(Switching to manual transmissions would probably reduce the brake dust. Id like to see if european roads suffer as much. Between automatic transmissions, weight, and some traction control schemes, NA cars chew through brake pads.)
With the exception of tunnels, where heavy particles are constantly being churned up from the road surface and re-circulated into the air, tyre and brake wear is a relatively minor contributor to urban air pollution.
Why do you say that? Would love to know more, but all the research I've read lists them as significant contributors, second only to resuspension, each now exceeding tailpipe emissions on both PM 10 and PM 2.5.
https://www.sciencedirect.com/science/article/abs/pii/S13522...
https://dot.ca.gov/-/media/dot-media/programs/research-innov...
As an aside, we'd probably agree that vehicle weight is the mediating factor across all of these sources, regardless of the ratios from one type to the other. Massive load hauling trucks are generating a disproportionate share of emissions of all types, this is not really about making sedans a little more efficient.
Here in London, some of the most obviously polluted and stinking roads are those where the traffic barely moves at all - lots of slow moving or idling vehicles. There isn't a great deal of brake or tyre wear when vehicles are standing still!
Huh, all the studies I've read and linked are comparing like with like within particle size categories. Idling considerations are addressed in the modeling too.
You seem fairly unshakable here, but the topic seems well researched and the results are pretty unambiguous to me.
If you're only counting the largest particles, then yes, a lot of them are going to come from tyres.
https://particleandfibretoxicology.biomedcentral.com/article...
In my experience, over braking is the greater problem. Front tires degrade more quickly than rears. The average driver brakes far harder than they accelerate.
I think the heavier EVs hit a crossover point because of regenerative braking, but weight does set them back, that's one of the whole points of this study:
https://www.sciencedirect.com/science/article/abs/pii/S13522...
This is a curve though. We could almost simplify the problem and only look at what heavy trucks generate and ignore all the cars completely, it'd be a non-crazy approximation.
FWIW if the fumes/particulate from burning them are any indication tires are probably way nastier than brakes.
Second paragraph, though: I've never been around a brake pad fire, but I'd rather breathe vulcanized rubber than "metal shavings of copper, steel, graphite, and brass bonded with resin":
https://www.yourmechanic.com/article/what-are-brake-pads-mad...
Being inert in the presence of most common substances tends to correlate well with low toxicity. It's the stuff that chemically reacts to all sorts of things that tends to be the most poisonous.
Tires break down over time under "normal earthly conditions" which includes a lot of the same temperatures and molecules that are found inside the human body. To me this is a massive red flag for toxicity.
High temperature tends to make things react more readily. Most of the stuff in brakes has to be really stable at high temperatures and being stable at high temperatures tends to correlate well with being chemically inert.
The most reactive stuff in brakes are the long complex molecules used to bind it all together. These sorts of molecules are similiar to the molecules used in tires and all sorts of other plastic like things. So all else being equal tires probably have more of the chemically interesting things that cause problems in the human body.
Burning brakes smells way better than burning tires which seems to confirm this (remember, your nose has millions of years of incremental improvement when it comes to indicating what is and isn't suitable to ingest).
And before anyone thinks they're gonna get some easy internet points by saying "but asbestos", the amount of asbestos in brake pads is nonzero (to account for the sketchy unbranded stuff that may or may not use it) but still tiny enough that people working in proximity to it have mostly stopped dropping dead at 60 thanks to lung cancer so I think that however much asbestos is in brake pads it's low enough to not be an issue from a public health POV.
TL;DR I'll take my chances with brakes over tires.
That said, as was pointed out below, changing the car's design to vacuum up brake dust would be much easier than getting away from rubber.
I'm not well versed enough on the specifics to tell you whether or not PM2.5 is a good measure of pollution. The experts in the subject of air pollution routinely use it so it can't be thaaaat bad.
It's not a fair comparison, because you don't wear through the entire tire material as extensively as a brake pad. Fortunately we don't have to back of the napkin this one, there's lots of research showing brakes are near peers or exceed tires in contribution to PM 2.5.
As to your second point that brake material might be less harmful -- there is some initial research on how composition mediates impact.
Aluminum, sulfate, nickel, arsenic, and silicon seem to have the strongest relations. Aluminum is a frequent abrasive in brake pads, they aren't merely contributing some form of benign 2.5.
I can't do a comparison, you might be right it's "less bad" than tires, which contain other heavy metals. But I do not think the research is powerful enough to precisely settle that question beyond the overwhelming academic consensus that both are bad and we should definitely try to reduce both.
https://www.greencarcongress.com/2019/07/20190714-nee.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3755878/
https://dot.ca.gov/-/media/dot-media/programs/research-innov...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4315878/#Sec6ti...
Edit: Upon reflection, I assume your comment meant that newer cars will somehow use engine braking themselves. Since electric brake systems are rare in ice cars, would this be referring to cruise control features?
https://en.m.wikipedia.org/wiki/Compression_release_engine_b...
When you hear a truck making popping noises like a machine gun, that's the Jake brake in action.
On highways and motorways, I rarely need to use brake at all. Of course, being a sensible driver helps (in contrary to what many people expect from me when they see the car and expect yet another immature aggressive driver)
When you are driving down a large hill (e.g. on a mountain) eventually the battery will become fully charged, so you can't use regenerative braking anymore. To provide some resistance so you aren't effectively driving in neutral, the car will spin the engine at high RPM without supplying any fuel (I'm not sure how this works in terms of lubrication, as I understand the fuel provides this too?). You can also engage B mode which does this at an earlier stage, so have more control without having to use the brake when driving down steep hills (like engaging a lower gear).
London hybrid busses do the same thing, as they come to a stop you can hear the engine spinning at high RPMs.
> The term is often confused with several other types of braking, most notably compression-release braking or "jake braking" which uses a different mechanism.
https://www.epa.gov/sites/production/files/2015-09/documents...
This doesn’t seem like a trivial improvement. Particulates are not the only toxic component of exhaust either; electric cars should produce no NOx, CO or O3 which is a big improvement. It’s also worth noting that brake wear particulates haven’t been a target because historically exhaust-related emissions were so much larger.
If we haven’t really tried to fix it, who’s to say we can’t?
All this is to say that yes, there are fine particulates from trains, but it should normally be much less than from living near a highway.
The days of using the transmission to slow down are over. Brakes are better and more reliable (and cheaper) than ever.
People think that's not a big deal and you just get used to it, but the truth is, your brain is ALWAYS processing that noise in the background as a source of potential danger, taking a long-term tall on your mental state.
I work in an office with poor CO2 PPM levels, and constant noise. I've started enjoying working from home, even though I used to absolutely hate doing that.
Moving an automobile a couple miles in a dense urban environment at very slow speeds shouldn't require much energy, at least from a pure physics standpoint.
If the terrain is flat, I agree. In hilly cities, not so much.
However, regenerative braking (like any other energy conversion process) is not lossless, and it turns out that low-speed, high torque acceleration is where they're least efficient [1]: required torque increases with the incline you're trying to accelerate up. And if you're staying at low speed, you'll be stuck in this low-efficiency regime, and you won't recoup much going back downhill.
There is also the issue of subway noise, which is more like a constant stream of periodic vibrations. that is probably not good for one's nerves either but it is fairly subtle.
The most stressful thing about urban living for me was the constant light, ugly sodium colored light at all times, flashing lights, emergency lights, etc. I now live in a rural area and I will bundle up and sit outside on my deck at 1 am in 20 degree weather just to enjoy the darkness. There was never total or near total darkness in the city at any time, not even indoors unless you have blackout shades which we did not.
the worst of all worlds are those folks living in those apartments that overlook the BQE and stuff like that. They look like expensive places and I think whoever is choosing to live there is completely crazy, they get the most particulate matter (except that their windows are probably sealed shut, which is bad in itself), the most noise, the most light, etc.
But it's usually pretty easy to install blackout curtains if you want them. Or even just to buy a comfortable eye-mask for sleeping. Effective sound-proofing is much more difficult and expensive.
I live near a semi busy urban road, but there’s a wall of buildings + an alley between me and it. Pm 2.5 is very low at my place, and so is noise.
Never thought about the nanoparticles pm 2.5 doesn’t measure, but am assuming it’s similar.
"However, the highest averages were recorded inside the cars and buses: the closer to the source of the pollution, the exhaust pipes spewing out the fumes, the higher the total number of nanoparticles. The difference between walking by the kerbside of the road, and by the building side, on the same pavement – just a few short steps – was an average of 82,000 particles versus 69,000. The same readings registered no change in PM2.5."
1: https://www.bbc.com/future/article/20191113-the-toxic-killer... HN discussion: https://news.ycombinator.com/item?id=21552934