Appendix A Expanding the GSATS Model Area into North Carolina Jluy, 2011
Table of Contents LONG-RANGE TRANSPORTATION PLAN UPDATE 1. Introduction... 1 1.1 Background... 1 1.2 Existing Northern Extent of the GSATS Model... 1 2. Impacts of Regional Developments on the GSATS Area... 3 2.1 Infrastructure Developments... 3 2.2 Demographic Developments... 8 3. Model Implications of Expansion... 10 3.1 Data Requirements... 10 3.2 External Stations... 12 4. Summary... 12 Lis t of Tables Table 1: Required Network Attributes... 11 Table 2: Eight ITE Land Use Categories... 11 Lis t of Figures Figure 1: GSATS Model Expansion in Other Studies... 2 Figure 2: Northern Extent of the GSATS Model... 2 Figure 3: I -74 Feasibility Study... 4 Figure 4: Potential Alignments near State Line... 5 Figure 5: Carolina Bays Parkway Extension Feasibility Study... 6 Figure 6: Potential Regional Network with I-73 and I-74... 7 Figure 7: Population by Census Block... 8 Figure 8: Population Density by Census Block... 9 Figure 9: North Carolina Communities Near State Border... 10 Figure 10: Proposed External Stations... 13 i
1. Introduction LONG-RANGE TRANSPORTATION PLAN UPDATE This Technical Memorandum discusses the advantages, disadvantages and implications of expanding the existing GSATS model northwards into North Carolina. The paper was prepared as one of the first tasks in developing the Grand Strand Area Transportation Study (GSATS) 2035 Long Range Transportation Plan (LRTP), which will utilize the GSATS model to evaluate potential highway improvement projects. 1.1 Background The existing GSATS Travel Demand Model (TDM) covers the same geographic area as defined by the GSATS Metropolitan Planning Organization (MPO) boundaries. The area covers portions of two counties in South Carolina, namely Georgetown and Horry. Two previous studies independently developed models that expanded upon the area of the current GSATS model: Southern Evacuation Lifeline (SELL) the GSATS model was expanded to cover the whole of Horry County, while maintaining the portion of Georgetown County within the GSATS MPO boundary. Georgetown Countywide Transportation Master Plan Study the GSATS model was expanded to cover the whole of Georgetown County, while maintaining the portion of Horry County within the GSATS MPO boundary. The model areas covered by these studies are shown in Figure 1. These two models will be combined in the GSATS 2035 LRTP study to provide a model area fully covering both counties. The question addressed in the paper is whether the model area should be expanded further into North Carolina. 1.2 Existing Northern Extent of the GSATS Model The northern boundary of the existing GSATS model is shown in Figure 2. This figure shows the model zone boundaries and road network between North Myrtle Beach (SR 9) and the North Carolina state line. Additionally, this figure shows the existing road network in North Carolina, as far north as Shallotte and NC 130. 1
Figure 1: GSATS Model Expansion in Other Studies SELL Study Georgetown Countywide Transportation Master Plan Study Figure 2: Northern Extent of the GSATS Model 2
2. Impacts of Regional Developments on the GSATS Area 2.1 Infrastructure Developments Two potential improvements to the highway network in the coastal area of North Carolina adjacent to GSATS are currently being considered by NCDOT. I-74 Feasibility Study - This feasibility study 1 addresses additional alignment alternatives for the proposed Interstate 74 from Union Valley Road (SR 1585) in Whiteville, Columbus County to the South Carolina state line in Brunswick County. This study is the initial step in the planning and design process for this project and is not the product of exhaustive environmental or design investigations. The purpose of this study is to describe the proposed project, including costs, and to identify potential problems that may require consideration in the planning and design phases. The study proposes a four-lane divided interstate freeway with full control of access including a variable median from 46 to 70 feet, 12-foot travel lanes, 10-foot full depth outside and 4-foot full depth inside paved shoulders, interchanges, grade separations and service roads within a minimum state maintained right-of-way of 350 feet. The alignments considered in the I-74 Feasibility Study are shown in Figure 3, while the alignments in the vicinity of the South Carolina state line are illustrated in Figure 4. Carolina Bays Parkway Extension - The Carolina Bays Parkway (CBP) extension project involves the development of a new multilane full control of access highway facility. The proposed route would continue the Carolina Bays Parkway (SC 31) from the existing interchange with SC 9 in Horry County, South Carolina, across the state line into Brunswick County, North Carolina. Once in North Carolina it would connect with U.S. Route 17 at a future interchange near the intersection of U.S. 17 and NC 904, Longwood Road. A feasibility study was conducted to consider alternative alignments. These alignments are illustrated in Figure 5. I-74 and CBP Extension combined will connect with the existing Carolina Bays Parkway (SC 31) to provide a fully access controlled interstate standard highway parallel to the congested U.S. 17 corridor from within North Carolina to south of Myrtle Beach. The potential regional highway network, including both I-74 and the proposed I-73 within South Carolina, is shown in Figure 6. 1 I-74 Feasibility Study, from Union Valley Road (SR1585) in Whiteville to the South Carolina State Line, prepared for NCDOT by RK&K, August, 25, 2005. 3
Figure 3: I -74 Feasibility Study
Figure 4: Potential Alignments near State Line
Figure 5: Carolina Bays Parkway Extension Feasibility Study
Figure 6: Potential Regional Network with I-73 and I-74 7
2.2 Demographic Developments The year 2000 population within the region of the state border can be seen in Figure 7 at the 2000 Census Block level. According to the US Census Bureau the population in Horry County has increased by over 31% since year 2000 and Brunswick County has increased over 41% in population. This information is based on the year 2008 population estimates of 257,380 for Horry County and 103,160 for Brunswick County. These figures indicate a higher growth in Brunswick County than Horry County in recent years. Figure 7: Population by Census Block The US Census reports an average population density of 173 persons per square mile for Horry County and 86 persons per square mile for Brunswick County in year 2000. For year 2008 the US Census estimates an average population density of 227 persons per square mile for Horry County and 122 persons per square mile for Brunswick County. This corresponds to a growth in population density of 31% in Horry County and 42 percent in Brunswick County. These figures indicate a higher growth of population density in Brunswick County than Horry County in recent years. For the area shown in Figure 8, the 2000 Census population densities are 370 persons per square mile for the sub-region in Horry County and 220 persons per square mile for the subregion in Brunswick County. These results reflect higher densities in the sub-regions compared 8
to the countywide values. The Horry County sub-region has 63% higher densities than the county and the Brunswick County sub region has 80% higher densities than Brunswick County. Figure 8: Population Density by Census Block The communities along US 17 between the SC state line and Shallotte, NC are listed below and are shown in Figure 9. Carolina Shores Calabash Sunset Beach Ocean Isle Beach Shallotte Some major developments in this area include: Brunswick Plantation Sandpiper Bay Sea Trail Plantation Brick Landing Plantation 9
Figure 9: North Carolina Communities Near State Border 3. Model Implications of Expansion 3.1 Data Requirements Highway Characteristics - The data required for North Carolina highway links are shown in Table 1. Such data include number of lanes, posted speed, functional classification, roadway capacity and average annual daily traffic (AADT) counts. Additionally, seasonal traffic count data will be needed to convert the AADT counts to peak season volumes. The seasonal count data consists of the average daily traffic (ADT) for the months of June, July and August. Roadways that would need to be included in any model expansion include: US Routes: 17 and 17 Business NC State Routes: 904, 179, and 130 Local Roads: Ocean Isle Beach Road, Old Shallotte Road and Pea Landing Road 10
Table 1: Required Network Attributes Attribute Lanes Posted Speed Capacity Functional Classification AADT Peak Factor Time Link Type Road Name Descriptions Total Lanes Miles per Hour Total Capacity Lookup Table (based on Total Lanes and Functional Class.) 1 Freeway 2 Expressway 3 Ramps 11 Divided Principal Arterial 12 Principal Arterial 13 Divided Minor Arterial 14 Minor Arterial 21 Divided Collectors 22 Collectors 23 Local 32 Centroid Connectors Average Annual Daily Traffic count Peak ADT (June, July, & August) Based on length and free flow speed Roadways = LINK Centroid Connectors = CC Name of the Road Land Use Data - The data required for North Carolina traffic analysis zones (TAZs) include land use data at the parcel level based on Institute of Transportation Engineers (ITE) land use categories 2. Land use data based on over a hundred detailed ITE land use categories is preferred to maintain consistency with the existing model. However, the eight ITE land use categories listed in Table 2 may suffice. Table 2: Eight ITE Land Use Categories Land Use Categories Single-Family Detached House Multi-Family Median Density Utilities Industrial Hotel-Motel Public/Semi-Public Recreation Commercial 2 Institute of Transportation Engineers, Trip Generation (Sixth Edition), an Information Report, 1997. 11
Approximately thirty-five zones would need to be created to expand the model into North Carolina and these zones would need to conform to the US Census geographies. US Census Blocks would be required to aggregate to a TAZ level based on major network roads and natural boundaries, such as waterways. 3.2 External Stations Figure 10 shows the existing external stations indicated by a red star. The most western of these external stations has been used only in the SELL project model, as it lies outside the current GSATS MPO boundary. The potential locations of external stations in an expanded model area are shown by a blue star. AADT counts would be required at these locations in Brunswick and Columbus Counties. These counts would then be factored to peak season counts based on seasonal count data. The factored counts represent the total volumes (two-way) entering and exiting the model area from the respective external stations. A major challenge of expanding a model boundary is the estimation of external-to-external and external-to-internal trips for the new stations in North Carolina. Assumptions will need to be made regarding the trip making behavior between NC 904, NC 130, US 17 and other external stations of the GSATS model since no observed data are available. 4. Summary In view of the potential changes/additions to major elements of the highway network in the vicinity of the state line, it is recommended that the GSATS model area be expanded to NC 130 in North Carolina. This would allow the model to better reflect the allocation of traffic between existing U.S. 17 and the proposed I-74, Carolina Bays Extension, and Carolina Bays Parkway interstate-standard corridor. 12
Figure 10: Proposed External Stations 13