Elements of highway engineering

Front matter

OlxirnrU ImuprBttg ICtbrarg

BOUGHT WITH THE INCOME OF THE

SAGE ENDOWMENT FUND

Preface

This book has been written at the suggestion of several professors of civil engineering who desire to use a didactic text, covering the principles of highway engineering, of such length as to be suitable for one-semester courses included in civil engineering curricula. The text of this work is made up of original manuscript, and also of material from the " Text-book on Highway Engineering," by Blanchard and Drowne, which has been revised and remodelled to meet the requirements of a book suitable for use by engineering students who take courses in highway engineering aggregating from one to three hours a week for one-half of the collegiate year. It should be noted that the " Text-book on Highway Engineering" was designed to be a comprehensive text for highway engineering students and a reference book for engineers.

Each chapter of the "Elements of Highway Engineering" has been written with a view to emphasizing the fundamental principles which have been evolved from past experience as well as from the modern practice of highway engineering which, as a science and an art, is rapidly developing in the fields of economics, administration, legislation, materials, and methods. Specifications, per se, examples of construction, and detailed cost data have been omitted, as such material is not considered essential to a broad general knowledge of the science of highway engineering. The text of the chapters, occupying 450 pages, has been profusely illustrated with 202 figures, equivalent in space to 85 pages.

As the nomenclature of materials and methods of construction and maintenance may be confusing to the student, a glossary, constituting Appendix I, has been included. Appendices II and vi PREFACE

III, containing, in detail, methods for determining physical and chemical properties of bituminous and non-bituminous highway materials, will be found of value to professors who wish to elaborate upon the subject of essential properties of materials and their determination.

For a course constituting one hour a week for a half year, it is suggested that the subject matter might be reduced in amount b}- the omission of the text covering examples of state legislation, pages 31 to 36; surveying and mapping, pages 64 to 75; mining and manufacture of bituminous materials, pages ig6 to 210; interpretation of tests of bituminous materials, pages 214 to 222; descriptions of machines, pages 98 to iii, 241 to 247, and 288 to 293; sidewalks, curbs, and gutters, pages 406 to 420; and highwa}' structures, pages 421 to 450. The total number of pages thus eliminated amounts to about no.

The author gratefully acknowledges his indebtedness to the engineers and chemists whose writings he has quoted, to technical periodicals for certain tables and cuts, and to numerous manufacturers for furnishing photographs to illustrate the text.

The author requests that users of this work as a text-book subniit suggestions pertaining to elaboration or reduction of the several sections of the book to meet individual requirements. It is also requested that readers call the attention of the author to errors which may occur in the text. Cooperation along the above lines will be appreciated.

A. H. B.

Columbia University, New York City, September i, igij.

Chapter I Page

Historical Review i

Ancient Highways of the Eastern Hemisphere — Early drecian Highways — Early Roman Highways — Early French High\\a\s — Early British Highways — Early American Highways.

CHAPTER H

Economics, Administration, Legislation, and Organization . . i6 Economics — Benefits of Improved Highways — Financing Highways— Labor Tax — Convict Labor — Direct Taxation — Direct Appropriation— Bond Issues — Private Subscription — Administration and Legislation — France — Germany — Great Britain — United States — Municipalities — Organization — State and County Departments — L^rban D,istrict Departments.

Chapter III

Location — Foundations — Drainage — Width — Local Materials — Climatic Conditions — Maintenance — Local Environments — ^'Esthetics— Traffic — Traffic Classification — Effect of Different Classes of Traffic — Loads and Tire Widths — Methods of Taking Traffic Census.

Chapter IV

Surveys for Roads — The Transit Line — Levels — Final Surveys — Staking Grades — Mapping Road Surveys — Plan — Profile — Cross- Sections — Surveys for City Streets — Traverse — Levels — Mapping Street Surveys — Design of State Highway Systems, City Highway Systems, and Park Highway Systems — Scope of Highway Design — Location — Widths of Roads, Streets, and Park Highways — Grades — Street Intersections — Curves — Cross-Sectionc of Roads and Streets — Crown Formulas — Drainage and Foundations — Selection of Type of Wearing Course.

vii viii ELEMENTS OF HIGHWAY ENGINEERING

Chapter V Page

Crading, Drainage, and Foindations 94

Grading — Excavation — Embankment — Classification of Materials— Shrinkage of Materials — Machines — Road Drags, Scrapers, Elevating Graders, Rollers, and Scarifiers — Drainage — Subdrainage — Pipe Drains — Surface Drainage — Side Ditches and Gutters — Foundations — Classification — Natural Foundations — Soil Classification— Loads on the Foundation — Artificial Foundations — Stone Foundations — Telford Foundations — V-Drain Foundations — Broken Stone Foundations — Cement-Concrete Foundations — Foundations Over Marshes — Old Pavements as Foundations — Bituminous Concrete Foundations.

CHAPTER M

F^ARTH AND SaND-ClAY ROADS 128

Occurrence — Soils — Sand, Clay, and Sand-Clay Construction — Drainage — Wearing Course of Earth Roads — Wearing Course of Top Soil Roads — Roads with Sandy Subsoil — Roads with Clayey Subsoil — Burnt Clay Roads — Straw Roads — Petrolithic Roads — Maintenance — Drags vs. Scrapers — Road Drag Regulations.

CHAPTER \II

De^'eloJ)ment — The Gravel — Formation and Occurrence — Requisites of Cjra\'el — The Binder — Testing Gravel — Mechanical Analysis — Construction — Preparation of Subgradc — Construction of the Wearing Course — Sizes of Gravel — Thicknesses of Courses — Spreading and Compacting the Gra\-el — Cost Data — Maintenance.

CHAPTER VIII

Rock Classification — Essential Properties of Rock — Testing the Rock — Abrasion, Cementing Value, Toughness, Hardness, Absorption, and Specific Gravity — Quarrying and Crushing — Drilling — Blasting — Crushing Plants — Voids and Weights of Crushed Stone — Construction — Tresaguet's and McAdani's Methods — Sizes of Broken Stone — Foundation and Subgradc — Construction of the Courses — Miscellaneous Roads — Slag Roads — Shell Roads — Cost Data — Maintenance — Causes of Wear — Ordinary Repairs — Resurfacing— Characteristics.

TABLE OF CONTENTS ix

PAH E

Bituminous Materials — Continued 192

Asphalt — Petroleums — Tars — Gas-House Coal Tar — Coke Oven Tar — Water Gas Tar — Tests and Specifications for Physical and Chemical Properties — Lists of Tests — Brief Descriptions of Tests — Interpretation of Results of Tests — Utilization of Tests in Specifications.

CHAPTER X

Dust Prevention and Bituminous Surfaces 227

Dust Prevention — Classification of Surface Treatment Methods — Development — Formation of Dust — Pathogenic and Other Effects of Dust — Use of Palliatives — Classification of Palliatives — Watering — Calcium Chloride — Emulsions — Light Oils and Light Tars — Bituminous Surfaces — Bituminous Materials — Construction Methods— Maintenance — Mechanical Appliances — Gravity and Pressure Distributors — Characteristics — Advantages — Disadvantages — Causes of Failure.

CHAPTER XI

Bituminous Macadam Pavements ... 253

Development — Bituminous Materials — Construction — Methods of Construction Losing Broken Stone — Methods of Construction Using Gravel — Cost Data — Maintenance — Characteristics.

CHAPTER XII

Development — Mineral Aggregates — One Product of a Crushing Plant — Combinations of Broken Stone and Fine Material — Mechanically Graded Aggregates — Topeka, Asphalt Block, and Bitulithic Pavements — Patents — Bituminous Materials — Bitumen Content — Wearing Course Mixtures — Construction — Subgrade and Foundation— Wearing Course — Manufacture and Laying of Asphalt Blocks — Mechanical Appliances — Cement-Concrete Mixers — Mi.xers with Heating Attachments — Dryers, Storage Bins, and Mixers — Cost Data — Maintenance — Characteristics.

CHAPTER XIII

Sheet Asphalt anu Rock Asphalt Pavements 29K

Development — Materials for Sheet Asphalt Pavements — Asphalt Cement — Binder Stone — Sand and Filler for Wearing Course — Construction of Sheet Asphalt Pavements — Subgrade and Foundation— Binder Course — Wearing Course — Asphalt Plants — Rock Asphalt Pavements — European Practice — American Practice — Cost Data — Maintenance of Sheet Asphalt Pavements — Repairs and Conditions of Guarantee — Characteristics.

ELEMENTS OY HIGHWAY ENGINEERING

CHAPTER XIV

PAGE

Development — Cement-Concrete — Construction — Subgrade and Foundation — Metliods of Construction — Mixing Methods — One- Course Pavement — Two-Course Pavement — Reinforced Pavements — Oil Cement-Concrete — Expansion Joints — Grouting Method — I^ituminous Surfaces on Concrete — Cost Data — Maintenance — Characteristics.

CHAPTER XY

Development — The Wood — Wood Preservation — Manufa( t ure of Blocks — Construction — Subgrade and Foundations — Cushion Layers — Construction of Wearing Course — F'illers — Cost Data — Maintenance — Characteristics.

CHAPTER X\T

Development — The Brick — Brick Clays and Shales — Size of Brick — Testing the Brick — Construction — Subgrade and Foundation— Cushion Courses — Methods of Laying the Brick — Joint Fillers and Expansion Joints — Cost Data — Maintenance — Characteristics.

CHAPTER XVH

Development — Stone Blocks — The Stone — Manufacture of Blocks — Size of Blocks — Tests for Stone Blocks — Construction — Subgrade and Foundation — Cushion Layers — Construction of Wearing Course — Joint Fillers — Durax and Kleinpflastcr Pavements— Stone Trackways — Cobble Stone Pavements — Clinker and Slag Block Pavements — Cost Data — Maintenance — Characteristics.

CHAPTER XVIH

Street Cleaning and Snow Removai 376

Street Cleanine — Hand Cleaning — Machine Sweenint'- — Hose

TABLE OF CONTENTS xi

CHAPTER XIX

PAGE

Development — Essentials of An Ideal Road or Pavement — Durability — Sanitary Qualities — Noiselessness — Slipperiness — Resistance to Traffic — Annual Cost — Methods of Comparison — Records and Cost Data Forms.

CHAPTER XX

Sidewalks, Curbs, and Gutters ^06

Sidewalks — Essential Qualities — Width and Slope of Sidewalks — Materials — Construction Methods — Cost Data — Asphaltic Mastic — Brick and Tile — Cinders — Cement -Concrete — Gravel — Small Stone Setts — Stone Flagging — Curbs — Stone and Cement-Concrete Curbs — Gutters — Methods of Construction — Cost Data.

CHAPTER XXI

Bridges and Culverts — Determination of Waterway — Culverts — Design, Location, and Construction — Vitrified Pipes — Cast- Iron Pipes — Corrugated Metal Pipes — Stone Box — Reinforced Concrete Box — Drop Inlets — Catch-Basins — Bridges — Design, Location, and Construction — Steel, I-Beam, Pony Truss, Plate Girder, Concrete, and Reinforced Concrete Bridges — Guard Rails — Wood, Pipe, and Concrete Rails — Highway Signs — Road Signs — Direction, Distance, and Danger Signs — Highway Department Signs — Street Signs — Car Tracks — Location — Track Construction — Rails — Surfacing Adjacent to Rails — Pipe Systems — Design and Location — Repaving Trenches.

APPENDIX I Glossary of Terms Applicable to Highway Engineering 451

Tests for Bituminous Materials 466

Specific Gravity — Flash-Point — Solubility in Carbon Disulphide — Solubility in Carbon Tetrachloride — Consistency — Viscosity Test — Float Test — Penetration Test — Melting Point — Loss on Evaporation— Distillation — Ductility — Solubility in Petroleum Naphtha and Character of Residue on Glass — Fixed Carbon — ParalBn.

XU ELEMENTS OF HIGHWAY ENGINEERING

APPENDIX HI

PA(,E

Tests of Nox-Bituminois Materials 4»6

Apparent Specific (Gravity of Rock — Apparent Specific (jra\ity of Sand, Stone Screenings, or Other Fine Highway Material — Absorption of Water per Cubic Foot of Rock — Abrasion Test for Broken Stone or Broken Slag — Abrasion Test for firavcl — Toughness Test for Rock or Slag — Hardness Test for Rock or Slag — Cementation Test for Rock, Slag, or Gravel Powder — Mechanical Analysis of Broken Stone, Broken Slag, or Gravel — Mechanical Analysis of Sand or Other Fine Highway Material — Mechanical Analysis of Mixtures of Sand or Other Fine Highway Material and Broken Stone, Broken Slag, or Gravel — Voids in Mineral Aggregates — Rattler Test for Pa\ing Brick.

Chapter I Historical Review*

It is the purpose of this chapter to give a broad general review of the development of the art and science of highway building to about a.d. 1840. Many of the various forms of modern pavements were not introduced until after this date. Since the later developments are intimately connected with the details of construction of roads and pavements, the historical review relative to each type will be of greater value if included in the chapter to which it specifically refers.

Ancient Highways of the Eastern Hemisphere. The economic value of highways in its broadest sense was not appreciated as much by the ancient races as it is to-day. The primary object of the roads built by them was to facilitate the movements of troops rather than for the development of commercial, industrial, agricultural, and social interests. History previous to 1900 B.C. is rather vague concerning the subject of highways. Herodotus tells of a road which was constructed about 4000 B.C. and over which materials of construction used in building the pyramids were supposed to have been hauled. Although Bibhcal history mentions in several instances that there were pubKc highways, the first roads of which there is any authentic record are those in the Assyrian Empire built about 1900 B.C. These roads radiated from Babylon, and the remains of one can still be seen to-day between Bagdad and Ispahan. This road, as well as the oldest bridge on record of ,

* Prepared by Mr. Henry B. Drowne, Instructor in Highway Engineering in the Graduate Course in Highway Engineering, Columbia University, and Engineer, Lane Construction Corporation.

any importance, which is that over the River Euphrates near Babylon, was built during the reign of Queen Semiramis.

Early Grecian Highways. History is not very definite as to the methods of construction of the roads of ancient Greece. Many of these roads were built as approaches to rehgious temples. One of the principal roads led from Athens to Eleusis, and served as a means of communication with Peloponnesus, Thebes, and Phocis, and the greater part of the North. The Greeks, according to some authorities, were not as attentive to drainage, in connection with the construction of their roads, as were the Romans. They paved their roads with large square blocks of stone. The royal roads of Greece were under the authority of the Athenian Senate, which levied taxes for the maintenance of the roads. In some of the largest cities, such as Thebes, the care of the streets was intrusted to a person of high rank.

Early Roman Highways. According to Isadore de Seville, who lived in a.d. 700, the Carthaginians were the first to build paved roads. Their methods were later copied by the Romans. Carthage flourished from about 600 B.C. to 146 B.C., at which time this empire was destroyed by the Romans. The Romans built roads on a more extensive scale than any of the other nations. Road building was a state policy in the Roman Empire. Gautier says that the Romans divided their roads into the following classes: royal roads, vicinal roads, and private roads. The royal roads included the main mihtary roads which traversed all of Europe and the northern part of Africa. The vicinal roads connected the royal roads with the towns or cities.. The private roads connected the royal roads or vicinal roads with some particular locality other than a town or city. By means of this system of roads the whole of the Roman Empire could be readily traversed. Soldiers were able to travel as much as twenty miles a day over these roads.

During the reign of the kings, the Roman roads were doubtless constructed of the natural soil. In the year 311 b.c. the censor Appius Claudius commenced the construction of the first paved road, which led from Rome to Capua. This road was named Via Appia (Appian Way), and was later extended and improved by Trajan. This marked the beginning of the construction of Rome's remarkable system of highways. During the next century Rome continued to flourish, and since the roads were an absolute necessity for the movements of troops to the various provinces, the construction of roads increased to such an extent that at the end of 200 B.C. the total system comprised about 48,500 miles. Many of the main roads were built under the auspices of different rulers and bear their names. Among these roads may be mentioned the Appian, Aurelian, Flaminian, and Domitian ways. Twenty-nine of these roads led to the capital. During the reign of Trajan, the Roman Empire reached its greatest magnitude, comprising Italy, Britain, Gaul, Spain, Western Germany, part of Asia Minor and Arabia, the northern part of Africa, and the islands in the Mediterranean.

It is evident in examining the old Roman roads, very clear traces of which appear in many of the European countries, that directness of line between two points was a prime object. A straight line was attained many times in spite of the natural difficulties which had to be overcome. Tunnels, bridges, and retaining walls remain as monuments to the skill of the Roman engineers. The Flaminian Way, in crossing the Apennines, passes through a tunnel about one thousand feet long; the Appian Way near Ariccia, for a length of about seven hundred and fifty feet, is constructed on a viaduct, the retaining walls of which have a mean height of 43 feet, while the viaduct contains three arch spans which serve as a waterway. In low and level land the roads were elevated to a considerable height above the adjoining ground.

Some of the great mihtary Roman roads were from 36 to 40 feet wide. The middle part, 12 to 16 feet in width, was generally paved or surfaced with some suitable material. This part of the road is supposed to have been used by the infantry. On each side of the middle portion was built a raised path, about two feet wide, which may have been used by the officers. Beyond these paths on either side was a width of about eight feet, which was supposed to have been used by the cavalry.

The breadth of the vicinal roads was fixed by the law of the "Twelve Tables" at 8 feet.

In constructing these roads two parallel furrows, defining the width of the road, were made, and the soil between these furrows was removed to such a depth that a firm and solid foundation was obtained. Sometimes when the soil was soft, it was made more compact by driving small piles into it. This trench was then filled up to a certain height with sand, which was firmly compacted. Upon this sand-bed four successive layers of masonry were built as follows:

1. The Statumen, lo to 20 inches thick, formed of large stones laid flat in courses and bonded together with mortarorclay.

2. The Rudus, about eight inches thick, composed of rubble masonry.

3. The Nucleus, having a thickness of 10 inches, built of masonry similar to concrete and often composed of fragments of pottery and brickbats.

4. The Summa Crusta, formed of very hard materials bonded together with a lime mortar. On many of the military roads large stones, bedded in the Nucleus, were used for this layer, while on other roads small stones mixed with mortar were employed.

The total thickness of the four courses was about four feet. All of the roads, however, were not constructed according to this standard. Some of the roads that were originally built of sand or gravel were later surfaced with stones of variable dimensions. The Appian Way between Rome and Brindisi for a length of about five hundred miles was surfaced with large stones, cut into irregular shapes, bedded very carefully in mortar, and laid, in some cases, with very close joints. These stones, 3, 4, and 5 feet square, were,- according to some authorities, transported more than one hundred miles for use in this road. In man}- places on the Domitian Way the surface was paved with square blocks of marble. In others, the stones were brought from the fields and laid in mortar. Between Nimes and Beaucaire, where the Roman road has been found to be intact in places, it was paved with dressed stones about seven inches thick. Excavations have shown in some cases that the

Statumen was replaced by broken stones of variable size. In other places the Statumen was replaced by a layer of compacted earth, the Rudus consisted of a bed of hme mortar, and a layer of broken stone replaced the Nucleus. Archaeologists have found that old Roman streets within the cities of Pompeii and Herculaneum were paved with large blocks of lava. They have also unearthed some paved streets in which the blocks of a similar size to those used to-day were laid on a mortar bed.

The reasons which led to the adoption of the different types of massive construction have not been given by historians. Without doubt, the availability of the materials influenced the use of different sized stones and the arrangement of courses. It is not difficult to imagine that the desire of the rulers to leave behind some substantial monument of their reign led to the use of some of the methods adopted. The traffic certainly was not such as to warrant the construction of roads four feet thick. Chariots and carts on two or four wheels, having a width of about five feet, were the principal types of vehicles used. First cost was probably of secondary importance, since a large part of the work was done by captives or by the armies.

The care of the roads was intrusted to a person of high rank. The office of Superintendent of Highways, or Curator Viarum, as it was then called, was one of great dignity and honor. Juhus Cassar was the first of high rank to occupy this office, and after his occupancy the office was rarely conferred upon any but men of consular dignity. Due to the fact that the roads played such an important part in the development of the Roman Empire, it is not surprising that the memories of Caesar Augustus, Vespasian, Trajan, and Domitian were honored, at the order of the Roman Senate, by the erection of triumphal arches.

Early French Highways. During the year a.d. 300 the wonderful system of roads, built up by the Romans in Gaul, was abandoned due to the Barbarian invasion. In 395 the Roman Empire was divided into two parts, the Eastern and the Western Empires. The Western Empire was finally destroyed in 476 and at its downfall road building practically ceased. Since the small amount of commercial traffic was accomplished with pack-animals, the highways outside the large cities became in time no better than bridle-paths. No care was taken of them, and the borders, as well as the roadway itself, became covered with small trees and bushes.

During the reign of King Charlemagne, from 771 to 814, some activity was again shown in building highways, necessitated by his various military expeditions. The work was done by the armies or by the people whom he vanquished. It was about 950 that the streets of Cordova, Spain, were supposed to have been paved. After the reign of Charlemagne, and up to A.D. iioo, conditions grew worse. In France the feudal regime was inaugurated and kingly rights were assumed by the dukes, counts, and other titled personages, who set themselves up as leaders of their districts. The whole nation was disturbed by the internal wars resulting from the disputes of these feudal chiefs. It was during this period of petty wars that the roads perhaps suffered the most, since at times they were torn up and destroyed as a matter of defence. The social state in the Middle Ages was such that the use of a road as a means of communication was practically abandoned. It was not safe for any one to travel, since both life and property were at stake. Where travel was possible the head of each fief demanded toll of the persons using the road, the money being used for his own private enterprises. Since the head of the fief had absolute and final authority in his particular district, the tolls were heav}' and an extreme hardship to those who had to pay them. From IIOO to 1200 the only road construction undertaken comprised the opening of some of the old roads incidental to the movements of troops in the Wars of the Crusades. The deplorable conditions, as outlined above, continued in France until the middle of the thirteenth century, at which time a few of the roads leading from Paris to the feudal provinces in the near vicinity were improved. This work was generally done under the direction of the provincial chiefs, and the paving was accomplished in a very primitive manner. The streets in the City of Paris were filthy early in the thirteenth century. On good authority it is stated that King Philip Augustus was so disturbed at the stench, when he opened a window in his palace one day, that he ordered all of the streets of the city to be paved with stone. This improvement was not demanded by the character of the traffic, as it was not until about 1300 that carriages, the use of which had almost entirely disappeared, again came into vogue. In spite of various edicts issued by royal proclamation from 1465 to 1600, the feudal system and the administrative organization of the government were such that the revenues, which should have been spent in maintaining the roads, were diverted to other channels. Roads of secondary importance were not improved at all, and the main highways, except in the vicinity of large cities, were not practicable for use as carriageways.

In 1 66 1, Colbert, who was Minister of Finance of France at that time, did much to try and bring about a change in conditions. In spite of his far-sighted policies with regard to the construction and maintenance of highways, no material progress was made in developing the French system up to 1700, with the exception of the construction of a few roads near Paris, among which were those of Orleans and Versailles. The construction and maintenance of the French roads for a long time had been generally carried out by means of the "corvee," which was a system of compulsory labor. M. Turgot, a minister of France, recognized the injustice of this system and suggested several reforms both as to the "corvee " and the feudal systems. Although Turgot was bitterly opposed, he succeeded in bringing about the general abolishment of the "corvee," in 1776. He was supported and defended by King Louis XVI until Marie Antoinette took part against her spouse. Turgot was forced to resign in 1777, and would have been imorisoned in the Bastille if the King had not interfered.

Due to the fact that Turgot had accomplished the abandonment of the "corvee," it became necessary to find some method of constructing the highways at a greatly reduced cost. This problem was successfully overcome by Pierre Marie Jerome Tresaguet, who at this time was chief engineer of the District of Limoges, France. It was due to his efforts and skill as an engineer that the first steps toward modern and scientific road-building were taken. Tresaguet's mode of constructing roads, as described by himself in 1764, and adopted generally in France in 1775, was as follows:

" The bottom of the foundation is to be made parallel to the surface of the road. The first bed (of stones) on the foundation is to be placed on edge, and not on the flat, in the form of a rough pavement, and consolidated by beating with a large hammer, but it is unnecessary that the stones should be even one with another. The second bed is to be hkewise arranged by hand, layer by layer, and beaten and broken coarsely with a large hammer, so that the stones may wedge together and no empty space may remain. The last bed, three inches in thickness, is to be broken to about the size of a walnut with a small hammer, on one side on a sort of anvil, and thrown upon the road with a shovel to form the curved surface. Great attention must be given to choose the hardest stone for the last bed, even if one is obliged to go to more distant quarries than those which furnish stone for the body of the road; the sohdity of the road depending on this latter bed, one cannot be too scrupulous as to the quality of materials which are used for it." He is also credited with being the first to propose a system of maintenance.

The Revolution naturally retarded the development of the national road system of France. During the period from 1804 to 1814, while Napoleon Bonaparte was Emperor of France, road-building gained a new stimulus. One result was the establishment of the remarkable system of national roads. It is very probable that Napoleon's various mihtary expeditions into the surrounding countries furnished the motive for the construction of these roads. About this time was created the renowned Department of Roads and Bridges, which was given control of road construction in France.

Early British Highways. Conditions in Great Britain after the fall of Rome and during the Dark Ages were similar to those in France. The roads were allowed to fall into a most deplorable state. An act passed in England in 1285 directed that all bushes and trees should be cut down for a distance of 200 feet on either side of the highway. The undergrowth had become so thick along the highways that it afforded an excellent hiding-place for robbers, which led to the improvement sought by the above act.

The first act for paving the streets of London was passed in 1532, and apparently for a somewhat similar reason as was the case in Paris. In the statute, the streets were described as "very foul, and full of pits and sloughs, so as to be mighty perilous and noxious, as well for all the king's subjects on horseback, as on foot with carriages." La^ge irregular boulders, 6 to 9 inches deep, were first used. Due to the wide joints between the stones, the irregular shapes, and the unstable foundations, the surface soon became very rough.