Foreigners continue to anathematize American roads after a tour over them, especially if the trip takes them through parts of the Middle West and the South or in the rocky regions of New England. But much as we recognize the justice of this criticism, we look with pardonable pride upon the obverse side of the shield. In the past five years we have redeemed upward of five thousand miles of highways from the wayward habit of going to the bad, rescued some six thousand more from sloughs and swamps of mud and water, and mapped out plans for improving many other thousands so they will in time become at least passable. We have inaugurated new systems of road building, framed new methods of taxation for highway improvement, and interested nearly every progressive community in the work of developing better highways. The ideal road is still in the stage of experimental evolution. Consult road engineers and experts, and one will inform you that Telford and MacAdam laid down the principles of road construction that cannot be properly departed from, and another will tell you that to attempt to adhere to such principles would ruin half the counties of a dozen States. One set of engineers places drainage as the chief aim in road building, but another will point to the fact that one-third of our roads cross arid or semi-arid regions, where drainage is not a factor of any considerable value. Others have made extensive studies of French and English roads, and are positive that we must duplicate these foreign highways here if we expect to secure ideal results. But happily the consensus of engineering opinion is crystallizing around the very simple proposition that road making is largely a local matter, depending upon the topography, climate, geological formation, and requirements of any community. The roads in the United States must be developed according to special standards, and not according to those set in other countries. The sentiment of the country is in favor of good roads, but not for French or English roads or necessarily for Telford or MacAdam roads. It is for good roads, worked out by engineers who can best appreciate the needs, conditions, and materials of any particular section. We have many typical illustrations of how certain sections have already solved the road problem according to special needs. In California there are the best types of oiled roads, which answer for the dusty highways of that State better than anything yet attempted. But what road making from the conservative point of view of a Telford or MacAdam principle! The roadbed of dirt and sand is first plowed, harrowed, rolled, and graded, until there is a layer of finely pulverized soil ten to twelve inches deep over the surface, but no signs of crushed or broken stone, no material whateverexcept a little sand on top such as is used for the foundation of the Telford or MacAdam, roads. Then when this graded road, has dried and settled, crude petroleum or asphalt residuums are spread over the surface. The oil is heated from 175 to 300 deg., and spread over the road at this very high temperature. From one hundred to three hundred barrels of oil are used on each mile of road, eighteen feet wide, at an estimated cost of $15 to $20 per mile. Coarse sand or gravel is spread over the oil, to increase the absorption and to protect passing vehicles. Sometimes a second coating of oil is put on within a few weeks. This method of road building in California costs about one and a half cents per square foot, while asphalt costs fifteen cents, and powdered granite about five cents. California's road problem is the suppression of dust and the modification of the hot glare on bright sand. The oiled roads become indurated and resilient with oil, so that the dust i.i permanently laid and the bright sand modified to dark brown. There are nearly 1,500 miles of these oiled roads in California, and with the exception of staining white dresses or shoes coming in contact with the oil, they make the best possible highways for hot, sandy, dusty regions, with hardly a single drawback. The surface is not easily cut up with wagon tires, for the oiled surface does not soften like asphalt pavement, and the rubber tires of motor cars are not injured by the oil, as first supposed. California has thus de a long stride toward at- taining the ideal road for the sandy strip of country reaching from the mountains to the coast. Other States with similar soil and climate have entered upon the work of building oiled roads. Texas has obtained some excellent results in this direction, and wherever oil is cheap the work has assumed considerable progress. Crude oil ranges in price in California from 70 to 80 cents per barrel, but in many other States the cost of oil makes road building of this character a physical impossibility. As a direct result of successful experiments with oil for roads in Californiaand in Oran, Africa, and several towns of Algiers where aloe and massot oil were usedroad builders took up the question of employing tar, either alone or in connection with oil for road surfacing. In France a mixture of tar and oil was tried in 1900, and by 1901 such good effects were obtained with various tar mixtures, that many miles of roads were surfaced with them. The French engineers pursued the subject with intelligent perseverance, and they secured some ideal roads for traveling. The tar is applied hot at about 210 deg., and only in dry weather. After the tar is applied, a sprinkling of sand is made over the surface to harden the mixture and to prevent slipping of horses and vehicles. By the addition of heavy oils, the tar is hardened more quickly, and the road thrown open to general traffic. All dust and mud are eliminated by the tarring process, and the roadbed itself is kept from injury by heavy traffic. The waterproof character of the tar surface keeps the water from entering the roadbed, and thus eliminates one of the most destructive agencies of highways. In England tar is also used quite extensively for the maintenance of the surface of the roads, and in this country it is also a well-recognized practice. One of the first applications of tar to the surface was made at Jackson, Tenn. The surfacing lasted about seven or eight months. In Montclair, N. J., a mixture of tar and screenings was tried in 1904 on a. steep grade, and for a year practically no wear or tear was noticeable on the road. Since then a number of other roads in that town have been similarly treated at a cost of about 17 cents per square foot, including the cracked stone and screenings. The tarring itself cost only about five to six cents per square foot. In several other New Jersey towns and on Long Island, roads are now being treated with tarred surface for eliminating dust and mud and for the protection of the road itself. The difference between the method of tarring the surface of roads in France and this country is in the use of sand or screenings. In France they merely sprinkle sand on the tar after it has cooled a day or two, but in this country cracked stones or screenings are either mixed with the tar or sprinkled upon the surface, with the purpose of incorporating them as much as possible with the tar. The French roads are excellent, and form a dry, dustless surface, but they do not last as long as the American roads of equal excellence. The tar and screenings, when properly mixed together, form a sort of cushion, 'which greatly reduces abrasion. The use of tar in territories where there are ample rainfalls is far superior to oil, for the latter then forms an emulsion with the water, which does great damage to vehicles and clothes. It makes the surface mushy, and resprinkling is necessary at intervals. But in dry, hot, arid regions the oil is superior to tar, and accomplishes the object of laying the dust and forming a smooth compact surface better. It is consequently a question of climate and topographical conditions which must determine the use of materials and methods in any part of the country. But probably the great problem of road building in this country is confined more to the Mississippi Valley. In this vast region road-building materials are scarce and expensive. The use of oil or tar for surfacing would prove of little value, unless the roadbed itself could first be built up of proper material. There is no good gravel, no slates, shales, or silicates available for the roads of this region, but there is plenty of rich land and heavy soil. Drainage is naturally poor, and road building becomes an engineering problem of great difficulty. In our New England and Eastern States stone and gravel are abundant, and road building is chiefly a problem of proper construction of beds with some of the nearby stones. Drainage is first essential, but this can be obtained by elevating the bed of the road sufficiently, and constructing ditches, culverts, and bridges at proper points. It is a work which any competent engineer can plan and carry to perfection. The principles of the Telford and MacAdam roads here come into vital use. Roads once properly built of the right material will, if repairs are made systematically: and scientifically, last indefinitely. At the recent International Engineering Congress in England, an engineer of that country who had four hundred miles of road under his jurisdiction, reported that he had only to rebuild two or three miles a year. The vital point which he wished to emphasize in this report was that if proper methods of repair and maintenance are early adopted, the roads can be made to last indefinitely, and practically do not require rebuilding oftener than once in a decade or two. The automobile has had a somewhat paradoxical effect upon our roads. It has been a tremendous factor in stimulating the construction of better roads, and a good deal of money has flowed from the treasuries of the motor associations into road building. But the automobile has increased the dust problem of many localities, and it has made the treatment of macadam roads on the surface with tar or oil mixtures to lay the dust essential. In Massachusetts the rescue of many of the highways simply means an application of some surface mixture to lay the dust of finely-powdered rocks and gravel. Several large appropriations have been made by the Highway Commission to test the various patent mixtures for solving the dust trouble, and the United States government is conducting some experiments near Wayland, Mass., for similar purposes. These dust layers consist for the most part of tar and oil in different proportions, and the very fact that so much attention is given to them by manufacturers and the public indicates a healthy condition of affairs, .and it must in the end contribute toward road improvement. But the larger aspect of the road problem in this country includes the construction of better highways in those great middle sections of our country where neither sand, gravel, stone, nor shales can be had without great cost. Where natural road-making material is abundant, the engineer has no very great problem to solve; and after good roads are once built, the rest depends upon good maintenance and the further improvement by dressing the surface with dust-laying materials of tar or oil. Good gravel, granite, and hard stones make the best materials for roads; but limestones, slates, shales, and the silicates are used in many sections with fair success. The soft limestones make fairly good foundations, but they do not last so long as harder stones, and the shales are affected by frost, so that they require renewal oftener. Some of the silicates, however, prove exceedingly durable, and it has been found profitable and economical to transport some of these two and three hundred miles for road building. In the great Mississippi Valley there is practically no good road-making material at hand, and whatever is used must be transported great distances at considerable expense. In Illinois, Alabama, Kansas, Iowa, and other middle central States the road problem is acute to-day. Occasionally gravel beds are found which yield fair road-making material, and in the hands of the engineer good stretches of highways have been made at no great cost. The drainage on these rich farming sections is almost as bad as it could be, and this increases the cost and trouble of the work. Traveling through thess States in an automobile makes one conscious of the great road problems facing our richest agricultural regions. In vain have local and national engineers sought to devise some means of making roads in these States without importing stones, gravel, and other building material. But apparently the roads must be built at great expense through the employment of materials transported from more favored sections. Transportation thus becomes the most vital factor in road making of the Mississippi Valley and of many of the Southern States. If good roads are to be had there, the materials must be brought by the railroads, and co-operation between the steam lines and local highway commissions must be secured. No hard and fast rules of highway building could be laid down for this great central region, although the best granite or gravel would pay the best in the end, for it costs no more to transport it than the cheaper shales and softer limestones. The question of durability and cost of maintenance would have to be seriously considered. In the experiments made by the government and local commissions, good roads of broken stones, such as granite, flint, and silicates, prove more economical than cheaper materials, and many of the middle western towns and cities have miles of excellent highways built at only thirty to forty per cent more than the cost of similar roads in the East, which, with proper care, will last for many decades. Good roads in the Mississippi Valley pay better than almost anywhere else in the country, owing to the vivid contrast between them and the natural poor roads. The increase in valuation of property along the line of macadam roads, in this section has been all the way from fifty to sixty per cent, and many new, thriving towns are to-day making strenuous efforts to attract settlers and investors through improving roads. It has proved an economical success to increase road taxation in order to secure higher real estate values. Road construction across the middle of our continent at the present rate of development should within another decade completely revolutionize conditions; and a trip across from ocean to ocean by automobile should prove a popular pleasure instead of a tiresome struggle with muddy, dusty, and heavy stretches of roads.
This article was originally published with the title "Rescuing our Roads" in Scientific American 97, 19, 321 (November 1907)