Saturday, 30 January 2016

Reducing delay at traffic lights

We've all had the scenario. Late for something, and the traffic light "just" turned red for you, or you're waiting and you don't see any side street traffic, and you just wished that you could treat it as a stop or yield sign or something like that? Well, there are many ways to reduce the delay.

First is to get rid of the light altogether. That does make it sound like the can you hear a tree falling in the forest if you aren't there to hear it sort of paradox, but it's true. This won't always be true of course, I think people would make lots of videos about how our woulds would be like the videos from India sometimes are if we suddenly took the lights away absolutely everywhere, but in many cases it is possible to remove the lights. You can use a roundabout, that often works. You can have a stop sign for low visibility cases and yield signs for other situations on the side streets. You can also have an interchange or a more simple grade separation, but that is not always a possible thing to have.

Of the lights that remain, a good way to reduce delay is to have specialized signals for each direction and mode, including bicycles and pedestrians, a separate lane and path for each direction, IE left, right and through (exact configuration varies) lanes, a separate sidewalk and a separate bicycle path as simple an intersection as you can, prohibit as many left turns by car as possible, full actuation, fully flexible cycle timings and a rest in red by default mode. Buses should have priority signal transmitters, and emergency vehicles should have preemption systems. This makes it so that you don't need the clearance interval and the yellow light delay all the time, just when other conflicting traffic came first. Here is an example.

We will have the major road, known as A, going east and west, and minor road, as B, going north and south, and all the directions and movements have their own signals in the way I just described, and it is a four way intersection, no turning movements prohibited.

On phase 1, we have the left turn going in just from westbound to southbound. But we don't have the westbound through movement at this particular time, because there isn't traffic detected in that lane. So we wait for say 10 seconds and how all of a sudden, a car is coming eastbound and is going to turn left to go north. Well, because we didn't give the westbound through traffic the green light, we don't have to wait for any yellow and red clearance intervals. We can give that car a green light as soon as it's detected and the controller computer calculates that there is no other traffic.

Now let's say that it's phase 2, and we have the right turn from southbound to westbound on the green, but because traffic wants to go westbound from road A, the phase is going to end soon. But wait, a bus is coming and it wants to make that right turn. It wouldn't originally have the ability to make that right turn, because it just couldn't make it in time, but because we took the few extra seconds to let it go first, it takes less time. And if there wasn't traffic behind the bus, then we would also save on time because then we wouldn't need a whole new phase for the bus only, it saves on the yellow and red time that would otherwise have to be repeated. This is especially useful to me because a bus route I often take makes a left turn on a protected movement, but often times it is just a little too slow to make that movement. Oh, and this reminds me. Having separate bus lanes also helps here because A the flows are separated by mass and speed, allowing for the signals to be coordinated to give the bus a slightly longer yellow time to account for the need for an increase in the stopping distance, especially given that if it has physically separated lanes, it is possible to give the bus a higher speed limit.

Having this actuation system also means that it can be configured to count the traffic as well given the right kind of actuation. Pedestrians couldn't be counted in this way, but other traffic can. It would give the city and province good information to make good decisions about who is making how many journeys in which direction. Maybe a left turn by bike is very popular, 20% of all the cyclists make that left turn from each approaching cycleway, and it's found that their delay is on average, say 50 seconds. A simultaneous green could be added, so that the left turn could say be done every 30 seconds, as in no more than a 30 second wait for cyclists and you can make that left turn all at once. It makes better use of data.

And another way this actuation system, and used in the right way and given good physical design, the lights can be programmed to flash amber in all directions, or possible yellow in 2 directions and flashing red in the other two depending on sightlines, when the traffic counters detect a pattern in the flow of traffic that is consistently low enough to go to flash mode. It obviously would be tailored to each 15 minute period of each day of each week, as in 9:PM on Saturdays could mean the lights to go flashing amber but it takes until 10:30 on Thursdays to do the same. It would take a few weeks to get enough data for an accurate picture of what the pattern is, but the flow would be much more efficient. How who goes first when all the lights are flashing yellow, and the turn arrows are flashing amber? Yield signs could be introduced to make it clear. In theory no yield signs could be used, but it would have to be having even lower speeds and volumes to be safe, and it needs to be clear that it would be an uncontrolled intersection. If these requirements are not met, they are just as good as shared space, which in the wrong volumes and speeds has proved a disaster.

To do this, the intersection should be well designed. One of the excuses the city put up about why they don't do this now includes drag racing. Well, I don't see why someone determined to race would obey a red light anyway, but we can still prevent the racing in the first place with good physical design. Narrower lanes help a lot in this field, practically nobody goes 80 km/h on a 50 km/h limited 2.8 metre wide lane. Especially if the 20 cm on either side of the curb used a brick paving line, so that there is a tactile feeling if you go too fast to control a car within 2.4 metres. There can be fewer lanes, preferably a single lane after the traffic light, and as few lanes as possible while still giving each direction it's own signal control. There can be a speed table designed for the actual limit but not more just before the stop line, this is an actual technique used in the Netherlands, and can be designed for a range of speed limits, generally 30, 50, and 70 limits. Raised medians in the middle of the road and between lanes divides crossings for cyclists and pedestrians who under flash mode would not have signals to guide them, well, flashing yellow for cyclists, no signal for pedestrians, and the raised tables provide speed calming.

Other elements of good design is making it clear about pedestrians, the city claims that the flash mode provides no protection, but then again, it would exactly as much protection as a similar street without traffic lights at all, and the red light itself can't do anything, it depends on drivers actually stopping. Pedestrians can have the zebra striped type of crossing to maximize visibility. I am still not entirely certain about whether it would be good or not to adopt how the Netherlands seems to have pedestrian priority at unsignalized crossings, one with the zebra stripes, where cars are absolutely required to stop, and must let them go first, vs the dotted line crossings, where traffic is only advised that pedestrians may be crossing and that it's probably a good idea to let them go first. Car drivers are used to stopping for pedestrians at most crosswalks, but I'm not sure. Either way, having refuges between the two directions when possible, and on multi lane roads, between each lane when possible (along with a raised ridge for about 80 metres before the crossing so that the traffic doesn't suddenly change lanes. This also helps cyclists. Generally when crossing 50 km/h roads parallel to the major road, cyclists will have priority over the minor road, when crossing parallel to the minor road, then when crossing the major road they will have to yield, using central medians for help. Crossing 70 km/h+ roads, you should probably not have the right of way over that road regardless of whether you are paralleling a major street or not. Given a low enough volume and good median islands and good lighting it shouldn't be too big of a problem though, that is after all the requirements to having flashing amber. Corner radii also need to be fairly tight so that you yield to traffic that is not turning, as you are legally supposed to.

Driver confusion is somewhat understandable. It will take time to learn. But it shouldn't take too long, it's like how quickly people get used to roundabouts. They are growing in popularity. And think about how quickly you can forget an old way of life. If you have moved homes within the last year, can you imagine life without your new home already? If you moved 5 years ago, can you imagine life without your new house? I can't (I moved from one house to another about 11-12 years ago, I can't really remember, I can't imagine how I would be living without the home I have now). Collective memory is quite short, especially for relatively low importance events, like a switch in how you behave on the roads. Besides, they will probably be willing to learn how to deal with fairly simple things like this to reduce their own delay that appears to be from a very obvious cause. Given the choice between say 1 minute of delay vs 10 seconds of delay, you will almost certainly pick the 10 seconds, especially given that there is very little cost to you, even in monetary costs. A programming switch is not a very expensive operation, and painting zebra stripes is pretty easy and cheap.

The Dutch also found that when they do this, it means that people look around their cars, and actually pay attention. It reduces the crash rate by a considerable number as long as the volume and speed isn't too high. With regulated yielding conditions, good road design, a little time to get used to it, low enough volumes and enough speed control, this can work very well. And so can the other options for traffic lights that also have really improved safety and time management.

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