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Q&A with Mike Mastaglio: Examining the Effectiveness of Roundabouts
Publication Date
September 2nd 2021, 12:00 pm

Urban’s multimodal engineering practice includes a team of innovative intersection and interchange design specialists. Nationally recognized roundabout specialist Michael Mastaglio, PE, PTOE, leads the team. He is an appointed member of the Transportation Research Board Standing Committee on Roundabouts and other Intersection Design & Control Strategies (AKD80, former ANB75T); the Institute of Transportation Engineers National Roundabout Standing Committee; the Penn State Traffic Engineering and Safety Conference Committee; and the Every Day Counts Committee. We talked to Mike about the safety benefits of roundabouts, how they can accommodate multiple modes of transportation, and how to better communicate their effectiveness to the public:


Q: Many people assume roundabouts are confusing and dangerous when they are in fact safer than a standard intersection. Can you explain in layman’s terms what makes a roundabout inherently less dangerous?


A: There are a lot of misconceptions about the modern-day roundabout. Many countries around the world use them and they have been around for a very long time. In the U.S., people are less familiar with them and that can make motorists uncomfortable because it places the decision-making back to the driver and changes their driving routine. A great article from Bloomberg City Lab explains how our country is trailing much of the world when it comes to this alternate intersection. They are a proven safety countermeasure to reduce severe crashes based on their geometric nature. By eliminating the left turn, reducing conflict points, and slowing driving speeds, roundabouts inherently reduce the severity and frequency of crashes - essentially eradicating right-angle collisions, which are typically the most severe. The Federal Highway Administration endorses them and supports the fact that they lead to improved operational performance while promoting lower speeds. They also reduce greenhouse gas emissions and distracted driving.


Q: What are some common concerns from community members about roundabouts?


A: Often times, community members are uncomfortable with roundabouts because they do not understand their safety benefits. The modern-day roundabout has a smaller diameter and sharper deflection, which reduces speed, and slower speeds make it easier for motorists to judge gaps for entry. It is a yield control. Roundabouts also remove the decision from traffic lights and put the responsibility back on the driver. Automatically driving slower and more attentively naturally increases safety.


Community members also often share concern that a roundabout intersection won’t handle the vehicular volume that a typical signalized intersection will. Unlike an intersection with a traffic light, motorists at roundabouts are not forced to stop, so it actually keeps vehicles moving. Models are used during the design phase of roundabouts on a 20-year horizon during peak hours to plan for volume. A capacity analysis is run to see what congestion will look like, so they are designed to meet the needs of the community.


People familiar with outdated New Jersey traffic circles or Massachusetts rotaries – which were implemented in the middle of the twentieth century – can be concerned about roundabout implementation, but the modern-day design is different from the T intersection of circles in the past and allow motorists to avoid changing lanes. Experts today are working to standardize roundabout design with things like yield upon entry.


Q: What factors go into deciding which standard intersections should be replaced with a roundabout?


A: Safety and capacity are the usual deciding factors in replacing an intersection with a roundabout. Typically, you look for an intersection that has a history of crashes or is performing poorly from a queueing or capacity standpoint. Designing a roundabout is an art and a science. No roundabout will be the same. Most roadway projects are lineal, and you design to that. Roundabouts require you to be more creative to accommodate the intersection’s surrounding, be it a historic building or wetlands. You also need to consider added capacity and safety.


People can assume there is an alternate agenda when a roundabout is proposed and think the design won’t work because an area is too tight or the vertical grade too high, but there is always a design solution. There are many styles and options. Single lane, multi-lane, or hybrid roundabouts can include multiple entrance and exit lanes, so you can design to whatever is most appropriate for the area. Single-lane roundabouts have been the standard, but multi-lane roundabouts are becoming more popular. The key to proper multi-lane design is that vehicles don’t have to change lanes; directing motorists to enter the correct lane when they yield into the roundabout. Safe proper multi-lane design is a specialty of ours at Urban.


Q: How can roundabouts accommodate bicyclists, pedestrians, and other forms of transportation?


A: Roundabouts can be designed to accommodate pedestrians and many forms of transportation. They naturally accommodate bicyclists because they slow traffic to harmonize with bike speeds. Riders have the option to travel through the circulatory roadway like a car upon entry. For walkers, paths and crosswalks can be designed across splitter islands. Islands shorten the lanes of traffic individuals need to cross and give them only one direction of traffic to look for at a time. You can also have a choice to design bike ramps ahead of the circles in the approach.


In the Netherlands, bike lanes have been included in roundabout design. More locally in the U.S., roundabouts in Pennsylvania’s Berks County were designed to accommodate bikes as well as horse and buggies used by the local Amish and Old Order Mennonite communities. Special meetings were held with these communities to familiarize them with the intersections and determine the appropriate design to harmonize buggy speed with the vehicle speed. The stakeholders felt more comfortable with the intersections after the discussions and the safety benefits were explained.


For all modes of transportation, it is important that roundabouts be illuminated or well lit. There are innovative ways to keep light shining on the roadway, blending it from bright to dark. It is crucial that pedestrian walkways always remain illuminated to assist with people walking or traveling at night.


Q: What more could be done to inform the public about the benefits of roundabouts?


A: Integrating information about roundabouts into driver education would do a lot to help inform the public about their benefits. There are people who think of the roundabout scene in London from National Lampoon’s European Vacation, which highlights driver hesitancy. It is important that drivers, new and experienced, understand how to maneuver through this type of intersection. As roundabouts become more prevalent, it is key motorists understand them. Normal signalized intersections are what most people know, so they need to become familiar with how roundabouts relate. Generally, once a driver proceeds through a roundabout, they remember how they did it, so it’s like riding a bike.

Informing businesses of the benefits of roundabouts is another opportunity. This intersection type can lead to greater access to businesses. They provide signage opportunities in their center and are often viewed as a gateway that is inviting motorists into an area. Roundabouts can also serve as a locator for a business, allowing them a focal point to say where they operate.


Q: What funding sources are available to municipalities and agencies looking to update an intersection to a roundabout?


A: The design and building of a roundabout can be completed with 100% federal funds. They don’t require a warrant analysis. When you are installing a signal at an intersection, you need to meet certain warrants. With a roundabout, there is less need because they are known to improve safety, access, and capacity.


The Federal Highway Administration bases funding on safety, so to get a roundabout funded, you need to prove that the benefit/cost is positive and shows a net benefit. The administration’s Highway Safety Improvement Program – also known as HSIP – typically requires a data-driven, strategic approach to improving highway safety on all public roads, so it is key to show the societal cost of an unsafe intersection versus the cost of designing and building it.


Reconstructing an intersection can be expensive, so the industry is always looking for ways to make them cheaper. Urban Engineers has provided more flexibility in roundabout design to fit the costs to implement them for clients. Designing mini-roundabouts or giving the ability to travel over the center are options. As long as the traffic flow is accommodated, you can design them at different scales. There are a lot of ways to make them fit a given intersection and budget.


Q: What is an example of a successful roundabout project you have worked on?


A: Urban does peer reviews to evaluate other consultant’s roundabout design in Pennsylvania and around the country. By being experts, our firm adds value by rightsizing a design. We can do a sensitivity analysis to see if capacity is reasonable or if the design can be adjusted to accommodate future growth when it may need additional capacity 10 years down the road.


A recent roundabout project that has gotten a lot of praise is the White Horse Circle improvement project in Hamilton, New Jersey. In the first six months since its competition, the improvements to White Horse Circle decreased the average total crashes per month by 71% and total injury crashes by 93%. The immediate positive impact these improvements are having on the traffic flow and safety of the traveling public is clearly evident. The project was honored with awards from ACEC New Jersey and the American Society of Highway Engineers’ Southern and North Central New Jersey chapters


Q: What do you foresee as the future for roundabout and alternative intersection design?


A: The future of roundabout design involves its designers and users. First, designers need a better understanding of how larger vehicles navigate and mix with cars. Overcompensating for tractor trailers reduces the safety benefits because it increases off-peak speeds. A better understanding of this important interaction will lead to smarter, safer, and ultimately, less expensive roundabout designs.


Second, motorists and the traveling public need to become more familiar with consistent rules of the road when it comes to roundabouts. Mixed rules regarding circular intersections lead to people thinking they are dangerous. Standardized signing and striping are very important, as well as nationalized design rules like, yielding on entry and providing deflection. These types of alternative intersections will ultimately make us all safer, but also greener too. Roundabouts require less maintenance than a signaled intersection. During off-peak hours, there is no idling at a light, and during peak times, congestion is relieved, so you will see a reduction in greenhouse gas emissions. As our technology improves, the design of these types of intersections will only get better.