Monday, 25 February 2013

Photogrammetry in Highway Engineering


Photogrammetry in Highway Engineering:

            Photogrammetry, often called “remote sensing,” is defined as the science or art of obtaining measurements by means of photography. Quite commonly it is construed more broadly to encompass procedures for photo interpretation and for converting single photographs into composite ones (called mosaics) and info maps. Photogrammetry in this broader sense, and particularly that based on aerial photographs, is today a basic working tool of the highway engineer. Applications appear not only in highway location, but also in planning, geometric design, rights of way, traffic studies, drainage, soil classification and identification, earth-work measurement, materials location, and pavement condition surveys.

Mapping by Photogrammetric Methods:

            In highway practice, aerial photography and the preparation of mosaics and maps may be done in part or in whole by a highway agency or by contract between private companies and the individual highway agencies. If done by contract, the agreement generally stipulates the “results to be obtained” and leaves the “manner and method” of specific photographic and photogrammetric equipment and procedure to the company. To illustrate, a common specification for accuracy of topographic maps states that 90% of the elevations be correct within one-half of a contour interval and remainder within one contour interval. Another requirement is that 90% of the planimetric features be positioned on the map within one-fortieth of an inch of correct location- the rest within one-twentieth of an inch. Incidentally, these specifications clearly demonstrate the high degree of accuracy that can obtained.  
            Vertical aerial photographs taken with the camera pointed straight down are the most useful for highway mapping purposes. The country to be covered is photographed in parallel runs with the individual pictures lapped both in the direction of flight (end lap) and between successive runs (side lap). For stereoscopic uses, end lap must be greater than half the picture width (possibly specified as not less than 55% nor more than 65%) in order that the center (principal point) of one photograph is included in both adjacent photographs. Side lap should average 25%, with percentage less than 15 or more than 55 unacceptable bases to height and width to height ratios. Selection of the height from which photographs are to be taken depends on the uses which they, or the maps to be made from them are to have for map-making purposes, the variables include the focal length of the aerial camera, the desired combination of map scale to photograph scale. The latter is, in turn, a function of the stereoscopic projector used for map making.   
            Several instruments of varying complexity are available for converting data from the aerial photographs into maps. These include the kelsh stereoscopic plotter, the Nistri photograph, the wild autograph, and the Zeiss stereoplanigraph. All utilize the concept that when the area common to a pair of matched photographs is viewed through a stereoscope, the topography is seen in relief. It is possible with any of these instruments to produce an accurate map showing all natural and artificial features. Also, contours may be drawn or spot elevations determined. Only those features that cannot be identified on the photographs must be located by ground measurement. Difficulties will of course be encountered in attempting to map heavily wooded areas where the ground is not visible in the photographs. Even in this instance, mapping is some times possible by taking photographs when the trees are bare or by setting ground elevations by using estimated tree heights.
            Commonly, map making form aerial photographs is done by a skilled operator. However, devices have been developed that determine the locations and elevations of points electronically for eventual punching into computer cards.
            Earlier procedures required ground-control survey points in every photograph to set its scale and elevation. Today, however, procedures have been developed to greatly reduce ground-control requirements by aero triangulation. This is done by successively trying together a chain of geometric figures defined by marked points on the ground. Other points to be incorporated into ground surveys also are marked for easy identification on the photographs.
            Accuracies of ground-control triangulation networks or traverses must be in keeping with the scale of the aerial photographs. It has been generalized that third-order triangulation is satisfactory in rural areas and second-order fro urban locations. For these, maximum errors in distance are 1:5000 and 1:10,000, respectively. Sufficiently accurate angular measurements are easily obtained with modern theodolites. Two new concepts of distance measurement have improved speed and precision. One class of devices, which includes the tellurometer and electro tape, employs high-frequency radio waves. A “master” unit is placed at one end of the line and a “slave” unit at the other. The second group, typified by the geodimeter, employs the phase relationships between outgoing and reflected modulated light waves. Signals from the instrument placed at the one end of the line are returned by a reflector placed at the other. Both kinds of equipment are rugged and portable.
            Increasingly, highway surveys are being tied into the state plain coordinate systems developed by the U.S Coast and Geodetic Survey as an adjunct to its nationwide triangulation network. These master coordinate systems provide a firm base and a check not only for ground-control surveys are only for ground control and for filling in detail that cannot be gained from the photographs. Scale for the finished maps is, commonly, for rural areas 1:62,500 or approximately 1 mi to 1 in.; for urban areas the scale is 1:24,000 ft to 1 in. state by-state lists showing the areas that have been mapped are available on request from the Geological survey.

HIGHWAY SURVEYS, PLANS, AND COMPUTATIONS


HIGHWAY SURVEYS, PLANS, AND COMPUTATIONS

INTRODUCTION:

Early highway locations were not based on engineering principles. For example, of the 2 ½ million mi of rural highways that had accumulated by 1890, many were positioned by the successive development of the trails. In the vast Mississippi valley area, roads commonly followed the north-south and east-west section and township lines. With state aid and state highway construction in the 1890-1920 decades came better road location. Then, with the development and increased use of the motor vehicle, alignments were improved and grades flattened. Even so, before World War II, rural highway locations in settled areas involved mainly higher standards for the width, line, and grade of existing roads. In urban areas the primary concern was with street realignment and widening and with subdivision layout. Only in the sparsely settled portions of the far west and pacific states and certain mountains areas were major new locations over long distances undertaken. These were carried out primarily on the ground using traditional techniques based on the transit, level, and tape.
            Since World War II, highway location practices have been revolutionized. First, the principle was established that access to major highway facilities must be controlled to protect them from encroachments by land-use activities; this forced the adoption of new locations for many major arteries in both rural and urban areas. For example, it has been estimated that 75-85% of the interstate system lies on new locations. Second, new techniques for surveying, mapping, and computation that have developed during and since the war have largely supplanted traditional methods, at least for the larger highway agencies.
            For modern highway location, engineers must do far more than determine a route that with reasonable economy meets certain minimum requirements regarding curvature and grade. Locations must blend curvature, grade, and other roadway elements to produce an easy-riding, free-flowing traffic artery that has high capacity and meets exacting safety standards. Furthermore, as indicated by Table 3-1 and 3-2, they must recognize and evaluate its economic and environmental impact on existent and future community, industrial, business, residential, science, and recreational values.
            Before surveying and mapping for any highway location are begun, tentative decisions regarding design speed, roadway cross sections, and maximum grade must be made. These, to be sound, must rest on estimates of the amount, character, and hourly distribution of traffic, coupled with knowledge of the area to be the location survey progresses, choices between possible routes and decisions regarding design alternatives must be selected. These often are made with the active participation of local officials and community groups.
            The remainder of this chapter deals with photogrammetry as a tool for highway engineers; some of the problems of highway location in rural and urban areas and the surveys required solving them; and also the realms of highway plans, specifications, and computations. The effect of such environmental factors as noise and air pollution on location is discussed in chapter 12.

CONSEQUENCES TO HIGHWAY USERS


CONSEQUENCES TO HIGHWAY USERS

Costs of Motor-Vehicle Operation:

            There is no single correct answer to the question: what does it cost to operate a motor vehicle? In the first place, the elements to be included in cost differ, depending on the purpose of the question and the viewpoint to be taken. Secondly, although much is already known about motor-vehicle costs, much is still to be determined by experiment and observation.
            Some operating expenses increase more or less directly with miles driven; in other words, their cost per vehicle-mile is relatively constant. In this classification fall such items as fuel, tires, oil, maintenance and repairs, and that portion of depreciation attributable to wearing out. Other costs vary mainly with time and are constant for a given period such as 1 yr; or, stated in costs per vehicle-mile, they vary inversely with the number of miles driven annually. Included here are drivers’ license and registration fees, garage rent, insurance, and obsolescence, which is the portion of depreciation that results from inadequacy or being out of date. Some items are dependent entirely or in part on speed. The most important of these is the travel time of operator and rider; any charges for these will vary inversely with speed. On, the other hand, some of the operating costs that vary primarily with miles driven, such as fuel and oil consumption and tire wear may also be influenced by speed and other factors such as roadway congestion.
            Of the costs mentioned here, running costs that vary primarily with mileage or speed are most often affected by highway improvements. It follows that these are of particular concern in highway economy studies, for justification of many highway improvements depends largely on savings in operating costs to offset proposed expenditures. However, care must be exercised to consider only those costs or savings that are relevant to a particular comparison. Stated differently, only those costs or savings that will be affected by the proposal should be included in economy studies. The importance of this distinction is made apparent by the fact that, although the average cost per mile of owning and operating a standard-sized automobile is 13.6, the incremental or running cost of driving an additional mile is in the range of 5.
            The motor-vehicle running costs presented here were abstracted from data developed primarily by Winfrey and Chaffey, and were updated by Curry and Anderson. Because of space limitations, with a few exceptions, the detailed information given here is only for passenger cars. No single multipliers are appropriate to convert the costs among vehicle types, since they would vary substantially, depending on the particular maneuver for which costs are desired.
Table 4-2.        First approximations of multipliers to determine running costs for other vehicle classes from those for passenger cars.   
Vehicle Class
Operating condition
5,000 lb Pickup
12,000 lb Single unit truck
40,000 lb Gasoline-driven truck (2-S2)
50,000 lb Diesel-driven truck (3-S2)
Continuous travel on relatively straight and level roadways.
1.15
2.0
2.8
3.2
Added costs for idling, and slowing or stopping and accelerating
1.15
2.5
9.0
11.5
Added cots for travelling curves and corners
1.15
2.2
6.0
6.0

Highway Agency Costs


Highway Agency Costs:

            Highway agencies are changed with the responsibility of planning, constructing, maintaining, and operating the roads under their jurisdictions. Where appropriate, the costs of these activities are included in economy studies. However, many of these agency costs, particularly those for planning and some of the overhead charges associated with other operations, are not affected by proposed investments and they should be excluded from economic comparisons. The costs per mile to construct and maintain highways vary tremendously. Construction costs may vary from a few thousand to ten of millions dollars. Maintenance costs also vary greatly. However, appropriate values are usually available in the records of highway agencies.

            For economy studies, the accuracy needed for the costs of rights of way, construction, maintenance, and operation will be different, depending on their use for example, it long-range projections are being made for needs studies or advanced planning, only average costs per mile might be considered, based on past experience in similar situations. At the other extreme, if, for example, alternative pavement designs or materials are being compared, the individual cost elements might be developed in considerable detail. Discussions of such estimating procedures are outside the scope of this book.


Interest as a Cost:

            In economy studies for private business, interest is always treated as one of the costs of invested capital. This is logical, since the money for the investment comes either by withholding earnings from owners or stockholders, from borrowing from others and paying interest on the borrowed funds, or by foregoing other investment opportunities that should produce a return. In the past in the public works field some have argued that interest should be charged only where borrowing will finance the proposed project. This viewpoint has now largely disappeared as two concepts have been accepted. These are (a) that capital can and should be productive and (b) that interest is a reward or incentive for deferred consumption, as is the case when money is invested in highways because of anticipated future benefits. Winfrey (op. cit., Chapt. 5) has proposed that the word overcharge be substituted for interest to distinguish those situations where no specific monetary return is anticipated.

            Among highway engineers today, two different viewpoints regarding interest as a cost are advocated and utilized:

1.      Interest should be charges at the current rate at which a particular highway agency can borrow money. The charge is included even though road improvements are financed from current income. If the uncertainty inherent in estimates of future happenings is recognized at all, it is done by adopting a conservative value for future benefits.
2.      Interest should be charged at a rate representing the minimum attractive return. This would e somewhat higher than the cost of borrowed money in order to recognize the risk involved in all predictions of future events. The rate would be set for each agency after representative projects which promise the best use of (usually) limited highway funds are analyzed. In any event, the rate of return would be high enough to discourage investments that do not appear attractive in the light of future uncertainties.

The decision regarding interest rates has a tremendous influence on the results of economy studies. Assume, for example, that interest rates of 0, 3, 6, and 10%, respectively, are employed for a proposal that has a first cost of $1000 and an estimated life of 30 yr. Then the annual return needed to recover the $1000 in 30 yr, using interest at 0%, will be $33.33; at 3%, $51.02; at 6%, $72.65, and at 10%, $106.08.

The first of the two viewpoints outlined above was adopted by the AASHO committee in its report. Several interest rates, ranging from 3 ½ to 6% were used in their illustrative examples. Federal water agencies use the same approach, but indicate that estimates must be conservative to allow for risk.

The second point of view, which comes closer to that found in private enterprise, is favored by a number of writers in the highway and other public works fields. The minimum attractive rate of return, 7% or higher, would include a charge for the use of the invested funds and a safety factor to reflect the risk involved in even the best estimates. The actual rate might be set at a some what higher level for higher risk projects. And, where funds are limited and there are many opportunities for investment in projects showing high rates of return, the rate should be set at the level where funds will be exhausted to avoid error or confusion in interpreting study results.

Service lives of Highway Elements


Service lives of Highway Elements:

            To develop information on service lives or life expectancies for all kinds of highways and their individual elements in various environments would be difficult. There are many variables such as soil, climate, topography, and traffic volume that will affect differently the life of essentially the same type of highway in different places. In flat country the alignment may remain unchanged for many years. On the other hand, a road in rolling or mountains areas originally built on cheap crooked alignment often becomes obsolete because of restricted speeds and is relocated long before the life of the pavement is reached. Also, the art of highway building changes so that the date of construction will influence the probable life of a new highway of given type. Finally, it is common to incorporate portions of an existing facility into any reconstruction, as when pavements are resurfaced or lanes, new roadways, or grade separations are added to increase capacity. In these situations, the practice of classifying resurfacing or reconstruction as a form of retirement might be questioned. In sum, forecasting service lives and time to retirement from historical data is difficult and uncertain.

            Studies of the service lives and life expectancies of pavements were begun about 1935 and have been updated form time to time. Some of the findings on past service lives and reasons for retirement of several pavements types are listed in table 4-1.

Table 4-1 Average Service livers and retirement causes for highway surfaces.

Method of retirement (%of mileage)
Surface
Service life (yr)
Resurfaced
Reconstructed
Abandoned
Retired
Low type
Soil Surface*
Gravel or stone*
4.0
7.5
37.5
58.0
58.1
30.4
1.2
2.5
3.2
9.1
Intermediate type
Bituminous surface-treated**
Mixed Bituminous+**
14.0
12.0
58.5
59.8
32.6
30.3
2.5
2.0
6.4
7.9
High type
Bituminous concrete++**
Portland cement concrete**
17.0
25.0
57.4
66.0
27.7
22.8
2.2
1.8
12.7
9.4
* Source: Public Roads, June 1956, p20.
** Source: HRB Record 252. Pp. 1-23.
+ Thickness of surface and base less than 7 in.
+- Mixed bituminous or bituminous penetration with of surface and base 7 in or more.

Several procedures for forecasting future retirements from such historical data have been developed. One of these, the annual rate method, employs data on retirements in a single year or band of years to develop “survivor” curves. In turn, “type survivor curves” selected from a family of such curves may be fitted to the plot. This approach is illustrated in fig. 4-1. Another procedure is called the “turnover method.” It compares the accumulated units in service with the accumulated retirements.

            Methods for forecasting service lives and life expectancies till reconstruction or resurfacing, based on AASHO pavement design procedures, have also been developed. Also, remaining service lives are being predicted by measuring the strength of existing pavements.

COSTS OF HIGHWAYS


COSTS OF HIGHWAYS

Determining Relevant Costs:              
           
            The total cost for improvements to a highway system or segment includes engineering and design, expenditures for planning, the outlay for acquiring rights of way, and the costs of constructing roadway, structures, and pavements. Selection of the cost items to be included in and excluded from specific economy studies requires straight and careful thinking. A detailed discussion is beyond the scope of this book. However, four of the most important considerations are as follows:
1.      In general, allocated costs, used for accounting purposes, should be omitted from economy studies. To illustrate, a given percentage may be added to estimated project costs for administration, planning, and engineering overhead. These costs probably will be incurred whether or not a specific project is undertaken; if so, they are not relevant in comparisons between possible courses of action. Stated differently, only the added or incremental costs are relevant.
2.      Expenditures made before the time of the economy study should not be considered. These are called sunk costs, in that they cannot be recovered by any present or future action. For example: the roadway and pavement of an existing road may be in good condition and have a substantial “book value” in the records of the highway agency. Nevertheless, if one alternatives in the economy study. Again, it would be improper to include costs incurred earlier for preliminary planning and design.
3.      All relevant costs must be included and all irrelevant charges excluded. In this regard, as mentioned earlier, transferred costs may be particularly trouble some. Assume, for example, that one of several plans for a proposed highway improvement requires a private utility company to move its facilities at its own expense. From a budgetary standpoint this cost is not chargeable against the project from a public works economy-study standpoint; however it is a proper charge. Economic resources are consumed. Even though paid from private rather than public funds.
4.      In certain types of economy studies. It is proper to make an allowance for the salvage value of a machine or structure at the end of its estimated useful life. As a general rule, salvage value should be neglected in economic studies for highways. It is conjectural at best to assume that an investment in a highway will have great worth 20, 30, or 40 yr in the future. One exception might be to assign salvage value to the land occupied by the road. Even in this situation only the raw value of the land in its predicted future use, after deducting the cost of converting it to that use, would be included. Other costs associated with acquiring the land in the first place, such as legal expenses and the cost of cleaning it of buildings cannot be recovered and would not be a part of the salvage value.

Proposed highway improvements often will bring changes in annual maintenance and operating costs. For present conditions, data for these should available from the cost records of the highway agency. Estimates of these costs for the proposed improvements must be projected. Here again, only the relevant costs are to be sure that only true cost differences are reflected.

HIGHWAY ECONOMY


HIGHWAY ECONOMY

INTRODUCTION:

            Governments have, of necessity, provided certain facilities that the private sector could not furnish. Among them are highways and public transportation. The intents of the expenditure for highways are to raise the level of the entire economy by providing for ready transportation of goods; to assist in problems of national defense; to make easier the provision of community services such as police and fire protection, medical care, schooling, and delivery of the mails; and to open added opportunities for recreation and travel. Highways benefit the landowner because ready access makes his property more valuable. Their improvement benefits the motor-vehicle user through reduced cost of vehicle operation, savings in time, reduction in accidents, and increased comfort and ease of driving. On the other hand, road improvements consume resources, including land, which might be used for other productive purposes by individuals or by government and the vehicles travelling produce air pollution and noise. From the point of  view of resources use, then, highways can be justified only if, in net sum, the consequences are favorable-that is, if cost reductions to highway users and other beneficiaries of the improvement exceed the costs, including some allowance for the return on the money invested. There are as has been indicated before, numerous other factors to be considered, but this chapter focuses on the economic or resource-use phases.

            Highway economy was under discussion over a century ago. W.M Gillespie, professor of civil engineering at Union College, in his Manual of the Principles and Practice of Road Marking, stated that “A minimum of expenses is of course highly desirable; but the road which is truly the cheapest is not the one which has cost the least money, but the one which makes the most profitable returns in proportion to the amount expended upon it.”

            The first detailed attention to highway economy developed about 40 years ago at lowa State College. It focused largely on the relative economy of various roads surfacing and, later, on the costs of motor-vehicle operation. The advent of the state wide planning surveys with the masses of data developed by them brought attention to many other factors of importance to the overall problem. Even so, attention to highway economy as a topic for detailed research and analysis has been small and sporadic. An accepting was that economic comparisons of alternative routes on the Interstate System were required by federal regulations. Many of these were based on the so-called Red-Book, developed by the AASHO Committee on the Highway Design. Further impetus for economic analysis on federal-aid projects many come through the Federal-Aid Highway Act of 1970 (Sect. 186) which required that in 1972 the Federal Highway Administration.

           





A Framework for Highway Economy Studies:

            Possibly the most difficult and error-prone phase of economy studies lies in placing the study in the proper framework or perspective. And if this phase is done incorrectly, inputs of the most reliable data and flawless procedures for analysis will still give erroneous results. Some of the guidelines to be followed in developing this framework are:

1.      Economy studies are concentrated with forecasting the future consequences of possible investments of resources. Past happenings, unless they affect the future, are not considered. This “forward” look is distinctly different from the “backward” look of accounting practice. This difference is illustrated by the discussion of incremental and sunk costs later in this chapter.
2.      Each alternative among which choices are to be made must be fully and clearly spelled out. As an example, if a freeway is proposed to parallel a busy street, there will be vehicle operating cost savings not only to those diverted to the freeway but, possibly, also to the remaining travelers on the street. On the other hand, traffic using this same freeway could increase congestion and vehicle operating costs on other traffic arteries. This likewise should be recognized. Thus, the first step in analysis is to make a complete list of consequences, both economic and other.
A clear distinction must be made between economic analysis (the use of resources) and financial considerations (the use of money). It has already been indicated in Chapt. 03 that decision making involve dealing with three elements in sequence. These are (a) economic, which is the use of resources; (b) financial, which deals with getting and expending money and, (c) political and administrative, a catchall phrase for all the no quantifiable forces that bear on the decision. It was also indicated that rational decisions were more likely to be reached if the best alternative from an economic point of view were tested in sequence for its financial and political and administrative viability. It this alternative failed either of these two tests the next most viable alternative would then be examined, and so on.  In the past analysts sometimes erroneously have included financial considerations in economy studies. A first illustration is the practice of including interest as a cost only if money is to be borrowed to finance a project. But it can be seen that, regardless of the source of funds, the same resources will be consumed in constructing, maintaining, and operating the proposed highway whether the project is financed with borrowed funds or with current revenues. Two more among the common situations where financial thinking can lead to errors in economy studies involve allocated and sunk costs. 

The Development of Highway Planning


HIGHWAY AND URBAN TRANSPORTATION PLANNING

The Development of Highway Planning:

            In the United States before 1930, the primary attention of highway agencies was focused on establishing a system of all-weather rural roads. With this objective there seemed to be little need for “planning” the problem was to get the roads built.

            About 1930 the attitude toward planning began to change. City streets were in relative distress, and many rural highways were overloaded. The practice of using all federal aid and the bulk of state highway funds for the improvement of main rural highways needed examination. And yet what were the next most important groups of roads or streets? Should their improvement supersede the demand for reconstruction of much of the main system that was rapidly becoming inadequate for increased traffic?

            From the data at hand such questions were unanswerable. To get facts on which to base decision, the so-called “highway planning surveys” were under taken. Beginning with the Federal-Aid Act of 1934, Congress authorized expenditures not to exceed 1 ½ % of federal-aid funds apportioned to each state for the making of surveys, plans, and engineering investigations of projects for future construction. In addition, the usual “matching” provision was waived. By 1940, all the state highway departments were assembling the facts necessary to develop long range highway- improvement programs.

            Today, planning has become a basic activity of every major highway or transportation agency. Data assembled by the planning departments are used to develop programs for the years ahead, and in almost administrative decisions. New planning procedures are under continuous development; in many of these activities, scientific applications such as special instruments, statistical methods, and computer analysis are replacing the cumbersome and time consuming hand-labour methods of earlier days. But in spite of developments such as these, the planning premises and approaches of highway agencies and the proposals for highway improvements stemming from them are being challenged on many fronts. As a result, some projects, particularly urban freeways, are not being constructed at all and others have been substantially delayed. For example: a 1971 study by the Texas Highway Department indicated that an average of 8 years and 5 mo elapsed between authorization to proceed with a project and its opening to traffic, and even longer lead times are anticipated when the environmental impact statements called for by the Environmental protection Act are required.









The Planning Dilemma:    

            As indicated in Chapter 1, the United States is, for better or worse, tightly bound to the motor vehicle. Until the early or middle 1960s, the attitude of the public and their elected representatives toward highways, and particularly freeways, was highly favorable. Even today, such attitudes generally prevail toward highway investments in rural areas, although some critics blame the automobile for such problems as the removal of land from productive use, its failure or that of alternative transportation schemes to provide for the movement of rural residents, particularly the poor, and the overcrowding and despoiling of recreational and scenic areas. But a possibly large segment of the population and many social scientists and politicians charge the motor vehicle and the freeways and streets that serve it with primary responsibility for such urban problems as air and noise pollution, urban sprawl, displacement of the poor and minorities from their homes, and the detoriation of the central city and close-in residential areas. Thus, where a few years ago highway agencies proceeded with their urban programs with little interference and with a feeling of certainty, they now operate in an atmosphere of confusion, uncertainty and distrust. This situation is not peculiar to transportation, for agencies charged with other public responsibilities also are being subjected to strong criticism.