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SATC 2017

Explore in-depth principles and design requirements for roundabouts to ensure optimal safety and operation for all users. Learn about critical elements, speed profiles, sight distances, apron designs, surfacing, signage, and more.

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SATC 2017

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  1. SATC 2017 Towards the Ideal Roundabout Design FH van Renssen Mowana Engineers M Watters WCG DoT CR Tichauer Mowana Engineers DR C Krogscheepers ITS International G Matthee ITS International

  2. AGENDA • Introduction • Principles and Requirements (P&R’s) • Some critical P&R’s discussed • From here

  3. Introduction • More and more requests for roundabout designs • What do you get… ALLSORTS…

  4. Introduction • WCG:DoT’s response: Planning and design principles • Volume 1 – International and national literature review, evaluation of existing roundabouts • Volume 2 – Planning document (P&R’s included) • Volume 3 – Roundabout Design Guidelines (later) • P&R’s developed • Design elements broken up

  5. Format and layouts of P&R’s

  6. Focus of the design elements To create a design which: Safe environment Optimal operation ALL USERS

  7. P&R: Design Vehicle • For consistency – SANRAL vehicles used

  8. P&R: Design Vehicle

  9. P&R: Design Vehicle • For consistency – SANRAL vehicles used

  10. P&R: Design Speed and Speed Profiles • Many elements affect design speed through Roundabout • One of the most critical items which needs to be adhered to • Speed profile values on each approach should not exceed this speed

  11. P&R: Design Speed and Speed Profiles (cont) • Aim: R1 < R2 < R3 • R1 and R2 at no time more than 10 km/h difference • Any 2 conflicting speeds within 10 km/h, not more than 20 km/h • Method of calculating prescribed

  12. P&R: Design Speed and Speed Profiles (cont) • R1 = 38 km/h • R2 = 34 km/h • R3 = 50 km/h • R4 = 25 km/h • R5 = 42 km/h Example: Min of SP

  13. P&R: Approach alignment • In most instances entrance to roundabout dictates the speed through a roundabout • Extension of approach should be on right of CL

  14. P&R: Approach alignment (cont) • Chicanes: Rural to Urban transition • Above 80 km/h, reduce in 20 km/h intervals • Not normal in Urban areas, but possible on arterials • Offset of chicane should be 7m (for double lane) – to prevent straight movement

  15. P&R: Sight distances • Approach Sight Distance (ASD): • Distance required to see yield line • This is a MINIMUM distance

  16. P&R: Sight distances (cont) • Intersection Sight Distance (ISD): • Distance required to determine safe gap in conflicting traffic • This is a MINIMUM and MAXIMUM distance

  17. P&R: Sight distances (cont) • Stopping Sight Distance (SSD): • Distance required to stop at any object/ intersection/ etc. • This is a MINIMUM distance

  18. P&R: Sight distances (cont) • Left Turn Sight Distance to Pedestrians (LTSD): • 3 m behind yield line to next full peds crossing • This is a MINIMUM distance

  19. P&R: Sight distances (cont) • Combined sight distances

  20. P&R: Internal and External Aprons (cont) External truck apron Internal truck apron

  21. P&R: Internal and External Aprons (cont) • Internal aprons: • Determined by WB-15 wheel tracks (2 m minimum) • Cross-fall 2% outfall • Mountable kerb, 50 mm high at apron

  22. P&R: Internal and External Aprons (cont) • Internal aprons:

  23. P&R: Internal and External Aprons (cont) • External aprons: • Only if no other option available for controlling speed at entry and exit • Use WB-15 for tracking path • 2% cross-fall (outfall) with V-channel • Pedestrian crossing to be clearly defined

  24. P&R: Internal and External Aprons (cont) • External aprons:

  25. P&R: Surfacing and pavement • Surface treatment can play important role in safety • Visual distinction between road, truck apron and peds/cycle crossings

  26. P&R: Road Signs and Markings • Road signs • SARTSM not consistent • Minimum required signs only in P&R • Rule remains – as little as possible • Not to obstruct peds and cyclists, but within legal requirements

  27. P&R: Road Signs and Markings • Road markings • Fishhook arrows – get permission from minister • In double roundabouts use WM7-series for proper lane usage • Lane lines should guide lane selection • All kerbs to have GM8 markings • All markings shall be Thermo-plasic or cold plastic • On surfaces other than asphalt, proper priming of surfaces required before painting

  28. P&R: Road Signs and Markings (cont)

  29. From here… • Inconsistency in design standards used – need for South African standards long overdue • WCG: DoT in process of providing a tool • Evaluation of roundabout as intersection control measure • Consistent safe designs • Will be ready shortly for use in the industry • Recommended that other National, Provincial and Local governments also consider this for use in their areas

  30. SATC 2017 Towards the Ideal Roundabout Design Thank you FH van Renssen Mowana Engineers freekvr@mowana-engineers.co.za M Watters WCG DoT CR Tichauer Mowana Engineers Dr C Krogscheepers ITS International G Matthee ITS International

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