REVIEW: Staff has previously presented the results of a cost-benefit analysis of three potential cross sections for the Davis Drive corridor (see DS00-166). These comparisons have been based on traffic projections from the Capital Area Metropolitan Planning Organization (CAMPO) traffic model and construction cost estimators. Council has requested additional information regarding utilizing a four-lane section with a 16’ median for the portion of the corridor between High House Rd. and Morrisville-Carpenter Rd.

This report includes additional information regarding the following:

• • Median Widths
  • Pedestrian / Bikeways
  • Land Use and Municipal Boundaries
  • Cost and Proximity comparisons of utilizing a 16’ median between High House Rd. and Morrisville-Carpenter Rd

Median Widths - NCDOT standards require that raised median sections be a minimum of 16’ to provide for a continuous roadway section and to allow for 12’ turn lanes while maintaining a 4’ median between opposing traffic. (Please note that the current 4’ median design is a compromise with NCDOT to provide separation between opposing traffic while maintaining as much of the existing infrastructure as possible.) The 16’ median does not provide space for vehicles to make left turns onto the roadway in two movements. AASHTO recommends median widths of at least 30’ so that drivers are not encouraged to attempt to make a left turn in two independent movements without being fully protected from opposing traffic.

The project length from High House Rd. to just north of Morrisville-Carpenter Rd. is 2.99 mi. Approximately 2/3 of this length will have a full width median while the remaining 1/3 will have reduced or no median due to turn lanes and intersections. If, in the future, an additional lane (even a reversible lane) were required, the 16’ median would provide adequate space for construction without acquiring additional R/W.

Pedestrian / Bikeways – The Town of Cary PRCR Division recommends a 10’ width for corridors shared between pedestrians and bicycles. The costs are comparable between a 10’ asphalt path and a 5’ concrete sidewalk. Also, if a 16’ median section were utilized, the 10’ Pedestrian / Bikeway would fit within a100’ R/W, which was the R/W required for the five-lane section in the earlier analyses. Bike lanes behind the curb will typically be used more by the recreational cyclist. However, alternate bike routes are being proposed for cyclists commuting through the area.

Land Use and Municipal Boundaries – The figures below indicate the Town Limits and Current Land Use in the area.

Cost and Proximity comparisons of utilizing a 16’ grassed median between High House Rd. and Morrisville-Carpenter Rd vs. existing 4’ concrete median design.

Cost and proximity comparisons of the earlier analyses were based on each cross section being utilized for a corridor length of 4.5 mi. This comparison differs by focusing only on the 2.99 mi. section of the corridor between High House Rd. and Morrisville-Carpenter Rd.

Additional required R/W and proximity damages - This cross section will require a 99’ R/W if the 10’ pedestrian / bikeway is utilized. The current design is based on the existing Thoroughfare plan and requires a 78’ R/W section. The proximity damages for he 16’ median section are nearly identical to the 100’ R/W (5-lane section) in the earlier analyses. The 99’ R/W will cost approximately $1,000,000 more than the existing design, as it did in the earlier analyses because most of these costs were incurred north of High House Rd.

Comparison of Paved Area – The amount of paved area per linear foot of roadway for the 16’ median section is identical to the current design. The only difference is that some of the "green area" is in the center of the roadway for the 16’ median section instead of behind the sidewalks in the current design.

Construction Costs – It should be noted that one of the assumptions in the original analysis was that the typical section extends for a corridor length of 4.5 miles. This assumption is no longer valid, and the following comparison of construction costs between these two sections is based on more project specific data for the 2.99 mile section of Davis Drive. The following comparisons indicate that the construction costs will be approximately $429,000 more for the 16’ median section.

• Curb & Gutter (c&g)– Each of these two sections will require approximately the same amount of concrete for the completed roadway section. The major difference is that the current plan utilizes much of the existing c&g (and sidewalk discussed below). The widened section will require the additional costs of removal and replacement of 5,080 of c&g @ $20 / lf or $101,600.

• Sidewalk (swk)– As with the c&g, each of these two sections will require the same amount of new sidewalk construction. Again, the cost difference is that the current plan utilizes much of the existing sidewalk. The widened section will require the additional costs of removal and replacement of 5,080 of sidewalk @ $30 / lf or $152,400.

• Drainage – By utilizing the existing c&g, the current design also utilizes the existing storm drainage system. In addition to having to move the existing drainage structures, the median section will require additional drainage structures along the median. The total estimated additional drainage cost for the median section is $100,000.

• Lansdscaping – Based on recent Town of Cary projects the estimated landscaping costs for the median throughout the 2.99 mi. corridor will be $75,000.

Based on the above analysis, the 16’ median section will have a total cost of approximately $1.4M more than the existing design.