Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. A large proportion of the South African rural road network consists of two-lane highways.
Some of these highways are carrying relatively high volumes of traffic with the result that
some roads are operating at low levels of service. Currently, the Highway Capacity Manual of
the Transportation Research Board is used for the analysis of the operations on these roads.
Concern has, however, been expressed that the methodologies described in the HCM may not
be appropriate or adequate for South African conditions.
An alternative model has been developed for the operational analysis of two-lane rural
highways. This model utilises queuing theory to model platoons of traffic along a highway.
The average platoon length is determined which can be utilised to determine evaluation
criteria such as percentage followers and to predict travel speed. This model can also be used
to model highways with wide shoulders where the shoulders are utilised by vehicles to provide
The Highway Capacity Manual uses "Percent time spent following" as the measure of
effectiveness in the evaluation of two-lane highways. This measure has the limitation that it
can not readily be observed in the field. It is therefore proposed that this should be replaced
by "percentage followers", although a new measure termed "follower density" should be used
for the evaluation of two-lane roads.
This paper was transferred from the original CD ROM created for this conference. The material on the CD ROM was published using Adobe Acrobat technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: email@example.com URL: http://www.doctech.co.za