WEIGHING OF TRUCKS ON PUBLIC SCALES IN CITY OF LOS ANGELES

From August 18, to August 20, and again from September 3 to September 8, men were stationed at the Licensed Public Scales of the Los Angeles Ice & Cold Storage Company at Fourth and Central Streets, and of the Los Angeles Hay Market on North Los Angeles Street, near the Plaza. These men were instructed to get the following data regarding all trucks weighed :

In addition to this data, several weigh-masters in the county were asked to co-operate by sending in weights for various sizes of trucks weighed on their scales.

The object in mind was to get data regarding the average and maximum loads carried by trucks by actual measurements, and also as a comparison with estimated loadings being made on the highways in all parts of this region. Tables by the Engineers taking traffic census give the information collected.

During this time, data was taken on 472 trucks and 117 trailers. 454 of the trucks and all of the trailers had solid rubber tires on the rear wheels.

Table No. 13, page 55, shows the maximum and average loads carried by the various sizes of trucks. It is very important to notice that the average loads carried exceed in every case the rated capacity, and as for maximum a 3-ton truck carried 19,570 pounds gross (9.7 tons), which was 6.28 tons or 2.79 times the load it was designed to carry.

The above table also shows the maximum and average load concentration of one rear wheel on approximately 500 trucks. This diagram should be of value in future design of road

ways.

Tables Nos. 13 and 14, pages 55-56, show, in addition to the average and maximum loads carried, the percentages loaded under capacity, capacity, capacity to 1-ton overload, 1 to 2 tons overload, 2 to 3 tons overload, 3 to 4 tons overload, and greater than 4 tons overload, the average and maximum rear wheel loads, the percentage of trucks measured using county or state roads, and percentage of various loads carried.

Violation of State Law Regarding Loads per Inch of Tire Width as Fixed by the Motor Vehicle Act

Table No. 15, page 56, gives data concerning the load on the pavement per inch width of tire. Violations of the State Law regarding allowable load per inch width of tire were found to be very numerous, ranging from 46% for 1/2-ton trucks up to 84% for 4-ton trucks. The weight of a truck and its load is unevenly distributed to the front and rear wheels, and thereby to the pavement. In this study 75% of the gross load is considered as being applied to the pavement by the two rear wheels. This percentage is used by tire manufacturers in computing size of tires for various capacities of trucks. This proportion is also checked by use of loadometers which are devices for measuring weights of trucks at any place.

The State Law says, "No motor or other vehicle. . . . shall be operated or moved upon or over any public highway or bridge, the weight of which resting upon the surface of said highway or bridge exceeds 800 lbs. upon any inch width of tire . . . ." The widths of tire measured in the observations were taken at the top of the tire, and not at the base, so that these widths are not those given by the manufacturer. They were also taken at a point on the tire not under compression at the time. From tests made by a large tire manufacturer on the spread of a

new 10" solid tire under capacity loading, it is shown that the increase in width is about 15%. Since the tires measured were, in most cases, more or less worn down, and since the resiliency of a tire decreases with the increase in the percentage worn, the percentage of spreading would be considerably less than 15%, and is therefore neglected.

Table No. 15, page 56, gives data on the condition and use of tires found on the trucks weighed.

From the above tables it can be seen that even the average loads per inch width of rear tire exceed in every case that allowed by the law, and maximum loads in several cases exceed double that allowed by the law. Of the trucks overloaded above 800 lbs. per inch of tread, it is found that the average overload ranges from 109 lbs. per inch width tire for a 3-ton truck to 345 lbs. per inch width of tire for a 31⁄2-ton truck, while the maximum overload per inch of tire width was 1,040 lbs. on a 5-ton truck. In addition to this flagrant violation of the State Law, it was found that quite a few of the trucks carried poor tires, reaching a maximum of 41% in the case of the 5-ton trucks.

These violations cannot properly be laid at the door of the truck manufacturer who has outfitted the car with a size of tire which, according to standards adopted by the Society of Automotive Engineers, is adequate for its rated capacity. Any departure from this rating in the direction of overload can be blamed on the owner and operator, and in some cases to the truck dealer. For example, the advertisement of the work of a 2-ton truck with an 8-ton load on it. This latter fact is responsible for a great deal of the deliberate overloading by the operator. The overloading reflects directly upon the condition of the tires, breaking down and crystallizing the rubber, and thus adds to the destruction of the surface of the road. Excessive speeding will also break down the tire by overheating it, and in some cases causing it to blow up. Diagram No. 4, page 57, shows total truck tonnage and average weights per truck, the upper half being 1,256 trucks weighed, and the lower half for 2,004 truck loads estimated by census takers.

Diagram No. 5, page 58, graphically illustrates the average weight of empty and loaded

trucks.

Table No. 13

14.

Maximum concentration of load-1 rear wheel.

4275

5159

8062

9438

8925

10960

10075

11280

Table No. 14

DATA COLLECTED REGARDING OVERLOADS CARRIED BY TRUCKS WEIGHED ON PUBLIC SCALES IN LOS ANGELES

DATA COLLECTED REGARDING TIRE LOADS ON APPROXIMATELY 500 TRUCKS WEIGHED IN THE CITY OF LOS ANGELES. TIRE WIDTHS BASED ON WEARING SURFACE OF TIRE. LOADS FIGURED AS 75% ON REAR WHEELS