Across North America, many cities are installing roundabouts rather than the traditional signalized intersections. The reason for the sudden surge of roundabouts is their ability to improve traffic flow as well as reduce crashes and the severity of crashes in comparison to a signalized intersection.
The Federal Highway Association (FHWA) stated that in converting a signalized intersection to a roundabout, severe crashes can be reduced by up to 78% and nearly 48% in overall crashes. To convert a two-way stop control mechanism into a roundabout can result in a reduction of up to 82% in severe crashes and a reduction of up to 44% in overall crashes.
The Insurance Institute for Highway Safety (IIHS) has conducted various studies to measure the effectiveness of roundabouts and found the following information:
- Reduced vehicle delays by about 62-89% on average where roundabouts replaced traffic signal or stop sign
- Reduced vehicle stops by about 52-56% on average where roundabouts replaced traffic signal or stop sign
- Reduced vehicle delays by 13-23% where roundabouts replaced stop sign
- Reduced vehicle stops by 14-37% where roundabouts replaced stop sign
Roundabout Concerns in Minnesota
Many residents within Minnesota have seen numerous roundabouts constructed across the state, but some worry about the safety concerns for pedestrians and cyclists. In the spring/summer of 2010, the Minnesota Department of Transportation (MnDOT) started a data collection process in order to determine the safety concerns of nearly 20 roundabouts across the state.
In September 2012, MnDOT released their findings in a report entitled, Investigation of Pedestrian/Bicyclist Risk in Minnesota Roundabout Crossings. This investigation and report focused on pedestrian and cyclist experiences who were utilizing crossings on roundabouts by investigating the conditions that could affect the yielding behavior of drivers. Pedestrians and cyclists were observed while using the roundabout crossings at two study sites.
Results of Pedestrian and Cyclist Risk in Minnesota Investigation
As predicted, the results show that there is some friction between the vehicles and the pedestrians and cyclists passing through a roundabout. As in many places, the law in Minnesota states that vehicles must yield for all pedestrians in the roundabout crossings.
Based on the findings, vehicles yielded depending upon the location and direction the vehicle was driving. For example, if a pedestrian or cyclist was crossing at a point that starts in the island, there is a higher probability for a driver yielding, whereas if the vehicle is exiting the roundabout, there is a lower probability the driver will yield.
The report hypothesizes that there is less ambiguity for a driver if the pedestrian is on the island because their intent to cross is obvious. In the case of the vehicle direction, the report hypothesizes that this may be the result of increased pressure for the driver to clear the roundabout as soon as possible, and therefore choosing not to yield to the pedestrian.
Vehicles exiting the roundabout that have entered at the immediate upstream entrance turn to have increased probability of yielding, in comparison to vehicles coming from other directions. According to the report, vehicles have a greater chance of noticing pedestrians even while they are still close to the yield line.
The yielding probability decreases if there is a vehicle trying to merge into the roundabout at the entrance next to the exit the subject vehicle encounters the pedestrian. The report suggests that drivers can be distracted when a moving vehicle enters their trajectory path and not notice the pedestrians. Finally, the more vehicles in the roundabout the lower is the probability of yielding to pedestrians.
Conclusions on Safety
The goal of this investigation and report was to evaluate the safety of the pedestrian, including those with disabilities, and cyclists using the roundabouts in Minnesota. Long periods of video and data were collected, but out of thousands of crossing events, there weren’t any accidents. There were about three ‘close calls’ the involved pedestrians, cyclists and vehicles.
The study would have been richer if pedestrian accidents were observed but the presented results do not lose any of their value.
Collecting Traffic Data
For this data collection, custom made units were created to capture video and traffic movements. In order to capture this data, cities could deploy Miovision’s Scout Video Collection Units which are easily setup by one individual within 10 minutes.
With an additional power pack, traffic data and video can be collected for up to one week. Collect various traffic studies including turning movement counts, average daily traffic, roundabout counts and other traffic studies.