such great waste of money in past years on the bridges on rural roads that the highway departments of most states have prepared standard plans and specifications which cover most needs of local road officials, and similar standards have been prepared by the United States Office of Public Roads and Rural Engineering. Structures of this character should only be built under competent engineering supervision, both as to substructures and superstructures. There is an unfortunate tendency on the part of highway commissions to endeavor to save money by omitting desirable precautions such as piling, which insure the safety of the bridges under conditions which an engineer recognizes as dangerous. For example, an unusually heavy rainfall in northeastern Iowa in June, 1916, washed out 163 bridges. Some were old structures that needed replacing at an early date, but others were expensive new structures of good design and construction except for the fatal omission of the piling under the foundations which was recommended by the engineers but left out to reduce the cost. Not a bridge built according to the standards of the State highway commission was damaged.

There are many bridges which have been in service for a long period of time without suffering any injury, although their substructures are in streams with an easily eroded bottom and banks. For example, the Walhouding aqueduct on the Ohio canal system, built about 1830, has four piers and two abutments in a stream with a fairly swift current, rising suddenly to a great height. Both its banks and bed near the aqueduct are rapidly eroded unless protected. The piers and abutments rest on double platforms of hewn timbers, laid crosswise and carried by piles driven close together near all four sides of each base. Brush and heavy stone were placed on the river bed around each foundation and a row of strong piles was driven across the river bed just below the aqueduct to prevent the removal of the brush and stones by the current. Such a record of endurance made by structures built before the beginning of the present era of scientific engineering shows how needless are most of the washouts of expensive bridges that occur every year.

As bridges on improved roads should be permanent structures, they should be designed to carry a heavy roller followed by a trailer loaded with coal. A bridge capable of supporting a 15-ton roller will carry any of the heaviest field guns now used in Europe.

Money is saved by having the plans and specifications for bridges of reinforced concrete or steel prepared by an experienced engineer, so that all bidders on its construction will base their estimates on the same structure and that structure will be adapted to the locality and service. If each bidder must prepare

his own plans, the expense of doing so is added to the cost of the fabrication of the steel and the erection of the structure. This makes a general increase in the cost of bridges in a district where the practice is followed, for many unsatisfactory plans must be prepared for one that is satisfactory. Furthermore the commission awarding the contract must not only pick out the lowest bidder but also decide which is the best plan, which may not be that offered at the lowest price.

In level country where a stream overflows its banks during heavy floods and bridges above the flood level require long expensive approaches, what are known as overflow bridges are coming into quite extensive use. They are structures designed to be submerged by the floods and to offer as little obstruction as possible to the water passing over them. If the floods are likely to carry large quantities of brush, the bridges are kept particularly low so the brush will pass freely over them when they are submerged. The roads leading to a number of such bridges have concrete pavements extending to the limits of the submerged areas, for earth, gravel and broken stone roads are liable to serious injury from water flowing across them. As the injury to overflowed embankments generally starts at the top of the downstream slope, the latter is often protected against scouring by covering it with heavy stone. Stone with rounded edges is less suitable for this purpose than stone of an angular shape, because the former is rolled about more easily.

Fords

Where money is limited, the cost of building even a submerged bridge is heavy, and the stream to be crossed is shallow, a ford is sometimes constructed as a serviceable temporary expedient. In Washington County, Utah, for example, there is a stream with a sandy bottom which is dry at some seasons and dangerous during floods on account of the treacherous nature of the wet sand. A ford has been constructed which consists of two rubble walls 4 feet deep and 2 feet wide, with a 2-foot rubble fill between them. The entire width of this rubble fill from one wall to the other is 20 feet, and the stones of which it is made were laid in a dense mixture of sand and clay, which is not easily washed out of the voids between the stones. The upstream wall was laid dry but had 16 inches of clay puddled against the entire depth of its outer face. The downstream wall was laid in lime mortar.

Near Shelbyville, Tennessee, fords have been made passable at all times by constructing a number of parallel culverts close together to carry the usual flow of the stream and building a concrete roadway over these culverts to give a safe footing for horses and a secure roadway for automobiles during high-water when the roadway is submerged.

EARTH AND SAND-CLAY ROADS1

As a very large proportion of our country roads must be earth roads for many years and the basis for any type of surfaced highway is a properly located, drained and graded earth road, the relative importance of this type is very great. If earth roads were properly constructed and maintained, and their culverts and bridges were permanent structures, a large part of the road taxes now wasted would produce useful returns. It is proper for both highway commissions and engineers to devote a large part of their time and money to the improvement of the main roads which are of service to the largest number of taxpayers, but there is a deplorable lack of efficiency in the care of the local dirt roads in many parts of the country. In some States, of which New York, Illinois and Iowa are examples, these roads are under some supervision, directly or indirectly, by the State highway department, but generally the local authorities do as they please. For instance, in 1916 there were 71,000 miles of roads in Wisconsin in sole charge of local officials, who spent about $4,500,000 on them. The work was subdivided among nearly 13,000 road districts, each with a road supervisor, and there were 3750 members of town boards with general control over road work. Of these 16,750 officials, about one-fifth drop out of office annually. During the ten years ending December 31, 1916, nearly 50,000 men were in charge of local road work and over $40,000,000 spent by them, with few perceptible lasting improvements. A system giving such results is manifestly wrong, and should be replaced by one with a smaller number of road officials having greater authority and responsibilities and serving longer terms. It will seem from the following notes that the construction and maintenance of earth roads calls for executive ability and skill that cannot be obtained unless fair permanence in office is assured.

The construction of earth roads falls into two general classes, that where there are cuts and fills and that where the road is formed by building a low embankment on the surface. Except where the length of road is great enough to use elevating graders with economy, these two classes are generally built by different methods.

1 Revised by W. S. Keller, State Highway Engineer of Alabama.

Cuts and Fills

In grubbing roots and breaking hard ground to a shallow depth, a rooter plow is often used, which is a heavy type of subsoil plow made for the purpose. The road plow is a heavy form of turning plow used in hard ground where the cuts are shallow. Either type is drawn by four to eight horses or a tractor. Plows are also specially made for pushing soil already loosened from ditches toward the center of the road.

When the cut is more than a few feet in depth and the material loosened with difficulty, it is often blasted. The fastest and most economical method of doing this is to sink holes across the cut on a line back from the face a distance about one-fourth greater than the depth of the cut and about the same distance apart. When the cut is 6 feet or more deep, the line of holes is kept about 6 feet from the face and the holes are sunk about 6 feet apart. They are loaded with a low-strength explosive and care must be taken not to loosen the ground below the finished grade line. The use of explosives in road grading in other material than rock has been extending rapidly on account of its low cost and the rapid progress that can be made under suitable conditions, for the blasts leave the clay or hardpan in a broken up condition making it easy to handle. On side-hill cuts in heavy ground, where the slope is steep and there is some question about the security of an embankment to carry the outer part of the road, a safe roadway can often be blasted out of the hill at a cost comparing favorably with a road partly supported by a retaining wall. Even on easier slopes, where a long side-hill cut in heavy ground must be made and the excavated material can be employed as an embankment to carry the outer part of the roadway, the excavation is often made by blasting. Blasting is also an effective method of breaking up stumps and boulders. Where the material is easily handled and can be dumped within 100 feet of the cut, slip scrapers are generally regarded as the least expensive equipment. The Fresno scraper is regarded as better than the slip scraper for hauls exceeding 100 feet. If the haul exceeds 100 feet and is under 1000 feet, wheel scrapers are ranked highly. The large sizes are most desirable for economy on hauls over 600 feet. The material is usually plowed so the wheelers can be loaded easily, and it is necessary to have about one of them for every 100 feet of haul in order to work most economically. Bottom-dump wagons can be made to give very low hauling costs if enough are provided so that while one is being loaded at the cut, the driver and team which brought it in can be used in hauling a loaded wagon.

In recent years traction steam shovels have been growing stead

ily in favor for road grading. They make shallow cuts as easily as deep cuts, and have taken out earth and rock at very low figures when the equipment for removing the excavated material was properly selected and used so as to keep the shovel working most of the time. The economy of steam shovel operation depends upon the proportion of the working day that it is actually digging, and this depends upon having wagons or cars ready to receive the excavated material. The wagons or cars may often be run along the top of the bank of a shallow cut and kept moving in a continuous line, saving the delay of turning and backing up to the shovel, which is necessary when they move over the graded cut. The utility of a shovel on roadwork is increased if it can be employed in a gravel pit or quarry when not grading.

The bottom of the cut should be carried down approximately parallel to the finished cross-section, and care should be taken not to disturb the material below the grade line. In very heavy ground, the final trimming is sometimes done by hand, but generally a road machine can be used to advantage.

Where a fill is made, the surface must be cleared. Stumps should be grubbed out1 and all large material liable to decay should be removed, for if left in place the fill will settle as it rots or have loose places likely to retain moisture. If the fill is on a steep side-hill, the latter should be cut into a series of level benches or steps and the drainage should receive careful attention. If the hill has a gentle slope, it is usually sufficient to plow parallel furrows, which will furnish a sufficiently uneven surface to hold the fill. The object in any case is to unite the material in the bottom of the embankment with that of the hillside.

If the road will be maintained as an earth road for several years, so it will have ample time to become consolidated under traffic before any surfacing is applied, there is usually little reason for limiting the thickness of the layers in which the embankment is built. But if a surfacing is to be given the road at an early date, the layers should not exceed 2 feet for high fills and 1 foot for low fills. The teams and scrapers moving over the fill compact it to some extent. Formerly little attention was paid to smoothing the surface of the layers, but of late this has been considered important in some states and drags are kept at work on a bank a large part of the time. George W. Cooley, State engineer of Minnesota, has explained this leveling work as follows:

1 It is not customary in the South to require green stumps and roots to be grubbed where the fill over their tops is as much as 18 inches. Any matter in process of decay must be removed but a green stump sealed in a fill so that air will not reach it lasts forever.