Part 2 Processes and approaches associated with the FHWA method 1 1 HPMS Vehicle Summary Data

How to Compute VMT Traffic flow rate x roadway segment length = VMT 2 Flow rate examples 100 vehicles per hour Segment length examples miles 2

VMT Computation Example 1: Total annual average daily VMT = Annual average daily traffic (AADT) x roadway segment length 3 2: Total annual average daily combination truck VMT = Annual average daily CT traffic (AADT_CT) x roadway segment length 3

Example: VMT of Route

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VMT computation is straightforward if AADT data for MC, Car, Light Truck, Bus, SUT, and CT are known for every segment of a roadway 9 9

10 Unfortunately we do not have such complete data! The best we have is the HPMS link level data. HPMS link level data contains: 1)AADT for all roadway segments, 2)AADT Single Unit Vehicle for sample and NHS segments, and 3)AADT Combination Truck for sample and NHS segments. 10

11 Example: VMT of Route

What Available Are 12 outside HPMS Traffic classification count data outside HPMS for a given location – counts and % of various vehicles passing through a counting point Route 100=286 miles Route 19 A B 12

Route 100=286 miles The Challenge 13 How to use such classification data to represent a system, an area, a state for VMT split? Route 19 A B 13

Method A – Simple Average 14 Simply add A and B together and divided it by 2 and use this simple average to represents the 286 miles long Route 100 Route 100=286 miles Route 19 A B 14

15 Route 100=286 miles Method B – Weighted Average 15 Your local knowledge tells that Station A represents well for segment east of Route 19 which is 218 miles (total VMT of 1,015,226 miles). Station B represents Route 100 well for the segment west of Route 19 (68 miles) with a total VMT of 641,376 miles. Now you can use a weighted method. – weighting by VMT on each of the segment) Route 19 A B 15

Route 100=286 miles Method B – Weighted Average 16 Route 19 A B 16

Method B – Weighted Average 17 Route 100=286 miles 17 A B

Route 100=286 miles Route 19 A B Method B – Difference Between Weighted Average (WA) and Simple Average (SA) 18 A

The Importance of a Weighted Average Weighted Average represents population more precise than Simple Average. 1: The more segments, the more precise of the weighting 2: The smaller the geography, the more precise of the weighting FHWA defers to States on specific weighting segments, weighting VMT and geography. 19

 Simple Average  Weighted Average  FHWA recommends Weighted Average Summary 20