Traffic on the Namibian paved road network comprises mainly light vehicles [2]. Traffic counts undertaken during the year 2000 on 12 test sections of unpaved roads in mainly the central parts of Namibia showed an average 94 % light vehicles and 6 % medium-sized trucks. For this Study the general assumption is for unpaved roads in the Study Area:

For paved roads the assumption is for the Study Area:

While for Namibia generally about 90 % of the unpaved roads have an EAADT of less than 50 vehicles/day and 70 % of the paved roads have an EAADT of higher than 200 vehicles/day [3], tables 2 and 3 show that the situation in the Study Area is different: about 66 % of the unpaved roads have an EAADT of less than 50 vehicles/day and 87 % of the paved roads have an EAADT of higher than 200 vehicles/day.

The average annual rate of traffic growth in Namibia between 1992 and 1999 was approximately 5,6 % while on paved roads it was 7,3 % and on unpaved roads less than 1 %. The distance that the vehicles have travelled (VKT) on the paved road network was 4 times higher than on the unpaved road network.

In order to establish the resultant level of service an experiment to measure the public acceptability criteria of the riding quality of unpaved roads in Namibia was launched by the Department of Transport during the 1980s. Subjective evaluations of specific unpaved roads representing a wide spectrum of different riding qualities encountered in Namibia were investigated. Contingency table analysis was done to determine the relationship between subjective riding quality evaluation and objective roughness measurements by precise levelling or by profiling (IRI). A regression analysis was used to develop a model. The dependent variable of the model is the subjective evaluation of the road by the road user.

The riding quality (expressed in IRI) is very important for the road user, having a direct impact on the road user costs in terms of vehicle operating costs saved and time and riding comfort. From above study it can be concluded that for 50 % of road users:

Endnotes:

[1]   Roads Authority of Namibia in co-operation with Technische Universität Berlin: Economically Justified Maintenance on Unpaved Roads in Namibia, Berlin, 2001

[2]    Roads Authority of Namibia in co-operation with Technische Universität Berlin: Economically Justified Maintenance on Unpaved Roads in Namibia, Berlin, 2001