From shockwaves to phantom traffic jams, scientists and engineers have found many issues causing gridlock, but what about solutions?
We all know our towns and cities are clogged with traffic meaning gridlock, delays and stress for everyone trying to get to work, school or home by car or public transport. When scientists and engineers study the problem of traffic in our towns and cities, what do they find - and what solutions are they proposing? Physicist and an assistant professor in science education at UCD's School of Education Dr Shane Bergin joined the Today with Claire Byrne radio show on RTÉ Radio 1 to share some insights. (This piece includes excerpts from the conversation which have been edited for length and clarity - you can hear the discussion in full above).
Bergin says science can only get us so far with this one and psychology has to get us the rest of the way. "The roads are a lot busier because there's a lot more people moving around. Our solution to this has been an engineered solution, which is that we will build bigger roads and that will surely help with the problem.
"Remember when the M50 wasn't there, or was only two lanes and there were traffic lights at every junction. We thought when they went to three lanes and it was free flowing that things would improve. But when you build bigger roads, people are more likely to drive and people also have more cars, so it's a space issue."
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From RTÉ News, a €215m upgrade of the Dunkettle Interchange on the outskirts of Cork city, one of the country's busiest interchanges, has been officially opened by Tánaiste Micheál Martin
The reality of driving is a lot different to what's often in our heads. "I think we all have this image in our heads of driving as an expression of our individual autonomy and freedom", says Bergin. "This great idea of the road trip. You close your eyes and imagine you're in the midwest of the United States and you're going down this beautiful road and there isn't anyone else and you have the top down on your magic convertible and you're listening to The Eagles and everything is great.
"The reality is that everyone else is trying to go around as well and our roads can only take so much. Once they get above a certain concentration of cars, you move from what we call a free flowing state to a congested state and that's where traffic comes about. While we can model it as a fluid, it only gets us so far and we can't really solve the problem."
There's often more to what causes traffic jams and hold-ups than you might think. One of these, says Bergin, is the shockwave. "You're going along a multi-laned road and you come up behind a car that's moving much slower than the average traffic and you have to go around it. Now, if it's quiet, you can do that easily. If the road's busy, you have to inch out into the overtaking lane and get around the car. If the car is going very slow - or maybe it's a tractor - you have to brake and then you have to get around it. This causes a delay and it causes a delay that moves backwards in traffic and we call it a shockwave."
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From RTÉ Radio 1's Morning Ireland, Dublin City councillors Nial Ring and Darragh Moriarty on the capital's plan to remove traffic from the city centre from August
Then, there's the phantom traffic jam. "The car right behind you brakes, the one behind it brakes and, if the cars are too close together, they brake very rapidly and all of a sudden, traffic stops a couple of kilometers back and that's what's called a phantom traffic jam. It happens because cars are not all moving at the same rate. It happens because there are too many cars on the road, and it happens primarily because of poor driver behaviour. People tend to drive too close to the car in front of them and so when that car brakes, they have to brake very quickly, and so you get this abrupt wave moving backwards."
So, are autonomous vehicles the answer here? "It's very tricky because what happens if there is an accident? Who's at fault? What happens if the car has to make a decision? 'I have to stop, there's an emergency, but I'm not able to stop safely, who do I hit?'
"There's a famous philosophical problem called the trolley problem where the person has to decide, there's this train and it's running out of control and they have to decide whether they pull a lever and it will kill a small number of people, or you let it keep going and it may kill a large number of people. If you are driving your car, you have responsibility for it. But what happens if that responsibility is shared between you and an artificial intelligence? Who's at fault?"
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From RTÉ Radio 1's News at One in November 2014, how the the opening of the flyover at Dublin's Newlands Cross means no traffic lights between Cork and Belfast on the motorway network
Scientists and engineers also have things to say about the effect of traffic lights on traffic. "The old systems have traffic lights where they're on timers", says Bergin, "they just go through a sequence. Now, studies say you can go with the flow. If you think that most traffic going into a town or a city in the morning is going inward, maybe you should have longer sequences so that you get more cars through the junction or more vehicles through the junction in any given time. That's one system.
There are also other systems that can be far more dynamic. If you have a big crowd of people in a corridor and there's only one little portal and they have to get through it, what happens is people would stop on one side to let others through coming against them, and then the pressure builds up because the crowd builds up on the opposing side. You get this ebb and flow of who gets to go first and there's a social pressure that builds up to say 'hey, we need to get through here'.
"Systems are now able to do that for traffic. They can sense using GPS in cars how much traffic is building up in a certain direction, and so the traffic lights should be changed to try and unclog the system as much as possible."
