Guide to Urban Traffic Volume Counting September 1981 This report - - PowerPoint PPT Presentation

Guide to Urban Traffic Volume Counting

September 1981

This report presents methods by which urbanized areas can develop and implement integrated traffic counting programs to serve the volume data needs of all agencies. Methods for estimating volume at a single location, volume across a cordonline or cutline, VMT within a corridor or other small area, and regional VMT are presented. Sound statistical sampling concepts permit the collection of volume data at predetermined levels of precision and in a cost‐ effective manner.

Acronym Quiz

VMT ADT AADT AAWDT AADTT AWB ATR HPMS AAWET PTR SADT TMG Vehicle Miles of Travel Average Daily Traffic Annual Average Daily Traffic Annual Average Weekday Traffic Annual Average Daily Truck Traffic Average White Band Automatic Traffic Recorder Highway Performance Monitoring System Annual Average Weekend Traffic Portable Traffic Recorder Seasonal Average Daily Traffic Traffic Monitoring Guide

Reasons for Estimating VMT

 Air Quality  Model Validation /Calibration  Performance Measures

 Demand on Highway System  Crash Data‐Rate  Evaluate Active Transportation

 VMT per Capita

Development of an Integrated Traffic Counting Program

 Consideration of Five Tasks

 Define program objectives  Select data collection locations for regional estimates  Select data collection locations for focused studies  Develop a data collection plan  Identify supplementary study needs

Define Program Objectives

 Determine the type of volume counts required

 Intersection  Midblock volume/classification  Cordonline/Screenline counts  Peak Period – Weekday ‐ Weekend

 Define the sample population

 Metropolitan Planning Area  Urban Area  Subarea(s)

Define Program Objectives

 Determine the desired level of precision

 Confidence Interval/Confidence Limits (tolerance)

 Acceptable difference between the obtained/estimated

measure and the true value

 Confidence Level/Confidence Coefficient

 Probability the sample estimate will fall within this range

Select Data Collection Locations for Regional Estimate

 Three Approaches for Obtaining a Regional Sample

 Rotational

 Count every location at some minimal time interval

 Randomly select locations to yield an unbiased VMT estimate  Three year rotation, randomly select 1/3 of locations for each

year  New Sample Every Year  Same Sample Every Year

Program Objective Trade‐Offs

 Higher precision levels‐larger sample‐higher cost  Value of estimating VMT for local roads  Investigate integration of multiple objectives

 A rotational sampling process for VMT estimate can be

integrated into an existing coverage count program

 Cordonline/Screenline counts  Subarea analyses  Other special counts

NIRCC desired Level of Confidence and Confidence Intervals

 Level of Confidence ‐ 95%  Confidence Intervals

 Freeways/Interstates ± 10%  Expressways ± 10%  Arterials ± 10%  Collectors ± 15%  Locals ± 25%

Define Sample ‐ Stratification

 Two Types of Stratification

 Reporting Strata

 Roadway Classification

 Sample Strata

 Volume Groups

Define Sample ‐ Stratification

 Two Types of Stratification

 Reporting Strata

 Interstates/Freeways  Expressways  Arterials  Collectors  Local Streets

 Sample Strata

 Volume Groups

Arterial Example

Sample Stratum Mileage Link Population Average Volume VMT Multi‐Axle Vehicles

0-4,999 40 80 2,500 100,000 2% 5,000-9,999 70 140 7,500 525,000 2% 10,000-14,999 50 100 12,500 625,000 2.5% 15,000-19,999 40 80 17,500 700,000 3% 20,000-24,999 30 60 22,500 675,000 5% 25,000-29,999 20 40 27,500 550,000 7% 30,000-39,999 15 30 35,000 525,000 10% 40,000-49,999 10 20 45,000 450,000 10% 50,000+ 10 20 55,000 550,000 10%

Estimating Sample Size for Regional VMT

 Define Sample Strata

 Reporting Strata  Sample Strata

 Compute Regional VMT estimate

 Known Mileage for Sample Stratum “h”  Average Volume for Sample Stratum “h”  VMTh = Mh x VOLh

Estimating Sample Size for Regional VMT

 Estimate Sample Parameters‐Uncertainty

 Spatial Uncertainty‐variability of volume between

locations

 Standard deviation of volume across locations

 Temporal Uncertainty‐variability of volume over time

 Standard deviation of volume across days within a season  Standard deviation of volume across seasons of the year  Standard error of seasonal adjustment factors

 Measurement Uncertainty‐variability due to traffic

counter error

 Standard error of correction factors (axle)

Sample Size Recap

 Sample Size Dependent on

 Desired level of precision  Acceptable difference between VMT estimate and true

value (±)

 Stratification and Stratum Variation  Sample Parameters ‐ error and introduced variation

SEASONAL ADJUSTMENT FACTORS

Report Stratum Period of Data Fse SADJe SEADJe

Freeway June, September – December 1.0105 0.0249 0.0124 Expressway March – November 0.9816 0.0185 0.0093 Arterial March – December 0.9816 0.0185 0.0093 Collector March – December 0.9735 0.0127 0.0064 Local March – December 0.9735 0.0127 0.0064

Fse – Seasonal Adjustment Factor for Sample Stratum “e” SADJe ‐ Standard Deviation of the Seasonal Adjustment Factor for Sample Stratum “e” SEADJe – Standard Error of the Seasonal Adjustment Factor Sample Stratum “e”

Interstate

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-19,999 3 3 11.95 2 20,000-29,999 5 2 9.43 3 30,000-39,999 2 2 4.18 Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-19,999 7 7 17.58 2 20,000-39,999 8 8 19.06 3 40,000-59,999 4 4 9.63 4 60,000-79,000 5 5 10.54

Original Sample Current Sample

Expressway

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-9,999 3 3 3.36 2 10,000-14,999 1 1 0.80 3 15,000-19,999 1 1 0.45 Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-19,999 19 19 12.65 2 20,000-29,999 5 5 3.02 3 30,000-39,999 2 2 0.86 4 40,000-49,000 1 1 0.65

Original Sample Current Sample

Arterial

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-4,999 294 11 146.48 2 5,000-9,999 344 9 111.53 3 10,000-14,999 197 6 59.06 4 15,000-19,999 137 4 34.68 5 20,000-24,999 53 2 13.67 6 25,000-29,999 55 2 12.72 7 30,000-34,999 11 2 2.87 8 35,000-39,000 7 2 2.08 9 40,000-45,000 5 2 0.81 10 45,000-50,000 1 1 0.54

Original Sample

Arterial

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-4,999 260 138 163.87 2 5,000-9,999 268 126 88.05 3 10,000-14,999 238 128 74.54 4 15,000-19,999 149 73 45.16 5 20,000-24,999 92 46 25.86 6 25,000-29,999 43 28 12.86 7 30,000-34,999 21 12 7.30 8 35,000-39,000 15 9 4.70 9 40,000+ 14 8 3.33

Current Sample

Arterial

Volume Group Original Links Current Links Original Sample Current Sample 1 294 260 11 138 2 344 268 9 126 3 197 238 6 128 4 137 149 4 73 5 53 92 2 46 6 55 43 2 28 7 11 21 2 12 8 7 15 2 9 9 6 14 3 8

Comparison of Samples

Collector

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-999 179 14 121.0 2 1,000-1,999 86 6 48.61 3 2,000-3,999 115 9 46.75 4 4,000-5,999 39 3 12.81 5 6,000-7,999 29 2 8.11 6 8,000-9,999 9 2 0.61 7 10,000+ 8 2 2.18

Original Sample

Collector

Volume Group Volume Range Number

• f Links

Sample Size Link Mileage 1 0-999 73 37 68.18 2 1,000-1,999 104 53 48.61 3 2,000-3,999 184 100 60.46 4 4,000-5,999 104 55 35.81 5 6,000-7,999 69 34 23.14 6 8,000-9,999 39 17 14.09 7 10,000+ 22 12 7.68

Current Sample

Collector

Volume Group Original Links Current Links Original Sample Current Sample 1 179 73 14 37 2 86 104 6 53 3 115 184 9 100 4 39 104 3 55 5 29 69 2 34 6 9 39 2 17 7 8 22 2 12

Comparison of Samples

2015 VMT by Street Classification

Level of Confidence‐95%

Report Stratum Average Weekday VMT Annual Average Weekday VMT Maximum Difference Between AAWD VMT and True Value

Freeway

2,172,031 2,114,343 ±108,591

Expressway

280,583 277,248 ± 8,190

Arterial

4,299,774 4,237,826 ± 85,264

Collector

840,000 816,311 ± 59,944 Total VMT

7,445,728 ± 261,989

Local

1,471,578 1,430,078 ± 334,367 Grand Total VMT

8,875,806 ±596,356

2015 VMT by Street Classification

Level of Confidence – 95%

Report Stratum AAWD VMT Desired Confidence Interval Achieved Confidence Interval

Freeway

2,114,343 ±10.0% ±5.14%

Expressway

277,248 ±10.0% ± 2.95%

Arterial

4,237,826 ±10.0% ± 2.01%

Collector

816,311 ±15.0% ± 7.34% Total VMT

7,445,728 ± 3.52%

Local

1,430,078 ± 25.0% ± 23.38% Grand Total VMT

8,875,806 ±6.72%

1,000,000 2,000,000 3,000,000 4,000,000 5,000,000 6,000,000 7,000,000 8,000,000 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015

4,139,589 4,614,101 4,460,225 4,740,168 5,010,248 5,316,228 5,219,414 5,401,848 5,737,554 5,989,143 6,204,244 6,385,638 6,487,092 6,787,292 6,960,667 6,876,220 6,863,980 7,140,708 7,032,114 7,137,764 7,331,072 7,410,562 7,418,167 7,336,515 7,252,988 7,062,317 7,164,314 7,234,999 7,214,635 7,268,982 7,445,728

VMT YEAR

Vehicle Miles of Travel 1985 – 2015 MPA

500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 3,500,000 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015

1,770,000 1,830,000 1,920,000 2,030,000 2,100,000 2,140,000 2,170,000 2,250,000 2,300,000 2,360,000 2,420,000 2,480,000 2,550,000 2,630,000 2,690,000 2,750,000 2,800,000 2,860,000 2,890,000 2,960,000 2,990,000 3,010,000 3,030,000 2,980,000 2,960,000 2,970,000 2,950,000 2,970,000 2,990,000 3,030,000 3,150,000

VMT YEAR

National Annual Vehicle Miles of Travel 1985 - 2015

(millions)

1990 2000 2010 Population 248,424 287,759 308,120 Vehicle Miles of Travel 5,316,228 6,876,220 7,062,317 VMT per Capita 21.4 23.9 22.9