surfacing is required has been found in New York State to be 7 years. The concrete pavements referred to are 8 inches in thickness at center and 6 inches at edge.

J. N. Mackall, Chief Engineer of the Maryland Highway Commission, in the Engineering News Record of May 6, 1920, page 914, states that in his opinion 10 years may be taken as the life of a concrete pavement under heavy traffic and from 15 to 20 years for the light traffic pavements. The Maryland concrete pavements are 8 inches thick at the center and 6 inches at edge.

In view of the above, 15 years has been taken as the average life of the California 4-inch concrete pavements. Where subjected to the same conditions, the various county concrete pavements are found to be in much the same condition as the state pavements.

The life of a bituminous pavement, and by such is meant all pavements in which bitumen is used as the binder, is indeterminate in that it may be resurfaced, or scarified and renewed at any period and thus maintain the essential qualities of the pavement.

A concrete pavement has reached the limit of its life as such when it becomes necessary to patch its surface due to deterioration.

A worn out concrete pavement, surfaced with a bituminous mixture has to a large extent lost its characteristic as a rigid pavement and may be classed as non-rigid. It is upon the above assumption as to life that deductions beyond the year 1920 are made.

In considering the cost of maintaining the state highways in Southern California, all expenditures of whatever nature, excepting the first application of 3-inch oil surfacing, made after the final acceptance of the road by the Commission, are classed as Maintenance and Upkeep. Many expenditures have been made which are for additions and betterments. They are all necessary for the continued use of the road and constitute an annual expense that is practically continuous in its occurrence. Illustrating this point, on the Ventura Road a storm drain. was constructed in 1919 at a cost of $9,319.00. This may not be strictly speaking a Maintenance charge but it represents a cost which will recur throughout the system. Had it not been built the probability is that a much larger sum would have had to be expended in replacing embankment and washed out pavement.

Much difference in opinion exists relative to the classification of the various expenses incurred in the upkeep of pavements. However, in this study consideration must be given to the sources from which revenues are obtained. The original construction is financed from the sale of bonds which bear an annual interest and are retired at given periods. The revenue for upkeep is provided from direct tax. Any reconstruction work charged to the construction fund would, therefore, incur fixed charges.

It was expected that the general maintenance charge would be a constantly increasing figure. This, however, is found to vary, partly due to storm damage and largely with the amount of money available. The section of road west of Universal City, designated as L. A. 2-A, was opened to traffic in January, 1914. During the period 1914 to 1919 inclusive the General Maintenance Charge proper was as follows: 1914-$500.00; 1915-$1,028.00; 1916—$2,280.00; 1917-$857.00; 1918-$836.00; 1919-$2,478.00, exclusive of overhead.

In the early part of 1920, 5.23 miles of this section were rebuilt at a total expense of $74,751.00 or an average of $14,293.00 per mile. During the first half of 1920 the General Maintenance on this section (6.55 miles) has been $209.00 or at the rate of $418.00 per year. Probably the larger part of this expense has been incurred on the remaining portion of the original. road, viz., 1.32 miles.

That portion of the State Highway leading from San Fernando to Pasadena, a length of 15 miles, was built under two separate contracts. The first 4.90 miles was opened to traffic in March, 1916. The second portion in January, 1919. The general maintenance, exclusive of overhead, of this road has been as follows: 1916-$139.00; 1917-$264.00; 1918-$416.00; 1919— $704.00; to July, 1920-$666.00. This shows a steadily increasing maintenance charge over the

Longitudinal cracks through cut, mile 11.2 north of Castaic School, "Ridge Route," Los Angeles County. This pavement is but one year old and was built on a road-bed four years old. The probable explanation is poor concrete.

period. For an average weighted age of 2.35 years this upkeep cost has been $62.00 per year mile. This is one of the light traffic roads on good soil. It is expected that its life as a concrete road will be much longer than that of the heavy duty roads.

One of the first roads built in Southern California by the State is just north of the city limits of San Diego, designated as San Diego 2-A. This road was opened to traffic in the latter part of the year 1913. The maintenance by year on this 8.58 miles has been as follows: 1914$192.00; 1915-$3,092.00; 1916-$4,256.00; 1917-$1,537.00; 1918-$2,275.00; 1919-$1,653.00; first half of 1920-$839.00. This section has had an average age of 7.40 years and is classed as 1.2 miles good, 4.2 miles fair and 3 miles poor in 1920.

The annual upkeep costs on oil macadam pavements are more constant. A slight increase is noted at stated intervals, occasioned by renewal of wearing surface.

If upkeep costs had been found to increase in a somewhat uniform ratio, the economic life of a given road could be readily determined.

The general maintenance charges for state roads have been assembled for purposes of study and comparison from data furnished by the Highway Commission, twenty per cent having been added to cover overhead, undistributed charges, repair to equipment, etc., by this authority. No item has been included covering maintenance grounds and buildings. If modifications of results are to be made it will probably increase the totals. These items include only that class of upkeep work known as General Maintenance, such as is usually done by the regular repair crews stationed on a section, making minor repairs to concrete base, and oil surface, replacing guard rail, mowing weeds, grading in shoulders, ditching, etc. There is shown an average annual expenditure for this class of work for 626 miles (including Inyo County) of $285.00 per mile or $0.0315 per sq. yd. for an average weighted age of 4.45 years. Deducting 78 miles, which includes mountain roads maintained for a period as oiled dirt roads, 12 miles of timber trestles in Ventura County and the plank road, an average of $235.00 per mile or $0.0263 per sq. yd. per year is obtained for an average weighted age of 4.38 years. The maintenance annually for the 78 miles is $598.00 per mile and $0.0607 per sq. yd. per year for an average weighted age of 4.94 years.

Similar maintenance cost on 26.09 miles of 5" concrete roads built by Los Angeles County and 8.67 miles of 4" concrete road built by San Bernardino County, including overhead and incidentals, indicates an annual cost for 34.76 miles of $138.00 a mile or $0.0122 per sq. yd. for an average weighted age of 3.28 years.

The tonnage carried by these county concrete roads is much less than for state roads and the average age is also less.

The expenditure for maintenance and upkeep for the 626 miles of state roads from 1912 to July, 1920, including reconstruction, resurfacing and widening, per mile year, to July, 1920, has been $615.00 or $0.0678 a sq. yd. for an average weighted age of 4.45 years. Adding to this average annual interest and bond retirement payments on a total first cost of $11,340,408, gives an average annual total charge of $1,353.00 per mile or $0.149 per sq. yd. This is summarized as follows: General maintenance $285.00; reconstruction $175.00; resurfacing and widening $155.00; average interest $390.00; average retirement fund $348.00; total $1,353.00, all per year mile.

The various items of maintenance for 96.75 miles of oiled macadam pavements built by Los Angeles County, including overhead and all items chargeable to maintenance, for an average weighted age of 7.88 years, have been annually: For reconstruction, $121.00 per mile or $0.0098 sq. yd.; widening and resurfacing, $380.00 per mile, or $0.0315 sq. yd.; general maintenance, $382.00 per mile or $0.0314 sq. yd.; total for upkeep $883.00 per mile or $0.0727 sq. yd. Adding average annual interest and bond retirement payments on 40-year serial bonds gives a total charge of $1,611.00 a mile or $0.1337 a sq. yd. per annum.

Maintenance and upkeep cost for 137 miles of Orange County concrete roads, for an average weighted age of 4.16 years, has been $164.00 per year mile or $0.0160 sq. yd. year. This includes overhead. Several miles of these roads will be surfaced in the near future. The following comparative data has been compiled:

The upkeep for Los Angeles County oil macadam roads is as follows:

The average total cost, including fixed charges per mile of the oil macadam pavements, is greater, while the square yard cost is less than the corresponding figures for the State concrete roads. This is due to the greater width of the macadam roads and the lesser first cost on which fixed costs are based.

The average first cost per mile for 626 miles of State concrete roads has been $18,097.00 against an average cost of $14,374.00 per mile for the 96.75 miles of macadam roads.

The total bond issues out of which the 626 miles of state roads have been built will be retired in 1962, while the County issue will be retired in 1949. The fixed charges on the State roads which amount to $738.00 per year mile will continue to 1962. This same fixed charge on the Los Angeles County macadam roads amounts to $728.00 per year mile and will continue to 1949.

The average annual tonnage for 502.22 miles of State roads has been 634,000 tons against an average annual tonnage for 107.39 miles of macadam roads of 1,230,000 tons. Expressed in ton miles for upkeep, exclusive of fixed charges, this is $0.00129 for State concrete roads and $0.00072 for county oil macadam.

The upkeep costs per ton mile are not in direct proportion to tonnage carried. In San Bernardino County, State Route 9 Section A, the tonnage is 876,000 tons per year. Expressed in ton miles upkeep this is $0.00029. Kern 2-F, a State concrete road, shows a ton mile upkeep charge of $0.00129 for an annual tonnage of 565,750. The average age in each case is approximately the same. Adjacent sections carrying the same tonnage show widely different

costs.

The Foothill Boulevard, an oil macadam pavement, carrying the same annual tonnage as San Bernardino 9-A, cost $0.00034 per ton mile for upkeep for an average age of 8.00 years. The Whittier oil macadam road over the same period has carried 2,153,500 tons at an annual upkeep charge of $0.00029 per ton mile.

The El Monte oil macadam boulevard over a 7-year period has carried 1,657,100 tons per year at an annual cost of $0.00099 ton mile.