Task Order 5.2 Benefits Analysis for the Georgia Department of Transportation NaviGAtor Program

APPENDIX D: SAMPLE COMPUTATIONS

As a demonstration of the methodology described in section 3.0, this section provides the computation steps for evaluating the benefits accrued from a level 3 incident occurring during the afternoon peak on a Tuesday on I-75/85NB between I-20 and Brookwood interchange.

Blocked lanes: 2

DOW: 2

TOD: 3

Lanes: 7

Incident duration: 38 minutes

Baseline duration: 73 minutes (From table D.1, corresponding to TOD=3, DOW=2, Level=3, Lanes=7)

Capacity = 13064 vph (From Table J-2 Segment 3N in Appendix J)

Therefore:

Capacity reduction factor = 0.57

Reduced capacity = 0.57 * 13064

Demand volume (from VDS data) = 10345 vph (From Table J-1 Segment 3N in Appendix J)

Queue Time Ratio (QRatio) = (μ - μ_R )/( μ - λ)

= (13064 – 0.57 * 13064 ) / (13064 – 10345)

= 2.0660

Total Delay Ratio (TDRatio) = 0.5 * QRatio * ( λ - μ_R )

= 0.5 * 2.0660 * (10345 - 0.57 * 13064 )

= 2994.1712

Total Delay _NaviGAtor = TDRatio * Incident Duration * Incident Duration

Total Delay _Baseline = TDRatio * Baseline Duration * Baseline Duration

Incident Delay Savings = Total Delay _Baseline – Total Delay _NaviGAtor

= TDRatio * ( Baseline Duration ²– Incident Duration ²)

= 2994.1712 * (73*73/3600 – 38 * 38/3600)

= 3231 vehicle-hours