Hard-braking events as indicators of road segment crash risk

I think it will also back down the cruise control (if set) if it detects that you are gaining on the car ahead. That might be MILs Toyota though.

I learned the "two second rule" in Driver's Education 45 years ago and generally follow that. Nothing more annoying than having the car behind you riding your bumper.

I am so glad it hasn't. Data point of one, but gamification now has the opposite effect on me: it's such a well-worn pattern that it just annoys me. It was great when it was novel. I wonder how many others feel the same but without sampling it's hard to know.

I'm all in for traction control and to some extent ABS, but braking hard and upsetting the car's balance when you don't need it is dangerous.

It also shows how close you are to the car Infront in "car length" units with a nice big indicator and the adaptive cruse control will follow that distance mostly on its own between 30-100mph

Instead of pretending to shift responsibility to the car, how about people do training every so often instead? Maybe every ten years for an hour or two.

The amount of work a young person has to do here to be able to obtain a "full license" takes literal years and multiple tests.

But then nothing for the rest of their life despite advances in technology (in and out of the car) and changed traffic conditions...

(the irony of looking at a meter on the dash to duplicate a piece of information I should be very clearly seeing out of the windscreen was not lost on me, though)

No smooth maintaining of speed and nice passes as able without slowing down.

Surprisingly, his accidents have mostly seemed to involve gas pumps, barriers, and other obstacles at low speed.

1. In any amount of traffic above “a few cars” people will cut in front of me, sometimes two, negating the safe following distance. Regardless of speed.

2. If I have a safe following distance while waiting for someone to get over. (I e they’re going 60, I want to go 70), if I have my distance set at a safe following distance, people are much more likely to weave / pass on the right. (My theory would be that the distance I’m behind the person in front of them signals that I’m not going to accelerate / pass when the person gets over ).

Disclaimer: I don’t usually have to drive in any significant traffic, and when I do (Philly, New York City), I’m probably less likely to use the automatic features because the appropriate follow distance seems to increase the rage of drivers around me.

It does require patience to do this, because all aggressive drivers will use the space you provide. But ultimately the travel time difference in flowing traffic is negligible.

Having driven all over NA, and Europe, I find it more prevalent in NA. Less distance, more people in large pickups throwing their weight around to make someone move out of the way.

And a design of giant freeway interchanges that require shifting lanes.

E.g. on the 405 in CA. 7 lines going South from the Valley towards Santa Monica.

That's 7 lanes you need to cross if you're in the HOV lane.

The only people who cut too close to me are driving recklessly.

That being said: If you're in the mode where people are constantly changing lanes in front of you, think a bit about how you're driving: On the freeway you're supposed to stay to the right except to pass, and you're expected to keep up with the flow of traffic. Are you going slow in the left lane? Are you driving too slow? Are you camping in the right lane by a busy interchange?

Somebody on the radio said that "just set the adaptive cruise control to max distance and your windshield will last way longer". It does feel overprotective at times, especially in slow and dense traffic, but I think there's a nice point in general.

I recently pulled my travel trailer from OK to Charleston, SC and back. I never drive over 65 MPH for safety and MPG reasons. I always stay in the right hand, slow lane except if I have to take a left lane exit. Since I was always driving slower then everyone else, not once did I have to hard brake. Tailgating is a choice and a dangerous one.

I was never honked at, even by the crazy semi truck drivers.

To be sure, it's more mentally taxing to hold a tight gap, so it's not something you want to do all the time, but it's fine.

it's largely a problem in the left lanes, thats where drivers will bunch up most. the subjective feeling is mostly a reptile brain issue though, the feeling you're getting done over. driving is 90% id, sadly.

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 down to maintain a safe following distance, another car sees a gap and changes lanes in front of you. Repeat for your entire commute.

This happens because literally everyone is tailgating each other so hard that the gap in front of you is the only gap that exists for people to change lanes to either get on or off the highway.

I just put adaptive cruise control on max distance and call it a day, gives me 4/5s to react, and also it starts beeping hard if intervention is required.

It has saved my bacon a couple of times.

People only take your lane if you are in the fastest lane. If you are in any slower lane, people tend to jump in and then leave and I have no problem with people who do that.

You can also keep a gap in the fastest lane but you need to keep track of other cars on the road. You’ll observe that most cars rarely leave their lane. People who tend to leave their lane keep smaller gaps in front of them. Use that knowledge. There are many more factors than just that but if you start observing everyone drive, your little simulation in your head will start putting other drivers into buckets.

I had a slow realization that I could just let people jump in. My goal is to maintain a constant speed and never have to hit the brakes, and I can usually still do that regardless of whether people jump line.

But yes, the principle of it is incredibly aggravating ("that space is for safety, not YOU, green Acura!!!") but I actually kinda like the practice of trying to be zen about it. I mostly get through a long trip at the same rate :)

Usually if you maintain the slightly slower speed you had to maintain a safe following distance it doesn't matter, as the distance will either increase or they'll leave for another lane. You have to get used to drivers doing messy things in front of you, but at a safe distance. When doing this you are in fact helping the traffic becoming more fluid.

E.g.

- Switzerland and (somewhat surprisingly) UK: pretty good, people doing idiotic shit is rare enough that I'll usually comment on it if there's another person is in the car. If someone is riding my ass I'll make the effort to try and shake them off.

- Italy and Spain: horrifying, impossible to relax at all on the highway, having someone 2 car lengths off your rear bumper is the default condition.

- France and USA: somewhere in the middle where there are a lot of idiots but they are still the minority.

Subjectively, the USA feels much more sketchy because the rules are so much looser around overtaking.

It’s not hard to do. It’s only frustrating if you let it be. It really barely slows you down at all.

For the sake of argument, assume you follow the "three second rule" and that the other driver is slightly aggressive and enters closer to the front of your safety buffer. You are now down to a two second safety buffer so rebuilding it back to three seconds costs you an extra second of travel time.

In practice this happens to me about a dozen times a day. It sometimes feels frustrating, as if each of these drivers is stealing another second I could have been playing with my kids! But ultimately it's worth spending the extra seconds to slightly increase the odds that I arrive home each day to play with them at all.

Also, a bad driver mis-breaking trips the cars behind into breaking too, which multiplies the energy waste and may also cause accidents through fatigue.

Mare experienced drivers will give you more leeway to avoid tapping the brakes with you, or simply go for a staring overtake.

I remember being too aggressive when I got to the Bay Area, and learning how nice it was to be let into the lane I needed to avoid being forced on a 5mi U-turn. When visiting back home I was too nice and people told me so.

I've reached a balance. Aggressive enough not to be taken advantage of, but being nice to drivers in need, specially when it doesn't really change things for me, like when letting a driver in costs me nothing because of how bad traffic is.

The only possible fix as a driver was to try to develop an intuition for spotting “stale” greens and start slowing down despite the green, anticipating the yellow.

I feel at least partially vindicated by the fact the lights in question eventually had their yellows extended.

What will happen if there's some oil spill or brake failure at the point you think you should break hard?

The incentives just don't line up.

This perfectly illustrates this broken mental model that leads to endless frustration.

Unless you put the car in reverse, you are still making forward progress. If someone merges in front of you at 30mph then you traveled hundreds of feet towards your destination in the time it took them to do that. Chill out.

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

I always pull away at the same speed as the car in front of me and maintain the same distance as when we were stopped. It is very easy to do and completely eliminates traffic build up if multiple people do it at the same time.

This is the same reason that we have amber lights on traffic lights, so that the drivers have time to get into gear and start pulling away so that when the light goes green they are imediately travelling through it, causing no excess traffic build up at the lights. Again unfortunately people dont concentrate when they are stopped at lights and so you have the situation where they see the light go green and then proceed to start changing into gear and remove the handbrake. By the time they are moving through the green light, they have already taken 10-20 seconds of green light time, eating well into the time alotted for cars to be travelling across the junction.

The only thing which will solve this is driverless cars, meaning that the cars can all talk to each other and move at the same time like a chain. I welcome this advancement to elimante human error in driving and get rid of traffic jams for good.

Also you then just leave a bigger gap in front of you for somebody to jump into, forcing you to break more and go further back to maintain your distance. This in turn just winds up the drivers behind you who end up overtaking you. All this chaos becasue you think you are helping by 'reducing compression'.

In heavy traffic I much prefer to quickly catch the car in front up and then sit stationary with my engine off. Much more efficient and less polluting than spending the whole time with your ewngine on managing gaps and braking distances at low speeds.

That postulate breaks down as soon as you move away from a laminar traffic assumption and include distracted drivers, lane changes, and weather influences. Which is why the wave theory model is important to understand the propagation of perturbations and their effect on maximum throughput.

> The throughput of a (full, i.e. rush-hour) road has nothing to do with speeds of people driving, and everything to do with following distance.

And yet, in the limit case of a bumper-to-bumper situation (or, in fluid dynamics parlance, an incompressible flow), the variable determining the change in mass flow-rate is the velocity of the medium. Mimetically, we could also look at ants. To ease congestion in a bumper-to-bumper situation, they accelerate.

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.

Have a look at a few dash cam accident videos [1]. There are many maladaptive patterns of behavior, but a frequent one that the average good driver can improve on is limiting speed on two occasions: when approaching a blind spot, and when passing stopped or slow traffic.

That second one gets lots of otherwise good drivers. They seem to think that by limiting their speed vs slow/stopped traffic they'd be encouraging people to dart in front of them. Which is somewhat true. But with limited speed, that's an avoidable or less injurious accident. By gunning it past stopped traffic, you make the accident unavoidable and more serious.

[1] https://www.youtube.com/@IdiotsInCars1

It’s this obnoxious audio warning that tells me I had a hard breaking and it’s 9/10 because I stopped at a red light that I would not have made on yellow. And then it sends me tips and reminders about reducing hard breaking events and it’s annoying. I know they have done the analysis but it detects moderate hard breaking which is frustrating. One of those things that I am sure in net is positive but perhaps slices of the population it does not benefit.

Most people have near zero defensive driving skill, and view someone pulling out in front of them as "nothing I could have done", when the dashcam shows the offending driver showed 5 signs of pulling out ages before the accident occurred.

of course if they change such that they don't break hard when needed that is bad, but if the change such that they don't need to break hard in the first place because they slow down in places that are dangerious that is the point.

There is a minor financial aspect (price of fuel), but I’m far more interested in seeing if I can get a better “green score” at the end of the drive.

The cause of hard braking isn’t mutually exclusive: bad driving or bad road design.

Google is measuring where on the road most hard braking events happen.

Insurers measure who is having the most hard braking events.

Of apparent surprises to the driver. And since actual, factual surprises are extremely rare, if a driver is regularly being surprised, they're a bad driver.

It’s still out of the norm braking for my style of driver but from what I see on the road, people drive aggressively like this. Especially in the US.

Where Google/Apple's coverage is quite valuable is for near-real-time speeds for atypical events -- say like yesterday's Super Bowl. But that's not what this blog post is about -- this post is about a well-established pattern that can be identified with historical datasets.

All that to say that vendors sell a wide variety of data products to transportation planners, but just because Google is now entering this niche market doesn't mean they'll be "the best" or even realize what their strengths are.

>Also, crashes are statistically rare events on arterial and local roads, so it can take years to accumulate sufficient data to establish a valid safety profile for a specific road segment.

That is exactly what this article is about.

> It's not a lack of knowledge by Caltrans or Santa Clara County's congestion management agency that is keeping that interchange as-is. Rather, it's the physical constraints of a nearby airport (so no room for flyovers), a nearby river (so probably no tunneling), and surrounding private landowners and train tracks.

The most recent budget estimate is $1bn for any changes to this interchange