Popular Science Monthly/Volume 51/May 1897/Highway Construction in Massachusetts
|HIGHWAY CONSTRUCTION IN MASSACHUSETTS.|
IN the course of time there have been many changes in the method of transporting merchandise from town to town and from one country to another. Here, as in everything else, we see the gradual evolution of transportation, at first by man or beast, and finally by steam and electricity. Early man used himself as a beast of burden, and finally the ox and other animals were made to do service in his stead. With every improvement in method came a wider and wider range of trade and its consequent benefits. Efforts to improve the means of transportation resulted in the early invention of carriage by water. Hence we see the maritime peoples were the first to attain any considerable commercial prominence.
At the time this country was settled the lack of adequate means of moving commodities, excepting by water, led to the settlement of lands bordering the ocean, streams, and lakes, while equally good lands, not in close vicinity to water, offered but little attraction to the settler. Gradually the frontier was pushed farther westward; the narrow and obscure Indian trails were transformed into paths for horses and eventually became carriage roads. Before the railroad was devised public roads that possessed any claims to excellence were limited to the more populous States bordering the Atlantic coast. It is without doubt true that, had not transportation by rail been invented until the present time, the public roads of this country would be in a far more satisfactory condition than we find them to-day. With the advent of the locomotive came the withdrawal of active interest in the character of our highways. All the energies of our people were devoted to extending and perfecting the vast network of railroads that cross and recross the United States. Railway construction has now reached an equation of demand and supply, and we once again see the Commonwealths awakening to the importance of good roads, many communities vying with one another in their efforts to lead the States and earn a reputation for the excellent character of their highways.
The natural conservatism of the farming element of our people has been a difficult feature of the problem of arousing public interest in better roads to overcome in the past. The farmer has had but few object lessons in what a road should be. Adding to this the objections he has to an increase of taxation, we perceive the difficulties that stand in the way of educating the people up to the point of appreciating the numerous advantages that would accrue to them with a system of highways properly constructed and maintained. Little attention has been paid by the rural dweller to the arguments in favor of good roads. His line of reasoning is that roads that were satisfactory to his father and grandfather are good enough for him. In vain has he been told that, with good roads all the year round, the farmer and merchant come into closer communication; that he can sell his stock and grain when prices tempt him, instead of being dependent upon a favorable state of the road; that he can buy his supplies on rainy days, and increase his number of perishable crops, which are of uncertain value with bad roads, but become of certain value when impassable ways cease to cause spasmodic transportation.
To-day State roads are furnishing the farmer the much-needed object lessons—roads which by their general excellence through-out the year are causing, as in some counties in New Jersey, a marked increase in farm values. Other States, as Massachusetts, are building highways with State money, one fourth of which is eventually returned to the State by the county traversed by the way, while the legislative enactments of other States require a portion of the expense to be borne by the county in which the road lies, and by the freeholders whose property immediately abuts the improved roads. The mutual benefit derived from improved highways by all classes of people is now generally recognized in the more thrifty States, and from now on we may expect with surety the gradual development of our highways until the principal thoroughfares of the country come up to the required standard of excellence.
Travelers have described the celebrated Peruvian military road, leading from Cuzco to Quito, that was constructed long before the time the Spaniards conquered that country, about 1544. This road is variously estimated at fifteen hundred to two thousand miles in length, passing over deep cañons and across high mountain ranges. Large sandstone blocks formed the foundation, and this was covered with a native cement of a bituminous nature, forming a very smooth surface possessing great durability. Some portions of the road are still in an excellent state of preservation. The Romans also constructed over ten thousand miles of paved ways; but none of these ancient builders understood the principles made use of to-day.The art of building the type of road known as the modern highway is not a new one. The second decade of this century in England witnessed the first examples of turnpikes constructed on scientific principles in that country as enunciated by Macadam. Like many discoveries, the first and one of the most important principles involved is one that we should expect would have been discovered and put in general practice long before 1816. At that
Plate 1.—State Highway. Westfield Mass. Showing subgrade rolled and first layer of broken stone in place. (From photograph loaned by the Massachusetts Highway Commission.
time it was the custom in Great Britain, as elsewhere, to build roads very largely of clay or gravel. Macadam observed that gravel never afforded a good, compact wearing surface until a large amount of traffic had passed over it, when it became hardened and cemented together. He sought an explanation of this phenomenon, and learned that when the pebbles were broken under the impact of heavy wheels they soon consolidated into a firm mass. Here was the great principle: angular stones solidify under pressure; rounded stones do not. Amplifying this principle, he built up a complete system of road building which is in use to-day, as best shown in Switzerland and France, in England, and in other foreign countries, and is being revived so generally in this country at the present time, where the farmer is learning its advantages in the appreciation of land values, and where the bicyclist promotes the cause as the advance agent of good roads.
As defined by Macadam, a good road should be a hard, somewhat elastic surface to receive the wear of all kinds of traffic at every season of the year and during the greatest vicissitudes of weather, which shall also serve as a roof to that part of the road lying below. To use his own words, "A road ought to be considered as an artificial floor, forming a strong, smooth, solid surface, at once capable of carrying great weights, and over which carriages may pass without meeting any impediment." In order to realize such a surface it is necessary that the substructure of the road should be kept free from water, since, by the alternating freezing and thawing of the water, the wearing surface of the broken stone is disrupted, the water is offered a passageway through it, and the road becomes rough and difficult to travel.
It was the custom of Macadam, after the engineering work was completed and the subgrade established, to spread on a layer of stone to a depth of ten inches and to roll this surface with a heavy roller drawn by horses. These stones were broken by hand with small hammers, frequently a whole family working together, and were broken small enough to pass through a three-inch ring, or were not to have a maximum weight of over six ounces. A family of five people could break several tons per day. Side ditches were excavated where necessary, so that at no season of the year could water penetrate to the substructure of the road.
In 1816 Macadam began the construction and maintenance of one hundred and eighty miles of turnpike in Bristol District, England. A modification of this system was adopted by Thomas Telford about this time, which substituted a layer, or foundation, of irregular broken stone, set up on edge on the subgrade. Nine inches was the maximum dimension of these fragments. The rough surface thus made was smoothed down by going over it and breaking off the tops of the blocks with small hammers and packing the pieces thus obtained between the large blocks. This surface was then rolled as before. Telford built the celebrated Holyhead road, extending from Holyhead through North Wales to Shrewsbury—a road that served as a model at the board of inquiry appointed by Parliament in 1823. Each system had its partisans, and to-day the best features of both methods have been adopted under different conditions, dependent upon the character of the ground over which the road passes.
In 1892 the State of Massachusetts appointed a commission to investigate and report upon the character of the highways of the State, and to point out the trend that legislation should take in the matter of framing laws appropriating a yearly sum of money for the construction of State roads, and defining the powers of the Highway Commission to be appointed under the same act. This commission made its first report in 1893, and, on June 20, 1894, the Legislature appropriated the sum of three hundred thousand dollars for this purpose, to be used at the discretion of the Highway Commissioners the ensuing year. This commission appoints its own chief engineer, who has ultimate authority with the commission in the settlement of all questions that arise in connection with the work.
The laws enacted at this time do not place the initiation of State roads directly in the hands of the commission, but make the commissioners the tribunal to which all petitions made by towns, cities, or counties of the State are referred for action. It is a part of the policy of the commission not to allow a random construction of isolated stretches of road, but to make all ways constructed fit into a general scheme that shall have for its object a system of thoroughfares traversing the State that shall benefit the greatest number of municipalities and the State as a whole.The method of procedure, as defined by the statute of 1894, is as follows: The selectmen of any town, the aldermen of any city, or the county commissioners must first file a petition with the Highway Commissioners, accompanied by a plan and profile of the road. Plans are then prepared by the chief engineer and submitted to the commission for its approval. It is a part of the
Plate II.—State Highway, Westfield Mass. Showing steam roller at work on screenings. Finished roadway in the distance. (From photograph loaned by the Massachusetts Highway Commission.
settled policy of the commission to reduce all grades to a maximum of five feet in one hundred—called a five-per-cent grade. After courses and distances are plotted, and the necessary data obtained for determining the quantity of the various materials used in the construction of a road, a conference is held between the petitioners and the State commissioners, in order to ascertain if a contract for the construction of the road is to be made by the municipality, and, if so, at what price it is to be done. In case the city or town authorities are unwilling to contract for the work upon the prices agreed, the commission advertises the same, and it is let to the lowest responsible bidder, subject to the approval of the Governor and Council. It is the custom in awarding competitive contracts to require the contractor to furnish bonds: one insuring a faithful completion of the work; the other to safeguard the interests of the town or city in case damage results from accidents during the building of the way. Upon the contract being made and a notification being received that the municipality or contractor is ready to proceed with the work, the commission appoints a resident engineer, who has personal charge of the work of construction, subject only to the supervision of the chief engineer.
Now comes the period of actual construction, and the first step in advance is the excavation and filling the road to the required subgrade. In general the subgrade is about nine inches below the finished grade; but the extent of excavation differs widely in actual practice, owing to the different treatment necessary as determined by the varying character of the ground. The subgrade established and rolled, broken stone is then added to a depth of six inches, the fragments varying in size from one and a quarter to two and a quarter inches in their longest dimension. This is then rolled with a steam roller until thoroughly compacted (Plate I). A second layer of broken stone, three inches thick, is next spread upon the road, the pieces ranging in size from one half to one and a quarter inch. This is then rolled as before, and a finishing coating of screenings, put through a half-inch mesh, is then added to a depth of half an inch. Water is now turned on until the broken stone is well wet down, when the final rolling is done, and the surface becomes firmly and smoothly knit together (Plate II). In the foreground of this picture the second layer of broken stone is seen. The main part of the road is in its completed state, having just been compacted with the steam roller. Some modifications are made in these steps of the process, depending upon the quality of the stone used and the amount and kind of travel to which the road is to be subjected. As pointed out by Macadam, it is not wise to place a layer of broken stone directly upon a subgrade of granite or other rock existing as a ledge. Owing to the loss of the element of elasticity, the road would soon become weakened in its coherency, and the rate of wear would be much increased. It is therefore customary to excavate, when a cut in rock is necessary, some four inches below subgrade, and to fill in to subgrade with gravel on which the broken stone is placed as before.
Another modification is practiced when clayey, wet ground is encountered. Under these circumstances it is generally best to excavate some sixteen inches below the finished grade and spread on a layer of gravel four inches deep. Upon this Telford foundation is laid by hand to a depth of eight or ten inches and carefully rolled (Plate III). A layer of broken stone is then put on, and a finishing coating of screenings is added as before.
As to the character of the roads already constructed in Massachusetts, Prof. N. S. Shaler, of the Highway Commission, informed the writer that, in his opinion, they are in no way inferior, in so far as quality and durability are concerned, to the celebrated Swiss roads.
So well pleased are the people of Massachusetts with the State roads already constructed, and so active are they in the cause of good roads, that the Legislature appropriated the additional sum of four hundred thousand dollars for highway construction during the year 1895 and five hundred thousand dollars in 1896.
At first glance it would seem that the engineering skill necessary to construct a Macadam road would not be of a particularly high order; and yet the problems involved in building roads in the latitude of Massachusetts, where great variations exist in the character of the soil, owing to the glacial conditions that once existed here, call for engineering ability of a peculiar kind, as well as an extended experience in the treatment of special cases and the economical application of the materials at hand.As an adjunct of the Highway Commission, a laboratory has been established in Cambridge, where the systematic study of road materials is carried on. It has come to be generally recognized that materials which possess the necessary qualities for a good road stone are both limited in kind and in quantity. It is the object of these laboratory investigations to classify the road stones of the State in the order of their fitness for this purpose, and to prepare a map showing the area and location of the most desirable varieties. Here are investigated the questions of the rate of wear of stones under impact, and the cementing and recementing value of the powdered rock on which the life of the road depends in a large measure. The hardness and toughness also come within the scope of the experimental work. Experiment has shown that a stone must possess certain all-around properties in order to come up to the desired standard. For
Plate III.—State Highway, Westfield Mass. Laying Telford foundation. (From photograph loaned by the Massachusetts Highway Commission.
example, quartz or quartzite has a hardness of seven in a scale of ten, and for this quality alone it is best suited for road building of any rock of common occurrence; but it does not possess any cementing power or elasticity whatever, and is therefore of little use for Macadam work. As a result of long trial on roads in England and on the Continent, it is found that the stone best suited for road metal must possess toughness and cementing qualities and as great a resistance to abrasion as is possible in a stone having the first two properties. It is an important fact that experimental investigation in the laboratory has pointed scientifically to the same conclusions that have been obtained from the severe test of long experience in actual use.
The most important road stones are known under the common names of "trap" or "dike stones." They are usually of a dark-green color, are fine-grained, and are composed essentially of the minerals pyroxene or hornblende and feldspar, the individual minerals often not being visible to the unaided eye. Geologically, they are rocks that have been forced up through fissures in the earth's crust from great depths, where they existed in a melted condition. Rocks of this kind are very numerous in eastern Massachusetts and generally throughout the old mountain ranges of the United States. The road engineer, however, has other materials besides quarry stone, which, though not possessing so many good qualities, nevertheless make excellent road metal under proper conditions. Among these may be mentioned the blue glacial gravels, kame gravels, beach pebbles, and field stones.
Another rock in common use in various parts of New England is granite (a mixture of the minerals quartz and feldspar) and the allied rock, gneiss. Both these rocks are normally coarse-grained, possessing a hardness, as measured by that of their component minerals, a little under seven. In its use as broken stone granite has certain advantages over quartz alone, in that the feldspar, when pulverized or decomposed by the action of the weather, has considerable cementing value; but the decomposition of the feldspar liberates the quartz, and the physical differences in the matter of hardness, cleavage, etc., between the quartz and the feldspar promote differential wear of the stone as well as other defects. Granite, however, is an important road stone, and is far superior to such rocks as limestones, slates, or marbles, which, owing to their softness, are rapidly worn out.
The production of broken stone has now assumed such importance that several concerns in Massachusetts are making a regular business of furnishing all sizes to the State or municipalities. Broken stone, as a commercial commodity, is now sold on the cars at about one dollar to one dollar and seventy cents per ton for the best quality of trap.
- It is not improbable that Macadam was acquainted with the Napoleonic military roads constructed in France about 1775, which involved the principle of a thin layer of broken stone placed on a rock foundation. These roads were the invention of Tresaguet, a Frenchman, at about this me, and to him seems to be due the credit of first constructing what is now known essentially as the Telford system.
- Although one of the earliest pieces of work on a large scale that was ever attempted, the report of the board of inquiry, referred to above, showed that similar roads had been built in Sweden previous to 1823.