Part 2Processes and approaches associated

with the FHWA method

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HPMS Vehicle Summary Data

How to Compute VMT

Traffic flow rate x roadway segment length = VMT

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Flow rate examples100 vehicles per hour

Segment length examples10.15 miles

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VMT Computation Example

1: Total annual average daily VMT =Annual average daily traffic (AADT) x roadway segment length

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

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Example: VMT of Route 100

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Example: VMT of Route 100

Segment ID

Beginning Mile Post

Ending Mile Post

Length (miles)

AADTCombination Truck AADT

1 0 20 20 1000 202 20 24 4 800 243 24 36 12 1200 684 26 38 12 1100 405 28 42 14 1400 1006 42 57 15 1000 287 57 82 25 1200 808 82 91 9 1600 609 91 99 8 1200 40

10 99 109 10 800 60Subtotal 129

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Example: VMT of Route 100

Segment ID

Beginning Mile Post

Ending Mile Post

Length (miles)

AADTCombination Truck AADT

Total VMT

1 0 20 20 1,000 20 20,000 2 20 24 4 800 24 3,200 3 24 36 12 1,200 68 14,400 4 26 38 12 1,100 40 13,200 5 28 42 14 1,400 100 19,600 6 42 57 15 1,000 28 15,000 7 57 82 25 1,200 80 30,000 8 82 91 9 1,600 60 14,400 9 91 99 8 1,200 40 9,600

10 99 109 10 800 60 8,000 Subtotal 129 147,400

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Example: VMT of Route 100

Segment ID

Beginning Mile Post

Ending Mile Post

Length (miles)

AADTCombination Truck AADT

Total VMT

CT VMT

1 0 20 20 1,000 20 20,000 400 2 20 24 4 800 24 3,200 96 3 24 36 12 1,200 68 14,400 816 4 26 38 12 1,100 40 13,200 480 5 28 42 14 1,400 100 19,600 1,400 6 42 57 15 1,000 28 15,000 420 7 57 82 25 1,200 80 30,000 2,000 8 82 91 9 1,600 60 14,400 540 9 91 99 8 1,200 40 9,600 320

10 99 109 10 800 60 8,000 600 Subtotal 129 147,400 7,072

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Example: VMT of Route 100

Segment ID

Beginning Mile Post

Ending Mile Post

Length (miles)

AADTCombination Truck AADT

Total VMT

CT VMT

1 0 20 20 1,000 20 20,000 400 2 20 24 4 800 24 3,200 96 3 24 36 12 1,200 68 14,400 816 4 26 38 12 1,100 40 13,200 480 5 28 42 14 1,400 100 19,600 1,400 6 42 57 15 1,000 28 15,000 420 7 57 82 25 1,200 80 30,000 2,000 8 82 91 9 1,600 60 14,400 540 9 91 99 8 1,200 40 9,600 320

10 99 109 10 800 60 8,000 600 Subtotal 129 147,400 7,072

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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

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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.

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Example: VMT of Route 10011

What Available Are

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Traffic classification count data outside HPMS outside HPMS for a given location – counts and % of various vehicles passing through a

counting point

Route 100=286 miles

Route 19

A

B

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Route 100=286 miles

The Challenge

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How to use such classification data to represent a system, an area, a state for VMT split?

Route 19

A

B

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Method A – Simple Average

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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

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Route 100=286 miles

Method B – Weighted Average

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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

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Route 100=286 miles

Method B – Weighted Average

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Route 19

A

B

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Method B – Weighted Average

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Route 100=286 miles

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A

B

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Route 100=286 miles

Route 19

A

B

Method B – Difference Between Weighted Average (WA) and Simple Average (SA)

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A

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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.

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Simple Average Weighted Average FHWA recommends Weighted Average

Summary

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