sr 60 “twin pairs” - City of Vero Beach

TRAFFIC VOLUME FORECASTS
To determine if the proposed cross-section would accommodate future volumes and to determine the
impacts to other roadways and intersections in the study area, we projected traffic data to reflect the 2035
conditions. The 2035 conditions correspond to the horizon year used in the latest Indian River County
Long Range Transportation Plan (LRTP). The Greater Treasure Coast Regional Planning Model
(GTCRPM) was utilized to forecast future volumes. The following model scenarios were used in this
analysis:
2005 baseline model
2035 model, which reflects the traffic and roadway conditions based on anticipated demographic
conditions and roadway network improvements identified in the 2035 LRTP (referred to as the “no
build conditions”).
2035 model modified to reflect the reduction of lanes on the SR 60 “Twin Pairs” (referred to as the
“build conditions”).
Model Calibration
The roadway network coding was reviewed to ensure the characteristics of the roadway network within
the study area are accurately reflected in the GTCRPM. This review included an assessment of traffic
analysis zones (TAZs) centroid connectors, laneage, speed, facility type, and projected volumes. Where
necessary, adjustments were made to the model network attributes, including modification of centroid
connectors. The network adjustments were made iteratively until the model network and volumes were
deemed to reflect actual roadway network conditions. The GTCRPM model output files are included in
Appendix C.
Growth Rate
We calculated growth rates by comparing the traffic volumes forecast in the 2005 GTCRPM and 2035
GTCRMP (no-build and build models). The purpose of estimating these growth rates was to establish
future year (2035) traffic volumes with and without the SR 60 “Twin Pairs” lane reduction. A summary of
model-based traffic volumes that were used to develop growth rates is included in Table 5. Based on the
review of traffic volumes, separate aggregate growth rates were applied for SR 60, 21 st Street, and the
north-south minor streets within the study area. These growth rates were applied to the existing traffic
volumes to determine future year 2035 traffic volumes for the study area roadway segments and
intersections.
SR 60 “Twin Pairs” Traffic Calming Feasibility Study Page 12