• Reconciling Travel Time Saving Estimates in the SPOT Process

    NCDOT Research Project Number: 2020-25

 Executive Summary

  • With nearly three billion dollars annually of NC taxpayer dollars at stake in the State Transportation Improvement Program (STIP) Prioritization process of ranking highway projects for funding, travel time savings (TTS) constitute a key input into the projects' benefit cost analyses. Yet, estimates of those savings for various competing projects are derived from models that are completely different in scales, both spatially and temporally, including a low-resolution statewide travel demand model, a highly detailed microsimulation model and a manual calculation based on very limited data. The method of reconciling those estimates across projects has varied from no adjustments in some past Prioritization rounds, to prioritizing based on the relative number of project requests (e.g. corridor vs. intersection improvements) as was done in Prioritization 5.0.

    This research is intended to study the current process and tools, and propose alternative reconciliation methods for the travel time estimates that can improve and make the ranking process more transparent, robust and replicable. The approach adopted in this project will include significant interaction with all the stakeholders involved in the process including the congestion management staff, its consultants along with the STI implementation team. Our approach also does not presume that any of the three modeling approaches (Statewide model, TransModeler and CALC) represent the ground truth. Our objective is to simply re-align the results generated by the three models in a manner that does not bias the resulting priorities to specific types of projects. Finally, and to enable the testing of the proposed reconciliation  methods with P6.0.0 selected projects and its full implementation as part of the P7.0 process in 2020, the research team requests an early start of this project, no later than July 1, 2019.

  
Nagui M. Rouphail
Researchers
  
Nagui M. Rouphail; R. Thomas Chase
  
Joseph E. Hummer
  
Lisa E. Penny

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 Report Period

  • July 1, 2019 - March 31, 2021

 Status

  • In Progress

 Category

  • Traffic, Mobility, Safety and Roadway Design

 Sub Category

  • Traffic Safety

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