Roundabouts improve cities for everyone
I’ve found in my career as a game developer and programmer that the simplest solutions are often the best. The ways that people interact with the system are better understood, has fewer unknowns, and is easier to maintain.
This design thinking can be applied to the transport problem many modern cities face. It’s a complex problem that can be systematically improved in order to move the most people to their destinations as safely as possible within a given timeframe, while keeping costs low.
I firmly believe that the best way to improve transport in a city is by making the streets more walkable and by taking more cars off the road. This post however, is about traffic throughput and only adjacently related to the walkability of cities.
And so, I’d like to propose an idea: replace most (if not all) of the traffic lights in Cape Town with traffic circles.
Ever since I stumbled onto this idea, whenever I’m stuck at a traffic light or intersection I watch how the cars move, and if the systemisation of who stops and who goes can be improved. What I’ve found is that in most places a traffic circle would improve the intersection elegantly, with little-to-no downside. Let me explain.
Slow-down instead of speed-up
Traffic lights inherently cause people to speed up (in order to make it through the intersection while the light is still green or orange). This is at the part of the road which is the least suited for high speeds. This is where other cars, as well as pedestrians intersect, and the last thing we want is for vehicles to speed up at this specific part of the road.
A traffic circle has the inverse effect and naturally slows vehicles down as they need to watch for other vehicles and navigate around an obstacle. This makes it safer for both pedestrians and other vehicles. For this reason alone traffic circles have shown to reduce fatalities1 while maintaining throughput when compared to traffic lights (and actually exceeding it).
This increases the safety for pedestrians significantly as crosswalks placed at traffic circles are more likely to be respected since the cars have already slowed.
Less noise pollution
As per the previous point, if cars and motorcycles are moving slower they don’t produce as much noise, which is great for the health2 of the residents of the city.
Slower cars in cities are better for everyone.
Increased traffic flow
This may seem counter-intuitive, since traffic circles slow cars down. I was surprised to find out that traffic moves more efficiently through a traffic circle, leading to a roughly 20% increase in traffic throughput3. This is due to 3 major things:
- At no point is everyone stopped. With traffic lights there are many instances, even with a well timed light, where everyone who is at the intersection is waiting for a light. This is something that frustrates me on the road (and the main reason people hop red lights). Yes, this can be improved by having vehicle detection on intersections and timing the lights accordingly, but that’s just more complexity to an already complex system.
- With a traffic circle you rarely come to a full stop. The way that traffic moves at a traffic light is all vehicles come to a full stop in a line. Then when the light goes green the first car starts moving, then the second, then the third, and so on. This inch-worm effect means that in many cases the cars near the back don’t even start moving before the light turns red again. As above, this could be solved using high-tech solutions like wireless car tethering, but that’s unrealistic to expect from all road users any time soon.
- Traffic lights need to be timed both for their intersection, but also within the context of the surrounding traffic lights. You’ve experienced hitting every red light down a stretch of road before. This is due to bad contextual light timing, and in many cases it’s impossible to get perfect.
Implicit vs. explicit rules
In game design it’s necessary to think about the explicit rules of an environment since they’ll need to be programmed. This is in contrast to the implicit or behavioural rules which the users need to abide by. A good example of this in the real world is a no-parking sign. The implicit rule is “you can’t park here”. The explicit rule is “if you park here, there may be a small chance you’ll receive a fine from a passing traffic officer”. An explicit rule for no-parking is a tree. It’s impossible to park there (while maintaining the integrity of your vehicle).
Now that the definition is out of the way; a traffic circle has very strong explicit rules, which are much harder to disobey. I personally feel aggravated when other road users ignore traffic lights, as I feel betrayed by my fellow citizens as they are breaking the rules that keep this operation running. The nice thing about traffic circles is that you can’t hop the red, and this keeps all other road users less resentful of one-another.
Due to a transition to a democracy, governmental mismanagement, and corruption in South Africa, there is not enough electricity to meet demand at certain times. This leads to load shedding4, which is the scheduled cutoff of electricity in areas, equitably distributed in 2 hour blocks all over the country. The underlying reasons for this are complex and may be a good topic for a future post, but for now we’ll only talk about the effect this has on traffic.
The problem here is fairly easy to deduce. No power = no traffic lights. This renders the carefully timed stop-and-go system a free-for-all. It technically turns it into a stop-and-go intersection (or some other configuration with self-regulating rules between drivers), but this generally means the most belligerent of drivers (in this case minibus taxis) get right of way, and everyone else sits in traffic getting frustrated.
Cheaper to build and maintain
Before traffic lights can be erected the electrical infrastructure needs to be installed, then the intersection can be laid. The poles and lights (which are fairly expensive) need to be set up and timed correctly by engineers, who return regularly to re-time them. There is also the issue of vehicles (generally driven by people under the influence) regularly taking out a set of lights.
Traffic circles, in contrast, are fire-and-forget. They’re an asphalt circle.
Opportunists and crime
Another semi-uniquely South African problem are that traffic lights are rife with people coming up to your vehicle asking for money. This is a serious societal problem which needs resolving, but one thing is for for certain with regards to road-safety: these are the people hit most regularly by fast moving traffic. In many cases they do not leave the road when the lights turn green and are obstacles for drivers. This is (very unfortunately) combined with a drug epidemic which sometimes causes erratic behaviour, which is not suitable in the middle of a busy road.
The second, and more serious matter is that South Africa has a high crime rate5, with smash-and-grabs, as well as hijackings being fairly common. This leads many people (who would otherwise obey traffic rules) to jump red-lights at night as to avoid putting themselves at risk by stopping. Both of the above issue are solved by the vehicles never explicitly coming to complete stop, and instead having a much harder to interact with flow.
Traffic circles are the perfect place for city beautification projects. I’ve seen imposing statues, gorgeous gardens, impressive water features, and other artefacts which emphasise the overall culture and feel of the city. The more traffic circles we have, the prettier the roadways of the city become. There’s even a roundabout appreciation society in the UK.
With the combination of speed reduction and less noise pollution, who knows, maybe people will enjoy walking again.
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Noise pollution & human health: a review↩
Traffic flow benefits↩
Demand response: Loadshedding↩
Crime in South Africa↩