Table No. 10

SUMMARY TRAFFIC COUNT

Tables showing numbers of overloaded trucks from approximately 2,000 observed, with the per cent of overload based on their rated capacity.

Numbers and per cent of total number of overloaded trucks

This is the first general traffic study which is available for the State highways of Southern California. Table No. 6, page 44, is a summary in which an estimate has been prepared adjusting the number of vehicles and the tonnage to a common twelve-hour basis for all observed points for purposes of comparison. It shows a wide variation in the use of these roads; Cajon Pass having 250 vehicles per twelve hours and the Los Angeles- Whittier Boulevard, at the cemeteries, having 2,800 vehicles. The Spadra Road in Fullerton, on the line of the State Highway, cannot be used in this comparison because the point of observation was in the town. There should be some relation between the volume of traffic passing over a road and the width of the road, the topography being the same. The State Highway Commission generally adopted the policy of widening the road as it approaches the larger cities and to a certain extent widening the trunk roads where the travel is heaviest, but generally speaking the standard width of 15 feet has been applied on all State highways. This widening of the road to meet traffic conditions is being met by the State Highway Commission frequently by the addition of shoulders rather than in the original design. The last column in Table No. 6 shows the tonnage passing over these respective roads. This has even greater variation, 328 tons per twelve hours having been observed on the Cajon Pass, 4,496 tons on the Whittier-Los Angeles road and 7,058 tons on the Spadra road in Fullerton, all between 6 a. m. and 6 p. m. From an engineering and practical standpoint there should be some rational relation between the tonnage on a road and the thickness of its pavement. The inspection of the present condition of Southern California roads does not show such direct relation because the life of the pavement is largely determined by the character of the foundation. If all conditions could be taken under consideration there must be some relation between the life of the road and the service to which it is put. The County of Los Angeles is taking this into consideration in the construction of its Harbor Truck Boulevard, which is to be a reinforced 8-inch slab laid on 6 inches of decomposed granite. It is proposed to build 1,798 miles of new roads under the Third Bond Issue. A large amount of the pavements on the main trunk lines of the State highways also will have to be resurfaced before many years. The roads that are designed and built in the future should take into consideration not only the condition of their foundations but the volume of traffic in determining their width and the weight of the traffic in fixing the thickness of the slab. While these dimensions must be more or less empirically determined, some such traffic study as is here presented is essential to a satisfactory formation of judgment.

An effort has been made in the report of the Committee on Maintenance to compare upkeep cost per mile and per square yard of pavement with the tonnage passing over the road. The same difficulties arise in such a study as indicated above because of variation in foundation conditions, the quality of workmanship, class and speeds at which the traffic moves. If all the facts entering into this subject were available, there should be some relation existing between the tonnage passing over the road and its annual maintenance cost per mile. The cost of a road to a community in its final and accurate analysis must be expressed in the charge per ton mile of the traffic passing over it.

Crushed edge of pavement 6 miles north of Grapevine Station, Kern County. Note the necessity of shoulders on this class of soil. This is very dangerous to traffic on narrow pavements.

Table No. 9, page 47, shows the estimated weight and overloading of approximately 2,000 trucks on the state highways at points widely distributed throughout Southern California. This is a matter of estimating and not weighing of these loads, but the observers. were checked up on approximately 500 trucks which were actually weighed and it was found that their judgment was accurate within about ten per cent, as previously noted. This table shows that twelve 1-ton trucks were overloaded 100% as compared with the manufacturer's rating. One 12-ton truck, six 2-ton trucks and three 3-ton trucks were also found overloaded 100%. These estimated weights show that the trucks traveling at remote and scattered points throughout the country are following much the same practice of overloading that was found to be the case with the trucks weighed in the City of Los Angeles on standard scales. The owners of the trucks seem to be perfectly willing to overload their vehicles when they have good pavements to travel on, disregarding both the recommendations of the manufacturers and the state laws.

Los Angeles County Road Department's Traffic Count on County Roads

The Los Angeles County Road Department has kept a count of traffic passing over the principal paved roads of the County since 1914. It was made in four six-hour shifts divided over the twenty-four hours of each day, and each six-hour shift was taken for seven continuous days. The results thus obtained were totaled to show the average of seven continuous days of traffic over the road. The counts were taken in hour periods, in order to determine the fluctuations of traffic during the day.

The results of the Road Department's count is indicated below, showing travel of automobiles and motor trucks over the following roads:

Slauson Ave. at Santa Fe Ave.

Washington Blvd. at City Limits.
Compton Ave. at Slauson Ave.

Valley Blvd. or Telegraph Road at Downey.

Monterey Pass at Metallic Brick Company's Yd.

El Monte Road at El Monte Bridge.

Long Beach Blvd. at City Limits.
Harbor Blvd. at City Limits.

As noted on page 42, the results of County Census were used to complete the State Highway census.

A table has been made from this data showing the relation between the travel during the night hours and that during the day hours, which follows:

The night automobile traffic is 38% of the day traffic and the night truck traffic is 21% of the day traffic between the hours indicated. These average figures applied to the twelve hour counts taken on the state highways in Table No. 7, page 45, gives the total tonnage carried by these state highway routes for twenty-four hours.

AUTOMOBILE AND TRUCK CENSUS CITY OF LOS ANGELES

As a matter of general interest, bearing on automobile traffic over various highways, the following results of a study of vehicles entering and leaving the City of Los Angeles are attached. An actual count of all autos and trucks entering and leaving the city was made, covering the daylight period from 8 a. m. to 6 p. m., June 28, 29 and 30, 1920. Observations were taken at fifteen selected stations on the main arteries of traffic.

In the table below and on the chart (next page) these stations are grouped together in four groups, as indicated. The figures show the hourly flow of traffic averaged for the three days. This count was made for the Automobile Club of Southern California.

On the accompanying Map No. 2, page 52, are indicated the points of observation. The purpose of the traffic count on the main highways entering Los Angeles, as shown in Table No. 12, page 51, which was made on week days, was to determine how many of the vehicles approaching the city passed through it to points beyond and how many had the city itself as their destination. The registration number of each car was taken and the direction of its movement. A detailed study was then made to determine how many of these cars approaching the city passed out of it to points beyond. The prime purpose was to find whether the congestion of the traffic in the city could be relieved substantially by construction of good roads around its perimeter in such a way as to not only relieve congestion in the city itself but to facilitate and expedite the suburban traffic. The results show that but three per cent of the machines entering the city pass beyond it immediately. Therefore, 97% of all these machines were coming into the city to transact business. The deduction is plain that the relief of the downtown congestion must come from the improvement of the street system in and around the business district.

This investigation was conducted by the Automobile Club of Southern California. It has been made the subject of a detailed report to that organization with recommendations for the development of a belt line system of streets around the congested district.