BSC CIVENG
UNIVERSITY OF CAPE TOWN
ADEEB ABRAHAMS
INVESTIGATION INTO THE IMPACT OF VEHICLE PERFORMANCE ON GEOMETRIC DESIGN OF ROADS
A research project
Conducted By: Adeeb Abrahams Supervisor: Professor Mark van Ryneveld
BACKGROUND
The dynamism with which modern urban population migration is taken place has led to the augmentation of urban policy have brought about new trends of densification and a push for more efficient use of city spaces. The result is that city space has become prime commodities leading civil engineering structures having to be made on tighter budgets and with tighter design restrictions. This research project will endeavour to re-establish the fundamental correlation that must exist between the road design and the vehicles that use them.
There are a multitude of vehicle performance characteristics that have a direct effect on road geometric design parameters, and design decisions however this literature review will focus only on stopping sight distance. By focusing the research on a particular aspect of road alignment a clear understanding of how these road design parameters are directly connected vehicular performance can become apparent.
CONCLUSIONS
This research project has delved into the assestion that vehicle characteristics have changed and that these changes should be incorperated into current road design guidelines.
The literary review has yeilded emphatic results as to the advancing nature of motor vehicle performance characteristics, as depicted above. The appliction of these revised performance characteristics has provided significant changes particularly when applied to a real world situation as done in the Case Study.
However it should be note that an aggressive adoption of these revised parameters need to be tempered by further research in the crash frequency increase or decrese they would likely incur.
FRICTION MODEL
What the research revealed was a marked increase in the adhesion coefficient on new tires, on current roads. this increase was attibuted to the new materials, and tread patterns used on modern tires.
METHODOLOGY
This research project is heavily influenced by past and current research in the field and in using the research aims to convince the reader that a cognitive approach to the road geometric design process will yield more appropriate designs.
Research Design
Research design proposed encompasses a theoretical study into the vehicle characteristics affecting the geometric design of roads.
There are many vehicle performance characteristics that have a direct influence on road design none more important that the vehicles’ ability to stop (Roussiamanis N, 2011). The factors influencing the ability of a car to stop are the brakes, weight the road-vehicle adhesion coefficient and driver reaction time (etc) See Figure to the right.
RESULTS
The results of my literary research are summarised below.
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These revised parameters were applied to the two prescribed SSD models and the result of that is presented below.
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The above graphic details the many aspects of Stopping Sight Distance, the research project specifically focussed on the branch encircled by the dotted line, and aimed to identify changes in those particular aspects.
'have cars changed that much?'
DECELERATION MODEL
The figure bellow depicts the reduced SSD that is accomplished by employing the revised deceleration rate of 5.6m/s2, to the existing SSD deceleration model.
CREST VERITCAL CURVE
CASE STUDY - BELMONT ROAD
The the revised design parameters (adhesion coefficeint, deceleration rate, driver eye height and object height) were applied to an actual road, Belmont Road in Rondebosch, to determine the changes they might effect.
The section of Belmont Road that was studied, is the portion that passes over the railway line near Rondeboch Station.
Crest Verical Curve with depicting design elements.
Google Maps: Belmont Road
CURRENT CURVE
REVISED CURVE
In this animation the camera is set to a height of 1.080m (Driver Eye Height) , and the green box has a height of 0.6m (Object Height), both of which are the current design standards for H1 and H2 as depicted in the diagram directly above the video.
What should be noted here is that by using these values, as the car aka the camera traverses the crest curve it looses sight of the top of the box, which constitutes a loss in visibialy and likely accident.
In this animation the camera is set to a height of 1.2m (Driver Eye Height) , and the green box has a height of 0.8m (Object Height), both of which are the revised design parameters for H1 and H2 as illustrated in the table above.
In this video however the top of the box is never lost during the entire journey, on an identical crest curve.