Talking CAVs and roundabouts with PhD researcher Mariló Martín-Gasulla

Mariló Martin-Gasulla is a PhD researcher at the University of Florida

Estimated reading time: 5 minutes

Passionate about mobility, committed to advancing women in transportation and dedicated to topics related to roundabouts, Mariló Martín-Gasulla is a PhD candidate at the University of Florida. When she is not working on her PhD dissertation, Mariló is busy as a member of the Transportation Research Board (TRB) Standing Committee on Roundabouts, takes up the role of vice chair of the Institute of Transportation Engineers (ITE) Standing Committee on Roundabouts and is the president of the Women in Transportation Seminar UF Chapter, a student organisation to strengthen the presence of women in the field. We talked to the Valencian-born mobility expert about CAV, traffic flow and roundabouts.

Several studies say roundabouts are safer and more efficient than signalised junctions because they eliminate hardware, maintenance and electrical costs associated with traffic signals. Are more roundabouts the key to better traffic flow?
You are right, but only if traffic flows dictate the suitability of a roundabout. So, planners and traffic engineers should study the traffic flows first.

However, in the US, the issue is that drivers often don’t know how to negotiate roundabouts. When drivers are already in the roundabout, they usually stop to allow others to enter even though they have the right of way.

Looking at multi-lane roundabouts, drivers often don’t use the inner lanes because it is difficult to get back onto the outer lanes again, when they want to exit. This is why, especially in urban areas, you rather put up traffic lights at a circular intersection. When traffic volumes are high, cities do not want to rely on drivers managing the roundabout, they prefer traffic lights. Then it is clear who has the right of way. On suburban roads, however, there could be more roundabouts because they provide a higher level of service and fewer conflict points than other intersections.

Space probably also plays a role because roundabouts usually take up more space than signalised junctions?
Yes, that’s one of the reasons why many signalised junctions are not turned into roundabouts. The real issue I see when they turn them into roundabouts is the need of matching the size with the capacity, which is often difficult and many roundabouts end up being bigger than they need to be, and finally, they end up signalised, too.

What about more vulnerable road users like pedestrians and cyclists? Aren’t roundabouts mostly made for moving car traffic, but do not represent a particularly safe space for people?
When talking about pedestrians, I agree and this is often the case because of the drivers’ mind-set. In the US, for example, turning right on red is allowed at signalised intersections. This means: Drivers focus on searching for a gap in the conflicting stream, so they usually forget about checking for pedestrians crossing from the right sidewalk. Therefore, I think it is a matter of how well pedestrian crossings are signed and marked.

When it comes to putting a crosswalk where drivers exit a roundabout, I see some more problems, as drivers might already be increasing their speed. You have to find a balance between the proximity of the crosswalk and the roundabout, its visibility and the distance pedestrians have to walk. It also depends on the speed of the vehicles. It’s not an easy task to find the perfect middle ground.

What impact will CAVs have on the flow of traffic in roundabouts? In general, can we expect the number of delays and vehicle stops to go down?
Yes, exactly. In fact, I just submitted two papers to TRB dealing with CAVs, one of them with CAVs and roundabouts. One paper I wrote with Dr. Jochen Lohmiller and Peter Sukennik from PTV, the other one with my adviser, Dr. Lily Elefteriadou. With Peter and Jochen I studied CAVs on highways and urbans streets, focusing on how the geometry of an intersection helps manage the creation of platoons. Platoons of a limited size certainly improve the performance of the traffic flow.

As we do not know exactly how car manufacturers are going to design CAVs, as they don’t share much information, everything we touch upon in our paper is still theory, talking about all intermediate scenarios, from low percentages of CAVs to 100% CAVs on our streets. But even if we consider the most conservative behaviour of CAV, the proposed idea indicates an important improvement in throughput and average delay per vehicle.

Your Bachelor’s, Master’s and now your PhD thesis all focus on roundabouts. Why did you choose that topic, what is it that you find most exciting about it?
I have to say, transportation engineering and roundabouts found me. When I started studying civil engineering, at the beginning I was more into hydraulics and later on I considered becoming a structural engineer. I was almost at the end of my studies and had quite some expertise in all the different fields of civil engineering, except in transportation. But then I took this one class on traffic operations which really caught my attention and enthusiasm. So when my professor asked me if I wanted to join him in one of his research projects, I said yes. This was the same professor who also introduced me to microsimulation and to PTV Vissim. Then, after visiting TRB Annual Meeting, and feeling like part of a family in the TRB Roundabouts Committee, I decided to go on with the same topic. There is so much more to be discussed about roundabouts.

Now that we talked about different modes of transport, what is your favourite and why?
Right now I’m in the US, so public transport is a little tricky. But when I’m in Europe, I like taking the tram, also because this is what I would do in Valencia. If I have to go somewhere, I prefer walking or using something that goes on rails. I love driving, but I know how busy it gets in cities. So I try not to use my car too much. If I can, I walk or use the tram or bus instead.

What is your favourite city and is it maybe your hometown Valencia?
I like Valencia a lot and I miss it. I love European cities and feel very much at home there. But the one city that I like most is Granada, in the south of Spain. Probably that one doesn’t have many roundabouts, but that’s okay. And since I visited PTV headquarters this summer, I have to add Karlsruhe, of course.

Thank you, Mariló, for your time.


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