2.0 ROAD NETWORK IN THE STUDY AREA

 

2.1 ROAD CATEGORIES IN THE STUDY AREA

 

The Oshikoto, Ohangwena, Oshana and Omusati Regions comprise 1858,52 km of unpaved and 755,48 km of paved roads. Unpaved roads are divided into gravel roads, earth roads and "not built" roads that mainly comprise of sandy tracks presently.

bulletGravel roads [1] in the Study Area have a base course made from (frequently borderline case and weak) pedocretes like calcrete, laterite and silcrete material. They have a designed and compacted (mostly at natural moisture) layer that is (in a few cases) vertically and horizontally aligned. Maintenance of gravel roads is carried out regularly.
bulletEarth roads are roads on which no transported gravel is used, the material is lightly compacted (usually by traffic). Earth roads are often shaped with material removed from the side of the road to form side drains. Local, mostly sandy materials are used. Maintenance of earth roads is carried out regularly.

The road categories are pictured in table 1:

TABLE 1: ROAD CATEGORIES IN THE OSHIKOTO, OHANGWENA, OSHANA AND OMUSATI REGIONS

 

Trunk Roads (km)

Main Roads (km)

District Roads (km)

Total (km)

OSHIKOTO REGION

Paved Roads

274,12

83,30

-

357,42

Gravel Roads

-

53,64

519,61

573,25

Earth Roads

-

-

111,35

111,35

Roads Not Built as Yet

-

Approx. 135,00

Approx. 45,00

Approx. 180,00

TOTAL

274,12

250,01

697,89

1 222,02

OSHANA REGION

Paved Roads

29,15

73,54

-

102,69

Gravel Roads

-

-

46,29

46,29

Earth Roads

-

-

4,27

4,27

Roads Not Built as Yet

-

-

Approx. 85,00

Approx. 85,00

TOTAL

29,15

67,22

141,88

238,25

OHANGWENA REGION

Paved Roads

35,13

71,88

3,48

110,49

Gravel Roads

-

157,38

163,55

320,93

Earth Roads

-

-

40,66

40,66

Roads Not Built as Yet

-

-

Approx. 25,00

Approx. 25,00

TOTAL

35,13

229,26

232,69

497,08

OMUSATI REGION

Paved Roads

-

177,77

7,11

184,88

Gravel Roads

-

-

233,95

233,95

Earth Roads

-

-

27,82

27,82

Roads Not Built as Yet

-

-

Approx. 210,00

Approx. 210,00

TOTAL

-

177,77

478,88

656,65

 

2.2 TRAFFIC

 

The traffic counts for all roads in the Oshikoto, Ohangwena, Oshana and Omusati Regions are shown in Annexure 1. The levels of traffic for unpaved and paved roads are pictured in tables 2 and 3 (according to the traffic counts as supplied by the Namibia Roads Authority):

 

TABLE 2: TRAFFIC LEVELS FOR UNPAVED ROADS IN THE OSHIKOTO, OHANGWENA, OSHANA AND OMUSATI REGIONS

 

LEVEL OF TRAFFIC

EAADT

1-10

EAADT

11-20

EAADT

21–50

EAADT

51–100

EAADT

101-150

EAADT

151-200

EAADT

> 200

OSHIKOTO REGION

Trunk Roads

Main Roads

District Roads

-

 

-

939,9

-

 

-

49,5

-

 

-

53,6

-

 

55,4

40,4

-

 

-

-

-

 

-

-

-

 

1,2

-

OSHANA REGION

Trunk Roads

Main Roads

District Roadsdds

-

 

-

-

-

 

-

97,5

-

 

-

25,5

-

 

5,5

-

-

 

-

-

-

 

-

-

-

 

-

-

OHANGWENA REGION

Trunk Roads

Main Roads

District Roads

-

 

-

47,0

-

 

-

39,3

-

 

84,7

94,5

-

 

74,6

-

-

 

52,2

-

-

 

-

-

-

 

-

-

OMUSATI REGION

Trunk Roads

Main Roads

District Roads

-

 

-

43,6

-

 

-

27,9

-

 

-

128,3

-

 

24,9

33,0

-

 

262,9

-

-

 

-

-

-

 

-

-

 

TABLE 3: TRAFFIC LEVELS FOR PAVED ROADS IN THE OSHIKOTO, OHANGWENA, OSHANA AND OMUSATI REGIONS

 

 

EAADT

< 200 

EAADT

201-1000

EAADT

1001-2000

EAADT

> 2000

 

OSHIKOTO REGION

Trunk Roads

46,8

269,8

3,9

-

Main Roads - 22,4 - 20,4
District Roads - - - -
 

OSHANA REGION

Trunk Roads

-

-

4,4

27,6

Main Roads 6,7 30,4 1,7 3,7
District Roads - - - -
 

OHANGWENA REGION

Trunk Roads

-

-

?

?

Main Roads - 71,9 - -
District Roads 3,5 - - -
  OMUSATI REGION
Trunk Roads

-

-

-

-

Main Roads 24,7 187,8 - -
District Roads 3,5 - - -



2.2.1 TRAFFIC COMPOSITION

 

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:

bullet90 % light vehicles and
bullet10 % medium-sized trucks.

For paved roads the assumption is for the Study Area:

bullet80 % light vehicles and
bullet20 % heavy-sized trucks.

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.

 

2.3 RIDING QUALITY

 

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:

bulletIRI < 4 is good
bulletIRI 4 to 6 is average
bulletIRI 6 to 8 is bad
bulletIRI > 8 is unacceptable.

Endnotes:

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

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

[3]    See endnote 2

 

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