Improved theory for the design of high-speed roundabouts to suit heavy vehicles

Tomarchio, Mark Daniel (2019) Improved theory for the design of high-speed roundabouts to suit heavy vehicles. [USQ Project]

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All roundabouts are effectively a series of 'reverse curves' that vehicles are required to negotiate. These curves limit the speeds that can be achieved by vehicles through the roundabout, which is the predominant reason that this form of intersection control is often considered the safest. However, there are significant differences between the performance and capabilities of cars and heavy vehicles. This research project investigates the differences in roundabout geometry required to safely cater for heavy vehicles as well as cars, and aims to improve the design standards and guidance for designers of such roundabouts.

Roundabout usage as a form of intersection control is becoming more common every day, and they are increasingly being used in high speed areas on major roads, with a wide variety of traffic composition, including heavy vehicles. This is in contrast to their more traditional usage in low speed urban environments, which the commonly available standards and guidelines currently reflect. It is important that roundabout designers understand the differences between truck and car capabilities if they are to ensure safe and effective geometry for both vehicle types.

A case study of an actual roundabout with perceived heavy vehicle issues is carried out. An asconstructed 3D model of the roundabout is obtained, speed data collected and analysis of car vs truck speeds performed. The travelled path of a semi-trailer through the roundabout is analysed via video, and simulated using Autoturn software. 12D road design software is then used to model and measure the actual radii and crossfalls that the vehicle encountered. Combined with the speed data, the side friction being generated by the vehicles and the rate of rotation of crossfalls is then calculated and compared to relevant design standards.

An in-depth critical review of the current roundabout standards, national and international, is also carried out, and tested against known heavy-vehicle specific requirements. It is found that cars can tolerate a much higher value of side friction at roundabouts than trucks. Additionally, a cars margin for error re side friction is much higher than a trucks, ie, if a car generates side friction in excess of what it can tolerate, it will typically slide, whereas a truck will typically roll. Therefore, trucks need to negotiate roundabouts at significantly lower speeds than cars, and unique geometric considerations need to be made to facilitate this. A supplementary set of standards is developed, combining recommend combinations of geometry, signage, and linemarking to safely cater for heavy vehicles at roundabouts, and the recommendations are tested and confirmed as successful using TMR’s A Roundabout Numerical Design Tool (ARNDT)

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Somasundaraswaran, Soma
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 18 Aug 2021 05:33
Last Modified: 26 Jun 2023 05:32

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