TR 12 The Economic Benefits of Concrete Road Pavements · The Economic Benefits of Concrete Road ... would rarely make economic sense to design a flexible pavement for ... The Economic

TR 12 The Economic Benefits of Concrete Road Pavements

The Economic Benefits of Concrete Road Pavements

Technical Report 12 (TR 12) ISSN: 1171-4204 ISBN: 0908956207

Introduction

TABLE OF CONTENTS I. Introduction..............................................................................................................................3

II. Discount Rate...........................................................................................................................3

III. Analysis Period ........................................................................................................................3

IV. Initial Cost................................................................................................................................4

V. Future Pavement Maintenance Assumptions...........................................................................4

VI. Pavement Rigidity Effects on Rolling Resistance and Fuel Consumption Characteristics .....5

VII. Pavement Surface Texture Effects...........................................................................................7

VIII. Rolling Resistance and Fuel Consumption due to Macro-Texture ..........................................9

IX. Tyre/Surface Noise Generation..............................................................................................10

X. Pavement Surface Micro-Texture and Skid Resistance.........................................................12

XI. Carbon Dioxide Emissions ....................................................................................................17

XII. Road Roughness.....................................................................................................................17

XIII. Travel Times Savings During Maintenance Activities ..........................................................19

XIV. Early Completion ...................................................................................................................19

XV. Summary ................................................................................................................................19

APPENDIX A: Maintenance Activities and Costs for Concrete Pavements ..................................21

Table A.1: Maintenance expectations for Plain Concrete Pavement. ...................................22

Table A.2: Maintenance Expectations for Continuously Reinforced Concrete Pavement. ...23

Table A.3: Maintenance Rates...............................................................................................24

APPENDIX B: Maintenance Activities and Costs and Roughness Predictions for Flexible

Pavements ..............................................................................................................25

Maintenance Expectations for a Conventional Flexible Pavement (December 2002)..........26

REFERENCES ................................................................................................................................28

TR 12 2 The Economic Benefits of Concrete Road Pavements


I. Introduction Concrete pavements are in widespread use throughout the world but have been little used for roads in New Zealand. Historically, New Zealand engineers have been constrained to use the cheapest first cost options in developing the national road network in a sparsely populated country and this has discouraged the adoption of concrete. The New Zealand road network has matured. Traffic densities and hence pavement costs have grown considerably. Economic efficiency in pavement design is still just as vital as ever but achieving it now requires a more sophisticated approach. Instead of simply minimising the first cost, it is also necessary to consider the long-term user and maintenance benefits of the various alternative pavement types available. The modern concrete pavement has been improved and now provides significant road user benefits as well as the traditionally recognised advantages of great durability and lower maintenance costs. The Transfund New Zealand Pavement Evaluation Manual is the accepted framework for economic calculation of the merits of road works. This Technical Report provides specific guidelines and commentary on the application of the principles and procedures of the Project Evaluation Manual (incorporating amendment No. 6, 2002), to the problem of calculation of the relative merits of concrete pavements and the competing flexible pavement options.

II. Discount Rate The Project Evaluation Manual(15), PEM, mandates the use of a discount rate of 10 percent. This rate is quite high compared with those used by road authorities in other developed countries. Typically values of between 4 and 7 percent are used. The consequence of using too high a discount rate is to focus on short term rather than long-term costs. The choice of appropriate discount rate factor probably has more significance on the decision-making process than many of the other variables considered in the evaluation process. It is therefore recommended that it is good decision-making practise to conduct a sensitivity analysis on the discount rate by varying the rate between 5 and 10 percent.

III. Analysis Period Section 3.2.2 of the Project Evaluation Manual requires the use of an analysis period of 25 years from the start of first construction. When using the PEM as a decision making tool for the comparison of one component of the project, for example, the pavement, the minimum evaluation period should be 25 years of pavement life. Failure to do this can lead to poor decision-making analysis. For example, some large construction projects may involve four years of earthworks construction prior to the construction of the pavement. If the evaluation period is started at the



commencement of the earthworks, significant known maintenance costs that occur in years 22 to 25 will be ignored in the analysis. Earlier versions of the Manual also used a 25 year period but under the heading “Residual Value”. This allowed the consideration of the flow of benefits 25 years beyond that period when two competing options had widely different service lives. The latest version only allows the service life difference to be noted, with no recommendation on how the effects should be quantified. Concrete Pavements are generally designed for 40 years. This is because the additional cost of designing a concrete pavement to last 40 rather than 20 years is very low, so the benefits of designing for the longer period are still significant even when discounting is considered. Since it would rarely make economic sense to design a flexible pavement for much longer than 20 years, the result is that comparisons using only a 25 year period can significantly affect the economic comparisons, and in some cases the concrete pavement option may be wrongly ranked. To overcome this problem, it is recommended that the economic effect should be quantified, in “noting” the difference in service life between options, by considering the flow of costs and benefits from years 26 to 50. The simplest way to do this is to use an analysis period of 40 years.

IV. Initial Cost Guidelines for initial cost estimates are too complex to be encapsulated in a short report like this. Clearly the cost per square metre will vary enormously depending on the scale and complexity of the contract, as it does for other pavement types. As a general rule of thumb, for large-scale projects, concrete pavements are economically most favourable if the subgrade is soft and the traffic volume is high. This is because subgrade stiffness and traffic volumes affect the thickness of a concrete pavement design much less than they do a flexible pavement design. At the other end of the scale, minor roads with difficult access for conventional road-making plant, may sometimes be economic to construct in concrete. The designer or analyst is encouraged to contact the Cement and Concrete Association of New Zealand for further detail in specific cases.

V. Future Pavement Maintenance Assumptions Low future maintenance is one of the principal advantages of concrete pavements. There are examples of well-designed and constructed concrete pavements that have required little or no maintenance well beyond their 40 year design lives. As a general rule, the analyst who is comparing the economics of flexible and rigid pavement options should take particular care to correctly identify the future flexible pavement costs. These generally will be considerably higher than the rigid option costs and so more significant in the comparisons. It is easy, especially with heavily trafficked flexible pavements, to underestimate the future maintenance necessary to meet designed standards of skid resistance and quietness. On heavily trafficked routes it is essential to consider the mutual interaction between maintenance costs and traffic delay costs. On motorways, night time maintenance is virtually mandatory. This



minimises user delay costs but greatly increases the maintenance activity cost. Traffic delays should be modelled/considered and the delay costs included in the analysis. The travel time and vehicle operating costs associated with maintenance on the road should not be underestimated. A study(14) of these costs associated with resealing a section of SH1 at Pukerua Bay (AADT = 16,000-18,000) revealed that the cost of delays was larger than the cost of the physical works.

Provided in Appendix A are recommended “most likely” maintenance assumptions provided by the Queensland Roading Authority (Mainroads). Also provided as Table A.3 are assumptions for the likely costs of these activities. These costs are averages of the rates suggested by the RTA and Mainroads. They have been escalated to January 2004 dollars using Transfunds construction cost index, and converted to New Zealand dollars. Provided in Appendix B are maintenance assumptions for the flexible pavement used for the SH 20 Mt Roskill Extension motorway project in Auckland. Within the maintenance costing for OPGA is a sum to regularly clean the asphalt to maintain its noise dampening characteristics. Alternatively larger noise walls could be provided to accommodate the increased noise, but this would obviously increase the capital cost of the project.

VI. Pavement Rigidity Effects on Rolling Resistance and Fuel Consumption Characteristics

Fuel consumption is a major factor in the economics of highways. The rolling resistance of the pavement is an important contributor to the fuel consumption and the corresponding CO2 production. The major influences on rolling resistance are the surface macro-texture, the mega-texture, the road roughness and the rigidity of the surface itself. This section deals specifically with the effect of rigidity alone as it is a significant factor, and it is essentially independent of the other factors influencing rolling resistance. These other factors are dealt with in section VII below. When a heavily loaded truck travels over a non-rigid pavement, energy is consumed in deflecting the pavement and subgrade, resulting in increased fuel consumption. The effect is not very significant for cars. A U.S. Federal Highways Administration Report by Zaniewski(1) showed this effect. Opus Central Laboratories has recently carried out sophisticated measurements demonstrating the importance of this effect. Preliminary reports (2,3) were able to demonstrate a linear relationship between Benkleman Beam deflection and rolling resistance as follows:

Change of Rolling Coefficient of Resistance = 0.0033∆D Where: ∆D = the increase in Benkleman Beam Central Deflection in millimetres.



This relationship was incorporated in section A5.3.3 of the Transfund Pavement Evaluation Manual. It is important to note that since the publication of the preliminary report, Opus Central Laboratories has considerably extended the range of surfaces tested. A more recent Opus report (4) has indicated that the original report considerably under-estimated the scale of this effect, and the benefits to concrete roads may be two or more times higher than indicated in the Pavement Evaluation Manual. Section A5.3.3 of the Manual suggests that a statistical analysis of Benkleman Beam test results should be used. This would be impractical for a concrete pavement option as there are presently few modern road pavements of that type in New Zealand. An alternative is required, one that gives a consistent comparisons between the options to be considered. The layered-elastic pavement analysis program CIRCLY is used to design the non-rigid pavement options. Although not appropriate for concrete pavement design, CIRCLY can be used in order to compute the central Benkleman Beam deflection for both options. A conservative estimate of the stiffness of normal weight concrete may be computed from the equation:

Ec = 3320(f’c)0.5 + 6,900 MPa

Stiffness values for other materials are to be found in the AUSTROADS Pavement Design Guide. Examples: A very major rural strategic road is designed for 30,000 vehicles per day on a CBR 4 subgrade. The cost difference per vehicle kilometre from table A5(b) of the PEM is 0.35 cents per millimetre difference in the pavement deflection. CIRCLY analysis gives deflections for the concrete pavement option of 0.35 mm. CIRCLY deflection for the very heavy granular pavement option (600 mm deep) is in excess of 0.9 mm, approximately 0.55 mm more. Hence, the change in rolling resistance cost is:

0.55 x 0.35 x 0.01 x 30,000 = $57.75 per day. Assuming a linear traffic growth of 4 percent and a 25 year analysis period, the Net Present Benefit of the concrete option is therefore: NPV of rolling resistance savings = 365 x $57.75 x (9.524 + 0.04 x 75.714) = $264,592/km. This already large figure is in July 2002 dollars and will require adjustment upward to current year values. Extending the analysis period will further enhance the competitive advantage of concrete. A more typical urban arterial carrying say 20,000 vehicles per day, would be more lightly constructed and have deflections of the order of 1.0 mm. The thickness of the concrete pavement would be almost identical so deflections for that option would be very similar. Hence the rolling resistance cost would be:

0.65 x 0.15 x 20,000/100 = $19.50/day, NPV of rolling resistance = 365 x $19.50 x (9.524 + 0.04 x 75.714) = $89,343/km.



VII. Pavement Surface Texture Effects Figure 1 below shows the tyre-road surface interaction effects of the different types of road surface texture. Tyre Wear Rolling Resistance

Tyre/Road Friction Exter or Tyre /Road Noise Noise in Vehicles Discomfort and Wear in Vehicles

Unevenness Mega- texture Macrotexture Microtexture

Texture wavelength 50 m 5 m 0.5 m 50 mm 5 mm 0.5 mm 0.02 0.2 2 20 200 2000 Spatial frequency (cycles/m)

Figure 1: Range of textures and evenness and their most significant anticipated results. A lighter shade means a favourable effect of texture over this range, while a darker shade means an unfavourable effect (5,6). Because the mega-texture and roughness factors are always detrimental, they are kept to the minimum for all pavement types. State of the art concrete and flexible pavement technologies are similar in standard so that any differences between them are negligible in the economic comparison of pavement options. Adequate micro-texture is essential for skid resistance. Although tyre wear is increased with greater micro texture, this detrimental factor is economically unimportant by comparison with the vital necessity of providing the maximum practical micro-texture for safety. Macro-texture affects noise, rolling resistance and skid resistance. Unfortunately, the provision of the optimum macro-texture for one of these important aspects will usually conflict with the optimisation of the other two. Rolling resistance is generally increased by deeper macro-texture, as measured by the sand-circle mean texture depth (MTD). The most fuel-efficient surface is therefore a totally smooth one. Even for extremely low traffic speeds, a totally smooth surface would be completely unsuitable for skid resistance. On open roads, the surface texture for skid resistance should not be below about 0.6 mm MTD, and preferably at least 0.8 mm. However, excessive macro-texture beyond a certain limit



that depends upon the traffic speed is not beneficial for skid resistance and very coarse texture will actually reduce it. Noise generally increases with increasing macro-texture, however this effect is quite complex. Even the relative ranking of the noisiness of different surfaces can differ with different types of vehicle and tyre. Some moderate macro-texture appears to be beneficial in reducing noise levels, particularly on wet roads and for tyned concrete surfaces. For high-speed roads there is a conflict between low noise generation and high-speed skid resistance. New porous asphalt and concrete surfaces are an exception to this rule as the porosity damps the noise. These factors are discussed in more detail in the sections on the economic comparisons of texture-related rolling resistance, noise and skid resistance. In this report it is assumed that the macro-texture levels for all options have been selected on the basis that sufficient MTD has been provided to ensure adequate macro-texture for the speed environment, but that control has been applied to minimise noise and rolling resistance. The options selected are as follows: For concrete, two types of pavement are considered: (i) Light hessian-dragging and light tyning, constructed to the most recent Australian

specifications, yielding a MTD of 0.9 mm. (ii) An exposed-aggregate surface using 8 mm coarse aggregate constructed to European best

practice, giving a MTD of 1.2 mm. For the flexible pavement alternatives, the following options may be considered: (i) A Stone Mastic Asphalt (SMA) with an initial MTD of 1.2 mm reducing to 0.8 mm after

trafficking.

(ii) An Open-Graded Porous Asphalt (OGPA) with a MTD of 1.5 mm.

(iii) A surface dressing with an initial texture of 2.5 mm, reducing to 1.5 mm under traffic. The option of a dense graded TNZ specification asphalt concrete AC with a MTD of 0.5 mm has not been considered, as this option is only suitable for 50 km/hr or slower speed environments.

The reasoning for choosing the differing initial surface textures is as follows: (i) At any given MTD value, transverse texture such as is achieved with tyned concrete, is more

efficient in the provision of surface drainage, and the consequent provision of skid resistance for moderate to high-speed traffic, than are the random textures of the other surfaces. It is noisier for the same MTD and the optimum texture is lower than for the random surfaces.



(ii) The texture of New Zealand AC is generally poor by international standards and cannot achieve levels of texture compatible with high-speed traffic.

(iii) The texture of gap-graded mixes can be adequate. Allowance has to be made for the

reduction of texture under trafficking that is an inevitable feature of flexible pavements under traffic.

(iv) Surface dressing must be provided with considerable initial texture, not only to allow for

reduction under traffic, but also to prevent bleeding. The choice of the differing textures has been necessary to provide data for the example economic calculations below. They are based on the best information available, and are considered to provide balanced comparisons for average conditions. In specific projects, the analyst-design team should check these assumptions against the performance of actual pavements in the field.

VIII. Rolling Resistance and Fuel Consumption due to Macro-Texture

The Transfund New Zealand Project Evaluation Manual (PEM) section A5.3.2, mandates an allowance of 0.15 cents per vehicle-kilometre per 1 mm increase in pavement surface macro-texture, allowing for fuel and tyre consumption costs. This increase in cost is applied to the AADT of the road surfaces considered, without differentiating between vehicle types. This is because this factor is most significant for cars and light vehicles. Fuel consumption of heavier vehicles is proportionally much less affected by macro-texture than are light vehicles, and the heavy vehicles are a minor component of the total traffic stream. The table below shows the results calculated for the same rural strategic and urban arterial pavements discussed in the sections above.

NPV ($/km) – (25 years @ 4% growth)

Pavement Surface Type

Texture (mm)

Relative Daily Cost(cents/veh.-km)

Rural Strategic Route

30,000 AADT

Urban Arterial Route

20,000 AADT Transverse Tyned 0.8 mm 0.00 $0 $0 Exposed Aggregate 1.2 mm 0.06 $82,470 $54,980

SMA 1.2 mm yrs 1-3 0.8 mm yrs 4-11

0.06 0.00 $27,799 $17,798

OGPA 1.5 mm 0.105 $144,323 $96,215

Chipseal 2.5 mm yr 1 2.0 mm yrs 2-3 1.5 mm yrs 4-7

0.255 0.180 0.105

$175,748 $98,631

Table 1: Rolling Resistance Costs Due to Macro-texture Differences.



These costs are clearly significant and as for Section VI will be increased by the PEM updating factors. They will be further increased if the long-term analysis period is adopted, as recommended in this Technical Report.

IX. Tyre/Surface Noise Generation The Project Evaluation Manual, in Appendix A8.4.5, values the variation in costs for an increase in noise levels as $190 x dB change x number of households affected. Obviously the consideration of noise is only significant when the road passes through built up areas.

There is yet no accepted way of calculating noise generation levels to be expected on any particular pavement, although there are rules of thumb that may be valid within a specific type of pavement. There is also a range of noise levels that have been measured within particular pavement types which are not readily accounted for. The noise generation ranges of the different types of pavement overlap to a considerable extent.

The following table is adapted from an Australian listing (7,8), where pavement construction is expected to be more similar than would be the case in Europe or the United States, the main alternative sources for noise data. The tabled values include the noise from the surface and joints (if applicable).

Surface Type Traffic Noise Level Variation [dB(A)]

Chipseal (Medium Grade 3) +4

Concrete: Tyned & dragged 0-3

AC 0

Concrete: Hessian drag -2.7

Concrete: Exposed Aggregate -3

OGPA (when new) -4

Table 2: Noise Generation Differences between Surfacing Types measured at the edge of the road.

There is a tendency for noise levels to be higher on transversely grooved surfaces than on random exposed aggregate textures, whilst longitudinally grooved surfaces are quieter again. With transverse tyned concrete it is important to carefully control the tyning pressures and timing of the operation, otherwise the result can be excessive or deficient macro-texture depths. In the former case, a noisy surface will develop.



It should be noted that OGPA has been shown to lose its porosity within about two years under levels of moderate to heavy traffic. This is acknowledged in the Transit New Zealand Surfacing Selection Algorithm for instance. After this has occurred, OGPA still provides a good macro-texture, but its noise suppression ability is no different from that of similarly textured asphalt or concrete pavements. This factor may have been obscured in New Zealand conditions, since even densified OGPA is quieter than the coarse chipseals that have been almost the only alternative to OGPA on high-speed roads. Australian experience with OGPA in similarly trafficked urban freeways, where designers have tried to get the optimum noise levels without undue loss of surface durability and skid resistance, has resulted in the very widespread use of noise barriers. If the full OGPA noise reduction is to be considered to act for the full analysis period, NCHRP 268 (5) recommends that the maintenance costs should account for the need for high-pressure water-blasting at 6 to 12 month intervals. If such cleaning is used, an estimate should also be made of the likely reduction in surfacing life. The relative differences in noise generation given in Table 2, are for a measurement at the road edge. Any increase in noise at that point will be attenuated and possibly absorbed as it travels to the house facades, at which point the PEM values apply. The attenuation and absorption will have no effect on the relative dB(A) levels of the traffic noise alone, but will reduce the traffic noise as a component of the total noise, thus reducing the dB(A) contribution to facade total noise levels. In order to calculate the facade effects, the optimum solution is to have a noise model for the entire area affected by the project. The PEM recommends the use of the U.K. Calculation of Traffic Noise (CRTN) (9) method. This gives:

L10(18hr) = 29.1+10Log10Q dB(A) +33 Log10 (V+40+500/V)+10Log Log10(1+5p/V)-68.8 Where: V = Traffic speed in km/h P = percentage of heavy vehicles (MCV, HCV I & II and Buses) Section A8.4.4 of the PEM gives: Leq(24hr) = L10(18hr) – 3

These calculations are only required if the ambient noise levels are known in Leq form and it is desired to calculate the effects of attenuation. In considering the economic values of noise, the United States Federal Highways Administration has stated that selection of a pavement surfacing type on the basis of noise generation should not be done. This is because limiting noise levels can result in sub-standard safety levels. Furthermore, the difficulty in estimation of noise generation should not be under-estimated. The alternative of horizontal and vertical alignment changes and noise barriers may be preferable. These alternatives have the benefit of being maintenance free. In New Zealand, the acceptable traffic noise levels will normally be defined in the resource consent application. In these circumstances, noise barriers are provided to ensure that the expected level of noise at the homes is the same for each pavement option. Higher and longer walls are provided for



noisier pavement options. The consequence of using a noisier pavement is therefore reflected in the cost of noise barriers.

X. Pavement Surface Micro-Texture and Skid Resistance

At slow speed, the micro-texture of a surface governs the skid resistance. The Sideways Force Coefficient at 50 km/h (SFC50) or the British Pendulum Number (BPN) give a fair representation of the low-speed skid resistance of a pavement surfacing and thus its micro-texture. Heavy vehicle traffic tends to polish the surfacing micro-texture, so that for 1-4 years after construction the micro-texture polishes until it reaches a lower equilibrium value that depends upon the intensity of the traffic loading. At low speeds, the micro-texture of a chip sealed, asphalt, or exposed aggregate concrete pavement surface is governed by the micro-texture of the coarse aggregate in the surfacing. The Polished Stone Value (PSV) of the coarse aggregate measures the tendency of surfacings using that aggregate to become polished and slippery under trafficking. The PSV and the density of Medium and Heavy Commercial Vehicle traffic can be used to predict the equilibrium SFC50 of the pavement in service. The most heavily trafficked areas of New Zealand, in northern New Zealand, have few sources of high P.S.V. stone that can provide good skid resistance for high traffic volumes and moderate to high intensity manoeuvring. Since the coarse aggregate makes up the bulk of the surfacing, it can be expensive or impractical to import high PSV stone from remote sources.

Centre Indicative PSV Auckland 47-62, typically 47-55 Wellington 53-59 Christchurch 56-59 Dunedin 43-61

Table 3: Typical Polish Stone Values, PSV, for Surfacing Aggregate An approximate equation relating the PSV to the skid resistance (SFC) can be found in TNZ T10(10).

1006.200663.0 −−

=CVDPSVSFC

Where: PSV = polished stone value of the chip. CVD = flow of commercial vehicles/lane/day. (In this case a commercial vehicle

is any vehicle that has a weight greater than 3.5 tonnes).



For high-strength concrete pavements which have not been treated to expose the coarse aggregate, the surfacing is provided by the mortar fraction of the mix. The equilibrium SFC50 of the pavement in service depends chiefly on the properties of the sand fraction and as before, the traffic loading. The most important sand property is its hardness as measured by its Aggregate Abrasion Value (AAV). A less significant factor is PSV for sand which can be measured on coarser particles from the same source. For typical New Zealand concrete sands, which are generally derived from the same source rocks as the coarse aggregates and sealing chip in the same locality, the mortar polishing value is greatly superior to that of the coarse aggregate. This means that transverse-tyned concrete will generally have a low-speed skid resistance far higher than that of asphalts and chipseals in the same area. Care should be taken to avoid excessive soft material such as calcium carbonate (shell or limestone). If high skid resistance is required, sharp silica sand gives an extremely high polishing resistance. Because the sand is only a small proportion of the mix, the cost of importing a better quality of sand for skid resistance is usually relatively low. The equilibrium skid resistance of a textured mortar surfacing is predicted using Figure 4, as there is no regression equation available.

12

10

8

6

4

Agg

rega

te a

bras

ion

valu

e

2

0

0 10 20 30 40 50 60 7 PSV of fine aggregate

Figure 4: SFC of Concrete Pavements(11) At any vehicle speed the wet road skid resistance is dependent on both the mtexture of the surface. Some macro-texture is necessary even for 50 km/h spe

TR 12 13 The EcConcr

SRV 50 (SFC 0.47)

SRV 55(SFC 0.53)
SRV 45
(SFC 0.43)

SRV 50(SFC 0.47)

SRV 60 (SFC 0.57)

SRV 65 (SFC 0.63)

SRV 55 (SFC 0.53)

Fine aggregates used

Type PSV AAV

Flint 28 0.8 Limestone 42 11.0 Dolerite 59 5.2 Gritstone 71 9.0 Calcined bauxite 73 1.2

SRV 80 (SFC 0.57)

Commercial vehicles per day on lane 3400 (motorway) 1600 (trunk road)

0 80

icro and the macro-eds, but the amount

onomic Benefits of ete Road Pavements


required is small and most non-flushed surfaces are adequate. At higher speeds, significant macro-texture is essential to preserve the skid resistance potential provided by any given micro-texture. Table 4 illustrates the reduction in skid resistance with speed as a function of the texture depth of the pavement. The table assumes normal road cross fall.

Texture Depth, mm Exposed Aggregate

Concrete, Chipseal or Asphalt

Transverse-Grooved Concrete

Percent Drop in Skidding resistance with speed change

from 50 to 130 km/h

2.0 0.8 0 %

1.5 0.7 10 %

1.0 0.5 20 %

0.5 0.4 30 %

Table 4: Skid Resistance and Texture Depth(12) Note that the texture depth required to obtain a specific skid resistance is significantly less with a transversely tyned concrete pavement than other forms of road surface. This is due to the fact that the texture in a concrete surface is more directional, meaning that water between the tyre and the road surface can more easily escape. The increasing attention to the safety benefits of high skid resistance has led to the use of synthetic aggregate surfaces. The stiff synthetic binders that these aggregates require have caused cracking problems with flexible pavements in New Zealand. Often a concrete surface could meet the skid resistance requirements. If greater traffic volumes in the future require the still higher skid resistance of a synthetic aggregate, a concrete pavement would than provide a stable base for the synthetic surfacing.

A recent Transit New Zealand paper (13) investigated the benefits of the Authority’s programme to improve skid resistance at locations where the SCRIM-measured skid resistance was below the TNZ T/10 standards. This revealed a benefit/cost ratio of approximately 40 for the program. The statistical analysis also reveals that even for pavements with moderate to good levels of skid resistance, the total injury accident rate will on average be reduced by 7% if a 0.1 increase in SRV can be provided (i.e. a 70% reduction for a 1.0 increase in SRV).

Clause A6.3.3 of the Transfund New Zealand Project Evaluation Manual recommends the use of an accident rate analysis when considering a new project. Therefore the procedure to estimate the benefits of improved skid resistance is as follows:



(i) Use appropriate values for PSV, AAV and CVD to estimate the SFC for each option as described above.

(ii) Estimate if there are other factors that may affect the SFC. Examples are loss of micro-

texture due to flushing. (iii) Use the texture depth, the operating speed of the road, and Table 4 to estimate the change of

skid resistance with speed and calculate the probable skid resistance at the operating velocity.

(iv) Calculate the percent difference in injury accidents between the options as:

Percent Difference = 70 x (SRVoption1 - SRVoption2).

(v) Using Appendix A6 of the PEM, calculate the expected accident rates for the facility for standard conditions and the cost of those accidents.

(vi) Calculate the difference in accident costs between the options as:

Cost Diff = Percent Diff x Std. Condition Accident Cost/100.

Examples: 1. Consider the heavily trafficked rural strategic highway described in the earlier examples:

(i) From Section A2.2.3 of the PEM, Rural Strategic Traffic has 22% of commercial vehicles, LCV, MCV, HCV I & II and Bus. 30,000 AADT therefore corresponds to 6,600 CVD or 1,650 CVD per lane if we assume four lanes.

Assume an OGPA mix is used using a high quality coarse aggregate, with a PSV of 55.

SFC50 = 0.01 x (55 – 0.00663 x 1,650 - 2.6) = 0.42 For the alternative option, consider a tyned concrete surfacing. The fine aggregate in the Auckland area typically has a PSV of 48, and an AAV of approximately 9 giving a SFC for 1,600 CVD of approximately 0.49. This is well above the acceptable minimum, but note that a higher SFC could be, and should be, achieved if sharp silica sand was used in the fine aggregate.

(ii) An OGPA under this volume of traffic may become blocked to the extent that flushing occurs, with consequent loss of micro-texture. For the sake of this example assume that this will not occur.

(iii) From table 4, estimate that the OGPA would suffer a 10% drop in skid resistance between 50 and 130 km/h. Estimate about a 6% drop for 50 to 100 km/h. The drop for the concrete surface is zero.

Hence: SRV100 – OGPA = 0.94 x 0.42 = 0.39 SRV100 – Conc = 0.49



(iv) Percent Difference in Total Accidents = 70 x (0.49 – 0.39) = 7.0%

(v) Using table A6.5(a) of the PEM for level terrain, the estimated injury accident rate is 12 reported injury accidents per 100 million vehicle–kilometres.

From table A6.13 from the PEM the cost per reported injury accident is $590,000 (July 2002). The probable annual cost of accidents = $590,000 x 30,000 x 365 x (12/108)

= $775,260 per annum/km

(vi) Cost Difference Between Options = 7.0 x $775,260/100 = $54,268 per annum. Taking into account the previously assumed 4% traffic growth and the reduction required in Table A6.1(b) of the PEM, a growth in savings of 3% is computed. Hence NPV of accident savings = $54,268 x (9.524 + 0.03 x 75.714)

= $640,113/km

2. Consider the urban arterial described in the earlier examples:

(i) From Section A2.2.3 of the PEM, Urban Arterial traffic has 15% of commercial vehicles. 20,000 AADT therefore corresponds to 3,000 CVD or 1,500 CVD per lane. Assume an SMA mix is used using a high quality coarse aggregate, with a PSV of 55.

SFC50 = 0.01 x (55 – 0.00663 x 1,500 - 2.6) = 0.42 This is well below the acceptable value of 0.55 listed in TNZ T/10 for approaches to traffic lights and pedestrian crossings, which are found on urban arterials. However, we will analyse the economic consequences of using this aggregate. For the alternative option consider a tyned concrete surfacing. The fine aggregate in the Auckland area typically has a PSV of 48, and an AAV of approximately 9 giving a SFC for 1,600 CVD of approximately 0.49. This is also just below the acceptable minimum, but note that a higher SFC could be achieved if sharp silica sand was used in the fine aggregate.

(ii) An SMA mix under this volume of traffic should not suffer flushing.

(iii) The operating speed is 70 km/h and at this speed the drop off of skid resistance should be negligible for all surfaces.

(iv) Percent Difference in Total Accidents = 70 x (0.49 – 0.42) = 4.9%.



(v) For this example, only mid-block accidents are considered and in an actual analysis the intersections should also be analysed. Using section A6.5.4 for an arterial in a commercial area, the estimated injury accident rate is 1.26 reported injury accidents per kilometre.

From table A 6.13 from the PEM the cost per reported injury accident is $370,000 (July 2002).

The probable annual cost of accidents = $370,000 x 1.26

= $466,200 per annum/km

(vi) Cost Difference Between Options = 4.9 x $466,200/100 =$22,844 per annum. Taking into account the previously assumed 4% traffic growth and the reduction required in Table A6.1(b) of the PEM, a 1% growth in savings is computed. Hence NPV of accident savings = $22,844 x (9.524 + 0.01 x 75.714)

= $234,862/km

XI. Carbon Dioxide Emissions The project evaluation manual requires the consideration of the limitation of carbon dioxide emissions. Sections A8.3.4(a) and A8.3.4(b) provide estimates for expected tonnes of CO2 associated with road links and intersections. The average cost of carbon dioxide emissions is assumed to be $30 per tonne. The formula in the Project evaluation manual are repeated below: Road Links: CO2 (in tonnes) = VOC (running costs) x 0.0015. Intersections: CO2 (in tonnes) = Fuel consumption (in litres) x 0.0027. Examples: Sections VI and VIII provide vehicle running costs savings associated with pavement deflection and surface macro-texture. Two examples are a rural strategic pavement with 30,000 vehicles per day and an urban arterial with 20,000 vehicles per day. These savings are summarised in Table 5. The CO2 saving for these two options are: Rural Strategic: Cost = $30 x (264,592 + 144,323) x 0.0015 = $18,401 Urban Arterial: Cost = $30 x (89,343 + 17,800) x 0.0015 = $4,821

XII. Road Roughness Modern concrete pavements are typically laid by machines which can achieve very low roughness counts. It is typical to assume for economic analysis that the roughness count for concrete



pavements will be less than 60 NAASRA throughout the pavements life. This is the zero cost roughness value in the PEM. For flexible pavements with a design life of 25 years, typical assumptions are an initial roughness of 25 NAASRA counts with an increase of 4 NAASRA counts per year. After each OGPA resurfacing treatment it is assumed that the roughness is reduced by 8 NAASRA counts. The rehabilitation at year 25 will reset roughness back at 25.

Examples: The roughness of a flexible pavement will be dependent upon the maintenance regime that is adopted. Using the above assumptions for roughness, and the maintenance schedule provided in Appendix A, the NAASRA count for the flexible pavement is expected to exceed 60 over the following periods. Applying the algorithm provided in Table A5.15, and assuming a 4% traffic growth factor provides the following discounted savings of adopting a concrete pavement, larger road roughness costs will occur if a lesser standard of road maintenance is adopted.

Discounted Roughness Costs Year SPPWF (10% Discount Rate)

NAASRA Count 30,000 vpd 20,000 vpd

15 0.2394 61 0 0 16 0.2176 65 0 0 17 0.1978 69 5,711 2,146 18 0.1799 73 6,412 3,527 19 0.1635 65 0 0 20 0.1486 69 4,827 1,814 21 0.1351 73 5,419 2,981 22 0.1228 77 4,468 3,667 23 0.1117 81 4,675 4,303 24 0.1015 85 7,061 5,121 25 0.0923 89 11,750 6,226 38 0.0267 61 0 0 39 0.0243 65 0 0 40 0.0221 69 1,572 590

TOTAL $51,895 $30,375



XIII. Travel Times Savings During Maintenance Activities

Maintenance activities disrupt the normal flow of traffic. The stopping, slowing down or diversion of traffic, all contribute to additional road user costs. When comparing low maintenance pavement options such as concrete with high maintenance options, it is important that these costs are considered. Travel time costs, including congestion, vehicle operating costs and CO2 costs, are all provided in the Transfund Project Evaluation Manual.

XIV. Early Completion The rigid pavement option may be constructed considerably faster than the asphaltic option - a single slip-form paver being able to lay up to 1.5 km of sub-base or base per day. Depending on the position of the pavement construction on the Contract Programme, this could lead to an accelerated opening to traffic and an earlier benefit flow.

XV. Summary The comparative economic benefits and disadvantages of appropriate alternative pavement types in the preceding cases of a Rural Strategic and an Urban Arterial road are summarised in the table on page 20. For the Rural case, it is assumed that there are few, or no, residential properties to be affected by noise, and a tyned and dragged surfacing is the logical concrete pavement alternative. The commonly used flexible pavement alternative is taken to be a deep granular pavement with a thin asphaltic concrete base and an Open Graded Porous Asphalt surface. The effect of using a chipseal surface, which has been used in such circumstances, is also shown.

For the Urban case, the worst case residential noise scenario is listed. A tyned and dragged surfacing is taken as one concrete pavement alternative and the exposed aggregate option is also investigated. The commonly used flexible pavement alternative is taken to be a deep granular pavement with a Stone Mastic Asphalt surface. The effect of using a chipseal surface is also shown. As Table 5 shows, there is a substantial economic benefit for concrete in all cases.

In the urban case the intangible factor of noise becomes very dominant. Although the noise calculation is based on what is thought to be a very severe case, it is not a completely unrealistic



scenario as far as the differential noise levels are concerned. It dominates to the extent that all other factors in choice of paving surface are relatively subservient. Since the value of noise is by far the least precise calculation, this is of concern, particularly as unlike all other factors this one may be insensitive to traffic volume and may result in fewer safe surfaces being chosen.

Road Type: Rural Strategic (30,000 VPD)

Urban Arterial (20,000 VPD)

Concrete Option: Tyned Concrete Tyned Concrete Exposed Aggregate

Flexible Option: OGPA Chipseal SMA Chipseal SMA Chipseal

Fuel due to Deflection $264,592 $264,592 $89,343 $89,343 $89,343 $89,343

Fuel due to Macrotexture $144,323 $175,748 $17,798 $98,631 ($37,182) $43,651Accident savings due to surface texture $640,113 $640,113 $234,862 $234,682 Not

calculated Not

calculatedCO2 18,401 19,815 4,821 8,459 2,347 5,984

Road Roughness 51,895 51,895 30,375 30,375 30,375 30,375

TOTALS $1,119,324 $1,150,163 $377,199 $465,570 $84,883 $169,353

Table 5: NPV Benefits of 1 Km of Concrete Pavement over Flexible Pavement Alternatives (25 years @ 4% Linear Growth).


Appendix A

APPENDIX A Maintenance Activities and Costs for Concrete Pavements


Appendix A

Maintenance Costs Table A.1: Maintenance Expectations for Plain Concrete Pavement.

Year Maintenance Activity 0 1 2 Cross stitching 30 m per lane Km with 10% requiring routing and resealing. 3 4 5 0.2% base replacement. 6 7 8 Cross stitching 30 m per lane Km with 10% requiring routing and resealing. 9 10 0.5% base replacement, replace joint sealant. 11 12 13 14 Cross stitching 30 m per lane Km with 10% requiring routing and resealing. 15 16 0.2% base replacement. 17 18 19 20 Cross stitching 30 m per lane Km with 10% requiring routing and resealing,

0.5% base replacement, replace joint sealant, 30% retexture. 21 22 23 24 25 26 Cross stitching 30 m per lane Km with 10% requiring routing and resealing. 27 28 29 30 0.5% base replacement. 31 32 33 34 35 Cross stitching 60 m per lane Km with 10% requiring routing and resealing. 36 37 38 39 40


Appendix A

Table A.2: Maintenance Expectations for Continuously Reinforced Concrete Pavement.

Year Maintenance Activity 0 1 2 3 4 5 6 7 8 9 10 0.3% base replacement, replace longitudinal joint sealant. 11 12 13 14 15 0.3% base replacement. 16 17 18 19 20 Replace longitudinal joint sealant, 30%retexture. 21 22 23 24 25 0.3% base replacement. 26 27 28 29 30 0.3% base replacement, replace longitudinal joint sealant. 31 32 33 34 35 0.3% base replacement. 36 37 38 39 40


Appendix A

Table A.3: Maintenance Rates

Activity Rate $/m2 (January 2004) Base replacement $215.00

Surface retexture $2.30

Reseal joints $4.60

Crack stitching $17.50

Route and seal cracks $7.00


Appendix B

APPENDIX B Maintenance Activities and Costs and Roughness Predictions for Flexible Pavements


Appendix B

Maintenance Expectations for a Conventional Flexible Pavement (December 2002)

Year

Annual Maintenance (cents per SM)

Occasional Maintenance Activity

Treatment (cents per SM)

NPV Total Cost

(cents per SM) 0 0.0 1 54.0 49.1 2 54.0 Levelling course and FC resurfacing. 1,250.0 1,077.7 3 54.0 40.6 4 54.0 36.9 5 86.0 OPGA cleaning to maintain quite surface. 239.7 6 86.0 300.0 48.5 7 86.0 44.1 8 86.0 40.1 9 86.0 36.5 10 140.0 Mill, levelling course FC resurfacing. 1,650.0 690.1 11 140.0 49.1 12 140.0 44.6 13 140.0 40.6 14 140.0 OPGA cleaning to maintain quite surface. 300.0 115.9 15 140.0 33.5 16 140.0 30.5 17 172.0 34.0 18 172.0 Levelling course and FC resurfacing. 1,250.0 255.8 19 172.0 28.1 20 172.0 25.6 21 172.0 23.2 22 172.0 OPGA cleaning to maintain quite surface. 300.0 58.0 23 172.0 19.2 24 172.0 17.5 25 172.0 125 mm structural overlay. 5,320.0 506.9 26 54.0 4.5 27 54.0 4.1 28 86.0 6.0 29 86.0 OPGA cleaning to maintain quite surface. 300.0 24.3 30 86.0 4.9 31 86.0 4.5 32 86.0 4.1 33 140.0 Levelling course and FC resurfacing. 1,250.0 59.8 34 140.0 5.5 35 140.0 5.0 36 140.0 4.5 37 140.0 OPGA cleaning to maintain quite surface. 300.0 12.9 38 140.0 3.7 39 140.0 3.4 40 172.0 3.8

25 year analysis period = $35.86 40 year analysis period = $37.37


Appendix B

Expected Roughness of a Flexible Pavement Consistent with Proposed Maintenance Regime

Year Occasional Maintenance Activity Predicted Roughness (NAASRA Counts

0 25 1 29 2 Levelling course and FC resurfacing. 33 3 25 4 29 5 OPGA cleaning to maintain quite surface. 33 6 37 7 41 8 45 9 49 10 Mill, levelling course FC resurfacing. 53 11 45 12 49 13 53 14 OPGA cleaning to maintain quite surface. 57 15 61 16 65 17 69 18 Levelling course and FC resurfacing. 73 19 65 20 69 21 73 22 OPGA cleaning to maintain quite surface. 77 23 81 24 85 25 125 mm structural overlay. 89 26 25 27 29 28 33 29 OPGA cleaning to maintain quite surface. 37 30 41 31 45 32 49 33 Levelling course and FC resurfacing. 41 34 45 35 49 36 53 37 OPGA cleaning to maintain quite surface. 57 38 61 39 65 40 57


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