1887

oa Civil Engineer in South Africa - Verbygaansigafstand vir enkelbaanpaaie in Suid-Afrika

Volume 23, Issue 4
  • ISSN : 0009-7845

 

Abstract

Die afstande benodig vir geometriese ontwerp en die aanbring van sperstrepe word as volg gedifferensieer :


1. Verbygaansigafstand vir geometriese ontwerpdoeleindes : dit is die totale afstand benodig vir 'n veilige verbygaanmaneuver. Dit is die sigafstand waarby, as dit voorsien sou word, geen verbygaanbeperking nodig sou wees nie.
2. Verbygaanafstand vir die verf van sperstrepe wat verbygaan verbied : dit is die afstand wat benodig word om die verbygaanmaneuver te voltooi nadat die kritieke punt tydens die maneuver verbygegaan is, dws waarna dit veiliger is om verby te gaan as om terug te vat.
Die huidige Suid-Afrikaanse standaarde is gebaseer op Amerikaanse standaarde. Sover vasgestel kon word, word hierdie syfers nie aangepas vir hellings by die toepassing daarvan nie.
Hierdie referaat handel oor 'n ondersoek om die verbygaanmaneuver vir Suid-Afrikaanse enkelbaanpaaie en voertuigpopulasie te evalueer terwyl die invloed van helling op die benodigde veilige afstande ook geïnkorporeer word.
Twee rekenaarmodelle is opgestel om elk van bogenoemde twee maneuvers te simuleer. As invoerdata is voertuigkarakteristieke van modelle van 1957 tot 1977 gebruik. Daar is gevind dat helling 'n groot invloed het op die benodigde afstand vir die twee verbygaanmaneuvers. Die bestaande standaarde blyk veilig tot oorveilig te wees vir negatiewe hellings maar hoofsaaklik onveilig vir positiewe hellings, veral by hoër ontwerpspoede.

The distances needed for geometric design and for marking nopassing zones could be differentiated as follows :


1. The passing sight distance for geometric design purposes : this is the sight distance that should be provided during design in order that no passing restrictions would be needed.
2. The passing distance for marking no-passing zones: this is the distance needed to complete a passing manoeuvre after the critical point during the manoeuvre has been passed. This is the point where it is safer to complete the manoeuvre than to fall back.
The present South African standards are based on American standards. As far as could be ascertained no allowance was made in the past for gradients in applying these standards.
This paper covers an investigation into the passing manoeuvre for South African conditions while incorporating the influence of gradients on the passing lengths.
A computer model to simulate each of the above-mentioned manoeuvres was developed. Vehicle characteristics of models from 1957 to 1977 were used as input for the programs. It was ascertained that gradients have a great influence on the distance needed to perform the above-mentioned two manoeuvres. The existing standards seem to be safe to unnecessarily safe for down grades but dangerously short for upgrades, especially for higher design speeds.

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/content/civeng1/23/4/EJC24844
1981-04-01
2016-12-10

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