“In the past, buses always got priority. Now every bus is tagged and the computer knows all the time-tables of every line. The system knows exactly when which bus needs to arrive at a certain intersection. The installation checks whether a bus is too early, on time, or running late and sets the lights accordingly.”
“On the cycleways we always have double loops, separated by 75 centimetres. That way we can measure speed and direction by combining the data the computer receives from the two loops. It also means we don’t need to reserve green time for a cyclist riding against traffic, away from the intersection.” And the pushbutton? “For cyclists that’s not really necessary. They’re only there for reassurance. You often see in the reports that people don’t even bother to push the button.”
I can't help but wonder if such aggressive timings discussed in the article are good for people with disabilities. People often panic when rushed by a change to red.
In my experience, if the intersection processes car traffic dynamically, it will also process pedestrian traffic dynamically, and generally favor pedestrians. If the intersection has static timing, it's not going to do anything different for pedestrians. I recall driving in Milwaukee near UWM two decades ago, every morning I could count on the lights showing exactly the same thing at the same time. If I left my apartment at the same time, I'd get the same sequence of missed or made lights. Most other places I've driven had car sensors (usually loops in the pavement, but cameras are cheaper and less maintenance now), so there's no schedule to be learned, although the behavior is predictable if you learn the cycles and observe the stimuli. (Although, sometimes sensors are broken or miswired; there was an intersection near one of my employers where the cyclist button was connected as an left turn lane occupancy sensor; resulting in consistently wrong behavior. it's also not uncommon for a disabled vehicle to be located above a loop, or sometimes a construction / utility vehicle to be parked above a loop; some control systems can adapt and filter that out, but many don't.)
The only partial exception is pedestrian-only crossings and then only if you are in the part of the phase where enough time still is available to return cars to green.
(194 comments on HN: https://news.ycombinator.com/item?id=34058004)
Buttons are old tech. https://www.flir.com/products/trafione/:
“The FLIR TrafiOne uses thermal imaging and Wi-Fi technology to adapt traffic signals based on the presence detection of vehicles, bicycles and pedestrians, even in total darkness or adverse weather.”
I don’t know how smart that version is, but there are versions that predict whether pedestrians have the intention to cross the street. https://www.tugraz.at/en/tu-graz/services/news-stories/tu-gr...:
“The innovative camera-based system recognises the intention of pedestrians to cross the road and switches to green automatically. What’s more, it optimises the traffic flow further, as Horst Possegger from the Institute of Computer Graphics and Vision explains by way of two examples: “The green phase can be extended in the case of large groups of persons, who require more time to cross the road. And if persons leave the waiting area before the lights have turned to green, this is also passed on to the lights. The traffic lights subsequently don’t switch to green and there are no unnecessary waiting times for motorised traffic.”
[…]
“Using the current configurations, our system signals that wish to cross three to four seconds before the button is pushed,” says Possegger.”
And I expect "person detection" to be much easier with an IR image, there's probably not many places where human body temperature isn't noticeably higher than the background should make it more accurate to pick out. And if you don't need accuracy of temperature reading, an IR camera isn't really any more expensive than a visual camera - it's the same CCD just with a different filter on top. And it completely bypasses any problems of darkness.
I also wouldn't be surprised if the actual camera unit was a near negligible cost of installing something like this, so even if it was multiples of the price, optimizing for that may be the wrong target if it affects accuracy at all.
Granted it's probably nothing too big in absolute terms, but does feel a little unfair, because vehicles usually get a few seconds head start for free due to being able to call a signal as soon as they reach the location of the green extension detector, which can be a few tens of metres in advance of the stop line.
(On the other hand yes, I do acknowledge the because "turning lanes" don't really work for pedestrian traffic, it's often hard to detect pedestrians much in advance because you'll have no idea which way they'll want to turn at the intersection. But it still feels a little unfair :-) )
And unless the default state of an intersection is "red for all directions", switching the lights will always take a few seconds even in the best of cases. By giving the traffic lights controller some advance warning of somebody approaching, it's possible to switch the traffic lights just in time so that that user doesn't have to stop (if traffic conditions allow it of course – with heavy traffic it's unavoidable that somebody will have to wait eventually).
With semi-flexible traffic light designs (where phase length and whether a phase is called at all depends on traffic conditions, but otherwise they still always cycle through the phases in a fixed sequence), there are also situations where a signal can only turn green (if called) until a certain point in the cycle no later than X (in which case it'll remain green until let's say for example X + 10 seconds). If you miss that time X, you'll have to wait a whole signal cycle until the signal can turn green again. If it just happens that you're reaching the intersection at a time X + 5 seconds, it means that if you could have called the signal while still six seconds away (i.e. at X - 1 second), you still could have crossed successfully (because in that case the signal would have been green between X and X + 10), whereas without that possibility you can only press the button at X + 5 seconds and now have to wait one whole signal cycle.
There is no traffic lights priority for public transport. Melbourne's tram avg speed is 10-15 kph. If you power walk you can go faster than the tram. It just sits there waiting on traffic lights more than moving.
There is no synced traffic lights. On long avenues you just stop every 200m because once the light goes green when you arrive at the next intersection the light there goes red. It seems it is synced, but to the opposite it should be doing.
https://en.wikipedia.org/wiki/Sydney_Coordinated_Adaptive_Tr...
> On long avenues you just stop every 200m because once the light goes green when you arrive at the next intersection the light there goes red. It seems it is synced, but to the opposite it should be doing.
I recall a link a while back (from HN?) that demonstrated that it's basically impossible to sync green traffic lights in both directions. Any attempt at syncing will priotitise one direction over the other. I can't find the source, and it was so long ago that it's very likely that I'm misremembering.
For a bi-directional green wave, intersections have to be spaced at intervals consistent half the cycle time (times the intended travel speed) of the traffic lights. In that case opposing vehicle streams will always meet each other at an intersection, thereby minimising the green time required along the green wave and maximising the green time available for handling crossing and turning traffic.
If an intersection deviates from that mathematically optimal location, it means that there'll be less of an overlap between the green times for the two opposing direction, meaning that there's less green time left over for cross traffic.
And since in real life, intersections are rarely spaced at the mathematically optimal interval, in practice this means that eventually you have to give up and just favour one direction depending on the time of the day. (To some extent you can try to salvage things by varying the assumed speed between intersections in order to keep the travel time from intersection to intersection constant, but there's only a limited usable speed range between too slow and the legal speed limit.)
And if you attempt to have multiple green waves crossing each other, you introduce even more scheduling constraints which might leave no room for a perfect solution.
These days I assume most people/companies/governments source their traffic flow info from Google because it has more 'active' sensors in so far as every car has at least one mobile phone. Telcos could and should also sell this type of data in an anonymous format. Large toll roads track individual vehicles with a combination of wireless billing systems and numberplate ID so they are effectively able to provide a similar solution for those high value roads.
Its not just timing, but also inefficient phases. I requested the dataset for phases, but after months was given a totally different dataset. I gave up.