Highway Engineering-II

Transcription

1 Highway Engineering-II Chapter 7 Pavement Management System (PMS)

2 Contents What is Pavement Management System (PMS)? Use of PMS Components of a PMS Economic Analysis of Pavement Project Alternative 2

3 Learning Outcomes understand highway management system, various types of distresses and rehabilitation techniques 3

4 A Conceptual Approach to Pavement Management You have just been hired as the City Engineer. You ve been given a budget of $1.8 million annually for the maintenance and rehabilitation of all 220 centerline miles of streets in your community, including concrete, asphalt, brick, and chip sealed roads. How are you going to decide where to spend this money? 1. Surveys what will you look for? 2. How will you decide what the right fix is? 3. Can you tell whether your efforts will improve the overall condition of the streets? If not, what would you need to do to be able to do that? These approaches are all forms of pavement management so let s look at a definition of pavement management 4

5 What is a Pavement Management System? Pavement Management A management approach used by personnel to make cost-effective decisions about a road network. Pavement Management System AASHTO Pavement Management Guide (2001) A set of tools or methods that assist decision-makers in finding optimum strategies for providing, evaluating, and maintaining pavements in a serviceable condition over a period of time. AASHTO Guide for Design of Pavement Structures (1993) 5

6 Use of Pavement Management Identify and prioritize maintenance and rehabilitation needs Select projects and treatments on an objective, rational basis Assist agencies in determining cost-effective treatment strategies Allocate funds so an agency can get the most bang for the buck (value for the money spent) Demonstrate impacts of alternate strategies 6

7 Managing Pavement Deterioration Pavements deteriorate. That s unavoidable. The key is being able to predict how pavements will deteriorate so that cost-effective decisions can be made. The challenge is keeping track of all the information on your entire road network and that s where a computerized pavement management system can provide a benefit to an agency. PCI Critical Condition Cost-effective time for preventive maintenance Cost-effective time for minor rehabilitation Costly treatments needed AGE 7

8 Pavement Management Components Network Inventory Network Definition Condition Assessment Reports Pavement Management System Database Analysis Tools System Customization Models Costs Treatment Rules 8

9 Network Inventory Type of Data to be Collected Physical characteristics Construction and maintenance history Traffic levels Climate information Soils information Minimal Amount of Information Required Surface type Last construction date Physical dimensions 9

10 Network Definition Used to link network inventory information to a physical location in the field Determine section boundaries by evaluating the road characteristics. Sections should be similar in terms of surface type, structure, and traffic Identify beginning and end points and width 10

11 Network Definition Local Agencies Most local agencies approach this task by defining sections with defined end points based on physical characteristics. For instance, if a road changes from asphalt to concrete, a section break is made. 11

12 Dynamic Segmentation and Concurrent Transformation Traffic Structure Composite PCC Composite PCC Composite DS CT Composite PCC Composite PCC Composite Composite 100 Composite 400 Composite 12

13 Condition Assessment All system recommendations are based on the current and predicted conditions of the sections in your network Therefore, the assessment of current condition MUST be objective and repeatable BUT, it must also match available resources Types of Pavement Condition Data Collected Surface distress (cracking, surface deform) Roughness (ride) Faulting Rutting Skid resistance Structure (pavement strength and deflection) 13

14 Approaches to Collecting Pavement Condition Data Manual Semi-automated Automated 14

15 Condition Indices Individual Indices Ride Index Structural Index Cracking Index Composite Index 40% Ride + 40% Structural + 20% Cracking Translate the condition information into condition indices so we can compare the condition of sections (it would be hard to compare two sections one that had 50 sq ft of medium severity alligator cracking with another section that had ½ inch of rutting). Which is worse? 15

16 RSL Calculation 16

17 Capabilities Once The Database Is Established Inventory reports Condition ratings By functional classification By surface type Pavement distress data analysis Overall condition Rate of deterioration Cause of deterioration Ranked lists of road needs Worst first or weighted rankings Database Inventory Data Condition Data Record Retrieval and Reporting 17

18 Building From a Database System To develop multi-year programs, To compare different options, To predict future conditions, You need a pavement management system that includes analysis models and multi-year programming capabilities 18

19 Benefits of Pavement Management More efficient use of available resources Ability to justify funding needs More accurate and accessible information on the pavement network Ability to track pavement performance Ability to show impacts on condition Improved communication AASHTO Pavement Management Guide (2001) 19

20 Economic Analysis of Pavement Project Alternatives

21 Introduction (1) The economic analysis of alternative pavement designs is an essential component of the pavement design process. The decision to construct new pavement alternatives A or B, for example (Figure), requires the ability to predict their performance and quantify their economic implications. Similarly, decisions for routine 4-R activities for existing pavements require economic analysis to ensure the best utilization of available funds. Pavement 4-R activity decisions are made at two levels, the network level and at the project level. 21

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23 Introduction (2) At the network level, the needs of all the roadway pavement sections in a jurisdiction compete for the limited budget available. At this level, the need for pavement 4-R is established on the basis of pavement surface condition (e.g., roughness, distress, friction) rather than economic considerations. For this purpose, particular surface condition threshold or trigger values are set, depending on road functional classification (e.g., a PSI value of 2.0, a rut depth of 0.10 cm, or a friction coefficient of 0.35). 23

24 Introduction (3) Pavement sections identified at the network level as due for a 4-R treatment are assembled into projects and further analyzed at the project level. At the project level, feasible 4-R alternative treatments are compared on a project-by-project basis to define the fiscally optimum alternative for each project over a selected analysis period. This process is known as life-cycle cost analysis (LCCA). LCCA is a process for evaluating the total economic worth of one or more projects, that is investments, by analyzing both initial costs as well as discounted future costs, such as maintenance and user costs over the life of the project. 24

25 Costs Components in Pavement LCCA Agency costs Pavement 4-R-related agency costs include all the expenses associated with designing, financing, constructing, and rehabilitating roadway pavements. They can be grouped into the following major categories: Initial pavement construction costs, which typically exclude the cost of acquiring the right-of way Future 4-R costs (e.g., overlays) Administrative/engineering/mobilization costs, which are typically calculated as a fixed percentage of the costs for initial construction or 4-R Financing costs Salvage costs, which are, in essence, negative agency costs, reflecting the residual value of the layers of a pavement at the end of its design life. 25

26 Costs Components in Pavement LCCA User costs Roadway user costs can be grouped into two major categories, namely vehicle operating costs and non-vehicle operating costs, each encompassing a number of components: Vehicle operating costs: Fuel Repair/maintenance, including parts and labor Tires Other (i.e., motor oil and usage-related depreciation) Non-vehicle operating costs: Travel delays due to lane closures for pavement 4-R Other (i.e., travel delays due to reduced speed caused by pavement roughness, pavement-related occupational injuries, cargo damage/packing costs, and pavement condition related accidents). 26

27 Overview of Time Value of Money Concepts LCCA involves comparisons of streams of money over an analysis period, hence requires an understanding of time value of money concepts. Clearly, the worth of sums of money varies with time as a function of market interest rates. Value of money is dependent on the time A sum of money on hand today is worth more than the same sum of money to be received in the future because the money on hand today can be invested to earn interest to gain more than the same money in the future. Studying the present value of money (or the discounted value) that will be received in the future is very important. 27

28 Discounted Cash flow Present Value Present Value (PV) of a future cash flow represents the amount of money today which, if invested at a particular interest rate, will grow to the amount of the future cash flow. The process of finding present values is called Discounting and the interest rate used to calculate present values is called the discount rate. Investing a current amount of money, P, for one year, with interest rate (r) will result in a future amount, C using the following equation. F = P. (1 + r) If P is invested for n years, then : F = P. (1 + r) n Where F is future amount of money, P is present amount of money, n is number of years, r is interest rate in fraction P = F/ (1+r) n For example, the present value of $100 to be received three years from now is $75.13, if the discount rate is 10% compounded annually. 28

29 Example 1 Find the present value of the following cash flow stream given that the interest rate is 10%

30 Discounted Cash flow Net Present Value (NPV) Net present value (NPV) is the summation of all PV of cash flows of the project, where expenses are considered negative and incomes are considered positive. A project will be considered profitable and acceptable if it gives a positive NPV. When comparing projects, the project with the largest (positive) NPV should be selected. 30

31 Example 2 The Table below illustrates the net cash flow of two projects over 5 years. Using the NPV, which project would you prefer if the discount rate 10%

32 Discounted Cash Flow Internal Rate of Return (IRR) The internal rate of return (IRR) of a capital budgeting project is the discount rate (r) at which the NPV of a project equals zero. At this point, a project's cash flows are equal to the project's costs. The term internal refers to the fact that its calculation does not incorporate environmental factors. The IRR decision rule specifies that a project with an IRR greater than the minimum return on capital should be accepted. When choosing among alternative projects, the project with the highest IRR should be selected (as long as the IRR is greater than the minimum acceptable return of capital). The IRR is assumed to be constant over the project life. IRR Net present value of costs of the investment (-ve cash flows) = Net present value of benefits of the investment (+ve cash flows) 32

33 Example 3 Calculate the IRR for both projects and compare among them using the resulted IRR. Assume the return on capital equals 10%. 33

34 Basic Time Value Relationships 34

35 Methods for Economic Comparison of Alternatives Analyzing the economic implications of pavement project alternatives requires application of one of the following methods of economic comparison: Net present worth (NPW) Net annualized worth (NAW) Benefit-cost ratio (BCR) Increment benefit-cost ratio Rate of return (RR) Incremental rate of return (IRR) 35

36 Net Present Value/Worth (NPV or NPW) The NPW method consists of translating streams of benefits and costs into present worth (i.e., time zero) and subtracting them to calculate the net present worth of benefits minus costs. It can be used to determine the feasibility of a single alternative or to compare two or more alternatives, whereby the alternative with the largest NPW is best. 36

37 Example 4 37

38 Solution 38

39 Benefit over Cost Ratio (BCR) The BCR method consists of translating streams of benefits and costs into either present worth or equivalent annual amounts and dividing them to calculate the benefit-over-cost ratio. It can be used to determine the feasibility of a single alternative or to compare two or more alternatives, whereby the alternative with the largest BCR over 1.00 is best. 39

40 Example 5 40

41 Rate of Return (RR or IRR) The RR method consists of establishing the interest rate that renders the present worth of benefits equal to the present worth of costs (i.e., the break-even interest rate). The RR is a good indicator of the economic feasibility of a particular alternative, by comparing the RR with estimates of the discount rate over the analysis period If the RR is larger than the discount rate, the project is feasible, otherwise, it is not. 41

42 Example 6 42

43 Solution to Example 6 i = 9.5 % 43