1. Quantification of the Natural Variation in Traffic Flow
12 July South African Transport Conference SESSION 3B
Frans De Jongh: AECOM
Megan Bruwer: Stellenbosch University

2. Traffic Variations Artificial Natural Hourly Manual Surveys Daily
Automatic Counts
Natural
Hourly
Daily
Monthly
Annual

3. Introduction Purpose of study: Assumptions and limitations:
Define natural traffic variations around SA
Develop method to adjust traffic volumes
Assumptions and limitations:
Urban and rural differences not considered
Applicable to higher order urban roads
Traffic data grouped into regions
All vehicles classifications together
Limited count stations per region

4. Traffic Variation
Hourly Variation:
Jordaan and van As
(1991)

5. Traffic Variation Daily Variation: Monthly Variation:
Jordaan and van As (1991)  hourly variation traffic pattern remains consistent over the days of the week, with slight variation on Friday PM
Monthly Variation:
Karacasu, et al. (2011)  observed that monthly traffic varied according to season, climate AND proximity to tourist destinations
Tourist sites: more traffic in summer
Climate: increase in summer traffic less significant in very hot climate

6. Traffic Variation: Importance?
Representative traffic:
Modeling: prepare transport models using neutral traffic with no seasonal influence (Chauke, 2015)
Design of transport infrastructure: 30th highest hourly traffic volume (Van As & Joubert, 1989)
0.25 of AADT  high peaking
0.12 of AADT  limited peaking

7. Data Collection
18 CTOS
10 regions
Jan 2007 to Oct 2015

8. Modification Factors Identifies the peak Scale of 0 to 1
Indicate traffic volume as a ratio to the peak
Hourly
Daily
Monthly traffic volume

9. Hourly Traffic Variation
Subject to
Work / school hours
Traffic congestion
Road category
CTOS 710: N2 Cape Town

10. Hourly Traffic Variation: Weekday

11. Hourly Traffic Variation: Weekday
Pretoria
Port Elizabeth
Bloemfontein

12. Hourly Traffic Variation: Weekday
Kimberley
Vryburg
Potchefstroom

13. Hourly Traffic Variation: Weekend

14. Hourly Traffic Variation: Weekend
Durban
Vryburg
Port Elizabeth

15. Daily Traffic Variation
Subject to
Work week / weekend
Public holiday
Road category
CTOS 710: N2 Cape Town

16. Daily Traffic Variation

17. Daily Traffic Variation
Pretoria
Vryburg
Port Elizabeth

18. Monthly Traffic Variation
Subject to
School terms / holiday
Religious holidays
Seasons
CTOS 710: N2 Cape Town

19. Monthly Traffic Variation

20. Monthly Traffic Variation
Kimberley
Vryburg
Bloemfontein

21. Monthly Traffic Variation
Cape Town
Port Elizabeth
Pretoria

22. Annual Variation Economic vs Traffic Growth Rate
Traffic Growth Rate 2007 to 2015: +1.6% per annum

23. Application of Modification Factors
Natural Traffic Variations
Hourly
Daily
Monthly
Annual
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝐻𝑜𝑢𝑟𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐻𝑜𝑢𝑟𝑙𝑦
AV: Adjusted Volume
CV: Counted Volume
MFAV: MF for hour desired
MFCV: MF for hour counted
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝐷𝑎𝑖𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐷𝑎𝑖𝑙𝑦
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦 𝑀𝐹 𝐶𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦
𝐴𝑉=𝐶𝑉 1+ 𝑖 𝑛

24. Application of Modification Factors
Natural Traffic Variations
Hourly
Daily
Monthly
Annual
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝐻𝑜𝑢𝑟𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐻𝑜𝑢𝑟𝑙𝑦
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝐷𝑎𝑖𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐷𝑎𝑖𝑙𝑦
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦 𝑀𝐹 𝐶𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦
𝐴𝑉=𝐶𝑉 1+ 𝑖 𝑛
𝐴𝑉=𝐶𝑉 𝑀𝐹 𝐴𝑉−𝐻𝑜𝑢𝑟𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐻𝑜𝑢𝑟𝑙𝑦 𝑀𝐹 𝐴𝑉−𝐷𝑎𝑖𝑙𝑦 𝑀𝐹 𝐶𝑉−𝐷𝑎𝑖𝑙𝑦 𝑀𝐹 𝐴𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦 𝑀𝐹 𝐶𝑉−𝑀𝑜𝑛𝑡ℎ𝑙𝑦 𝑖 𝑛

25. Conclusions and Recommendations
Modification factors established on scale of 0 to 1
Use case 1: define traffic variation
Use case 2: apply factors to establish peak traffic volumes
Similar hourly and daily traffic variations in all regions
Monthly variation quite different among regions
Recommendations:
Only for urban higher order roads, investigate other classes
Investigate application of modification factors to calculate design volumes

26. THANK YOU
Questions?
Contact: Megan Bruwer