Transportation research finds roundabouts are the way to go for drivers of any age

January 21, 2013, University of Maine

A few years ago, a baby boomer turned 63 every seven seconds in this country, leading the New England University Transportation Center to proclaim that in fewer than 20 years, the United States would be a "nation of Floridas."

Designers of highways and byways are taking those aging driver demographics into account when planning for the future of transportation in the U.S. That includes research by University of Maine Per Garder, who is helping transportation officials in their quest to successfully navigate the road ahead.

With a more than  $94,000 grant from the NEUTC, Garder conducted a two-year study of roundabout design and navigability by drivers, including the elderly.

A roundabout is a circular type of intersection around a central island. Drivers travel in one direction around the roundabout and exit onto intersecting roads. In recent years, roundabouts have gained popularity in the United States. Garder says there are currently more than 2,200 in the country and about 20 in Maine.

Garder is an expert on transportation—from roundabouts to rumble strips. His research frequently centers on improving safety for pedestrians, bicyclists and drivers.

T. Olaf Johnson, then a master's degree student in civil engineering at the university, coauthored the study.

A hidden video camera observed 2,366 drivers using the roundabout where Maine, Vermont and Texas avenues converge near Bangor International Airport.

Drivers using the roundabout were classified into one of seven age groups: younger than 20, 20s, 30s, 40s, 50s, 60s, and 70 and older. The researchers studied whether age, gender and cell phone use impacted the minimum time interval when an approaching driver could safely join the flow of traffic.

They concluded a roundabout is a viable solution for intersections, regardless of their proximity to schools and retirement housing.

According to the study, the average gap, or headway, needed for the average driver to enter the roundabout was 3.26 seconds.

Drivers younger than 20 needed the longest gap—4.85 seconds, while drivers 70 and older, on average, needed 3.95 seconds.

"I was surprised that 20-year-olds were not more aggressive," Garder says, but adds that their longer wait times might be because of their inexperience navigating roundabouts.

Drivers in their 30s waited for a gap of 2.90 seconds before entering the roundabout. Drivers in their 40s waited for a 3.17-second gap, and drivers in their 50s waited for a gap of 3.19 seconds, on average.

Overall, on average, males waited for a 3.19-second gap and females for 3.33.

Because of the limited number of drivers observed in the youngest and oldest age groups, as well as in the cell phone user group, researchers couldn't validate that large numbers of those drivers would substantially increase waiting times—and therefore lead to a lower level of service.

Garder recommends that a larger study, or a continuation of this study, be done.

When it comes to talking about elderly drivers, Garder says elderly is a relative term.

Today, he says many experienced drivers in their 60s and 70s have good eyesight and decision-making skills. In general, Garder says driving skills deteriorate around the age of 80. According to statistics, he says driver safety peaks in the 50s, followed closely by drivers in their 40s and 60s. Garder says people behind the wheel in their 80s, teenage years and early 20s are statistically the least safe.

Roundabouts in general, says Garder, are the way to go. There are fewer crashes in roundabouts than at intersections with signals, as well as fewer traffic delays and less fuel consumed.

The roundabout used in the study opened in August 2007 at a former designated high-crash location at the intersection of Texas and Maine avenues in Bangor.

In the three years prior to the opening of the roundabout, nine crashes were reported at the intersection; four resulted in injuries and hospitalization was required in three instances. Damages associated with the collisions totaled $300,000, says Garder.

In 2008–2009, three crashes were reported on the roundabout, none of which resulted in injuries. Damages associated with the accidents totaled $8,800, he says.

With regard to traffic flow, drivers may be able to sail straight through roundabouts, just as they may an intersection with a signal light. With routine traffic on a roundabout, though, generally proceed through more quickly than if they have to stop for a red light, he says.

The researchers computed that a driver who travels straight through 10 similar roundabouts daily versus 10 signalized intersections would annually save 14 gallons of gas. If every licensed driver in the country did the same, Garder says 2.7 billion gallons of gas would be saved annually.

Emerging technologies, including automobiles that parallel park themselves and slow in school zones when children are present, show great promise, Garder says. So too do autos in which the driver's seat shakes if the vehicle crosses the center line.

Garder says these and other technological advances could do for automobile safety what technology has done for large-scale commercial air travel. He credits computerized cockpits with being the main reason there has not been a fatal crash of a large American commercial jet since November 2001.

Explore further: Roundabouts emerging as the ideal intersection between driver safety and efficiency

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5 / 5 (1) Jan 21, 2013
Actually, in the northeast they're called 'rotaries' rather than 'roundabout'.
3 / 5 (2) Jan 21, 2013
"I was surprised that 20-year-olds were not more aggressive," Garder says, but adds that their longer wait times might be because of their inexperience navigating roundabouts.

Maybe younger drivers are just more aware that they won't be able to afford another car if they smash the one they're sitting in?

Alternatively older people could simply be worse at judging distances/speeds.

Garder recommends that a larger study, or a continuation of this study, be done

Can't they just look at studies from other countries? There's plenty of them which have started building massive amounts of roundabouts.

I love science, but using 100K (and more for further study) on this subject seems a bit frivolous.

10 similar roundabouts daily versus 10 signalized intersections would annually save 14 gallons of gas.

It's not as straight forward. Roundabouts can get messy at rush hour. They're mostly a good idea - but not everywhere (picture New York with roundabouts instead of lights)
4 / 5 (1) Jan 22, 2013
I'd also echo the sentiments regarding congestion. Just from my own observation of the few roundabouts I know of in the U.S.

Not mentioned, but it seems that size matters - the more traffic, the larger must be the circumference. Busy intersections are unfortunately likely to be in places where space is at a premium.

Was there any analysis regarding the cost of replacing intersections with roundabouts?

Any conclusions regarding U.S. drivers I accept with reservations - the inexperience is ephemeral. It would be better to use drivers who are used to roundabouts.
2 / 5 (4) Jan 22, 2013
There should be a design rule that limits the minimum distance between roundabouts in a stretch of road.

Nothing is more annoying than driving in some towns where they've planted 5-6 roundabouts every 100 yards. It feels like you're driving through a slalom course. I can't believe that is going to save you any fuel unless you crawl 10 mph between the roundabouts so you don't have to accelerate, but going that slow is fuel-inefficient anyhow.

Smart traffic lights are often a better solution, especially on roads with high traffic along the way and less traffic crossways. I live along such a road, and it would be murder if they replaced all the intersections with roundabouts. Now it's just green all the way straight through if there's no crossing traffic. If somebody wants to exit the road, they take the turning lane and the lights stop the oncoming traffic while letting the rest through.

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