The Village Council held a discussion with NCDOT Division 10 traffic engineer, Sean Epperson at a special meeting February 10, 2015. Mr. Epperson presented a slide show that covered various topics such as safety, capacity, peak-hour analysis, costs and aesthetics of roundabouts versus the signalized intersection. The following is a summary of the discussion.
SAFETY - Modern roundabouts increase safety mainly by reducing conflict points. A conflict point is where two different vehicular paths either merge or split, or cross. There are 32 non-pedestrian conflict points at conventional intersection and only 8 at a roundabout. Entering traffic always yields to the circulating roadway. Speeds are kept low, so if there is an accident it’s not high-impact versus rushing through a signal.
CAPACITY AND OPERATION - For many locations, a roundabout will handle peak hour traffic better than a traffic signal. In off-peak periods with low traffic volumes on a main road, a roundabout will be more efficient, because a driver entering from the side street can proceed without stopping. At a signal, that driver would need to wait about ten seconds for the signal to clear (yellow and red) from the main street and then give the green signal to the side street. Roundabouts are not just for intersections with relatively low traffic. A single lane roundabout can process over 20,000 vehicles per day, while a multi-lane roundabout can handle over 40,000.
The chart above is an intersection analysis at Waxhaw Marvin Road and Marvin School Road. It shows that the two single-lane roundabout option provides a much better Level of Service (LOS), lower delay and shorter queue length than a 4-leg intersection option. At 122% of existing volumes or 10+years, a second westbound thru lane will be needed. The Village will plan ahead to acquire the necessary right of way so a through lane can be added when needed at minimal cost.
AESTHETICS – Two single lane roundabouts will make a visually pleasing entry into the historic area of Marvin. Marvin’s greenway master plan shows a greenway connecting the existing ‘Marvin Loop’ with Waxhaw Marvin Road and eventually to the Marvin Ridge Middle and High School. The roundabout will provide a safer crossing area for pedestrians and bicyclist. Additionally, the new proposed land use plan shows mixed uses or community type uses in this area. The two single lane roundabouts can be landscaped and brand the Village Center. It allows Marvin to create an identity for itself.
Above, is a draft design for the Marvin School Road and Waxhaw Marvin Road intersections. The roundabout locations will be adjusted to take advantage of vacant parcels and to avoid utility conflicts. The Waxhaw Marvin Road roundabout will be built so it can be modified to accommodate a second westbound thru lane with minimal existing infrastructure impacted. Both roundabouts will include a dual lane entry from both directions on New Town Road.
The cost of construction for a roundabout is about $400,000, not including any additional right-of-way acquisition. While the upfront cost of this type of improvement is higher than a typical signal installation, which is about $100,000, maintenance costs are much lower, with no significant costs beyond typical pavement maintenance and mowing and future improvements are less than improvements to a signalized intersection . In the long term, roundabouts are less expensive than signals. If turn lane construction is necessary, a roundabout often will be cheaper to build than a traditional intersection, both in retrofits or in new construction.
The Village of Marvin has budgeted $200,000 for this project. Toll Brothers is funding up to $500,000.00 and the State is contributing $500,000.00. Additional funding needs will come from the State’s Spot Safety Fund due to the number of crashes at these intersections combined.
The initial timeline given was to complete design and right of way acquisition throughout 2015. Construction would be planned to begin in the summer of 2016. NCDOT prefers to perform construction of roundabouts in the summer months to avoid road closures during the school year. The Village is working in conjunction with NCDOT to try to make this a summer/early fall 2015 project.