Towards the Ideal Roundabout Design 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

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

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

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

Format and layouts of P&R’s No Description 1A Inscribed Circle Diameter (ICD) 1B Design Vehicles 2A Design Speeds and Speed Profiles 2C Approach Alignment 2E Sight Distances 2G Entry Width 2H Entry Angle 3A Internal and External Apron Cross-section Detail 3C Circulatory Roadway widths / Truck Accommodation 4A Gradient / Vertical Alignment 4B Cross-fall 4C Approach Detail (Vane) 4D Central / Splitter Island Treatment 4E Surfacing and Pavement 5A Pedestrian Movements and Accommodation 5B Bicycle Movements 6A Road Signs and Road Markings 7A Lighting 8A Access In and Close To Roundabout 9A Left-turn Slip Lane 10A Staged Implementation 11A Directional Roundabout 12A Public Transport Stops 12B Preferential Lanes 13A Abnormal Loads 14A Signal Control

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

To be accommodated within circulatory lane P&R: Design Vehicle For consistency – SANRAL vehicles used Vehicle Type Requirement Primary design vehicle: BUS To be accommodated within circulatory lane

Can encroach on truck apron or adjacent circulatory lane P&R: Design Vehicle Vehicle Type Requirement Secondary Design Vehicle: WB-15 Can encroach on truck apron or adjacent circulatory lane

Ensure appropriate sight distances are achieved/not exceeded P&R: Design Vehicle For consistency – SANRAL vehicles used Vehicle Type Requirement Sight distance design vehicle: PV Ensure appropriate sight distances are achieved/not exceeded

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 Design Speeds (km/h)   Single Lane Double Lane Urban 30 km/h 35 km/h Rural 40 km/h

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

P&R: Design Speed and Speed Profiles (cont) Example: Design Speeds (km/h)   Single Lane Double Lane Urban 30 km/h 35 km/h Rural 40 km/h R1 = 38 km/h R2 = 34 km/h R3 = 50 km/h R4 = 25 km/h R5 = 42 km/h Min of SP

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

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

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

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

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

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

P&R: Sight distances (cont) Combined sight distances

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

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

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

P&R: Internal and External Aprons (cont) 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

P&R: Internal and External Aprons (cont)

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

P&R: Road Signs and Markings 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

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

P&R: Road Signs and Markings (cont)

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

Towards the Ideal Roundabout Design 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