4.0 PRINCIPLES OF A ROAD MAINTENANCE STRATEGY

 

4.1 INTRODUCTION

 

A Maintenance Strategy for the Oshikoto, Ohangwena, Oshana and Omusati Regions will be based on the following basic principles:

 

  1. Data on the deterioration of roughness as a result of traffic loads on the most common types of unpaved and paved roads in the Study Area;
  2. Data on roughness improvement achieved with the normal practices of routine maintenance of unpaved roads, i.e. grader blading (the roughness improvement by normal routine maintenance of paved roads is normally not measurable) [18];
  3. Prediction Models of the development of roughness based on 1. and 2.

The rate of deterioration of paved and unpaved roads is effected by the behaviour of the surfacing material in the pavement and the roadbed and the effect of the traffic loads and environmental factors. This deterioration is characterised by the increase of the roughness as function of time. The roughness is defined in units of a standard roughness scale such as IRI (m/km). The IRI-value characterises the road pavement unevenness in a longitudinal direction and is one of the most important input values in road maintenance programs. The Estimation of Roughness Values in terms of IRI is shown in table 19 [19]:

 

TABLE 19: ESTIMATION OF IRI-VALUES FOR DIFFERENT PAVEMENT TYPES

 

IRI

DESCRIPTION OF PAVEMENT TYPES

2

4

6

8

10

12

20

Good Bitumen

Bad Bitumen

Good Gravel

Bad Gravel/Earth

Cleared Track

Natural Track

Heavy Sand Track

This rough estimation is insufficient for the economic evaluation of a maintenance strategy. Such a maintenance strategy should be based on the establishment of accurate IRI-values by high speed devices such as LDI and RRMI. Unfortunately such roughness data are currently in most cases not available for the Oshikoto, Ohangwena, Oshana and Omusati Regions.

 

4.2 UNPAVED ROADS

 

4.2.1 COST AND QUALITY OPTIMISED MODELS FOR UNPAVED ROADS

 

Cost and quality optimised models compare the future flow of benefits of a facility with the initial cost of construction as a basis. Therefore it is necessary to consider the time value of money. This is done by discounting the future costs and benefits to a present value (Net Present Value 'NPV' of the Costs and the Present Value of the Future Benefits) by using the discount rate or the opportunity cost of capital (OCC). For investments OCC is assumed to be an average of the short-term and long-term rates of interests. When the effect of public investment in highways is considered, the interest rate must reflect the return on investment in the national economy. Normally in Namibia an OCC of 10% was used to illustrate the effect of the OCC on a comparison of the alternatives. Such cost/quality optimised models are assisting the establishment of the NPV for gravel-surfacing and bitumen-surfacing of roads which are based on real cost-optimised justifications and not on guess-work. The NPV of a given investment is obtained by subtracting the present value of the costs from the present value of the future benefits. The benefits as well as the costs are discounted at the OCC interest rate. The investment is feasible if the NPV is positive [20].

 

4.2.1.1 DETERMINATION OF OPTIMAL BLADING FREQUENCIES

 

To predict the optimal blading frequency of unpaved roads it is important to know the roughness levels of the existing road network, the velocity of its degradation and the efficiency of blading activities.

The standard maintenance of an unpaved road is done by a blading device such as a motor grader. Grading frequencies were in the past in many cases mainly established by empirical means. In formulating an optimum maintenance strategy the total costs between blading and road user costs have to be minimised. The basis for such a cost optimised maintenance model is research in this field. It was experienced during this maintenance strategy study and confirmed by Namibian maintenance experiences that any maintenance model has to differ between dry and wet cycles because both require different maintenance methods. During the dry season, for instance, the gravel-bearing course should never be touched but a thin gravel blanket should be graded over it. During the wet season, however, the gravel-bearing course can be compacted under moist conditions effectively by grading. But, it must also be stated that Namibian experiences have shown that this empirical rule is in many cases not applied, with consequent detrimental effects regarding costs and maintenance [21].

Many international studies revealed that every specific unpaved road has its own minimum between blading and user costs. The optimal maintenance state can be seldom achieved and it will be a realistic objective to achieve 60-80% of the optimum. Following this course the total optimised maintenance costs on a district level can be achieved. Another sound empirical rule is that for each spent N$ for grading maintenance three N$ in saved user costs have to be returned. On this basis the maintenance budget can be established including the road nodes, the road lengths, the total number of bladings per year, the dry blading frequency and the wet blading frequency.

Another important parameter for this optimisation program is the establishment of a sound IRI service level. For each road the low, the medium and the still acceptable high IRI value has to be established. Research studies in Namibia proved that the predicted IRI values compared very well with the actual measured IRI values. During a validation research effort of one of the studies the average predicted IRI of one of the test sections was 5,4 and the actual measured one was 5,2. The same experience was made on several test sections in Namibia. An ideal IRI service level has to be established on ground of user costs. During one of the research studies it was revealed that IRI is climbing steeply if the frequency of blading will be cut, for instance, to half. If, on the other hand, the frequency will be determined too high with a resulting very low IRI, a very unfavourable economic balance will be the consequence [22].

On the empirical basis of one spent N$ for three saved N$ in ' VOC' the Namibian optimised roads model regarding the optimal point of grading unpaved roads, dependent on costs, roughness IRI and ADT was established. Preliminary results showed that the accumulated 'VOC' for unpaved roads with different roughness levels from an excellent road with IRI=3,0 to an unacceptable road with IRI=10,5 in dependence of the average daily traffic. The total vehicle operating costs 'VOC' were used for Namibian conditions, for cars (85%) and heavy trucks (15%). This traffic composition 85% light and 15% heavy mirrors average Namibian traffic conditions. For an excellent unpaved road with an average IRI=3,0 a 'VOC' of N$ 54.264/km/year for 100 vehicles (85% light/15% heavy); N$ 63.840/km/year for 100 vehicles for a good unpaved road (IRI=5,0), N$ 78.960/km/year for a bad unpaved road (IRI=7,5), N$ 87.360/km/year for an undesirable bad unpaved road (IRI=9,0) and N$ 95.760/km/year for an unacceptable unpaved road (IRI=10,5) was established.

It was established by research that an unpaved road with roughness’ between IRI=7,00 and 9,00 is regarded as undesirable. Therefore, for this cost/quality optimised model, it was decided to take a road with an IRI=7,50 as an offset point which is extreme under Namibian conditions. With average grader maintenance costs of N$ 220/km (N$ 44,00/blade km: 5 blades wide) and with savings of vehicle operating costs for an improvement of an unpaved road from IRI=7,50 to IRI=5,00 it can be derived that for an 'ADT' of 100 (85% light, 15% heavy) a grading of 17 times/year is cost/ quality optimised. However, it has to be stated that under Namibian conditions a VOC-saving/maintenance relationship of a 3:1 ratio represents a rather low level of maintenance. To date the Namibian road user is used to a higher maintenance level of 3:1 for such traffic load (ADT=100) under average conditions which probably is too high to be cost/quality optimised [23].

Thus, blading (grading) in Namibia is not a traditional grading operation where the grader-blade is cutting the gravel surface and redistributing the gravel-wearing course. The technique of blading which has been developed through he years could be named "capping", indicating a thin sand blanket (< 10 mm) is distributed over the gravel wearing course (sand or fine materials are picked up from the edges or slopes). The capping protects the wearing course from wearing off and the method has proved to work very well for low volume roads in Namibia. Even if the required blading frequency as recommended in table 22 is higher than by the 1 : 3 principle, it appears to be economically viable as long as the traffic volume is low. The reasons behind are the higher-grade capacity for this type of grading, the reduced gravel loss (the regravelling cycle is stretched out) and less need for gravel patching [24].

Based on these findings and adapted for the circumstances for the Oshikoto, Ohangwena, Oshana and Omusati Regions blading frequencies as function of different traffic classes are summarised in table 22.

 

4.2.1.1.1  ROUGHNESS PROGRESSION (C-Value)

 

In order to develop deterioration mechanism for unpaved roads as function of the wearing course material, traffic loads, maintenance standards and practices and environmental effects a simplified model was developed [25]. This model establishes a Roughness Progression Value-C in which there is a linear relationship for relatively short time intervals for the deterioration of the IRI level. The Roughness Progression can be calculated as follows:

                                                            IRI2 – IRI1
                                                                  C = -----------
                                                             ADT x dt

Where:

bulletIRI1 = roughness at the time t1
bulletIRI2 = second roughness at the time t2
bulletADT = Average Daily Traffic
bulletdt = relatively short time interval t2 – t1 between two consecutive IRI measurements without blading

Some measured roughness values (IRI) before/after blading and their corresponding Roughness Progression (C-Values) for different material types are shown in table 20:

 

TABLE 20: IRI-VALUES BEFORE/AFTER BLADING AND ROUGHNESS PROGRESSION (C-VALUES) FOR DIFFERENT MATERIAL TYPES

 

 

Earth Road

Calcrete Road

Quartzite Road

IRI Before Blading

After Blading

8,6

5,57

7,42

5,71

7,2

5,18

C-Value + Standard Deviation

Average C-Value

- Standard Deviation

0,009

0,0065

0,004

0,0047

0,0027

0,0007

0,004

0,0022

0,0004

 

These measurements show the following tendencies:

 

bulletCompared with the results from other countries the C-Values are on the high side. This fast increase of IRI during the first few days after blading can be explained by the loose sandy material lying uncompacted and without cohesion on the surface;
bulletNo significant difference in C-Values for calcrete and quartzite wearing course material could be observed;
bulletC-Values for earth roads are significantly higher than for gravel roads (calcrete or quartzite roads). Due to the peculiar materials situation with mainly weak and sandy pedocretes in the Oshikoto, Ohangwena, Oshana and Omusati Regions C-Values on the high side will be used for any estimates;
bulletNo C-Value determinations have been undertaken so far in the Oshikoto, Ohangwena, Oshana and Omusati Regions.

 

4.2.2.1.2  BLADING EFFICIENCY (GE)

 

The Blading Efficiency (GE) expresses the improvement in the evenness of the road surface as a result of the blading action. The effect of blading on roughness depends on the following factors [26]:

bulletQuality of Blading Work
bulletRoughness level before blading
bulletMaterial properties and
bulletMinimum roughness.

The minimum roughness on unpaved roads depends on the particle size, gradation and PI of the wearing course material.

The Blading Efficiency (GE) can be calculated as follows [27]:

 

       (IRIb – IRImin) – (IRIa – IRImin)
GE = ------------------------------------- x 100 (%)
                      IRIb – 3

 

        (IRIb – IRIa)
GE = ---------------- x 100 (%)
            IRIb – 3

Where:

bulletIRIa = roughness after blading
bulletIRIb = roughness before blading
bulletIRImin = 3 (roughness on newly bladed road)

 

In general the evenness after blading is better than before blading, making the blading efficiency positive. In some cases due to loose stones being bladed onto the road or to a bad blading work (cutting into the road prism for instance) the GE-values may be negative (IRI increase due to blading).

Some measured Blading Efficiency (GE) values (IRI) before/after for different material types are shown in table 21:

 

TABLE 21: BLADING EFFICIENCY (GE) FOR DIFFERENT MATERIAL TYPES

 

 

Calcrete Road

Quartzite Road

Blading Efficiency (%) + Standard Deviation

Average C-Value

- Standard Deviation

59

45

31

58

43

28

These measurements show the following tendencies:

bulletThe Blading Efficiency GE scatters to a large extend from approximately 10 % to 80 % with an average of 45 %. This shows the important influence of the working conditions and the quality of the blading work;
bulletIn certain cases the blading work may be inefficient;
bulletThere is no significant difference between the Blading efficiency on different wearing course materials (calcrete/quartzite). However, due to the peculiar materials situation with mainly weak and sandy pedocretes in the Oshikoto, Ohangwena, Oshana and Omusati Regions GE-Values on the low side will be used for any estimates;
bulletNo measurements for the Blading efficiency (GE) in the Oshikoto, Ohangwena, Oshana and Omusati Regions have been undertaken so far. An estimated Blading Efficiency of 50% will be assumed for the Study Area.

 

4.2.1.2 DETERMINATION OF OPTIMAL GRAVELLING FREQUENCIES

 

Any unpaved road is subject to loss of gravel due to traffic and environmental factors like for instance wind. This gravel loss has to be replaced. Gravelling and re-gravelling is an expensive exercise and should be optimised by restricting the gravelling effort to the minimum. Use should be made of much more spot-gravelling, re-compacting and of more mechanical means to reduce the oversize of coarse wearing course materials. This, however, does not represent a major problem in the Study Area, due to the prevailing material’s situation.

In Namibia approximately 30-50% of the total gravelling effort is currently used to compensate for gravel losses. The balance of gravelling is done to provide for new gravel surfaces or to replenish existing gravel surfaces. The 'MDS' system gave a prediction for a total gravel loss for all unpaved roads of the Windhoek district of 160.000 m3 for 1984/85. The total gravel used for all unpaved roads in this district was for the same period 370.000 m3. This represents a gravel loss replacement of approximately 43%.

Namibian research to predict gravel losses is based on traffic data, materials data and geometrical data input which can be used to compare the predicted losses with the real ones. The data compiled by Namibian research estimate for average Namibian gravel loss conditions for an average daily traffic of 300 vehicles per day a gravel loss of 25 mm/year, which has to be replaced. This means a regravelling cycle of 6 years for an average 150 mm gravel layer for this relatively high traffic number. For a more realistic 'ADT' of 100 vehicles a gravel loss of 8 to 10 mm/year can be expected, with a regravelling cycle of more than 15 years for a 150 mm gravel layer. The optimal point of regravelling has to be established for each individual material and traffic dependent case. Cost/quality optimised systems can, for instance, be used to prove that it can be economical to bring better material over larger haul distances to get the cost optimum. Laterite gravel needs less blading maintenance than quartzitic gravel, whereby the blading costs are increasing from fine laterites to coarse quartzites. This example can be used to prove that larger haul distances for more expensive gravelling materials can be compensated by lesser maintenance and road user costs [28].

It has also be borne in mind that above gravel loss is only caused by traffic action and no environmental factors were taken into account. Consequently the optimised point of regravelling could even be reached for considerable smaller traffic numbers.

 

4.2.1.3 DETERMINATION OF OPTIMAL MAINTENANCE FREQUENCIES

 

Based on these findings and adapted for the circumstances for the Oshikoto, Ohangwena, Oshana and Omusati Regions optimal blading and regravelling frequencies as function of different traffic classes are summarised in table 22 [29].

 

TABLE 22 RECOMMENDED ROAD MAINTENANCE STRATEGY FOR UNPAVED ROADS IN THE OSHIKOTO, OHANGWENA, OSHANA AND OMUSATI REGIONS

 

LEVEL OF TRAFFIC

ADT

1-10

ADT

11-20

ADT

21–50

ADT

51–100

ADT

101-150

ADT

151-200

ADT

> 200

BLADING

Number of bladings per year earyearyear

Number of days interval

 

5 (*)

 

73

 

15 (*)


24

 

24 (*)

 

15

 

 

52 (*)

 

7

 

52 (*)

 

7

 

52 (*)

 

7

 

52 (*)


7

REGRAVELLING

Regravelling frequencies

Number of years interval

 

50

 

30

 

20

 

10

 

 

5 (**)

 

5 (**)

 

5 (**)

 

 (*) The higher blading frequencies compared to other parts in Namibia are calculated on the assumption of a Roughness Progression of C = 0,010 for the Study Area due to the weak materials.

(**) The higher regravelling frequencies compared to other parts in Namibia are calculated on the basis of the peculiar materials position in the Study Area. For a traffic load ADT > 100 no regravelling is envisaged anymore but rather the provision of a single seal pavement.

 

4.2.1.4 PROBLEMS WITH ROAD BUILDING MATERIALS IN THE STUDY AREA

 

One of the major problems in the Oshikoto, Ohangwena, Oshana and Omusati Regions is that good construction and maintenance road materials are not readily available in the Study Area. The materials available in this area are limestone, calcrete, silcrete or sandstone. A high proportion of good quality borrow pits are already depleted and this necessitates the need to open up new borrow pits, which are becoming more and more scarce.

The material from many of these sources does not meet the specification of the specifications of the "Roads Authority: Contract No RA/MC-MRP/01-2002: Construction and Maintenance of Roads in Namibia". Problems known to occur are that the Plasticity Index (PI) is too high, the grading of the material too fine and a very common problem is the salinity of the road materials in the Study Area. It is also experienced that the bearing capacity of the material in its natural state is insufficient. In the past this problem was overcome by mixing a stabilising agent of lime or cement with the material. A number of problems were, however, encountered in the four regions of the Study Area.

It should be mentioned that the most suitable construction and maintenance materials are usually found under the most arable land. The impermeable calcrete layer underlying the fairly sandy soil prevents the nutrients and moisture from being leached out. The increased needs for construction and maintenance materials will result in the degradation of good arable land, which is in any case scarce and which is extremely important for the sustainable existence of a large rural population in the area [30].

In general, for a standard paved road with 6,8 m wide surfacing about 3,3 m3 of good material will be required per running metre, i.e. 3.300 m3/km, for the construction of the base course, shoulders and sub-base. In the Study Area the thickness of the good quality material layer is usually in the order of 1,5 m. This implies that an area of 2.200 m2 or 0,22 ha of land has to be cleared and excavated for each km of bituminous paved road. For the construction of a gravel road this area will initially be less since material of a lower quality may be used. In the long term however, a gravel road will consume more gravel material because the good material will inevitably be used for regravelling purposes [31].

If such surface of land were systematically taken from the stock of arable land, this would aggravate the already mentioned shortage of arable land resulting from the increase of the population in the Oshikoto, Ohangwena, Oshana and Omusati Regions. Thus, borrow pits for material in cultivated land should be avoided. In all cases, borrow pits should be re-instated to their original state and this should be easily achieved. The overburden could be stripped and placed next to the borrow pit and the suitable road-building material excavated and placed on the road. The excavated material would then be partly replaced by the overburden, which is the most important soil medium for plant growth. The entire area should be re-instated so as to blend in with the surrounding area and to permit the vegetation to re-establish itself. Steep slopes should b avoided and the area should be shaped to even contours [32].

In conclusion: Due to the peculiar and complex material conditions in the Oshikoto, Ohangwena, Oshana and Omusati Regions and the scarcity of appropriate road building wearing course materials special arguments have to be taken into consideration. This can mean that even for small traffic loads gravelling of an earth road or light bituminous surfacing of gravel roads (Dust-free gravel roads) will be warranted.

 

4.3 PAVED ROADS

 

4.3.1 COST AND QUALITY OPTIMISED MODELS FOR PAVED ROADS

 

To achieve the objective of the establishment of consistent and sound maintenance priorities the Namibian Department of Transport decided during 1983 to implement a computerised "Pavement Management System" (PMS) which has been developed by the "Division of Roads and Transport Technology" of the CSIR. The basis for such a system is to perform an inventory of the entire pavement network and to evaluate its condition. This data-collecting visual-sensitive operation is a tedious task but with a well designed rating procedure and properly trained and motivated data collecting personnel, it has been proved that this system, with some shortcomings, runs smoothly under Namibian conditions [33].

Although no universal system exists to evaluate and assess a road pavement quality system, the data collecting evaluations has to include:

- All pavement structure data

- Traffic counts

- Construction and maintenance history

- Drainage structures data

To achieve these objectives the Department of Transport developed a visual inspection method for paved roads including a point-allotment and seriousness rating index system, supported by a "Linear Displacement Integrator" (LDI) to measure the driving quality on pavements. The Computer Section of the Department of Transport developed, with the assistance of the 'DRTT', a reseal algorithm for the departmental computer system, a HP 1000 F mini-computer, to establish reseal priorities for paved roads. Computer models play a major role in estimating the cost tradeoffs among the various maintenance and rehabilitation strategies with consideration of the transportation costs.

To establish reseal-priorities the following basic activities are required, based on visual-sensitive methods:

1. Objective visual inspections to determine defects and other pavement properties;

2. The allotment of seriousness ratings to the defects;

3. A decision procedure to establish under which circumstances maintenance, resealing and rehabilitation will be justified. Furthermore it will be required to determine a procedure to compare the defects and other pavement properties of all pavements in Namibia and consequently develop a list of reseal and rehabilitation priorities [34].

With these basic requirements as starting point the first Namibian 'PMS' was developed during 1983 consisting of a procedure for visual surveys, the allotment of seriousness ratings and the establishment of a computerised algorithm to determine reseal priorities [35].

4.3.2 DETERMINATION OF OPTIMAL PAVED ROAD MAINTENANCE

 

The design life of bitumen roads is generally twenty years during which period no general structural or serviceability improvements should be necessary. In Namibia paved roads have shown to last well beyond that time, essentially because a relatively sound preventative maintenance system was always in place and because of the dry climate, which prevails in most of the country. In the Oshikoto, Ohangwena, Oshana and Omusati Regions, however, for material and historically related reasons the design life of practically all paved roads is considerably shorter than in the remainder of the country.

The rehabilitation of a paved road should be regarded as a heavy maintenance procedure aimed at bringing back the original capacity, riding quality and strength before the road fails completely. A road that has failed completely calls for full reconstruction, whereas rehabilitation can only involve the application of a new bituminous overlay. Rehabilitation may also include the upgrading of a paved road to a higher standard to cater for future needs [36].

Routine paved road maintenance includes activities such as [37]:

bulletBase repair;
bulletCrack sealing;
bulletSurface sealing;
bulletDepression levelling;
bulletEdge repair;
bulletPothole patching;
bulletShoulder clearing;
bulletShoulder gravelling; Bleeding repair; and
bulletEmergency maintenance.

Periodic paved road maintenance generally refers to the resealing a surfaced road. The interval between successive reseals is determined by factors such as the pavement design, the traffic volume, axle loads and climatic conditions. The hot and dry climate in Namibia and the high ultra violet radiation results in the early weathering of the bitumen and a brittle wearing course develops. A preventative measure is the timely application of a rejuvenation spray. The recommended intervals for periodic maintenance measures are established in table 23:

 

TABLE 23: RECOMMENDED ROAD MAINTENANCE STRATEGY FOR PAVED ROADS IN THE OSHIKOTO, OHANGWENA, OSHANA AND OMUSATI REGIONS [38]

 

LEVELS OF TRAFFIC

ADT

< 200

ADT

201-1000

ADT

1001-2000

ADT

> 2000

REJUVENATION SPRAY

Frequency (number of years)

RESEAL OR SLURRY SEAL

Frequency (number of years)

REHABILITATION

Frequency (number of years)

 

3

 

 

20

 

3

 

 

15

 

 

35

 

3

 

 

12

 

 

30

 

 

 

3

 

 

9

 

 

25

 

4.4 MAINTENANCE STRATEGIES FOR LABOUR-BASED BUILT ROADS

 

4.4.1 A CASE FOR LABOUR-BASED METHODS

 

Income distribution in Namibia is extremely unbalanced. The richest 10 % of the population earns an average of more than N$ 83.000 per capita while the poorest 25 % have an average annual income of N$ 460 (National Household Income Survey, 1994). Most of the poor people are living in the northern rural areas of Namibia (Namibian Poverty Profile, 1995). The groups that are most vulnerable are the young, elderly and women.

One of the policies of the government of Namibia is to alleviate poverty and inequality. Experience elsewhere has shown that only growing economies can achieve this. An employment-oriented path is necessary for an overall orientation towards economic growth. One of the methods to reduce poverty is to concentrate on labour-based works because of their potential to alleviate poverty [39].

The development of labour-based methods in Namibian road construction has to be based on systematic and scientific arguments. It will be attempted to develop a basic model taking into account all factors influencing the choice of labour-based construction methods against equipment-based ones. Such a model will establish the limits of labour-based activities. The point where the engineer has to say "no" to such activities in favour of equipment-based ones has to be clearly marked. Labour-based construction and maintenance costs should not be regarded as "social costs" but have to compete with equipment-based construction and maintenance methods. But, it must also be stated that the limits where labour-based activities are economically feasible can only be established for Namibian conditions after more field data are obtainable which as yet have not been established. If the objective of competitive labour-based pricing cannot be achieved, the D x factor has to be funded by general taxes and not by the Road Fund Administration [40].

In order to tackle the Namibian unemployment problem it has to be considered to do those road construction activities, which can compete with machine labour, labour-intensively and thus simultaneously improve the dignity and life-style of impoverished Namibians. Such activities could be, for instance, some "low-volume road" principles, which are based on labour-based foundations. Such labour-based road works have to be proved by various pilot projects since independence to be an excellent example to provide feeder roads in the sandy areas of northern Namibia where labour-based technologies in construction and maintenance are economical propositions, bringing self-contained farming communities within reach of larger markets. An additional bonus could be the creation of an informal indigenous Namibian construction sector and the development of new skills.

Labour-based methods are designed to use labour resources rather than mechanical equipment where this is economic. While they may be described as "labour-intensive" rather than "equipment-intensive", the objective must be to provide a road suitable for its purpose and not just to provide employment. Within labour-based methods there is a wide spectrum of possible labour organisation structures, management methods and technologies to maximise the efficiency of labour as the main construction and maintenance resource. The quality of the road constructed by labour-based methods must conform to the standard specifications. Labour-based construction does not imply a lower standard.

Labour-based methods may broadly be divided into two types. In some cases such as the construction and maintenance of rural roads, local casual labour may be used on a temporary or seasonal basis. In other cases, where a road passes through a sparsely populated area, labour gangs may be recruited on a longer term basis. In either case, the basic economic resource is labour that is employed within the economy in a productive fashion.

Labour-based works provide equitable opportunities for employment to women and men and of all groups, subject to the laws of the Republic of Namibia. Women that seek employment can thus be in a position to purchase land and become self-sustained in the subsistence agriculture economy prevailing in the Study Area.

Labour-based works can only be implemented successfully if the community fully participates in the road-building activities. The participation of the community is voluntary and the benefits of labour-based works should therefore be very clear to them. Useful, productive employment brings not only employment but also a measure of human dignity, enhance selfworth and hope for a better future [41].

It can also be stated that labour-based technologies should not be implied if it is much more economical to use machine labour, but road projects have to be planned and designed accordingly to make them effective for labour-based methods. Further it has to be observed that labour-based road programmes by their nature will be real asset-creating programmes on long term. Such roads have to be modestly engineered in keeping with the aim of appropriate low-volume roads that can be negotiated with reduced design speeds to avoid massive earth works (design speeds of 100 km/h and more, as applied currently in Namibia, are an unwarranted luxury). Mechanical equipment is limited to that equipment which has to move material over longer hauls. Excavations have to be minimised by appropriate design, but when required they have to be strictly tackled by pick and shovel and other special hand tools. Most earth work movements should not involve high cartage since the road profile is developed by throwing soil to the centre line from the ditches, or to one side where the ground has a cross-fall. The off-set points for labour-based road activities versus equipment based activities are based in table 24 [42]:

|==================================================================|
|         OPERATION              |    MAN-DAY LABOUR COST (US $)   |
|                                | 0-3     3-6      6-9     9-15   |
|--------------------------------|---------------------------------|
| Site Clearance and debushing   |  *       *        *             |
| Gravel shoulder maintenance    |  *       *        *        *    |
| Slope trimming                 |  *       *                      |
| Excavation (a) ditches&trenches|  *       *        *             |
|            (b) bulk (soft,loose|                                 |
|                 soils)         |  *       *                      |
|            (c) bulk (other     |                                 |
|                 soils,soft rock|  *                              |
|            (d) caissons (soft, |                                 |
|                 loose soils)   |  *       *        *             |
|            (e) caissons (other |                                 |
|                 soils,soft rock|  *       *                      |
| Refilling bridge and culvert   |                                 |
| excavations                    |  *       *        *             |
| Loading and unloading bulk     |                                 |
| material                       |  *       *                      |
| Short haulage (a) up to 200 m  |  *       *                      |
|               (b) up to 1 km   |                                 |
|                    (animals)   |  *       *        *             |
| Placing, spreading & shaping   |                                 |
| bulk material                  |  *       *                      |
| Mixing concrete (cement/bitum.)|  *                              |
| Stone production               |                                 |
|       (a) aggregate 25 to 50 mm|  *       *                      |
|       (b) undressed stone 50 mm|  *       *        *             |
|       (c) dressed stone        |  *       *        *             |
| Culverts (a) concrete          |  *       *        *             |
|          (b) corrugated metal  |  *       *        *             |
| Formwork for structures        |  *       *        *             |
| Reinforcement (a) bending      |  *       *        *             |
|               (b) fixing       |  *       *        *             |
| Small bridges:                 |                                 |
| Concrete                       |  *                              |
| Timber or masonry              |  *       *                      |
| Paved roads :minor roads 4)    |  *                              |
| Gravel roads : dispersed 5)    |  *       *        *             |
|              : average         |  *       *                      |
|              : large,concentr. |  *                              |
| Earth roads  : very dispersed  |  *       *        *        *    |
|              : fairly dispersed|  *       *        *             |
|              : other projects  |  *       *                      |
| Road widening, rehabilitation, |                                 |
| upgrading and regravelling     |                                 |
|               : large projects |  *                              |
|               : other projects |  *       *                      |
| Road maintenance:              |                                 |
| Gravel/earth roads:very disper.|  *       *        *(6)     *(6) |
|               : other projects |  *       *        *(6)          |
| Other unpaved roads            |  *       *                      |
| Paved roads                    |  *                              |
| Maintenance of road drainage   |                                 |
| ditches                        |  *       *        *        *    |
|==================================================================|
NOT
E TO TABLE 24:
Investigations by author on trunk road 2/3: Karibib-
Omaruru between 1977 and 1980, adjusted for December 1989 prices, and supported by investigations by the World Bank, Transportation Department, Washington, 1978
1. '*' indicates suitability for labour-based projects based on economic arguments as investigated on trunk road 2/3: Omaruru-Karibib, based on effectivity measures between labour-based and equipment-based activities.
2. Parts of large, concentrated projects may still be suitable at labour costs higher than those shown in table 44.

3. Table 44 is based on 1989 wages and machine tariffs.
4. "Minor roads" are defined as those due to carry such light traffic that any delay caused by using labour-based methods would not seriously reduce user benefits: An '
AADT' of 500 is suggested as an upper limit for this category. The majority of Namibian roads are in this category.
5. Provided haul length do not generally exceed 5 km (assuming tractor/trailer haulage).
6. Periodic maintenance will include regravelling and resealing.

One point of cardinal importance for this study is to create an optimised special maintenance strategy based on community participation for labour-based constructed roads in the Oshikoto, Ohangwena, Oshana and Omusati Regions.

 

4.4.2 PRINCIPLES OF A MAINTENANCE STRATEGY THROUGH LABOUR-BASED METHODS

 

Roads that have been constructed by labour based methods should be maintained by labour based maintenance methods and not by conventional methods like grader maintenance on labour-based-built roads. The organisation of the maintenance of labour-based built roads should be based on locally based Maintenance Units (Road Maintenance Units (RMU) thereby improving the personal responsibility of the maintenance staff (including local casual workforce) towards their maintenance work and also providing quick and easy access to the workplace. Appropriate equipment should be used for an optimised usage on labour-based built roads like for (retarding minor deformations like corrugations) during the dry season. Ideally community based work force units should be used which already have to be trained for maintenance tasks for labour-based built roads during the construction phase.

There are two main categories of routine maintenance activities: Equipment Based Activities – mainly for maintaining the road carriageway in an appropriate condition, and Labour Based Activities for maintaining the drainage systems and road surroundings: See Figure 1 [43]:

 

FIGURE 1: ROUTINE MAINTENANCE FOR LABOUR-BASED BUILT ROADS

 

 

The frequency and duration of labour-based equipment activities are pictured in table 25:

 

TABLE 25: FREQUENCY AND DURATION OF EQUPMENT ACTIVITIES

 

TRAFFIC

AADT

TOWED GRADING

WET SEASON

January – March

No. of Cycles/Month

TYRE DRAGGING

DRY SEASON

April – December

No, of Cycles/Month

> 30

1,0

4

10 - 30

0,5 (1 cycle per 2 months)

2

< 30

0,25 (1 cycle per 4 months)

1

OUTPUTS

   

Km/Day

10 km per 8 hr day

30 km per 8 hr day

4.4.2.1  TYPICAL TYRE DRAGGING CIRCUITS


Typical Tyre Drag Circuits are shown in figure 2[44]:

 

4.4.2.2  LABOUR ACTIVITIES

 

Labour-based activities include the repair of potholes, verge clearing, opening of drainage structures and road sign maintenance. It has been found for a number of reasons (organisational, supervision and material resources) that it has to be investigated whether for the maintenance of labour-based constructed roads casual labour should be employed. Such casual labour which has to be properly supervised and which has to work according to strict specific maintenance requirements should comprise local residents who live within the maintenance unit area.

Experiences in Zimbabwe [45] show that such a maintenance strategy for labour-based built roads can be quite efficient. Maintenance costs by tractor based towed grading during the wet season and tyre dragging during the dry season are probably more efficient than conventional grader blading methods (US $ 144,-/year for 130 km maintained rural roads which represents approx. N$ 1 250/km for traffic loads to up to an AADT = 40 against an average of N$ 600/km for earth roads and average 3 900 N$/km Financial Unit Costs and 3 354 N$/km Economic Unit Costs for gravel roads). The costs for the Zimbabwe experience which can be compared to the circumstances in the Oshikoto, Ohangwena, Oshana and Omusati Regions are shown in table 26 [46], but they have to be critically evaluated for Namibian conditions which are at variance with the Zimbabwean experience (in Namibia tractor costs are higher than conventional grader costs).

 

FIGURE 2: TYPICAL TYRE DRAG CIRCUITS

 

TABLE 26: OPERATIONAL MAINTENANCE COSTS: RURAL ROADS: ZIMBABWE (US $/km/year)

 

 

4.5  UPGRADING OF EXISTING ROADS

 

4.5.1 INTRODUCTION

 

Upgrading means improving a road in terms of pavement type, alignment or cross section. Upgrading is to be considered to be an economic question. Therefore the traffic limits for upgrading (upgrading from earth to gravel road and from gravel ro paved road) are essential for the economic maintenance management. This issue is especially important for the development of a Roads Maintenance Strategy for the Study Area. Due to the peculiar and complex material conditions in the Oshikoto, Ohangwena, Oshana and Omusati Regions and the scarcity of appropriate road building wearing course materials special arguments have to be taken into consideration. This can mean that even for small traffic loads gravelling of an earth road or light bituminous surfacing of gravel roads (Dust-free gravel roads) will be warranted.

The developed cost/quality optimised system can be used to investigate the optimal point of surfacing an unpaved road. This point is a function of the traffic load and the Net Present Value (NPV) of the investment as well as the riding quality in terms of roughness.

The minimum required discount rate which is needed to calculate the time value of money would normally be the true or real rate of interest in the long term (opportunity cost of capital: OCC). This is because all economic calculations are prepared using constant prices and make no allowances for future general inflation which is assumed to affect costs and benefits equally. For Namibian average conditions, taking into account the true rate of interests of internal and foreign loans, an OCC of 10% will be used in the model [47].

To establish this point two economic comparison criteria can be used, both being basically the same:

  1. The Internal Rate of Return (IRR). The IRR of a given investment is defined as the discount rate at which the present value of future benefits and the present value of costs are equal. It is a measure of the marginal efficiency of capital. For a project to be feasible, the IRR has to be greater than the OCC. The Economic Internal Rate of Return (EIRR) is the discount rate for which the Net Present Value for the project will be zero.
  2. The Net Present Value (NPV) is defined as the difference between the discounted benefits and the costs of a project. Benefits are derived from savings in road user costs and in road maintenance. The calculation of NPV is therefore simplified by comparing the difference between the present values of costs for the two alternatives. The NPV depends on the discount rate. When high discount rates are used, a lower NPV is obtained. The NPV of future benefits should exceed the NPV of costs during the lifetime of a road [48]. The NPV on a paved road should be equal or less the NPV on an unpaved road, i.e.:
  3. The Benefit/Cost Ratio equals the present value of public benefits divided by the present value of the expenditures of the Roads Authority.
  4. The First Year Rate of Return is the of the project benefit in the first full year after construction divided by the project costs over the analysis period [49].

The relationsship is shown in the following formula [50]:

Cp + MCp + VOCp < CCu + MCu + VOCu

or NPVp < NPVu

p = paved; u = unpaved; (Accident and time related costs are not included due to lack of data).

where:

CC = Initial construction costs per km + Net Present Value of
replacement for 20 years and 10% discount rate p.a. (OCC) with
a salvage value of the project of 50% of the initial costs/km
- NPV of salvage value after 20 years at 10% OCC;

MC = Short term routine + long term reseal maintenance + overhead
administrative costs
s = short term (routine maintenance);
l = long term (periodicmaintenance);
a = administrative overheads

VOC = Total Vehicle Operating Costs for Namibia dependent on
roughness IRI on the basis 85% cars and 15% heavy trucks.

 

4.5.2 INPUT DATES

 

In the quality/cost optimised Roads Maintenance Strategy for the Study Area analysis like the Economic Evaluation Spreadsheet-Program will be used [51]. It has to be considered that apart from the vehicle operating costs argument, road users can also take account of generally higher speeds and improved road safety on paved roads against unpaved roads. This can be argued in the case of performance criteria for dust where it could be stated that dust can force the surfacing of an unpaved road long before cost/quality optimised levels have been reached.

Different upgrading scenarios for earth and gravel roads depending on traffic loads will be developed in table 27.

 

TABLE 27: FOUR UPGRADING METHODS FOR THE STUDY AREA

 

Option: Earth Road

Alternative

Description

Do Minimum

0

Earth Road without Gravel Layer (routine maintenance by labour-based blading according to Section 4.4.2 based on riding quality and depending on traffic load)

Upgrading

A

Add a gravel of 150 mm according to Section 4.5.3 (Traffic Limit: AADT = 30)

Option: Gravel Road

Alternative

Description

Do Minimum

0

Gravel Road with a 150 mm gravel layer (routine maintenance by blading based on riding quality and depending on traffic load

Upgrading

A

10 mm single Surface Dressing on 150 mm Gravel layer ) (Traffic Limit: AADT = 120)

B

20 mm double Surface Dressing on 150 mm Basecourse ) (Traffic Limit: AADT = 160)

C

40 mm Asphalt Concrete on 150 mm Basecourse)

(Traffic Limit: AADT = 200)

The Road Owner Costs are based on tables 4 to 8 and are summarised in table 28:

 

TABLE 28: APPROXIMATE ROAD OWNER COSTS IN THE STUDY AREA

 

       

ECONOMIC COSTS

FINANCIAL COSTS

 

 

 

 

 

 

 

Road Owner Costs

Maintenance

Paved Road

Crack Seal (every Year)

Slurry Seal (after 10 Years)

Unpaved Road

Blading:

bulletAADT = 80
bulletAADT = 120
bulletAADT = 160

 

Km

 

Km

 

 

Km
Km
Km

 

4 000

 

103 200

 

 

3 120
4 420
5 720

 

4 878

 

125 854

 

 

3 630
5 140
6 650

Improvement

Unpaved Road

Reconstruction

Regravelling

Paved Road

A Single Surface Dressing

B Double Surface Dressing

C Asphalt Concrete

 

Km

Km

 

Km

 

Km

Km

 

162 500

104 000

 

438 000

 

555 000

657 000

 

222 600

142 500

 

600 000

 

760 000

900 000

4.5.3 UPGRADING FROM EARTH TO GRAVEL ROAD

 

Various research projects investigated the economic viability of upgrading earth roads to gravel roads [52]. An essential criteria included the Economic Internal Rate of Return (EIRR)-value (EIRR is the discount rate for which the Net present Value of the project will be zero) which was calculated with the Economic Evaluation Spreadsheet-Program of the Roads Authority [53]. Apart from two exceptions, only roads with an AADT > 40 have EIRR-values < 15 %. Apart from two exceptions, roads with an AADT < 30 have EIRR-values < 15 %. Therefore the upgrading of earth roads to gravel roads with an AADT < 30 is generally not economically justified. In the average under Namibian conditions the general traffic limit between earth and gravel roads can be set at an AADT = 30.

The lowest traffic loads which are economically justifiable for earth roads have been calculated [54] with an average AADT = 5. Maintenance of earth roads with an AADT less than 5 is generally not economically justified.

 

4.5.4 UPGRADING FROM GRAVEL TO PAVED ROAD

 

Research in the past (1985-1989) [55] concluded that it would be advantageous to improve a bad unpaved road (IRI=7,50) to a good gravel road (IRI=5,00) (Financial Costs: N$ 150 000 /km) for a traffic load of more than an AADT of 40, for instance by adding a gravel wearing course to an earth road. In the absence of suitable natural road building materials for such a road it would be advantageous to pave such a road (IRI=7,50) with a light single surface dressing to an IRI-level 4,30 of (Financial Costs: N$ 480 000/km) for more than 125 vehicles per day. It would be advantageous to improve a bad unpaved road to a paved road level with favourable geometric and drainage properties (Financial Costs: N$ 700 000/km) for more than 190 vehicles per day while it will not be cost/quality optimised to surface a good unpaved road (IRI=5,00) carrying less than 110 vehicles per day, To build a full-scale conventional paved road (Financial Costs: N$ 1 100 000/km) will only be cost/quality optimised for a bad unpaved road carrying more than 330 vehicles per day or a good gravel road carrying more than 500 vehicles per day. Aspects like dust and all-year-trafficability and social factors like labour-intensiveness are difficult to quantify, but these factors play a role to justify the construction of a paved road at levels below above cost/quality optimised levels (economic costs). It should also be borne in mind that above criteria are broad boundaries only. Every project has to be investigated individually to establish the real individual optimal point of surfacing an unpaved road, taking into account all factors.

New research [56] has confirmed these traffic boundary conditions and lead to similar conclusions. The results from the Economic Evaluation Spreadsheet-Program [57] and verified by the HDM-4 Computer Program for different traffic loads and the three upgrading options for the EIRR and the NPV values are shown in the following tables:

 

TABLE 29: UPGRADING FROM GRAVEL TO PAVED ROAD: ECONOMIC INTERNAL RATE OF RETURN (%)

 

 

 

 

 

EIRR (%)

 

AADT

 

80

120

160

Option A: Single Surface Dressing

13,28

20,58

27,50

Option B: Double Surface Dressing

6,69

11,52

15,89

Option C: Asphalt Concrete

5,55

10,00

14,00

 

TABLE 30: UPGRADING FROM GRAVEL TO PAVED ROAD: NET PRESENT VALUE

 

 

 

 

 

NPV

 

AADT

 

80

120

160

Option A: Single Surface Dressing

48 763

165 568

282 373

Option B: Double Surface Dressing

- 78 538

38 266

155 071

Option C: Asphalt Concrete

- 116 903

- 99

116 706

Thus it can be concluded that the traffic limits for upgrading from a gravel to a paved road are as follows:

Single Surface Dressing: AADT @ 120

Double Surface Dressing: AADT @ 160

Asphalt Concrete: AADT @ 200

Due to the peculiar and complex material conditions in the Oshikoto, Ohangwena, Oshana and Omusati Regions and the scarcity of appropriate road building wearing course materials special arguments have to be taken into consideration. This can mean that even for small traffic loads gravelling of an earth road or light bituminous surfacing of gravel roads will be warranted (Dust-free gravel roads). The economic/financial costs factor between conventional and labour-based construction methods is 0,55/0,73 = 0,75. Under these circumstances a single surface dressing is economically feasible for an AADT of 90. If the material’s argument is taken into account upgrading from a gravel to a paved road could be economically feasible for traffic limits up to an AADT = 70.

 

Endnotes:

[18] Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

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

[20] Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[21]  See last endnote

[22]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[23]  See last endnote

[24]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: National Transportation Master Plan Study: Volume 2, Windhoek, 1998

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

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

[27]  See last endnote

[28]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[29]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: National Transportation Master Plan Study: Volume 2, Windhoek, 1998 and recalculated by Dr. Klaus Dierks for the Study Area

[30]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: The Oshikoto, Oshana, Omusati and Ohangwena Roads Master Plan Revision, Volume 1, Windhoek, 1999

[31]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: The Oshikoto, Oshana, Omusati and Ohangwena Roads Master Plan Revision, Volume 1, Windhoek, 1999

[32]  See last endnote

[33]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[34]  See last endnote

[35]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[36]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: The Oshikoto, Oshana, Omusati and Ohangwena Roads Master Plan Revision, Volume 1, Windhoek, 1999

[37]  See last endnote

[38]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: National Transportation Master Plan Study: Volume 2, Windhoek, 1998

[39]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: The Oshikoto, Oshana, Omusati and Ohangwena Roads Master Plan Revision, Volume 1, Windhoek, 1999

[40]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[41]  Government of the Republic of Namibia: Ministry of Works, Transport and Communication: Department of Transport: The Oshikoto, Oshana, Omusati and Ohangwena Roads Master Plan Revision, Volume 1, Windhoek, 1999

[42]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[43]  Gongera, K.S.: The District Development Fund: "Routine Road Maintenance System" for Rural Roads in Zimbabwe, 2000

[44]  Gongera, K.S.: The District Development Fund: "Routine Road Maintenance System" for Rural Roads in Zimbabwe, 2000

[45]  See last endnote

[46] See last endnote

[47]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

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

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

[50]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

[51]  Kellerhals, C,; Engelien, M.: Economic Evaluation Spreadsheet-Program, DOT, Namibia, Windhoek, Jan. 2000

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

[53]  Kellerhals, C,; Engelien, M.: Economic Evaluation Spreadsheet-Program, DOT, Namibia, Windhoek, Jan. 2000

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

[55]  Dierks, Klaus: Technical Aspects for Appropriate Low-volume Roads in Namibia, Ph.-D.-Thesis, Berlin, 1992

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

[57]  Kellerhals, C,; Engelien, M.: Economic Evaluation Spreadsheet-Program, DOT, Namibia, Windhoek, Jan. 2000

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