance......so would the impact then not be higher than 33km/hr?

Here is a little typo diagram

A...108km........distance travelled........reaction time.....braking......stopped

B...113km.................distance travelled.............reaction time.....braking.......stopped

I guess what remains the same is once both start to brake, but distance travelled is what makes the difference.

ummm the video stipulates that they hit the brakes at the same time while driving neck-to-neck, though one is faster.

otherwise why not:

A........................108........dist.reaction........braking..........crash

B...113.........dist.reaction..........braking.......................stop

On a side note, none of the freeways we have with the speed limit of 90+ are not controlled access, so the situation is moot to begin with!

If the reaction time is approx 0.1 s, in that time the driver at 113 will travel exactly 139 mm (5.5 in) ahead of the 108 guy. If you take the reaction time to be 0.2 seconds, that's 278 mm (11 in)... When you are taking 50 m to stop, that difference in negligible, I also did round well more up when calculatin for 113 guy as opposed to 108 dude.

Good work with the calculations, racer.

One more variable to add. Let's say a cargo van weighing, oh, say, 6000 pounds is travelling 60 km/h. What would his stopping distance be compared to a Civic/Corolla/Cavalier that weighs half as much, but is going 80 km/h?

Also... couple of other things to mention...

You have a 50% chance of being killed if you are rear-ended at 105 km/h, broadsided at 75 km/h, or hit head-on where both vehicles are doing about 45 km/h. That, of course, assumes that those speeds are attained at the moment of impact.

A pedestrian has a 90% chance of surviving if they are hit by a car at 32 km/h, but a 90% chance of dying if hit by a car at 65 km/h. Makes you wonder why residential side-streets have 50 km/h limits. Yeah, pedestrians shouldn't be in the middle of the road, but little kids will be more likely to chase after a soccer ball on a quiet sidestreet as opposed to a busy arterial throughfare.

Radar Identified wrote:

Good work with the calculations, racer.

One more variable to add. Let's say a cargo van weighing, oh, say, 6000 pounds is travelling 60 km/h. What would his stopping distance be compared to a Civic/Corolla/Cavalier that weighs half as much, but is going 80 km/h?

Also... couple of other things to mention...

You have a 50% chance of being killed if you are rear-ended at 105 km/h, broadsided at 75 km/h, or hit head-on where both vehicles are doing about 45 km/h. That, of course, assumes that those speeds are attained at the moment of impact.

A pedestrian has a 90% chance of surviving if they are hit by a car at 32 km/h, but a 90% chance of dying if hit by a car at 65 km/h. Makes you wonder why residential side-streets have 50 km/h limits. Yeah, pedestrians shouldn't be in the middle of the road, but little kids will be more likely to chase after a soccer ball on a quiet sidestreet as opposed to a busy arterial throughfare.

Thank you, physics is my primary area of interest...

Physics tell us that a loaded cargo van will have a greater friction force acting on it due to its weight, therefore (providing the tires lock) it will take the vehicle the exact same distance to stop at it would for a smaller vehicle!

Here, m doesn't matter, μ is known to be 0.9, g is constant at 9.81 m/s, and 2 is 2. So the only thing that affects your braking distance are your brakes and speed!

Radar Identified wrote:

A pedestrian has a 90% chance of surviving if they are hit by a car at 32 km/h, but a 90% chance of dying if hit by a car at 65 km/h. Makes you wonder why residential side-streets have 50 km/h limits. Yeah, pedestrians shouldn't be in the middle of the road, but little kids will be more likely to chase after a soccer ball on a quiet sidestreet as opposed to a busy arterial throughfare.

Do you have the numbers for cyclists? I bike a lot (helps keeping the weight down with all the donuts), and I prefer to be a live cyclist to a dead one, thus I never go on the street with a posted limit of 60+.

And bigger vehicles have bigger brakes, larger swept area....

Interesting data on the weight/braking/stopping. Clears up a few things!

As far as the risk of a cyclist being fatally injured goes, I think I have the data somewhere, I'll see if I can find it. I can't imagine it being that dissimilar to the risk for pedestrians. Most of the information on the risk-of-death-versus-type-of-collision came from the New Zealand Ministry of Transport, I'll see if there's any data out there.

Along with this.

Is it a law soon all new cars must come with electronic stability control?

I know there was talks of this.

Is it also law all new cars must come with disc brakes on all 4 wheels. I dont remember i thought i heard some ramble about this.

Didn't hear about those. I heard that some people might want ESC but that could be a hinderance to "expierienced" drivers

I did hear about stability control, along with TMPS, being mandatory. Stability control is different from traction control, in that stability control tries to keep you straight on the road and traction control keeps you from spinning your tires. I like stability control but hate traction control. TC helps a bit with open differentials, but most of the time it feels like you're driving on sheer ice because of the way the engine cuts back on power.

Racer - you say mass has no effect when the tires are locked, and that sounds right even though it's late at night and I haven't really looked at the formulas.

But what about throwing ABS into the mix? I also bet that most seasoned truckers are pretty good at threshold braking. To me, it seems logical that threshold braking would produce shorter stopping distances than locked tires, but a light vehicle will stop even shorter than a heavy vehicle using threshold braking.

Bear - to be fair, let's assume both vehicles are travelling neck-to-neck at the moment they both see the hazard. The faster vehicle would still be at a disadvantage, even assuming identical stopping distances:

A: 108.....reaction time.......braking......stop
B: 113.....reaction time............braking......crash

racer wrote:

If the reaction time is approx 0.1 s, in that time the driver at 113 will travel exactly 139 mm (5.5 in) ahead of the 108 guy. If you take the reaction time to be 0.2 seconds, that's 278 mm (11 in)... When you are taking 50 m to stop, that difference in negligible, I also did round well more up when calculatin for 113 guy as opposed to 108 dude.

reaction time is 1.5 seconds (time person sees the danger, processes "oh *EDIT*" in the mind, then tells the body to move the foot, then the foot to depress the brake)

that being the case, in 1.5 seconds the faster driver will move ahead by 2083 mm (2.1 metres). In the end the numbers are such that they do not differ much from what I have...

Again, going those speeds, which are reasonable for 400-series, you simply do not see such a situation. On the city roads, where a truck pulling up on you is much more feasible, when you go 60 you take 15.75 m to stop after you hit the brakes, while going 65 you will take 18.5 metres, or add 2.1 metres and you end up with 20.55 m. A lot is dependent on the speed you are travelling at - ABS on or off, driver skills are all moot when it comes to "oh *EDIT*" reflex, which forces the driver to floor the braking pedal (and yank the handbrake if s/he can still think straight), the stopping distance will always be proportional to the square of the speed.

ABS and the rest can work great, but we are taking worse-case scenario. If you use tires with better grip (you will also see more smoke) you will reduce your stopping distance. And some people will try to drift out of trouble, which might work, but for which ABS does not help at all... The only real practical use for the ABS is stopping on icy road, and as we all well know, driving 100 on ice = pileup, be it 80 or 120.

(and yank the handbrake if s/he can still think straight),

and downshift and throw both hands out the sunroof for aerodynamic drag

Reflections wrote:

(and yank the handbrake if s/he can still think straight),

and downshift and throw both hands out the sunroof for aerodynamic drag

or the coefficiency of "soles" vs road...seems to work for the Flintstones!!

Big rubber boots or sandals????????/

Reflections wrote:

Big rubber boots or sandals?

I was thinking of a boat anchor. Works great when there's potholes!

Haha some parts of the 401 in toronto look like a giant slice of swiss cheese there is so many holes.

The worse part is you cant close that highway or the traffic backup would be ridiculous.

I was thinking of a boat anchor. Works great when there's potholes!

Haha some parts of the 401 in toronto look like a giant slice of swiss cheese there is so many holes.

Ah HA......there is the cause.....too many boat anchors making holes in the road!