4.4 Overall Summary of Performance Each of the three alternative sets were compared to the E+C model results to determine if an alternative set could provide a benefit to the overall network wide performance. Table 9 and Table 10 compare the volume, V/C, average speed, and travel time results of the key roadway segments within the study area during the AM and PM peak, respectively. In these tables, the V/C ratio, average speed, and travel time of each of the alternatives is compared to the E+C model and color coded based on the significance of the percent change. These travel time results can also be seen graphically on Figures 40 and 41, which show a comparison for the following eight different roadway segments within the study area: Gibsonton Drive (US 41 to SB I-75 Terminal Ramp) Gibsonton Drive (SB I-75 Terminal Ramp to NB I-75 Terminal Ramp)
widening. Northbound US 301, however, does see a modest increase of the V/C ratio, but is still within the threshold to be considered not congested. Travel times are not significantly different between the three alternatives compared to the E+C Model. The one instance of a significant increase in travel time is the eastbound segment of Gibsonton Drive between the two ramp terminals. This can be attributed to the new signal at the northbound I-75/Gibsonton Drive ramp terminal intersection. In the E+C model, this intersection was unsignalized, with the eastbound and westbound through movements operating freely, but under all three alternatives, it becomes signalized to provide a safe crossover maneuver for the DDI. Providing a signal will result in a reduction in speed and increase in travel time for this section as there may be stops and queuing that were not present under the E+C Model. In the PM peak period: The conversion of the Gibsonton Drive interchange allows northbound I-75 users to access eastbound Gibsonton Drive easier, increasing the volume along Gibsonton Drive, east of I-75. Many of these latent vehicles appear to either continue along Gibsonton Drive towards Balm Riverview Drive or south along US 301. Both of these segments see an increase in V/C, although the US 301 segment is the only one that sees a significant increase and approaches the congested threshold based on its V/C ratio. Many of the segments along Gibsonton Drive experience a reduction in the V/C ratio, mostly due to the Gibsonton Drive widening. Symmes Road also sees a reduction in V/C, as vehicles shift from using eastbound Symmes Road to eastbound Gibsonton Drive. As was the case in the AM peak period, travel times are not significantly different among the three alternatives. The segment between the two ramp terminals continues to see a reduction in speed and an increase in travel time, due to the conversion of
Gibsonton Drive (NB I-75 Terminal Ramp to US 301) Gibsonton Drive (Balm Riverview Road to US 301) US 301 (Symmes Road to Gibsonton Drive) Symmes Road (US 41 to East Bay Road) Symmes Road (East Bay Road to US 301) Symmes Road (US 301 to Balm Riverview Road) In the AM peak period:
The conversion of the Gibsonton Drive interchange from a traditional diamond to a DDI , along with the widening of Gibsonton Drive from I-75 to US 301, diverts some traffic away from Symmes Road. Traffic volumes are decreased along westbound Symmes Road, while traffic along all westbound portions of Gibsonton Drive and northbound US 301 see an increase in volumes. The increases along westbound Gibsonton Drive do not cause an adverse change in the V/C for these segments , mostly due to the
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