Earlier quoted context omitted.
From everything you've said so far, it sounds like people in your area have a lot of sense.
Also we don't get snow.
Yeah, that would do it.
Hard-braking events as indicators of road segment crash risk
481–490 of 577 posts
Re: Hard-braking events as indicators of road segment crash risk
#482Earlier quoted context omitted.
I understand perfectly, 20 years driving, I think people just don't like that the safe answer is to be slow. You will not fix others behaviour, so your options are be slow and generous, get out of the chaotic lanes (unless that's all of them), or join them and be aggressive, claim space, be stressed and annoyed your whole trip. There is no solution to traffic here sorry, this is more about managing your own frustrati…
I object to the "late" argument made by etho's parent. The difference in time to destination will inevitably be dominated by lights, in city travel, not by modest speed differences (say 45 vs 55) on a highway. Being safe & out of the way is the trick! It would be nice if we got rid of left & u turns and build our roads for that!
45 vs. 55 is not modest; that's 5 minutes over only 20 miles. Up around 60 vs. 70 is where it becomes "modest" IMO.
Re: Hard-braking events as indicators of road segment crash risk
#483Earlier quoted context omitted.
A fraction of the data they collect, to keep up appearances.
Publicly releasing 100% of the maps data they collect would be the most gigantic privacy violation the world has ever seen.
Are you seriously suggesting that google is gatekeeping the data because they care about privacy ?
Re: Hard-braking events as indicators of road segment crash risk
#484Earlier quoted context omitted.
The issue is that when you slow down, you’re (a) creating ‘turbulence’ in the traffic flow with increased speed differential between cars and increased lane changes, which increases accident risk for everybody, and (b) it’s not even solving the problem because you still perpetually have some impatient driver wedging themself in directly in front of you, deleting your buffer zone. It’s safer to drive a little closer,…
> The issue is that when you slow down, you’re (a) creating ‘turbulence’ in the traffic flow with increased speed differential between cars and increased lane changes, which increases accident risk for everybody, and (b) it’s not even solving the problem because you still perpetually have some impatient driver wedging themself in directly in front of you, deleting your buffer zone. That's very obviously not true. Slo…
Slowing down on a busy highway does not reduce turbulence at all, it add chaos and unpredictability to the system. Once car suddenly slowing down to create a buffer zone causes the car behind to slow more and more and can often lead to a stop further back. This has been proven time and again on closed loop systems studying highway traffic flow. They are known as "phantom" traffic jams or shockwave traffic jams. Example, https://www.newscientist.com/article/dn13402-shockwave-traff...
Re: Hard-braking events as indicators of road segment crash risk
#485Earlier quoted context omitted.
In the auto cruise example, it’s leaving perhaps 2 - 2.5 car distances. In close traffic the average human I would bet is leaving 1 or less then 1. The issue is not that I can’t rebuild the following distance, the point I’m trying to make is that even if I constantly rebuild the following distance it sets off a cascading effect. I’m following at set speed, car cuts in front, hits brakes, I now slow down, car behind m…
> In the auto cruise example, it’s leaving perhaps 2 - 2.5 car distances. In close traffic the average human I would bet is leaving 1 or less then 1. At 60 kph (16.7 m/s) 1 car distance (about 5 m) is less than one third of a second. Even 2.5 car lengths is less than a second. I use traffic aware cruise control on my Tesla set to the maximum separation which is about three seconds, so 50 m at 60 kph. Three seconds se…
3 Seconds is also the recommended following distance in the US. This is a change from when I took drivers training when 2 was recommended.
Almost nobody follows it, but that is what the rule is.
Re: Hard-braking events as indicators of road segment crash risk
#486Earlier quoted context omitted.
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…
By 2 sec following distance I am referring to their back bumper to your front bumper. So cars "overlapping" in your example is not possible
If you want 4 sec gap at higher speeds that's fine, the formula is speed-independent for throughput, not speed-independent for following distance. If you want 4 seconds at high speed then use 4 sec instead of 2 sec (i.e. 1 car/ 4 sec)
>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.
"Lowering the speed limit reduces oscillations." Exactly, that is my whole point, that (again, locally analyzed) you can ignore the waves, and instead look only at the following distance of the slowest car in the lane, to determine throughput of the road behind that car. Your idea of "lowering the speed limit" to eliminate waves is the same net effect on throughput as observing that the throughput cannot exceed that given by the longest-following car on the road.
Re: Hard-braking events as indicators of road segment crash risk
#487Earlier quoted context omitted.
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.
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…
-Slow down a bit to create another buffer.
Now you've just created a shockwave traffic jam.
Re: Hard-braking events as indicators of road segment crash risk
#488Earlier quoted context omitted.
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…
If you take this measurement as the goal it would be best at near standstill speed (around 4m/s). If you want to maximize the traveled distance of the group it is around 60kph, which is the metric most people actually care about when discussing throughput.
1 car / (actual max following time) no matter the speed. Where do you see speed in the equation? It's not. You can put it in of course but my point is it's unnecessary if you know following distance, which is theoretically more invariable than speed on a road anyway
Re: Hard-braking events as indicators of road segment crash risk
#489Earlier quoted context omitted.
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…
> If you double following distance, you halve the throughput. If you halve following distance, you double your throughput. 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…
YES to all! You're so close. Drivers do not accelerate in bumper-to-bumper the way ants do. They maintain a 2sec (or whatever they are trained) following time instead. Which therefore dictates velocity (car lengths per following time). Thus the limiter on flow-rate is actually following time!
Re: Hard-braking events as indicators of road segment crash risk
#490Earlier quoted context omitted.
Yes. If people are constantly moving into your appropriate head way this is doubtless annoying but the correct response is allow yourself to decelerate slowly to re-open that space again, repeat as many times as necessary, even if it means a bunch of agros end up in front of you. Better for them to be in front where you can see them, than behind or to the side, were you can't.
This algorithm is garbage because it puts no value upon the danger cause by other traffic changing lanes when they would not have otherwise. You're just going to wind up being approximately the slowest person on the road, which is fine if you're constantly trying to go slower to build space but this means that a bunch of traffic that would have not gone around you will do so. This ups the danger vs a steady flow less…
Drivers could change lanes safely if everybody wasn't tailgating.