The The Leading Municipal Magazine $4 a Year Every issue of THE AMERICAN CITY contains valuable articles contributed_by authorities in their respective fields. The all-important topics of city planning, traffic control, zoning, water supply, sewers, sewerage and sewage disposal, waşte collection and disposal, street lighting, municipal ownership, legal tangles, new methods, materials and equipment, are discussed each month. Our Catalog Department maintains a distinctive service and is always ready to see that you receive promptly the catalogs you wish from any manufacturer of materials or equipment used by any city department. Service always has been and always will be the ideal of THE AMERICAN CITY, which is published in the interests of city and county officials and helps them through its editorial pages, through cor respondence with subscribers and through the Catalog Department to improve methods of administration and construction. 443 Fourth Ave., New York City Tribune Tower, Chicago, Illinois REPAIR COSTS OF CITY PAVEMENTS By R. H. Simpson, Chief Engineer, Division of Engineering and Construction, Department of Public Service, Columbus, Ohio During the past few years there has been considerable investigation and research work carried on by various agencies for the ultimate purpose of determining improved methods of design and construction of roads and pavements. The greater part of these investigations has consisted of a study of the behavior of pavements that were constructed especially for the purpose of testing them under known traffic conditions. The conclusions reached have given us information of value, relative to the required strength of pavements to resist the strains produced by moving loads, but they do not tell the whole story of pavement wear or weakness, because they do not take into consideration all of the factors that enter into the life and wear of pavements, such as the continuing action of the sun, rain, snow, ice, frost, etc., each of which acts differently on different types. While the contributions to the literature on the general subject of roads and pavements has been rather voluminous it is quite astonishing that so little is known, or so little has been published on the subject of wear or of maintenance cost. Surely these are important considerations, for to determine the economic pavement we must know not only the first cost but the ultimate cost. It is true, of course, that many figures on the cost of main tenance of roads are published in the reports of various highway departments, but they are usually given in terms of cost per mile, and include a lot of miscellaneous work other than the actual repairs to the pavement, and therefore it is impossible to make any comparisons. There are also occasional reports made on repair costs of city pavements. These are also usually given in such terms that it is difficult to form a basis. for definite conclusions and comparisons. For instance, we frequently see a report from some city that the cost of maintaining a certain type of pavement for a certain year was two cents per yard and that the cost for another type during the same year was two and one-half cents per yard, and the inference is that the latter is the more expensive type from the standpoint of maintenance, which may or may not be true. This information is usually misleading unless other factors affecting the cost are stated, such as the relative age of the pavements and the character and volume of traffic carried. To illustrate how misleading data of this kind may be, it may be stated that during the year 1924 there was expended on the 3.900,000 square yards of brick pavements in Columbus about $90,000.00, or $0.023 per yard, and on 1,800,000 square yards of asphalt pavements about $19,000.000, or $0.011 per yard. This would indicate that the repair cost for brick pavements is more than twice as much as for asphalt pavements, which is not true, the greater cost for brick being due, in part, to the fact that the average age of the brick pavements is greater than that of the asphalt. I think we may all agree that as a pavement becomes older it will cost more for maintenance and that unless we know the age of a pavement or something of the traffic it carries the repair cost does not mean much and is misleading. On the data presented herein the repair costs will be given in terms of the age of the pavement and the analysis will show costs compared for light and heavy traffic. In order that you may know something about the character of the pavements under discussion, it will be well to give briefly a few facts about their construction and maintenance. Prior to 1900 the asphalt pavements in Columbus were laid on a six-inch natural cement concrete base, except for a few improvements, where old boulder pavements were resurfaced with asphalt. Subsequent to 1900 a Portland cement base six inches in thickness has been used. During the first few years the concrete mixture consisted of one part cement, four parts sand and eight parts crushed stone or crushed gravel. This mixture has been strengthened from time to time and for the past twelve years the proportions have been one part cement, two and one-half parts sand and five parts stone. The thickness of foundation has remained at six inches. Subsequent to 1900 the use of subdrains along each curb line has been standard practice. During the past twelve years about 175,000 square yards of asphalt has been laid over old brick pavements. The asphalt mixture has followed standard practice in sand grading and has contained from ten to eleven per cent bitumen. About 82 per cent of the yardage is Trinidad Lake Asphalt and 18 per cent oil asphalt. On most of the improvements the wearing surface has been one and one-half inches of sheet asphalt laid on one and one-half inches of binder. During the past ten years, however, a two-inch sheet asphalt top has been used almost exclusively on heavy traffic streets. Prior to 1900 the brick pavements were laid on a macadam base, the joints in most cases being filled with coal tar pitch. Subsequent to 1900 the base has been the same as described for asphalt pavements. Between 1900 and 1910 pitch was used almost exclusively for the filler. From 1910 to 1915 a cement filler was used on a considerable portion of the pavements. Since 1915 asphalt filler has been used almost exclusively. Both shale and clay brick have been used and since 1900 the standard rattler test has been required on all construction. Practically all of the repair on asphalt pavements has been done by the "cut out" method. Surface heaters have rarely been used. Prior to 1907 the asphalt repairs were made by contract, the repaired area being measured and payments made on a unit price basis. Since 1907 all repair work has been done by city forces. To ascertain the cost of repairs of asphalt pavements, the repaired area is measured and recorded at the time the repair is made, but the unit cost to be applied is determined at the end of the season's work, by dividing the total expense for the year, including labor, material, supplies, repairs to equipment and plant, a charge for use of plant, superintendence, etc., by the total yardage of repair made. This gives a unit cost to apply to each pavement and a total for same that is not influenced by the location of the pavement nor its distance from the plant. A more rational comparison between pavements is thus obtained than if the actual repair cost of each particular improvement was used. The repairs to brick and block pavements is handled by small crews furnished with the necessary supplies, tools and equipment for such work. These crews are supervised by a general foreman who measures all repaired areas. In the case of brick and block pavements the actual cost of the work in each particular improvement is recorded as the work progresses, to which is added 15 per cent to cover the cost of handling materials at the yards, the repairs to tools and equipment, superintendence, etc. The maintenance of all pavemetns in Columbus always has been under the direction of the Chief Engineer of the Service. Department, and in direct charge of two deputy engineers— one on asphalt repairs and the other on other types. A record of the repair costs has been kept for many years past. In the case of asphalt the record is complete for all pavements constructed since 1888, and for brick and other types those constructed since 1900. The work of tabulating and classifying the figures has been completed for all asphalt and brick pavements, about 1000 separate improvements, totaling 5,700,000 square yards, of which 1,800,000 square yards are asphalt and 3,900,000 square yards brick. At the end of the year the repair costs for all pavements are recorded on cards prepared for the purpose, one side showing the construction data and the reverse side the maintenance. Figure C shows the card used. It will be noted that the maintenance data consists of the area of the improvement; the area repaired each year; repair cost each year; the unit cost in terms of total area; the cost per yard per year, and the total cost to date or accumulated cost. The cost per yard per year is really the service test of a pavement and gives a more rational comparison between two or more pavements than if the actual cost at each age period is used, as the latter is usually erratic because of the influence of shortage of repair funds in some years. The cost per yard per year is the average yearly cost of repairs for the period under consideration. It is obtained. by dividing the total cost of repairs for the given number of |