Traffic Data Analysis for the Road design

Design

1. Application of Low Volume Roads Manual APPLICATION OF LOW-VOLUME ROADS MANUAL Lesson 10: Traffic Data Analysis Eng. Lameck Methusela

2. 2 OUTLINE Application of Low Volume Roads Manual 2 Lesson 10: Traffic Data Analysis Conversion of Traffic Counts Design Life What is Design Life Factors Influencing Choice of Design Life Design Traffic What is Design Traffic Procedure for determination of Design Traffic Initial Traffic Volume Traffic Growth Determination of Design Class Determination of Traffic Load Class

3. Application of Low Volume Roads Manual 3 1. CONVERSIONOF TRAFFIC COUNTS 1.1 General Main input parameters for road design are: Annual Average Daily Traffic (AADT) i.e the number of vehicles passing a point in both directions per day taking into account the variation in the traffic flow throughout the year Cumulative loading over the design life of the road i.e. the total number of standard axles for the same traffic volume, commonly termed as mESA ) Notes: AADT used to determine Design Class (DC) mESA used to determine Traffic Load Class (TLC) Lesson 10: Traffic Data Analysis

4. Application of Low Volume Roads Manual 4 1. CONVERSION OF TRAFFIC COUNTS 1.2 Determination of ADT Converting 12-hour traffic count to 24-hour flow by using applicable conversion factors to obtain an Average Daily Traffic (ADT) Lesson 10: Traffic Data Analysis

5. Application of Low Volume Roads Manual 5 1. CONVERSION OF TRAFFIC COUNTS 1.3 Determination of AADT Scenarios Urban Inter-urban Recreation High 1.016 1.115 1.271 Medium 1.000 1.060 1.141 Low 0.989 1.016 0.962 Annual Average Daily Traffic is the average traffic that is expected to use a particular road over a year (365 days) AADT = T-ADT/365 Where: AADT = Annual Average Daily Traffic T-ADT = Total Average Daily Traffic Conversion of ADT to AADT factors Lesson 10: Traffic Data Analysis

6. Application of Low Volume Roads Manual 6 2. DESIGN LIFE 2.1 Meaning the time span in years considered appropriate for the road pavement to function before reaching a terminal value of serviceability after which major rehabilitation or reconstruction would be required Design Life is decided depending on Importance of the road or expected level of service Importance/Level of Service Low High 5 – 10 Years 10 – 15 Years Lesson 10: Traffic Data Analysis

7. Application of Low Volume Roads Manual 7 2. DESIGN LIFE 2.2 Factors Influencing Choice of Design Life Functional classification. Strategic importance of the road. Funding considerations. Maintenance strategies (highly trafficked facilities will demand long periods of low maintenance activity). Anticipated time for future upgrading of the road. The likelihood that factors other than traffic, e.g. a highly reactive subgrade , will cause distress necessitating major rehabilitation in advance of any load-related distress. Lesson 10: Traffic Data Analysis

8. Application of Low Volume Roads Manual 8 3. DESIGN TRAFFIC 3.1 What is Design Traffic Lesson 10: Traffic Data Analysis For geometric design The total number of vehicles anticipated to be passing through a point of the road in both directions at the middle of Design Life For Pavement design The cumulative number of standard axle loads that will have passed through a point of the road in one direction from the start to the end of Design Life

9. Application of Low Volume Roads Manual 9 3. DESIGN TRAFFIC 3.2 Procedure for Determination of Design Traffic Lesson 10: Traffic Data Analysis

10. Application of Low Volume Roads Manual 10 Lesson 10: Traffic Data Analysis 3. DESIGN TRAFFIC 3.3 Initial Traffic Volume

11. Application of Low Volume Roads Manual 11 Lesson 10: Traffic Data Analysis 3. DESIGN TRAFFIC 3.3 Traffic Growth

12. Application of Low Volume Roads Manual 12 Lesson 10: Traffic Data Analysis For Geometric Design purposes, LVRs are classified into the following Design Classes: Road Design Class AADT at Mid Design Life ( vpd ) DC 5 200 – 400 DC 6 50 – 200 DC 7 20 – 50 DC 8 < 20 Important NOTE: AADT during the design year is projected to AADT at mid design life e.g. if the design life is 20 years, mid design life is 10 years 3.4 Determination of Design Class (DC)

13. Application of Low Volume Roads Manual 13 Lesson 10: Traffic Data Analysis Where: AADT mid = Estimated geometric Design Traffic AADT = Initial Traffic r = Traffic Growth Rate N = Design Life 3.4 Determination of Design Class (DC)

14. Application of Low Volume Roads Manual 14 Lesson 10: Traffic Data Analysis Group Exercise: Given the following Traffic data, determine the road Design Class. Assume Design Life is 12 years. Vehicle Class Small Cars Pick-Ups/ Vans Small buses Large Buses LGV MGV HGV VHGV AADT 3 12 6 4 7 6 3 1 Growth Rate 8.7% 4.0% 10.0% 5.0% 4.0% 3.7% 3.1% 2.7% 3.4 Determination of Design Class (DC)

15. Application of Low Volume Roads Manual 15 Lesson 10: Traffic Data Analysis 3.5 Determination of Traffic Load Class (TLC) Static axle load data on the vehicles expected to use the road is required to determine: The mean axle load Equivalency Factor (EF) and, The mean Vehicle Equivalency Factor (VEF), i.e. the sum of the axle load EFs for each vehicle. 3.5.1 Vehicle Equivalency Factor (VEF) Note: The global standard Axle Load is 8.16tons

16. Application of Low Volume Roads Manual 16 Lesson 10: Traffic Data Analysis 3.5 Determination of Traffic Load Class (TLC) Where: VEF = Vehicle Equivalency Factor n = Number of axles Ai = Individual Axle Load in tons x = Power exponent between 2.5 and 4.5. For LVRs, 4.0 is adopted 3.5.1 Vehicle Equivalency Factor (VEF)

17. Application of Low Volume Roads Manual 17 Lesson 10: Traffic Data Analysis 3.5 Determination of Traffic Load Class (TLC) 3.5.1 Vehicle Equivalency Factor (VEF) Individual Exercise: Calculate VEF for a bus with the following axle loads: Axle 1 = 7,680kg Axle 2 = 10,250kg

18. Application of Low Volume Roads Manual 18 Lesson 10: Traffic Data Analysis 3.5.2 Average Vehicle Equivalency Factors Class Type Nr of Axles Average VEF per vehicle C Small Bus 2 0.3 D Large Bus 2 2.4 E Light Goods Vehicle 2 1.5 F Medium Goods Vehicle 2 4.0 G Heavy Goods Vehicle 3 4.5 H Very Heavy Goods Vehicle ≥ 4 7.0 I 2-Axle Trailer 3 8.0 J 3-Axle Trailer 3 10.0 K 4-Axle Trailer 4 12.0

19. Application of Low Volume Roads Manual 19 Lesson 10: Traffic Data Analysis 3.5.3 Mean Daily Equivalent Standard Axle Loadings DESA = Daily Equivalent Standard Axle Loadings. The estimated mean daily ESAs for each vehicle class is obtained by: DESA = AADT x VEF

20. Application of Low Volume Roads Manual 20 Lesson 10: Traffic Data Analysis 3.5.4 Cumulative Equivalent Standard Axle Loadings The cumulative equivalent standard axles (CESA) in each direction for each traffic category expected over the design life is obtained by: Where: DESA = mean daily ESAs for each vehicle class in the design year (each direction) r = Assumed Annual Growth Rate, expressed as a decimal fraction N = Design Life in years (+ 2 to 3 yrs for construction)

21. Application of Low Volume Roads Manual 21 Lesson 10: Traffic Data Analysis 3.5.4 Cumulative Equivalent Standard Axle Loadings Individual Exercise From the following data, calculate CESA of the given vehicle class for the proposed design life Description Design Data Vehicle Class Bus VEF 3.3 Initial AADT 18 vpd Growth rate 6.0% Design Life 15 years

22. Application of Low Volume Roads Manual 22 Lesson 10: Traffic Data Analysis 3.5.5 Traffic Lane Distribution Driving pattern is very channelized Traffic in both directions use same lane Overlap in the center of the road Minimal traffic overlap in the center Majority of vehicles use one lane in each direction Width Distribution Notes

23. Application of Low Volume Roads Manual 23 Lesson 10: Traffic Data Analysis 3.5.6 Traffic Load Class For Structural Design purposes, TLC for LVRs are: Traffic Load Class Cumulative traffic load during design life ( mESA ) TLC 1.0 0.5 – 1.0 TLC 0.5 0.3 – 0.5 TLC 0.3 0.1 – 0.3 TLC 0.1 0.01 – 0.1 TLC 0.01 < 0.01

24. Application of Low Volume Roads Manual 24 Lesson 10: Traffic Data Analysis 3.5.6 Traffic Load Class Group Exercise: Given the following Traffic data, determine the Traffic Load Class. Assume carriageway width 6.0m and Design Life is 12 years. Vehicle Class Small Cars Pick-Ups/ Vans Small buses Large Buses LGV MGV HGV VHGV AADT DirA 3 12 6 3 2 6 3 1 AADT DirB 5 10 5 4 7 8 3 2 Growth Rate 8.7% 4.0% 10.0% 5.0% 4.0% 3.7% 3.1% 2.7%

25. Application of Low Volume Roads Manual 25 Thank you! Lesson 10: Traffic Data Analysis