Summary

The City of Hilliard commissioned a final study by Burgess & Niple and Kittelson & Associates to identify potential long-term intersection improvements for the Hilliard Triangle. The Hilliard Triangle is an area comprised of three closely spaced intersections: Scioto-Darby Road / Cemetery Road (unsignalized), Scioto-Darby Road / Main Street (signalized), and Cemetery Road / Main Street (signalized). The Hilliard Triangle area is fully developed with a variety of land uses that include schools, medical offices, and small-scale commercial uses. As a system, the Hilliard Triangle currently operates near capacity during the weekday a.m. and p.m. peak hours. Approximately 65 crashes have occurred at the study intersections within the past three years. Based on regional planning model estimates, the study area is expected to undergo significant growth over the next 25 years.

Two intersection improvement alternatives (signalization enhancement and roundabout conversion) were evaluated to mitigate existing safety concerns and to accommodate future traffic projections. The results of the evaluation show that signalization of the Scioto-Darby Road / Cemetery Road intersection and conversion of the two signalized Main Street intersections to double-lane roundabouts provide the best combination of system intersection operations, safety enhancement, right-of-way impact minimization, and property access.

Analysis of Alternatives

Traffic counts were taken for the study intersections on a mid-week day in June 2005 to establish current traffic volumes. Year 2030 traffic volume projections were developed to account for regional growth in the study area. The 2030 year traffic volumes were based primarily on a regional planning model and take into account planned transportation improvements in the study area.

For year 2030, calculation of volume to capacity ratios, average delay, and queue lengths indicate that, with signalized intersections, Main Street, Cemetery Road, and Scioto Darby Road will all need to be expanded to provide two travel lanes per direction with widening at the intersections to accommodate additional turn lanes (up to six lanes of total pavement). Even with these improvements, significant queues and delays are anticipated at all of the study intersections. As a result, queue spillback from the Scioto Darby Road / Main Street and Cemetery Road / Main Street intersections would effectively limit left-turn ingress and egress to all driveways located within 400 feet of the respective intersections.

 Roundabout operations were evaluated for the study intersections using the same year 2030 peak hour traffic volume projections. Acceptable intersection operations were achieved under year 2030 traffic conditions with the installation of a two-lane roundabout at the Scioto-Darby Road / Cemetery Road intersection and installation of three-lane roundabouts at the Cemetery Road / Main Street and Scioto Darby / Main Street intersections. This roundabout alternative provides greater capacity, less delay, and shorter queues than the signalized alternative with fewer traffic lanes required.

However, given the low probability of widening Main Street to the north, a two-lane roundabout scenario was explored as a viable interim solution, and potentially a viable long-term solution until such time as significant transportation improvements are made system-wide, enabling full realization of the regional model’s projected demand. The two-lane roundabouts are more pedestrian friendly and require less right-of-way.

 Assuming linear growth rates from 2005 traffic volumes to 2030 projections, and estimating that southbound Main Street (north of Cemetery) will reach its capacity at year 2020 projected volumes, two-lane roundabouts at the Scioto Darby Road / Main Street and Cemetery Road / Main Street intersections would operate acceptably until at least 2020 or beyond until such time as significant regional transportation improvements are made. The corresponding signalized alternative at the Scioto Darby Road / Main Street and Cemetery Road / Main Street intersections for year 2020 would still require two travel lanes per direction with widening for turn lanes and significant queues and delays still anticipated.

Recommendation

From an operational and safety perspective, the dual roundabout alternative provides superior performance over the signal alternative. Additionally, roundabouts can accommodate u-turn maneuvers which improve access to properties located in their immediate vicinity. The drawback for roundabouts is the amount of right-of-way needed at each intersection. Right-of-way constraints at the Scioto Darby Road / Cemetery Road intersection effectively eliminate a double-lane roundabout as a potential alternative at that location. Balancing the needs of the system against reasonable right-of-way requirements, the final recommendation is for two-lane roundabouts at the intersections of Scioto Darby Road / Main Street and Cemetery Road / Main Street, and a traffic signal at the Scioto-Darby Road / Cemetery Road intersection.

Conceptual Design