Table No. 4

TABLE SHOWING CONSTRUCTION AND MAINTENANCE COSTS OF VARIOUS OIL MACADAM HIGHWAYS

Remarks:

Table No. 4, page 38, shows costs and maintenance of various oiled macadam roads built and partly maintained by several counties. The original cost is generally higher than concrete roads since they are usually thicker and wider.

The following costs apply to typical Reconstruction jobs. The California Highway Commission's designation of this class of work is "Resurfacing and Widening" and "New Pavement on top old base." In this report the above items are included in reconstruction or upkeep and are considered as maintenance costs. Twenty per cent has been added to the figures furnished by the State.

*The last item in the above is for original Willite pavement laid on the desert east of Holtville, and reflects high material costs as some of the aggregates used were for experimental purposes and hauled long distances.

With a given width of pavement the cost per mile of construction for a concrete slab is not in direct proportion to its thickness. The preparation of the road-bed and the subgrade is the same. The cost of buying and placing the equipment for the construction work is also much the same. Surveys, supervision and overhead are practically alike. The increased cost would vary rather directly with the volume of the materials used in the slab. Satisfactory data on these comparative costs for California roads is not available. Table No. 3, page 37, however shows that 160.35 miles of pavement, 4 inches thick and 15 feet wide, were built by the State in flat country in Southern California at a cost for grading and paving of $12,343.00 per mile between the years 1914 and 1917. Another item shows that 43.75 miles of pavement, 4 inches thick and 18 feet wide, were built by the State during the same period in flat country in Southern California at a cost for grading and pavement of $10,858.00 per mile. Orange County built 137 miles of pavement between the years 1914 and 1919, in flat country, 49 miles of which was 16 feet wide, 76 miles 18 feet wide, and 13 miles 20 feet wide, all 4 inches thick, for $9,267.00 per mile. Los Angeles County built 13.2 miles of pavement, 5 inches thick and 20 feet wide, in 1916, in flat to rolling country, for $13,700.00 per mile, and again on another job 12.8 miles of the same dimensions, between the years 1914 and 1917, in flat country, for $17,820.00 per mile, these figures all being for both grading and pavement.

Table No. 3 shows that on State work in flat country during the same years there is little difference between the cost of pavement 15 feet wide and 18 feet wide, both having the same thick

ness.

The following information has been obtained on this subject for certain roads in the State of Washington: On April 22, 1920, three bids were offered in Pierce County, Washington, upon concrete pavement, both 6 and 7 inches thick. They were as follows:

6-inch pavement, per square yard...

7-inch pavement, per square yard..

$1.88
2.01

$2.20
2.40

$1.90 $2.10
1.90 2.20

$2.30
2.41

On another job in the same county on November 28, 1919, the following bids were received: 6-inch pavement, per square yard... 7-inch pavement, per square yard...

.$1.87
2.00

$2.30

2.41

In the city of Seattle three bids were received on pavements 7 and 8 inches thick, as follows:

7-inch pavement, per square yard...
8-inch pavement, per square yard.

.$2.25 $2.34
2.50 2.59

$2.40
2.60

In the same city on March 21, 1919, three bids were presented for building pavements 6, 7 and 8 inches thick, as follows:

In the first piece of work referred to, the rate per inch of thickness per square yard under the low bid was approximately 31c per inch thickness for the 6-inch pavement, whereas the 7-inch pavement cost less than half that rate for the additional inch, to-wit: 13c. The same condition prevailed in the second job noted. In the bid for the City of Seattle, the 6-inch pavement cost approximately 31c per inch thickness per square yard, whereas the 7-inch thickness cost approximately the same rate, and the 8-inch thickness a cent less. The county bids on the basis of a pavement 16 feet in width show a difference in cost between the 6 and 7-inch pavements of approximately $1,220.00 per mile. The 6-inch pavement on the same job cost at the rate of $11.28 per cubic yard, whereas the 7-inch pavement cost $10.33 per cubic yard, or approximately 10 per cent less per cubic yard. In the City of Seattle the 7-inch pavement cost at the rate of $11.57 per cubic yard and the 8-inch pavement $11.25 per cubic yard, or a less difference in price per cubic yard than the difference in price between the 6 and 7-inch pavement, showing that the difference in rate bid per square yard is more apparent on the thinner sections than on those that are thicker. It follows that a much greater difference in cost per cubic yard will occur when the comparisons are made between pavements 4 inches thick and 6 or 8 inches thick.

TRAFFIC CENSUS OF STATE HIGHWAYS

A traffic census of the State highways coming within the scope of this report was made during the month of August, 1920. The passenger travel during this month is probably at its peak in that summer outings are being enjoyed. The number of trucks generally traveling throughout this section of the State is probably not as heavy during August as in September and October, or during the months of harvesting our principal crops. On the other hand, there was a great deal of hay and grain and miscellaneous loads, so that taking the month of August as a whole, the vehicular traffic will probably represent a normal condition. Two men with suitable blanks were sent to designated points which were considered as representative of the sections under investigation. Generally a census was taken from 6 a. m. to 7 p. m., but in several cases a twenty-four hour count was made. Passenger automobiles were divided into two classes, light and heavy. The weight of a modern Cadillac 7-passenger touring car, 4,000 pounds, was taken as the dividing line between the two classes. The heavy class includes auto busses. It was estimated that the light class of automobiles carried an average of three passengers and baggage equivalent to one more passenger; and that the heavy cars carried an average of six passengers, with baggage equivalent to one more passenger. This estimate of passengers carried is borne out by the observation of 1,640 light cars and 466 heavy cars, supplementing the census.

Trucks were also counted and classified according to their rated capacity, varying from a one-ton truck, or the usual Ford type, to the heaviest truck operating at the present time of 71-ton capacity. The loads and rated capacities of these were estimated by the observers. Some practice was taken by them and very often their estimates were checked with the actual

18-1 Loaded trucks on Ridge Road, Los Angeles County. One of the causes of wrecked pavements. is gross disregard of law relative to both loads and speed of trucks.

Thero

Excessive irregular cracking and crushing down of pavement mile 3.0 north of Forest Reserve Inn, "Ridge

weights. It was found that they were within 10 per cent of correct in all cases. A truck passing was counted and classified according to its rated capacity, and also according to the load it was carrying. If trucks were pulling trailers, this fact was recorded and also the weight of the load on the trailer.

The detailed results of this census will be found on pages 42 to 65, inclusive. Page 44 is a diagram and summary for a common twelve-hour period for the purposes of comparison of traffic. Page 45 is a tabulation of traffic count and tonnage expanded from traffic observed during the hours as indicated on the several station sheets to a twenty-four hour period. The expansion of the observed traffic was accomplished by the use of the traffic census as found by Los Angeles County. See page 50.

Thirteen different points on State highways were selected, one point on a county road and two points on city streets, to give a comparison of the traffic over these roads with the State highway. The sixteen points at which traffic was observed are as follows:

Page 46 is a diagram of summary traffic count in tonnages showing number of tons per hour per foot of traveled road and maximum loads. The zone of travel was obtained by observation of where it generally is in relation to the center line of the road. This table also shows maximum single gross loads on four wheels.

Page 47 shows diagrammatically number of loaded, empty, partially loaded, capacity loaded and overloaded trucks with the average and maximum overload in tons.

On page 48 is a summary showing numbers of overloaded trucks with the percentage of overload.

In this traffic count some two thousand trucks were observed and it is pleasing to note that the estimated weights were in fair agreement with those determined by actual weighing.