is in fine condition over all classes of soil except at its extreme north end, where it was laid through the small town of Westley, largely under the direction of the local authorities as distinct from the regular organization. The procedure as laid down by Mr. Aldrich in this work for the preparation of the sub-base was as follows:

1st.

Plow the entire space across the roadway between gutters for a width of 40 feet. 2nd. Make fill with scrapers in layers of not over 6 inches.

3rd.

4th.

5th.

6th.

7th.

8th.

9th.

10th.

As fills are made the material is pulverized with a spiked roller such as was used in former days with oiled roads. The fill is then sprinkled and built up in thin layers so as to moisten the adobe but not to work it into any liquid or soft condition. The moisture in this sub-base is brought to a consistency such as is contained in the underlying deeper soils.

A ten to twelve-ton three-wheel roller follows the pulverizing and the entire forty feet of road-bed is thoroughly rolled in this manner to a uniform degree of hardness. As much attention is paid to the rolling of the shoulders as to the central portion of the road.

Header boards are all set in excavation. That is, a groove is dug in which the header board is brought to a solid condition of rest. The sub-base is then scarified to a depth of 3 inches between the header boards. The loose material is then taken out from between the boards to within a depth of 3/4 inch of subgrade.

The subgrade is then sprinkled and rolled again or not, as required.

The surface is then cut to true subgrade with a special cutting machine. No cuts in excess of 1/4-inch are permitted. Any holes that are developed in this process are scarified, filled and rolled.

The finished subgrade is then sprayed with water so it shows a sheet over its entire surface. This does not mean a standing pool of water, but rather a film of water. This sprinkling is repeated on the following day.

The subgrade is then left for five or more days to dry.

(Mr. Aldrich states that shrinkage cracks do not develop in the subgrade during this period.)

The concrete is then cast on the subgrade.

This procedure is as exacting as that required by engineers in the construction of an earthen dam. No shrinkage beneath this slab was observed. This thorough preparation of the sub-base is in contrast with other road construction jobs that were visited.

It is essential that care should be exercised in the preparation of a sub-base, otherwise no amount of detail in the preparation of the concrete slab will save the pavement.

It is surprising that with such great expenditures as have been made on highways throughout the United States so little experimental work is known of relative to the remedy for the expansion and contraction of clay foundations. Even the successful instances have not been used for the guidance of subsequent work. The efforts of the engineers of California should be untiring to find a specific remedy.

The report of the Committee on Subgrade presents numerous cases of pavements that have been laid on good and bad foundations and reference is made thereto.

The County of Los Angeles began its good road work about 1909. The traffic in this region has been very heavy and the experience of this county in the construction and maintenance of roads of various types has probably been more extended than in any other county in the State. The county authorities are now building a freight road for trucks from the city to the harbor, as follows: 8 inches of decomposed granite is rolled onto the sub-base. The slab is 24 feet wide and 8 inches thick, reinforced with No. 6 quadrangular mesh weighing 4 pounds per square foot.

In Contra Costa County a unique type of pavement is being laid composed of two separate 8-foot slabs with 4 feet of macadam pavement in the center, apparently the idea being

Typical shoulder condition on heavily traveled concrete roads.
omitted. This is severe on pavement and dangerous to traffic.

Adequate shoulder construction has been

to permit of the shifting of the base of the road without the forming of the longitudinal cracks. These slabs are 4 inches thick. Sufficient experience has not been had to demonstrate the advantage of such type of pavement. The weak point of a pavement is the edge of the slab and as this type of pavement would have four of these instead of two, it appears not to be an improvement.

The consistency of the adobe beneath the concrete slab might be maintained in a more satisfactory manner if wide shoulders of some impervious material like asphaltic concrete or oil macadam were used. These shoulders being flexible and the evaporation apparently taking place within the four outer feet of the pavement, it appears that they would substantially protect the concrete slab proper. Favorable results were obtained in Monterey and Bonita Counties in this manner. However, with a slab which is but fifteen feet wide and with a heavy traffic, the tendency is for a truck to travel with one wheel on the macadam shoulder and one on the concrete pavement, the shoulder being the weaker breaks down and is apt to shear from the slab, making a rut at the point of juncture, and to a certain extent destroying the purpose for which it was placed. This is illustrated in Photograph No. L-13-12-A on the State Highway about three miles east of Ventura. Maintenance is essential to any type of pavement.

If the concrete slab was made wider, say eighteen to twenty feet, and an impervious shoulder then placed outside of it, this adverse argument would not apply so much, as there would then be less tendency for a truck to travel partially on the shoulder. It is believed that shoulders under these conditions would nevertheless be a benefit.

Width of Pavement

California pavements are dangerously narrow. The legal width of a truck load is 8% feet or less. It is impossible for such vehicles to pass on a 15-foot pavement. The crowding of a narrow highway decreases its efficiency and is a cause of positive danger to life. On our thin pavements, the crowding of the traffic on and off the edge of the concrete slab causes it to break down. This is shown in Photograph No. 18-7. If the pavement were wider its life would be longer. California has lagged in the development of an adequate pavement to meet increasing traffic. Most of the 4-inch pavement that has been laid from the First and Second Bond Issues was composed of a 1-212-5 mixture. The present mixture is 1-2-4.

There is no economy in the construction of light pavements when the capitalized maintenance and upkeep charges are included with the first construction cost as shown by the report of the Committee on Maintenance.

Abrasion

If a concrete mixture of adequate richness is used, such as 1 cement, 2 of sand and 3 of stone, and the quality of these materials is satisfactory and workmanship of proper standard, the resulting pavement will be such that abrasion due to surface wear will be a matter which may be neglected. Even with the California pavement as well constructed abrasion is not a serious menace within the limit of the length of the life of the slab.

Tires

Pneumatic tires are less destructive to pavements than those of solid rubber. A. T. Goldbeck, Engineer of Tests of the Bureau of Public Roads, states in "Public Roads," July, 1919, that trucks with solid rubber tires, traveling at 15 miles an hour, passing over an obstruction one-quarter of an inch high will deliver a blow on the pavement equivalent to three and a half times the static load.

The results of tests made with a Packard 3-ton truck with a 4-ton load, having a total weight on each rear wheel of 7,000 pounds, of which 1,700 pounds were unsprung, are