In the face of challenging topography, site conditions and stakeholder concerns, DAVENPORT provided transportation engineering services for a proposed mixed-use development at 501 South Greensboro Street in Carrboro, NC.
DAVENPORT was initially retained to provide a transportation impact analysis, when the developer was facing difficult zoning issues. A nearby neighborhood did not want a connecting road and threatened to fight rezoning. DAVENPORT’s transportation impact analysis showed little impact to the neighborhood.
The developer also wanted to install a traffic signal at the site entrance, but DAVENPORT’s analysis showed a signal was not warranted. A traffic signal had been proposed for the entrance, however a new signal was not warranted, would have required additional turn lanes, additional right-of-way and removal of several protected trees. Purchasing right-of-way was not feasible as not all land owners were willing to participate. Furthermore, removing trees was not an option due to the strict tree ordinance within the Town of Carrboro.
Alternatively, DAVENPORT proposed a roundabout for the intersection, addressing the concerns associated with the signal while also providing much-needed traffic calming to the roadway corridor and a gateway entrance to the City of Carrboro.
The roundabout solution had several design challenges, however. First, the existing roadway contained a 9-10% grade approaching the roundabout, which is double the typical maximum for a roundabout site. DAVENPORT’s design held the grade on the north side and presented a softer transition leading up to the roundabout on the south side, thus reducing the grade to 4-5% at pass-through. Importantly, the team also coordinated closely with NCDOT to make sure the design adequately mitigated the grade concerns.
Second, a mobile home park sits 15-20% below grade on the southwest corner of the roundabout site. DAVENPORT made sure the roundabout did not encroach on the park’s fill slope so the developer would not incur additional costs to stabilize it. Finally, the entire area encompassing the development is low-lying, so flooding is a concern. DAVENPORT’s design accommodated drainage by routing all water to bypass the flooding area within the roundabout site.
DAVENPORT’s conceptual plans were accepted, and the firm was retained to finalize design plans and coordinate agency approvals. Ultimately, DAVENPORT’s roundabout design provides amicable solutions for the developer, the Town of Carrboro, NCDOT and the surrounding property owners.
Before the developer can move forward with site build-out, flooding along the project corridor must be addressed. Thus, the developer is working with NCDOT on plans to replace an undersized cross pipe on South Greensboro Street with a large box culvert. Collaborating with the developer and NCDOT, DAVENPORT proposed constructing the roundabout at the same time as the box culvert. Though careful coordination with separate contractors would be required, simultaneous construction of these two major roadway projects would minimize road closures and associated traffic maintenance, which ultimately would mean less disruption for residents and business owners along the corridor and lower traffic maintenance costs for the developer.