Traffic roundabouts: Better or worse than traditional intersections?
This is the week designated by the Federal Highway Administration as National Roundabouts Week.
While engineers admit that roundabouts typically aren’t the most popular solution to traffic issues, experts say much of that is due to a lack of education about the benefits of a relatively new traffic pattern.
The public reaction usually flips to positive within a year or two of them being installed and open to traffic.
A study of three communities where single-lane roundabouts replaced stop sign-controlled intersections found that only 31% of drivers supported the change before construction. However, after more than a year support soared to 70%.
Studies by the Federal Highway Administration (FHWA) show that roundabouts achieve a 44% reduction in crashes and reduce serious injury and deadly crashes by nearly 90% at two-way stop intersections.
When roundabouts replace a traffic signal, FHWA found a 48% reduction in crashes and a nearly 80% drop in serious injury and deadly crashes.
Roundabouts have proven to be much safer than traffic signals. The projected injury crash rate for roundabouts is half that of traditional signals.
There are many differences between roundabouts and traffic circles. Unlike traffic circles, roundabouts are used on higher volume streets to allocate right-of-way between competing intersection movements.
Traffic circles have a large diameter, which contributes to high circulating speeds; roundabouts have a smaller diameter, promoting low circulating speeds. Roundabouts have lower entry speeds compared to traffic circles and feature a yield at every entry point, promoting low speed and no weaving.
Roundabouts can move traffic more efficiently which reduces delays and fuel consumption. This is because traffic generally doesn’t need to come to a full stop at the intersection.
A study by the Insurance Institute for Highway Safety (IIHS) estimated that the conversion of 10 percent of the signalized intersections in the United States to roundabouts would have reduced vehicle delays by more than 981 million hours and fuel consumption by more than 654 million gallons in 2018.
There are often concerns about how large farm machinery or semi-trucks will navigate roundabouts. One way this is accomplished is with truck aprons - an area between the central island and the traveled way that is mountable by larger vehicles but not used by passenger vehicles.
Research shows that drivers quickly adapt to the roundabout traffic flow. For instance, Vail and Avon, Colorado, both feature many high-capacity roundabouts and are major tourist destinations with thousands of first-time roundabout drivers using the roundabout intersections each year.
Despite large numbers of drivers who have not driven roundabouts previously, these intersections work well and do not confuse motorists. Proper use of signing and road striping at roundabouts assists motorists and minimizes the potential for confusion.
Data from PennDOT shows a decrease in fatalities, injuries, and crashes after 33 intersections across the state were replaced with roundabouts.
One of those roundabouts is in Mercer County. The intersection of Dock Street and Connelly Boulevard was replaced by a roundabout in 2018.
"We continue to see that Pennsylvania's roundabouts save lives and reduce crash severity," said PennDOT Secretary Yassmin Gramian. "While they aren't the right option in every intersection, we're pleased that they help to make our roadways safer."
PennDOT's data on roundabout safety comes from a review of 36 roundabouts at intersections that were formerly stop or signal-controlled. Prior to replacing these intersections, data shows a total of 387 crashes. Following the replacements, there were 220.
More data based on police crash reports show:
- 76% reduction in suspected serious injuries;
- 22% reduction in suspected minor injuries;
- 70% reduction in possible/unknown severity injuries
- The total number of crashes decreased by 9%.
- Suspected serious injuries were reduced by 76%;
- Suspected minor injuries were reduced by 22%;
- Possible/unknown severity injuries were reduced by 70%; and
- Total number of crashes decreased by 9%.
In addition to the 36 roundabouts included in the study, PennDOT has added 38 other roundabouts on state routes with over 30 more in the works.