November 30, 2012 By Brian Heaton
Drivers who feel antsy about navigating through traffic circles — also known as roundabouts — may breathe a little easier when approaching them in the future.
Researchers at Rensselaer Polytechnic Institute (RPI) in Troy, N.Y., have developed a new roadway illumination concept that uses low-level lighting with super-reflective markers and roadside vegetation to more clearly identify directional paths and pedestrian crosswalks in and around traffic circles.
Called ecoluminance, the idea was demonstrated twice at a roundabout in Bethlehem, N.Y. According to findings from RPI’s Lighting Research Center (LRC), the results were promising: Roadway edges and pedestrians were more visible than under conventional overhead lighting, and vehicles approaching the roundabout did so with similar or slightly lower speeds.
Led by LRC Director Mark Rea and John Bullough, a senior research scientist with the center, the first test consisted of a single night in 2011, where only one portion of the roundabout was modified, along with some pedestrian and landscape lighting. The second demonstration happened this past June over a period of several days, where the entirety of the ecoluminance concept was evaluated at the traffic circle.
The project was sponsored jointly by the New York State Energy Research and Development Authority and the New York State Department of Transportation (NYSDOT).
Bullough said traffic circles are seen as useful as they tend to reduce delays normally seen at intersections and can reduce the severity of crashes. He explained that you typically don’t see collisions at 90-degree angles at roundabouts because vehicles are usually going in the same direction.
But while traffic circles may be a safety benefit, Bullough said an emerging practice of putting up many high-powered, 250-400 watt streetlights around the area can be a budgetary challenge for the government entity responsible for the maintenance of and power for the lights.
Ecoluminance addressed that issue by using light-emitting diode (LED) lighting on poles that were typically 15 feet high around sidewalks and the roadway — significantly lower to the ground than many conventional streetlights. LED lights also consume less energy.
“Rather than lighting from higher distances and using high levels of light as a blanket on everything, we thought about what people need to see,” Bullough said. “It’s really the contrast that people need to see that may be more important, rather than the absolute light level.”
In addition, the area inside the roundabout was peppered with inkberry shrubs and bushes that have natural reflective properties. The vegetation is “semi-evergreen,” and while it sprouts new leaves each year, the leaves on the plants stay green before they are pushed out by new growth.
Bullough explained that since the roundabout in Bethlehem was about 100 feet in diameter, they used a handful of lights to enhance the reflective power of the inkberry shrubs and existing trees to make the area more visible.
Each of the landscape light fixtures produces just eight or nine watts, a significant reduction to the higher-intensity streetlights that would normally be present around a traffic circle.
Golf ball-sized glass retro-reflective markers were also set up around the curb perimeter of the roundabout to clearly delineate the path of traffic to oncoming vehicles. Retro-reflective surfaces bounce a significant portion of the light directly back at the source, whereas a simple reflective item such as aluminum foil reflects light to a variety of angles with only a small portion going back to the source.
Bullough added that had the demonstration been a permanent installation, those markers would be embedded around the roundabout island.
“What that does is shine the light that comes from approaching vehicles’ headlights back toward the driver, so they basically see this dotted line outline of a circle,” Bullough said. “That really helps make it much more visible.”
As for the future of ecoluminance, don’t expect the concept to become a spin-off business venture from the LRC. Bullough explained it’s now up to the NYSDOT or other transportation agencies to use the findings where they deem it appropriate.
“Depending on the location, [ecoluminance] is almost like an a la carte menu,” he said. “They could use components of the concept to reinforce what they’re doing, and it might allow them to reduce the number of streetlights in some locations or remove overhead street lighting entirely.”
Photo: A roundabout in Bethlehem, N.Y. lit up using the Ecoluminance concept. Courtesy of the Lighting Research Center at Rensselaer Polytechnic Institute.
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