7 ms·
It's more like traffic lights being turned off.
by babuskov 7y ago
It's more like traffic lights being turned off.
- vanderZwan 7y agoI grew up near a city where they set up the traffic lights along one of the main roads in such a way that if you kept to the speed limit you would always arrive at the next light just after it turned green, so you never would have to brake or accelerate. I wouldn't be surprised if there are concurrency patterns analogous to that.
- dekhn 7y agosystolic matrix multiplication is roughly analogous to that. Great Highway in SF, if you drive 35MPH you will just get greens on the evenly spaced lights. The worst is when you get stuck behind a person who drives 40, then brakes heavily, then drives 40, then brakes heavily, etc.
- V-eHGsd_ 7y agothere's a 3 or 4 mile stretch of road in san francisco called the great highway that's like this (https://www.google.com/maps/@37.750302,-122.5062241,14.64z https://www.google.com/maps/@37.750302,-122.5062241,14.64z) It was one my little pleasures to drive along that at 35 (or 30, I forget what the speed limit was) and see cars zip ahead at each light at 45, only to watch them ride the brakes as they hit the next red.
- guan 7y agoWhen there’s not too much traffic, Ocean Parkway in Brooklyn also has a green wave.
- Doubl 7y agoSlow drivers must cause extreme road rage on that road
- IggleSniggle 7y agoIn my experience, it is the “fast” drivers that cause road rage by being slow. They race to the next light, stop, and because they are stopped, prevent everyone from riding the green wave because they now must accelerate from stopped. Sooooo frustrating. Just go the speed limit and none of us will need to stop you idiots! Edit: (or go double the speed limit if you must but please stop creating stops)
- Fnoord 7y agoAh yeah, groene golf (green wave [1]). I grew up remembering my parents also using that. Except it never bloody worked. [1] https://en.wikipedia.org/wiki/Green_wave https://en.wikipedia.org/wiki/Green_wave
- vanderZwan 7y agoWorked fine for my family near Drachten, but that had the advantage that they also had a sign showing your speed next to the road. I suspect one issue is that the speedometer in cars are not that accurate
- SECProto 7y agoI live somewhere with lots of roadside speed signs (they flash speed in red if you're speeding, green if under). In the tens of cars I've driven/ridden here, the speedometer is always within a small range (±2km) of what the road sign says
- kevin_thibedeau 7y agoradar detectors always read lower than your true speed since they can't be positioned directly in your line of travel.
- SECProto 7y agoIn the situation I experience on my commute daily: I'm 40m back and the detector is 3m perpendicular off my line of travel (reasonable approximation, as they're on a roadside light standard, the lane width is 3.5m, and the car is centered in the lane), that is a very minor discrepency. On the order of 0.2 km/h
- perl4ever 7y agoThere are some weird speed signs near me. One that particularly irritates me is set up to flash if you're over 25 mph. But the speed limit is 30! There's also a flashing sign by a school, that is left on at times that the regular sign specifically says the school speed limit is not in effect.
- nashequilibrium 7y agoThe road I take to the gym is exactly like this, if you keep just under 40mph.
- swebs 7y agoIn both directions? How would that work?
- ninkendo 7y agoYou can actually do all 4 directions. Imagine a translucent checker board of blue and black squares overlaid on top of a map of roads. You can see the color of the squares but you can also see the roads underneath them. If a light falls on a blue square, make its principal north/south direction Red at t=0 and it’s principal east/west direction green. For black squares do the opposite. Calculate how long it would take cars to travel through each square unimpeded. It helps if this time is roughly the same regardless of direction. It also helps if the squares are roughly large enough that it takes roughly one light phase worth of time to travel through it. Call that time N. At t=N, switch the lights to the opposite color, so now north/southbound traffic gets green lights on blue squares, and east/west gets red. Black squares get the opposite. What you’ll see if you imagine yourself as a car driving through this, is that as you enter a black square as it turns green, the green lights will stay green until you enter the nearest blue square, at which point the phase shifts and now the blue square gets green lights as you drive through it. This works in both directions, with both north and south bound traffic. Now, this falls apart when roads are diagonal, although it’s mitigated if diagonal roads have higher speed limits. It also means if you make a turn, you’re in the wrong light cycle, but it will correct itself after the next red light. It also doesn’t work well at all if you have left turn arrows complicating your light cycles, so you’ll need to have something like a Michigan Left and the requisite wide medians to make this work. It’s not as ideal as I described in real life, but the basic principle works.
- cameronh90 7y agoI'm guessing it doesn't work so well if the stretches of road between lights are of significantly different distances.
- AnimalMuppet 7y agoOr, worse, if the roads aren't on a rectangular grid. But for square blocks, it can work very well.
- smolder 7y agoThey did this on a few roads around where I grew up.(Southern Tier of New York.)
- hawski 7y agoThere's a road in Berlin (and probably it's not an exception) that has overhead displays showing how fast you should go to be on a green wave. At least that's how I understood how it works from driving there several times. Additionally it has variable number of lanes for each direction signaled by lights. Here it's street view of the road, it's not perfectly visible, because those are LED displays: https://goo.gl/maps/T7RzQCUS4nk3QVZN9 https://goo.gl/maps/T7RzQCUS4nk3QVZN9
- philjohn 7y agoYou run the risk of the computational equivalent of speedo not beeing 100% accurate, e.g. clock innacuracy.
- deleted 7y ago[deleted]
- svnpenn 7y agoSounds like branch predictors https://stackoverflow.com/questions/11227809/-/11227902 https://stackoverflow.com/questions/11227809/-/11227902
- perl4ever 7y agoThere's a highway near me with periodic lights triggered by the cross traffic such that you almost always have to stop. The limit is 55 mph, but if you see someone on the side street and speed up to, say 70, to try to beat the light, you will probably see it turn yellow within a second and have to stop anyway. There aren't that many lights, but you almost always have to stop for every one because of the cross traffic taking precedence.
- PyroLagus 7y agoSo lock-free datastructures such as ring buffers are like roundabouts, huh?