the effect of heavy vehicle composition on design traffic loading calculations (E80s)

1. the effect of heavy vehicle composition on design traffic loading calculations (E80s)

2. introduction traffic loading can be defined as: • the placement of traffic on a network • use of space • stressing of the pavement layers • the concept of the damage – E80

3. background • traffic loading data - 34 permanent counting stations widely spread • Comprehensive Traffic Observations (CTO) yearbooks from 1986 – 2002 • traffic data randomly selected

4. background (2) • the calculation of the design traffic - depends on various factors, inter alia, • the type of data available (e.g. vehicle classification, method of traffic counting, • obtaining of axle load (weighing), • calculation of growth rates etc, and • the application thereof • engineering judgement

5. 3 elements – traffic loading • vehicle loading - legally loaded vehicle, • vehicle overloading - overloaded vehicle, • vehicle lading – utilisation of the vehicles’ load capacity

6. 3 elements – traffic loading (2) • growth in heavy vehicles (hv) – important role in design traffic calculation + prediction of damage • interwoven into the hv composition & ave. E80/hv factors • influence & impact of the changes – exp. 3 elements

7. important changes to be considered • shift in heavy vehicle (hv) composition (% hv split) • increase in average E80/hv factors • changes in legal axle load limits

8. shift in heavy vehicle (%)composition (split) • composition of heavy vehicle – past 10 to 15 years – confirmed in various countries + data from this study • changes – lead to an increase in the : • growth in E80s/hv, • average calculated E80s/hv, • total E80s • composition of hv = 2-axles, 3 axles, 4-axles, 5 axles, 6-axles etc

9. shift in heavy vehicle (%)composition (split) (2) • hv different load configurations – 3 classes: short, medium & long • 6 / 34 permanent traffic counting stations - randomly selected - “trends” • continued shift in the composition – 2-4 hv axles to 5-7 hv axles

10. shift in heavy vehicle (%)composition (split) (3)

11. increase in average E80/heavy vehicle factors • growth in E80s = growth (hv & E80/hv) shift in the composition of hv + ass. growth in hv = increase in growth in E80/hv & average E80/hv • TRH 16 (1991) - reliable estimates – reviewed & updated • recent study - Southern African Transport & Communications Commission (1998) - increase • confirmed by results from this study

12. increase in average E80/heavy vehicle factors (2)

13. increase in average E80/heavy vehicle factors (3)

14. changes in legal axle limits

15. important changes - conclusion • shift in heavy vehicle (hv) composition (% hv split) - confirmed • increase in average E80/hv factors - showed • changes in legal axle load limits – permissible / legal loads - doubled

16. design traffic loading calculations – practical example (e.g.) following steps are required • traffic & traffic loading data – gathering available data, • axle load data – assesses & determine the E80 factors • growth rates - past & future • sensitivity analysis • calculation of the total E80

17. design traffic loading calculations – e.g.traffic & traffic loading data information from historical traffic count data

18. design traffic loading calculations – e.g.axle load data • expected traffic – pavement structure is calculated as the equivalent std. 80kN dual wheel single axle (E80), • vary considerable from route to route, • average E80/hv factors (different hv traffic classes) + hv composition = average E80/hv factor

19. design traffic loading calculations – e.g.growth rates (general) • growth rate in E80/hv occurs on most roads • variations in traffic loading are complex - enough information is required • growth in E80 (an exponential compound) - at least 5 yr period (preferable) • growth rates obtained from short term surveys (2-3 yrs) - used with caution

20. design traffic loading calculations – e.g.growth rates (historic)

21. design traffic loading calculations – e.g.growth rates (future)

22. design traffic loading calculations – e.g.sensitivity analysis E80 growth rate = [(1+h/100) x (1+v/100)-1] x 100 where: h = heavy vehicles growth rate v = E80s per heavy vehicle growth rate • growth in E80’s depends on factors: • growth in total traffic • growth in the % hv vehicles as a % of total traffic • growth in E80s/hv

23. design traffic loading calculations – e.g.sensitivity analysis (2)

24. design traffic loading calculations – e.g.sensitivity analysis (3)

25. design traffic loading calculations – e.g.sensitivity analysis

26. design traffic loading calculations – e.g.design traffic loading calculations – E80 growth

27. design traffic loading calculations – e.g.design traffic loading calculations – HV growth (2)

28. conclusions • composition of heavy vehicle traffic - changed dramatically • continues shift towards the “long” heavy vehicle composition • effect of an increase in the permitted legal axle loads has a major impact on the permitted legal E80/hv

29. recommendations • TRH 16 (1991) be reviewed and updated • more information is gathered, analyzed & processed - provide new E80 factors / norms - in order to accommodate the shift towards the “long” heavy vehicle composition on the roads in southern Africa

30. acknowledgements information & input provided by the following persons / organisations is appreciated and gratefully acknowledge • Dr. Gerrit J Jordaan – Tshepega • Mr. Geoff Ackerman – SANRAL • Me. Michelle van der Walt – Mikros

31. the effect of heavy vehicle composition on design traffic loading calculations (E80s)