Countywide Dialogue on Transportation: BCA Technical Overview

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Countywide Dialogue on Transportation


The Board of Supervisors tasked the Department of Transportation with creating a benefit cost analysis tool to analyze a selection of transportation projects for the County.  A consultant was hired to assist county staff in developing the methodology and tool.  The decision was made to use an existing benefit cost analysis application, and redevelop it to function for Fairfax County.  Ultimately the Caltrans model was chosen and redeveloped for the County.

The tool developed for the benefit cost analysis can compare highway and transit projects on the basic factors of an overall benefit/cost ratio.  The bicycle and pedestrian tool analyzes projects using a more qualitative approach.  The benefit cost analysis tool uses the basic approach of using a build versus no build comparison to calculate the benefits of constructing the project under review.  A 20 year window is used to capture the cumulative benefits and costs.

Tool Inputs and Assumptions

The benefit cost analysis tool requires a set of location specific transportation system activity and operations inputs to estimate the benefits of the project build against the non-build alternative.

Highway Project Inputs:

  • Current daily traffic
  • Current road configuration
  • Proposed road configuration
  • Current speed limit
  • Construction period
  • Project cost
  • HOV considerations

Transit Project Inputs:

  • Annual ridership year 1 & 20
  • Annual revenue miles year 1 & 20
  • Capital costs
  • Year by year operating costs

Bicycle & Pedestrian Inputs:

  • Cost per linear foot
  • Transit Proximity
  • Employment/Housing density
  • Connectivity

Countywide Factors

  • Fuel prices
  • Hourly wages
  • Growth rate
  • Transit and HOV Mode split
  • Vehicle occupancy rates

Basic Calculation Methodology

This takes the reduction of delay each year, and sums the years as the total delay reduced by the project.

The reductions are monetized by calculating:

  • Fuel Savings
  • Travel Time Savings
  • Emissions Reductions
  • Vehicle Operating Savings


Besides the benefit/cost ratio, the tool also provides:

  • Life cycle costs
  • Life cycle benefits
  • Net present value
  • Rate of return
  • Payback period

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