Lower Roswell Road East: Safety and Operational Improvements
A Shared Community Resource
As part of a SPLOST (Special Purpose Local Option Sales Tax) program that focused on road safety and operational improvements in Cobb County, Georgia, Cobb County Department of Transportation (DOT) solicited GS&P to design upgrades to a nearly 3-mile section of Lower Roswell Road East in Marietta, Georgia, from Davidson Road to the Fulton County Line. The project was included in the SPLOST initiative due to a number of safety and operational concerns along the existing stretch of roadway.
“The corridor starts out commercial along the Johnson Ferry side, but the land use quickly changes over to an upscale residential area midway through the project," explains senior transportation engineer Eric Rickert. "At the eastern end, it’s adjacent to the Gold Branch unit of the Chattahoochee River National Recreational Area and National Park Service, so there were several land-use changes along the 3-mile section of road.
"Some of the original problems that had the project added to the 2005 SPLOST vote included a high crash frequency in several locations along the corridor, as well as heavy bicycle traffic with no designated bike lanes. There were also several storm drainage issues along the project, and only piecemeal pedestrian facilities with no connections between the adjacent residential developments or different land uses.”
To determine where operational improvements were needed, the GS&P team performed an initial traffic study along the corridor and recommended tentative improvements that were balanced against site constraints. GS&P and Cobb County DOT then conducted an extensive public outreach effort involving various project stakeholders to receive input on the potential improvements. Based on feedback, the team modified their conceptual design in order to reach a consensus among land owners, elected officials and other key stakeholders. The resulting design not only enhances operational efficiency and addresses safety concerns, but also minimizes impacts to the corridor while achieving a context-sensitive solution.
“The County made certain this project was executed with the community’s input to ensure that everyone had a voice and was heard,” notes Kent Black, executive vice president for GS&P’s Transportation market. “We had numerous public information open-house gatherings, plus meetings with representatives from three separate subdivisions.”
GS&P’s resulting design solution is a Complete Street accommodating the needs of bicyclists, pedestrians, recreationalists and motorists. To improve access to commercial and residential properties, as well as decrease congestion and back-up during peak traffic times, left- and right-turn lanes were added at key points throughout the corridor. Increased safety for bicyclists and pedestrians was achieved by providing 4-foot dedicated bike lanes on both sides of the roadway, and a 5-foot concrete sidewalk on the north side. Along with the sidewalk, an 8-foot-wide multiuse trail on the south side gives residents the option of walking to nearby destinations without relying on motor vehicles. Both serve as a connection to existing pedestrian and bicycle facilities within the City of Roswell and the Chattahoochee Nature Center. All components were incorporated into the design with significant attention paid to limiting the impact to both residential and commercial properties.
“Our goal was to preserve the community,” says Rickert, “so we minimized the design footprint and retained as much of the existing vegetation along the corridor as possible. To help achieve this, we kept our roadway fairly narrow, incorporating 11-foot travel lanes for motorists.”
"The recreational benefits of the area are greatly improved by providing a multiuse trail," adds senior transportation engineer Jody Braswell. "It adds another link to the County's overall trail plan."
Enhanced Safety in a Roundabout Way
Based on citizen input, a roundabout intersection at the corner of Willeo Road, Timber Ridge Road and Lower Roswell Road on the eastern end of the project was found to be the optimum solution.
“The existing intersection had a number of operational challenges,” says Rickert. “It was on a tight, almost 90-degree curve at the foot of a steep grade which had poor sight distance, and there had been numerous crashes at the intersection. On top of that, there were several constraints at the intersection. You had the National Park Service on one side, Willeo Creek was on another side, and there was a sewage pumping station on yet another side.”
GS&P’s design solution was to place a three-legged, 115-foot-diameter roundabout at the intersection that would channel the flow of approaching traffic around a center island, making for a smoother and safer flow of traffic.
“A lot of coordination was required with the National Park Service with this section of the project,” notes Black. “The intersection is adjacent to the Chattahoochee River National Recreation Area, and the design had to comply with mitigation efforts required by the National Park Service based on an environmental assessment prepared by our subconsultant. This included the use of river rock for erosion control instead of typical granite riprap, the incorporation of indigenous grassing species, and landscaping with native vegetation.”
“The county line is at the bridge on one side of the intersection, so the roundabout provides a nice gateway into the county,” adds Braswell. “It’s an uncorporated area of the county, so once you reach the roundabout, you know you’ve arrived in East Cobb.
“The implementation of a one-lane roundabout solution is a big improvement over the previous intersection. The legs were designed to have offset left-deflection for lower entry speeds, which means fewer conflict points. It also reduces congestion, eliminates the need for traffic signals, and will ultimately decrease operation and maintenance costs in the long term.”
Cost-effective and Sustainable
The GS&P team was excited to introduce the Lower Roswell Road East project as a breakthrough example of how to cognitively design roadway systems while addressing the sustainable needs of the community. The project was evaluated using the new Cobb County DOT PEACH (Preserving Environment And Community Heritage) Roads—a transportation environmental ratings program that recognizes cost-effective, sustainable practices in transportation projects—and was the first project reviewed using this criteria to score Gold Certification.
“GS&P incorporated a considerable number of sustainable features into the design, many of them having a high level of environmental and community preservation impact,” explains Braswell. “For example, in order to retain the upscale, wooded character of the existing corridor, we went to great lengths to reduce the project’s footprint against residential and wooded areas while still adhering to AASHTO and GDOT design guidance.”
Special care was also used to limit impacts to the various residential subdivision entrances along the corridor. To preserve large trees deemed important to the community, alignments were used that minimize impacts to one side of the road, retaining walls were used instead of slopes, and the grass strip between the back of the curb and sidewalk (and trail) was narrowed.
A Multimarket Design
Along with roadway improvements, GS&P also prepared water system improvements to replace water distribution and sanitary sewer services lines impacted by the project. The scope of work included the replacement of an existing asbestos cement water line along approximately 15,000 linear feet of the heavily traveled connector road.
“This was a multimarket design effort that involved staff from GS&P’s Water Resources market and their extensive coordination with Cobb County Water System [CCWS] to determine the optimum alignment for a replacement water line,” says Braswell. “There were several design challenges, including limited and congested rights of way that involved a high-pressure gas line and a 20-inch sewer force main, in addition to other related design constraints. Careful coordination with the existing roadway project was also required.”
GS&P’s review of as-built and field conditions during the design phase identified and avoided major potential conflicts with the existing gas line and sewer force main, resulting in significant savings to CCWS, and the prevention of potential construction problems.
An Improved Quality of Life
Recognized with an Honor Award from the American Council of Engineering Companies (ACEC) of Georgia, GS&P’s context-sensitive, sustainable design benefits motorists, pedestrians and bicyclists alike, offering residents a vastly improved, safe and inviting new streetscape.
“The client was extremely pleased that the final project cost came in $1.4 million less than original cost estimations,” says Black. “We’re really proud of the work that was performed, and that we cultivated improvements without mass disruption to the parkland and lake as well as the wetlands area.”
Rickert also weighs in on the project’s success:
“Not only did we keep costs down, but we provided the community with a shared resource. When you go out to the project on any given day, particularly on a weekend, you see the increased amount of bicycle and pedestrian activity along the corridor, and you see the motorists using the roundabout. I think the most gratifying part for me personally is that GS&P created something that without doubt improves the quality of life in East Cobb.”