Cool vid!
A few weeks ago I sent the paper around the local bike committee (includes the Council person).
Maybe I'll follow up with this easy - to - grasp video. The crash dummy footage gives a very visceral effect. As in, imma be eating less for dinner now.
@CelloMomOnCars @AdrianVolt I have a very hard time believing that the size doesn't matter, only the shape of the grille! Size correlates both with blind zones (even a slated hood will leave a bigger zone on a bigger car) and with weight, and weight is incredibly important both on direct deadlines and on wear and tear on asphalt and tires, creating deadly air pollution and micro plastics.
I will come back at you later because I believe that the shape of the grille is actually much more important than size as far as blind spots are concerned.
Meanwhile, there are some hints that FortNine may not be wrong about vehicle mass being comparable unimportant in the event of a crash against a pedestrian or cyclists:
- Long before the #SUV trend, vehicles got significantly bigger and heavier, yet traffic deaths went down significantly.
- FortNine correctly states that the kinetic energy in a moving vehicle (even at relative modest speeds) is so high, that the comparable tiny mass of a pedestrian is basically nothing.
Perhaps the 2 ton SUV will accelerate your body to 30 kmh instead of the 29 kmh the 1.5 ton vehicle and the 28 kmh of the 1 ton vehicle. (This is not a physic calculation). The difference is still only 2 kmh in acceleration and while higher peak acceleration g-forces are of course worse, one might argue that the small difference in your end speed
isnt going to be deciding in your survival or death.
The way the impact happens and where those acceleration forces are transferred meanwhile almost certainly matters a lot. The entire reason of Airbags saving so many life is quite simple their ability to cushion the impact, reducing peak G-Forces and transmitting them also over a much larger area of your body.
- Modern active safety systems (that add weight) as well as better (but heavier) tires and brakes also help to avoid or at least mitigate the severity of accidents.
Nuff said... the 3 ton SUV coming to a screeching stop 30 cm before you is much better for your health than the 500 kg #PersonalLightVehicle slamming into you at 25 kmh.
Small vehicles may be space efficient, but the limitation of length also means that any rammed pedestrian is much more likely to hit the hard and unyielding parts of the passenger safety cell. Very small cars may have almost no hood, but as a result, their impact on a pedestrian is
similar to an SUV with its high hood.
- Assuming your body can handle the g-forces - and humans can withstand quite impressive ones - for VERY short amount of times - the next grave danger is getting rolled over/getting under the wheels as the weight of the vehicle will then do devastating crushing damage to you.
Vehicles with low ground clearance will delay that and instead push you ahead of them until they come to a stop. Which is not something to looko forward to, but much less injuring than getting run over.
- Mass in motion alone does not necessarly kill unless the acceleration g-forces on your struck body become to high: We had a young man wearing headphones here a few years ago who managed to get in the way of a fast tram. Besides an emergency brake it struck him at something like 35+ kmh. He impressively survived besides the tram massing over 50 metric tons thank to
- a lot of dumb luck
- the tram being low floor, which saved him from being run over
- not hitting
anything that would have torn him apart with the tram pushing him from behind. (If you get caught in a pole with the tram pushing from behind, something will give in and it is not going to be the pole or the tram).
(Such an type of accident is pretty much the only accident where the trams of my city killed passengers in a car. The tram rams the car, that alone is not fatal, but the car is pushed ahead into one of the catenary wire pole and then is smashed between the heavily braking but still moving tram and the pole. )
He certainly spend a long time in hospital and I am unsure if he ever will fully recover... but what can you expect when you insist on a boxing match with 50 tons of speeding steel.
So yes, I would argue that while more vehicle mass is obviously not beneficial, it probably is not the large deciding factor if a struck pedestrian will survive.
I will make a seperate post regarding wear and tear and air pollution.
I think that wear and tear on the road is much more complex than vehicle weight and tire size:
- Any type of tire creates vehicular movement by bracing itself against the road. Once the force/torque applied to the wheel is higher than the static friction + rolling resistance and any other driving resistances, the vehicle begins to move. This continued transfer of force/traction however wears down the tire. Even the steel wheels of railroads over time wear out, although obviously far less than any rubber tire.
The more traction force is transfered, the higher the wear. So from a wear and energy efficiency standpoint, you want to minimize traction. Which unfortunatly is only possible by reducing maximum traction. The steel wheels of a railroad have very low rolling resistance but also very poor traction, leading to enormous braking distances and the need for guided rails for any kind of steering.
But back to rubber tires:
Traction is based on
- Tire size - how much rubber is in contact with the road
- Weight load on that tire (depends on the mass and weight distribution of the vehicle)
More rubber on the road that is pressed onto the road with more pressure (due to higher mass) will result in higher grip = superior acceleration, braking and cornering potential. This explains why modern large trucks brake almost as good as any car, they dont have that much more rubber on the road but their weight presses that rubber onto the road much harder, allowing much higher forces to be transmitted.
Smaller tires (diamater) need more rotations to move the vehicle the same distance. Since each part of the tire contacts the ground once per every rotation, tire wear is not so much based on distance but actually rotations. Or in english, smaller tires wear out faster than larger ones because they have significantly more rotations behind them for the same distance:
This however does not
mean that smaller tires create more air pollution. Just that they last for more distance because they have fewer rotations behind them.
To understand road wear and rubber abrasion, we have to look at something else:
-Size of the contact patch = the rubber that is in contact with the road at any given time.
-Pressure on that contact patch (how much weight bears down on it)
The actual contact patch on tires is actually very small... arround the size of your hand without the fingers. Those 4 patches (4 wheeled vehicle) transmit ALL the forces of the vehicle to the road. Impressive, isnt it? Less than a sheet of paper is capable of delivering more than 1g of acceleration and deacceleration forces on a heavy vehicle. But such force transmission of course comes with abrasion on the rubber, the higher the transmitted force, the more wear on the rubber. Accelerating or braking, hard as such leads to increased wear. Limiting forces meanwhile prolongs lifetime.
There is however
another major factor: The ratio between pressure and size of the contact patch:
The smaller the contact patch for a given vehicle mass, the higher the pressure per square cm on the road. The more pressure, the more strain on the rubber and the road below it. So to decrease road wear, we want to spread out the weight of the vehicle on as much rubber contact patch as possible. There is however a catch... more rubber contact patch on the road naturally also increases rolling resistance. The contact patch also increases very slowly compared to the diameter of the tire, meaning that you need far more than double the tire diameter for double the contact patch. So why not go into beam instead? Fatter tires increase the contact patch much faster but also lead to higher rolling resistance faster.
Because possible vehicle beam is much more limited than vehicle length, there is a upper limit of tire fatness, a fact not helped by the need to have steering and power on some axles at
least.
So unsurprisingly, heavier vehicles like busses and trucks simple go with more axles but use large diameter tires that are however pretty thin.
Fuel consumption = good because we still only have a pretty small contact patch, not that much larger than on a average car tire.
Large Diameter = low RPM = long distance lifetime
The much higher weight of the truck however means, that the weight bearing down on that contact patch can be 10+ times higher than for a car. While not having much more area to spread that weight.
It is this resulting much higher ground pressure compared to average car tires, that help explain why busses and trucks damage to road thousands of times more than a car.
Yeah... that one transit bus serving your small town damages the road more than the 5000 cars of the inhibitants. It also follows the same track all day, doing that damage to pretty much the same part of the road.
UnfunFact: Because law in Germany makes it possible to make local
residents pay for street repairs, we have citizens here fight against a busline (good for air pollution and climate) with everything they can muster, because they - not entirely unjustified - fear that they will end up paying the road repair every 15 years which is going to cost them thousands of €, driving up total costs (road repair + higher rents due to public transit availability) uncomfortable close to what owning a car would cost.
The difficult to answer question now is, how much worse are heavier cars compared to busses and trucks.
EVs are significantly heavier while not having space for significantly larger tires as they are still cars. They also aim for thin, energy efficient tires to increase range (at a certain cost of traction and braking performance)
It seems reasonable to assume, that EVs for the foreseeable future will be slightly more damaging to the road and as a result of that higher friction will also emit more fine dust compared to the
TIRES
of a ICE
If that damage is as significant as from trucks and busses however seems doubtfull. EVs may have 25 % more mass but that pales in comparsion to the 10 - 12 times contact patch pressure that average trucks and busses put on the road.
On the other hand, the instant power of an EV makes spinning the tires much more easy. Yes, traction control will intervene, but strong acceleration always leads to more rubber on the road.
And while I hate #SUV with a passion, their large fat tires could actually reduce pressure per square cm to a level comparable or even below average cars. Still a shitty type of vehicle that needs to die asap.
Also this:
https://digitalcourage.social/@AdrianVolt/112152730876302932
Thank you
One thing might make it particular valueable. It is posted by a channel that normally does motorcycle stuff, which is giving it a lot more street credibility in motorist circles compared to the average "Critical of cars" channel.