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Hard-braking events as indicators of road segment crash risk

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Re: Hard-braking events as indicators of road segment crash risk

#431

Post by blitzar »

sagarm wrote: post #95
mountain_peak wrote: post #46

Earlier quoted context omitted.

Maintaining a safe following distance is incredibly challenging on busy freeways where hard braking is often 'required'. Most people have likely found themselves in this situation: vehicle changes lanes in front of you; you slow down to maintain a safe following distance, another car sees a gap and changes lanes in front of you. Repeat for your entire commute. Incredibly frustrating, and I've driven all over North Am…

If you think highway driving requires hard braking, you're a bad driver.

Rounded to the nearest whole percentage point - highway driving is 0% braking.

Re: Hard-braking events as indicators of road segment crash risk

#432

Post by direwolf20 »

maerF0x0 wrote: post #219
Sohcahtoa82 wrote: post #213

Earlier quoted context omitted.

> vehicle changes lanes in front of you; I will never understand why this is so rage-inducing for people. Changing lanes is a necessary part of navigating, even during busy traffic. People on an on-ramp will need to get in front of somebody . People needing to move back to the right because their exist is coming up will need to get in front of somebody . Your lane is not a birth right. Let people merge. > you slow do…

It's frustrating because someone is taking your safety buffer as their opportunity to travel faster. And it results in you having to travel slower and slower to maintain the gap that is constantly consumed, tragedy of the commons style, by opportunists.

Someone else is taking your safety buffer as an opportunity to travel at all.

This exemplifies the problem with America. People will cut off their own welfare to make sure their neighbor doesn't get any either.

Re: Hard-braking events as indicators of road segment crash risk

#433

Post by direwolf20 »

crazygringo wrote: post #331
ehnto wrote: post #326

Earlier quoted context omitted.

Slow down a bit to create another buffer. You can even do this before they have merged, as part of the bit where you allow them to safely merge. I think if you reflect a bit you'll find you are being the same kind of person as them, if you are getting angry that you have to slow down and give up space for someone else. I understand some people can be aggressive though, that can be frustrating regardless of the outcom…

I don't think you're understanding. The point is that 20 people in a row will take advantage of your buffer to slow you down again and again and again, which makes you get to your destination later... because they're being selfish to get somewhere faster, and you're not so you get to where you're going slower . We're not talking about where they're changing lanes to take the next exit. We're talking about where your…

You mean 20 people who were trying to merge finally get to merge because someone came past who wasn't a massive asshole?

Re: Hard-braking events as indicators of road segment crash risk

#434

Post by direwolf20 »

adw wrote: post #390
apparent wrote: post #382

Earlier quoted context omitted.

It is more dangerous to be slow and have people constantly merging in front of you, rather than be slightly faster and not have all the merging. Accidents happen when vehicles are going different speeds, all things equal.

American road laws are insane here. The law should be simple; you must be in the outside lane at all times unless you are overtaking, and once you're done overtaking, you should merge back into the outside lane. https://www.highwaycodeuk.co.uk/overtaking.html

That seems rather inefficient on an 8– or 16–lane road.

Re: Hard-braking events as indicators of road segment crash risk

#435

Post by wongarsu »

tiagod wrote: post #393
JimBlackwood wrote: post #106

Earlier quoted context omitted.

They point in opposite directions because they’re not measuring the same things. Google is measuring where on the road most hard braking events happen. Insurers measure who is having the most hard braking events.

Problem with insurance companies measuring risk this way is that local government externalises costs of bad road design to the people who are unfortunate to have to drive there.

Makes you wonder why there aren't more insurance companies out there using their data to lobby local governments to fix their road design. They have all the data to find hotspots, and reducing accidents would increase their margin.

Maybe this would require an insurance company to have outsized market share in a specific area so they are the main beneficiary of the improvement

Re: Hard-braking events as indicators of road segment crash risk

#436

Post by mnw21cam »

CGMthrowaway wrote: post #365
OneOffAsk wrote: post #140

Aim to make the road laminar. Every time you hard brake, you're causing the milk jug to glug, making a ripple of entropy as momentum turns to heat from your brakes and those behind you, sometimes in perpetuity. I learned this while doing a 1.5hr daily commute in a Subaru with a clapped out manual transmission. I wanted to conserve energy shifting, but realized I was now participating in large choreographed dance of "…

Of course braking/change in velocity creates waves. But this effect is overemphasized in my opinion. Locally analyzed, traffic can be simplified incredibly by observing that a lane's maximum throughput is simply given by following spacing, measured in time. If drivers are using a 2 second following distance, commonly taught in driving school, then max throughput is simply 1 car / 2 sec If you double following distanc…

This assumes that a 2 second interval is appropriate for all travelling speeds.

This assumption is untrue at very low speeds, particularly when it takes longer than 2 seconds for a car to pass a point. For instance if we assume cars are 4m long, then with an interval of 2 seconds the cars would be touching at 4.47mph

The assumption is also untrue at very high speeds. You'll want a larger gap. That's partly because at such high speeds the ability of a vehicle to decelerate differs - if a vehicle with good brakes does an emergency stop and the car behind it has a respectable 2 second gap but has worse brakes then they can end up colliding. It's also partly because a 2 second gap at very high speeds means the car in front is further away, and that can cause a greater delay before the driver realises what is happening. As a third reason a greater margin needs to be used at very high speeds simply because the consequences of a crash are that much greater and should therefore be avoided even more than at lower speeds.

Therefore there is a kind of U-shaped curve in the "safe" following interval, and consequently a speed at which safe throughput is maximised.

That's why variable speed limits have been introduced in various places. For instance, in the UK which normally has a 70mph speed limit on motorways, in very high traffic conditions this can be lowered using electronic signs to increase the safe throughput of the road. It's commonly reduced to 50mph, though it does get lowered further in sections approaching a queue of vehicles that has actually stopped.

There's also the issue of speed oscillations. With a high speed limit and vehicles following too closely, a little variation in speed in one vehicle can turn into a larger variation in the following vehicles, causing a backwards-travelling wave of braking (sometimes to an absolute halt) and speeding up again. Lowering the speed limit reduces this.

Re: Hard-braking events as indicators of road segment crash risk

#437

Post by moring »

Gigachad wrote: post #358
Someone1234 wrote: post #28

This type of research is highly valuable but too rare; this is generally because of how we view Road Accidents at a core level: - Road Accidents: "A driver caused this, let's determine who, and find them at fault." - With Air Accidents: "The system caused this, let's determine which elements came together that ultimately lead to this event." The first is essentially simplifying a complex series of events into somethi…

Because for air travel we pre filter out the morons who are drunk, untrained, scrolling facebook, etc. Any incident left is overwhelmingly more likely a systems issue. For a road incident, the most likely cause was just one driver was violating one or more rules. The only system failure was not canceling their license beforehand.

> The only system failure was not canceling their license beforehand.

Why was their license not canceled beforehand?

Did they not get caught? If so, why? Likely other drivers have noticed the bad driving behavior. If so, why did they not report it? If they did report it, did the reports get ignored? Is there even a system and process in place for such reporting?

If they got caught, was there hesitation to revoke their license? If so, why? A potential factor would be driving in an area where you have to drive to get anywhere, which is common in the US. Why has it not been addressed that you have to drive, even if your driving habits are bad?

If bad driving behavior is too hard to punish, why? If regulations do not allow adequate punishment of bad driving behavior, why have these regulations not been changed? If evidence is missing, what evidence would that be, and how could it be collected?

If the driver was drunk, what would have been the alternative to driving? Is there adequate public transportation for drunks to get home? "adequate" depends on the drinking culture in the area where that happened.

If the driver was untrained, why were they allowed to drive? You wrote about canceling their license, so they did get a license. How was that possible without training? Does the process for handing out licenses have to be changed? Is frequent re-training necessary (more data is needed for that; if that data isn't avilable, why not?)

Obligatory link to the CAST handbook in case you want to follow that line of thinking: http://sunnyday.mit.edu/CAST-Handbook.pdf

Re: Hard-braking events as indicators of road segment crash risk

#438

Post by mnw21cam »

luxpir wrote: post #210

Wait, what do they teach in North America? Never heard the term "following distance" before now. Sounds misleading. In Britain at least we call it "braking distance" and you're supposed to leave 2 seconds at least between you and the person in front. Count it off a lamp post/sign etc. In certain at-risk areas they use chevrons on the road and signs telling you to keep at least 2 chevrons between you and the car in fr…

Braking distance and following distance are two distinct things.

Following distance is the rule that you should leave a 2 second gap in front of you. That is often less distance than the braking distance.

You should be always able to see that your braking distance is or will be clear, and that sets the maximum speed you should drive at as you approach areas with reduced visibility, like corners or the brow of a hill. You must learn braking distances for the driving test.

Re: Hard-braking events as indicators of road segment crash risk

#439

Post by mschuster91 »

shepherdjerred wrote: post #329
mschuster91 wrote: post #74

Earlier quoted context omitted.

Yeah well fuck insurers. We are supposed to get spied upon by our cars with their blackboxes, by our insurers, by Google, by national security services of various countries... and what do we get in return? Dinged for other people's bad behavior which we cannot reasonably control. Either you follow the car in front of you very closely and get hard braking events, or other people switch lanes in front of you and in the…

So, what's your proposal? What should insurers be doing differently?

Operate like they did before they had access to surveillance technology that would have made Gestapo and Stasi blush

Re: Hard-braking events as indicators of road segment crash risk

#440

Post by 4gotunameagain »

sspehr wrote: post #421

Google Maps is definitely one of the technically coolest big tech products imo. It's fascinating what kind of non-obvious insights you can get from the combined user data (E.g. Crowdedness of public places, insights like in the article etc.)

The value of said data is tremendous, and could lead to great societal benefits if available for research.

So much so that I would argue that google (et al) should be compelled to make the data publicly available.

They have enough money, let's make society better.

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