4. Those which are military.

Agricultural roads comprise those leading from farm to town and are used chiefly for marketing, and for social, educational, and religious activities. Recreational roads are either local, upon which driving is done for pleasure, or through, those followed by tourists in traveling over the country. Either of which may lead to places of interest within or without the state. The national park roads and forest highways can be classified under the head of recreational. Commercial highways comprise those exclusive of agricultural, upon which the haul is chiefly of a business nature such as freight and express and bus traffic. The War Department of the United States during the war refused to designate any roads as special Military Highways, saying a road which would adequately serve the agricultural; recreational, and commercial interests would serve the military. However, it might be well to keep in mind this possible use of the highways. A classification of roads into National, State, County and Town has frequently been suggested. Since national roads do not exist as such in the United States the most densely traveled routes and those used largely for through traffic are usually designated state roads, and all others local roads. Keeping the cost and use of the roads in view the problem before the road planner is: (1) To secure the most economical routes in construction and maintenance and future haulage, taking into account topography, alignment, grades, and amount of traffic. (2) To accommodate the greatest number of people commensurate with the money available for expenditure. (3) To utilize existing roads as far as practicable. The system will ordinarily consist of one or more trunk lines to be laid down first and several branch lines connecting with the trunk lines. Some of the essentials to be considered are: (1) Ruling points. These ordinarily will be (_a_) the main community centers--the large cities and villages, for to and from these will naturally flow the greatest traffic; (_b_) Natural configurations such as mountain passes, low points in hills, ridges and valleys, rivers and bridge sites; (_c_) Parks, scenery, and recreational and amusement centers; (_d_) Articulation with the highways of adjoining jurisdictions, so that they may eventually be united into one continuous passage. (2) Branch lines and detours. The question will frequently arise whether to run a branch line to some locality or detour the trunk. Much pressure will be brought by the inhabitants along the way and the deciding power will needs have firmness and fairness in the highest degree. (3) Alternate routes. If two roads of equal or almost equal importance are available a choice must be made between them. (4) Existing highways and principal streets of cities should be utilized as much as practicable. Although sometimes betterments so great may come through changes that old routes should be discontinued, in which case the (5) Vested rights of citizens living along discontinued routes and damages caused by any improvements made must be considered. (6) The widening of existing roads and streets and costs of the same. (7) The location of railways, trolley lines, and street car tracks may influence the layout for grade crossings should be eliminated, or at least placed where there is clear vision each way for a considerable distance. (8) Bridges, culverts, and railroad crossings should, preferably, be directly along the highway and at right angles to the obstruction. (9) Ruling grades, dependent upon the class of road will also affect the layout. (10) Esthetics. Perhaps the people of the United States have been too materialistic and have paid too little attention to the beauty and interest elements in highway location. Especially for pleasure riding and recreation should the esthetic side be considered. =Motor Transport Efficiency Outline.=--At this point it would be well for the road planner to consult an excellent paper by M. C. Horine and his efficiency chart which is substantially as follows:[175] ECONOMIC EFFICIENCY Highway Efficiency Adaptability of road to carrier Road capacity Width of road Pressure capacity Impact capacity Seasonal limitations Tractive resistance Grades Route Curves and corners Adaptability of carrier to road Dimensions Capacity and weight Speed Climbing ability Accelerating ability Stopping ability Turning radius Tractive effort Transport Efficiency Adaptability of carrier to volume and character of load Total load units to be carried Range of load units to be hauled Average load units to be hauled Density of load Length of haul Route Number and probable duration of stops Comparative adaptability of motor transport Horse transport Highway efficiency Transport efficiency Vehicle efficiency Public health Railway transportation including trolley express Transport efficiency Economy Haulage cost Packing cost Adaptability of carrier to traffic Legal restrictions on equipment and operation Possible average running speed Bridges and ferries Vehicle Efficiency Operation Moving factor Loading delays Unloading delays Waiting for loads Clerical delays Loafing Traffic delays Load factor Body capacity Special deliveries Return loads Outside hauling (custom work) Pickups Deliveries Trailers Maintenance Active factor Disability layups Chassis repairs Body repairs Accessory repairs Tire repairs and replacements Overhaul and painting Driver’s disability Requirement layups Seasonal fluctuations Off-peak period Shut downs Labor troubles Economy Earning factor Unit miles Packing cost Loading cost Unloading cost Time in transit Marketability Insurance Interest on value Shrinkage and breakage Perishability Tracing and follow up Advertising value Goodwill of trade Increased radius of trade Increased business turnover Cost factor Operating cost Fixed charges Maintenance charges Running charges Overhead Loading devices Shipping room devices Office and clerical expenses Telephone Labor Loaders Watchmen Clerks Supervisors Accountants Traffic department Miscellaneous =The Highway System Unit.=--Ordinarily the units will be the same as the political divisions, that is, national, state, or local. A national system would include the whole United States and will comprise trunk lines paralleling each other across the country east and west and north and south, considering, of course, ruling points, with a few branch lines of importance. The total number of miles of such highways should probably never exceed 2 per cent of the total mileage in the United States, or about 50,000 miles. A national highway committee estimated that this mileage of roads would serve 87 per cent of the people. The arguments made in favor of a national system of highways may be briefly summarized as follows: (1) Political lines would be obliterated, thus welding together and unifying all the people. Commercial and social intercourse would wipe out sectional differences, hatreds, and enmities. The people of one section would learn that the people of another section are human beings as they themselves are, and are actuated by the same instincts and inspirations. (2) Economic, commercial, and pleasure routes cut across state lines and it would be much better to have the roads continuous and administered by one central control. They would then be kept in a more uniform condition of usefulness. The roads radiating from New York City are mentioned as an example. They pass out of the state of New York and into the states of Connecticut, Rhode Island, Massachusetts, New Jersey, Pennsylvania, Delaware, Maryland, and the District of Columbia. On any one of these roads it would be difficult to say which state you are in by observing the license tags on the trucks and automobiles. A Connecticut traffic census on a road carrying approximately 3000 passenger cars and 500 trucks per day showed that 47 per cent of the cars in the analysis came from without the state. (3) Military. All roads would become military during war. It is frequently stated that the good roads of France saved Paris from invasion and probably saved the war to the allies. The German General Kluck admits that while he was advancing upon the British and French south of the Marne, an army of which he had no suspicion had struck outward from Paris and put his flank in deadly peril.[176] This army was one that Joffre had concentrated in Paris under General Maunouri, which had been brought over two or three good French roads from Paris by motor trucks and lorries to a point within striking distance of the German right flank, where he attacked and began the First Battle of the Marne. In the Second Battle of the Marne, motor cars performed a very important part in the concentration of troops which were to make a surprise attack. In addition the motorized armed cars known as tanks played an important part. On this side of the ocean the trunk line roads during the war supplemented the railways, which were badly congested at the eastern terminals, by hauling large quantities of men, materials and munitions. It is said that 16,000 trucks were engaged in this work. (4) The benefit of example. The federal government not hampered by local prejudices may construct roads of the highest type along best possible locations which when completed will serve as an example for state and local officers to pattern after. The people having seen such roads will more willingly vote bonds and taxes for road betterment. =State System.=--The benefits to be derived from and the arguments for a national system of roads apply with equal force to a state system. In fact it may be better to avoid the two extremes of one consolidated central control for the whole country and a very highly dispersed decentralized local control. The state seems to be a sufficiently large unit to do good work and sufficiently small to be approachable. Competition with other states may bring out developments which under a single central control would never have been thought of. Notwithstanding the excellent research work that is being carried on by the Bureau of Public Roads there is no doubt but that that which is being done by the several states more nearly solves those special problems arising on account of climate, topography, soil, and so on of the particular state. The state system should cover a greater per cent of the roads than a national system can hope to do. The effort seems to be to take over about 10 per cent of the established roads as state highways. Such roads, if carefully selected and located, can accommodate from 90 to 95 per cent of the inhabitants of the state. The remaining roads would continue under local--county and town--authorities. A county system might be laid out and money expended upon its roads about in proportion to their use. Again there is a feeling on the part of many that the first expense of improving a road (that would include grading, bridging, and paving, even if the latter should be done some time subsequent to the former) should be borne by the state and the abutting property, that the maintenance should be under the direction of the local authorities, and paid for by local taxation and by a portion of the state automobile license and gasoline taxes to be returned to the county for this purpose. =The Procedure of Laying out a Road System.=--To fix the mind definitely suppose it to be a state road system that is to be laid out. It is generally conceded that the planning should be done by an unprejudiced commission headed by an engineer of wide experience, one who is fair but will show no favoritism. The first question, after deciding to make a layout and who shall make it, is what shall be the determining factor of the lay-out. Shall it be primarily a farm to market system, primarily a commercial system, or primarily a recreational system? A wise commission will, no doubt, attempt to embody all these features in one system, as they should be, for, nowadays, more than half the population of the country reside in the cities and villages. They pay taxes and are as much entitled to road facilities for their particular industries and pleasures as are the “farm bloc,” and every fair-minded person will admit this. Good maps must of course be obtained. Government contour maps when available will assist materially in selecting roads that will come within a ruling grade. On these maps will first be noted the trunk line terminals and other ruling points. The trunk lines should be as direct as practicable from one ruling point to the next. An endeavor should be made to have the roads with the greatest travel upon them the straightest, so that the total future haul may be a minimum. The roads having the greatest travel will usually be those connecting the largest cities of the state or articulating with roads leading to large cities of other states. Then will be drawn in branch lines and detours so that when the plan is complete every county seat, every village of more than 1000 inhabitants, and every manufacturing, scenic, and pleasure resort of importance will have been reached, as well as connections with the main roads of adjacent states. This will form a tentative system. Observation upon the roads themselves will now be necessary. A reconnaissance survey may be made quite rapidly from an automobile. Two men are necessary. The engineer will ordinarily drive while the topographer will be supplied with a clip board and ruled sheets of paper. The straight line up the center of the sheet represents the roadway. Small squares on the sheets represent distances and areas. The scale should be made according to the work. On a road with few houses and few topographical features to be recorded 1 inch to the mile might be sufficient. With more houses, and other features, 1 inch to the quarter mile might be none too much. As speedometers (odometers) usually read to a tenth of a mile cross-section paper with ten smaller divisions equal to one larger is convenient. The engineer will observe features and the recorder will record them as the machine is driven along. The miles may be marked off on the sheets ahead then very quickly by a series of notations, such as a [Illustration] for a farm house, a dot with a roof over it [Illustration] for a school house, a steeple or cross on top [Illustration] makes a church. A crossing wagon road [Illustration], railroad track [Illustration], a trolley line [Illustration], stream [Illustration], and so on. Written explanations can be made along the margin where necessary. The reconnaissance survey should cover all routes on the tentative map together with alternative or competitive routes and others when found to be worthy of consideration. The record will show all farm houses within a prescribed limiting distance of the roadway, factories, stone quarries, sand and gravel pits, schoolhouses, and churches. All intersecting roads, railroads, trolleys, mail routes, creeks, canals, rivers, drainage and irrigation ditches, culverts and bridges, together with the approximate angle of crossing the highway. Note should be made whether grade crossings may be eliminated by underground or overhead crossings, or by change of route. The character of the soil whether clay, loam, gumbo, or sand, when it differs from the general run of soil should be recorded, also hills, swamps, bad condition generally with brief notes as to how they may be bettered. Turns in the road itself may be noted by an angle thus [Illustration], [Illustration], [Illustration], [Illustration]. Where no turn is shown, straight away is understood. Other information and natural or artificial features that may prove interesting or helpful will suggest themselves for record as the survey proceeds. Of course the mileage of each route as measured by the odometer or speedometer from fixed and known points on the map will be taken. By tabulating and mapping the information recorded it will be possible to get at the comparative merits of alternative routes. A few simple surveying instruments will be useful in the work of reconnoitering. A steel 100-foot tape, a hand level and inclinometer, a pedometer, a pocket compass, a small aneroid barometer in mountainous countries, a pioneer ax for blazing, and a small spade may be mentioned. After the reconnaissance, hearings should be held, usually at county seats, notice of such hearings having been given ahead of time. At these hearings the maps are shown and a statement made relative to the procedure. After which an invitation for suggestions and constructive criticism and even complaints is given. From these people who are locally interested in the roads many valuable suggestions will be received, and if they cannot be followed the reasons therefor may be stated. The people will thus know the investigation and the location of the road have been fairly made and that any suggestions that cannot be settled offhand will be duly considered before final location. The final location will usually be arrived at or at least influenced by the following considerations: Alignment and distance, population served, grades, amount and character of haulage, other kinds of transportation available, character of soil (sand, clay, gumbo, loam), structures, bridges, railroad grade crossings and their possible avoidance, discovery of entirely new routes, topography, geological formation, and other natural features and numerous local conditions, including availability and freight charges of road materials. These are not intended to be in the order of importance, for no two roads may have the same determining factors. The character of the road surface to be used in construction may greatly affect the location. For example it does not pay to use steep grades with hard smooth pavements. But steeper grades may be used with earth and gravel roads without material loss in efficiency. It will seldom be necessary to resort to preliminary or complete survey to lay out the plan. Sometimes further viewing of alternative roads may be desirable and many times compromises will have to be made. A traffic census on the several routes would be extremely valuable for it would determine to which class, agricultural, commercial, or recreational, the road belongs, and also the character of the traffic and what type of construction is best suited. Especially where there are alternative roads, as is usually the case in midwestern states where the roads were established along the section lines of the U. S. land survey, it is very difficult to determine which is the important highway without a traffic census. It must be remembered, however, in this connection that the improvement of a road will often draw to it much traffic from an equally short competing line. It is quite likely that if 10 per cent of all roads, provided they are properly selected, should be well improved they would carry 90 per cent of all traffic. =Financial Considerations.=--While little has been said of financial considerations they are, of course, of prime importance. The amount of money as a whole that may be expended is usually limited by the taxes voted or the bonds issued. The planner must cut the garment according to the cloth. He must know the approximate unit costs of the roads that will be constructed as well as the mileage of the several types. To know this he must estimate the amount of traffic that will pass over the road, he should know also about what part of this is local and what part through, in order that a just division of the cost may be made between the local and larger units. If all the money of construction were to be furnished by the national government, say, and only through traffic were considered, directness and grades between controlling points would be the determining factors. But since local traffic cannot be excluded from the use of such roads it is but just that part of the cost of building be paid locally, and if so, that modifications in the lay out be made to accommodate the local conditions. While the first cost of the road or the road system is of very great importance and will probably be the greatest influencing factor for any particular improvement or layout, the continued cost or cost covering a series of years approximating the life of the road surface should also have consideration. =Traffic Census.=--An important consideration in the selection of a road alignment, of its grades, its width, and of the type of its foundations and surfacing, is the amount and the character of the traffic which will pass over the roadway after it is built. The best way to get a reasonable estimate of this is to take a traffic census. This is to be used as a basis and to it should be added an estimate of the increase in traffic which the improvement itself will produce by drawing from parallel and contributing lines, and by the probable change that the improvement will work in the character of the farming, the industries and the settlements along its way. The alignment will be affected by the quantity of traffic, for the cost of haulage depends, though not proportionally, upon the length of haul. No less will the alignment be affected by the class of traffic. With horse-drawn vehicles curves of 40-foot radius were perfectly acceptable, but with the automobile a 200-foot radius is none too great. The new road systems now being adopted by states quite generally endeavor to make all curves to have radii greater than 200 feet except in mountainous regions, with a preference of 500 to 800 feet. [Illustration: © _Underwood and Underwood_ TRAFFIC ON FIFTH AVENUE, NEW YORK CITY] The longer radii allow the turns to be made without slowing up the traffic, providing there is proper superelevation of the outer edge. The longer the radius, that is, the flatter the curve, the less superelevation is required, and the less the tipping sensation experienced by slow-moving vehicles on the turn. Moreover, on short curves a considerable widening of the pavement is required in order that the inner and outer edges, and therefore all traffic lanes, may have the same degree of curvature. Also, clear vision for the longer distances necessary for fast-moving traffic is easier to obtain on flat than on sharp turns. The minimum grade of a roadway is usually a question of drainage, but the character and quantity of traffic is a determining factor in the establishment of steeper grades. Passenger cars can more easily negotiate grades than can commercial trucks. The average passenger car shifts to second gear at about a 7 per cent grade and there is very little shifting necessary on a long 6 per cent grade, hence for such cars 6 per cent may be considered a maximum for the high-speed gears. This same car will have to drop into low at about 10 per cent. Hence from the standpoint of the convenience of operating a passenger car there is no justification in going to great expense to cut a 10, or a 9, or an 8 per cent grade to a 7 per cent grade. For the average 5-ton truck 4 per cent and 8 per cent are the maximum grades for convenient running in high and intermediate. There may and possibly are many other reasons for cutting grades wherever possible. Where time is an element economy is effected by the possible speeds on grades. The width of the roadway will likewise be influenced by the quantity and character of traffic. With slow-going wagons a width of 8 feet was sufficient for one lane of traffic, but with the automobile safety demands 10, and the Good Roads Conference of 1922 voted that no road should be less than 22. The best type of foundation and surface is a factor of quantity and class of traffic, and while as yet all engineers do not agree, the numerous experiments now being made may lead to standardization. Just as an example may be mentioned the change that has taken place in the effect of vehicles on waterbound macadam. Under horse-drawn, iron-wheeled wagons and carriages this was considered an ideal pavement. The horses’ shoes and the iron tires wore off of the stones a sufficient amount of dust to keep the road crust well cemented. The rubber tires of the automobile do not do that; furthermore, what dust is on the road is picked up and scattered to the winds. The force of the drive wheels also is sufficient to loosen the stones and roll them from their bed, causing the roadway to ravel and disintegrate rapidly. These arguments might be multiplied indefinitely, but enough has been given to demonstrate the value to the road planner and the road designer of a traffic census. =Methods of Taking Traffic Censuses.=--It is well known that the traffic on any road is not constant. A count, then, made on a single day could not be applied for an entire year. Counting every day for the year would, of course, give a correct total, but that is impracticable. It is customary, therefore, to take the count on a limited number of days and consider their average to be the average for the year. There seems to be a seasonal variation in traffic and a weekly variation. The season variation in crops affects all sorts of commercial enterprises, of which the road traffic is one. Sunday traffic is largely pleasure traffic, and is more dense as a rule than week-day traffic, which is partially pleasure and partially business. In France, where more regular and scientific censuses have been made than in any other country, the counting days are divided uniformly between the seven days of the week and the four seasons of the year, in order to eliminate, as far as possible, the periodic variation. The number of counting days per year is therefore, 28, and these are so arranged that each of the days of the week figures once in each quarter. The interval between counting days is, consequently, 13. For 1923, then, the count might be made as follows: -----------+-----------+----------+----------+----------- Days of the| | | | Week |1st Quarter|2d Quarter|3d Quarter|4th Quarter -----------+-----------+----------+----------+----------- Monday | Jan. 1 | Apr. 2 | July 3 | Oct. 2 Sunday | 14 | 15 | 16 | 15 Saturday | 27 | 28 | 29 | 28 Friday | Feb. 9 | May 11 | Aug. 11 | Nov. 10 Thursday | 22 | 24 | 24 | 23 Wednesday | Mar. 7 | June 6 | Sept. 6 | Dec. 6 Tuesday | 20 | 19 | 19 | 19 -----------+-----------+----------+----------+----------- This method distributes the counting days uniformly over the entire year, but evidently the expense would be considerable unless it can be done by the regular patrolman. For the purpose of laying out a system of highways quicker results might be desired. In Massachusetts, Connecticut and other states two counts were made about two or three months apart. If one were taken in July, say, and another in October and the results averaged it is thought they might fairly represent the year. Each period could cover an entire week, thus giving an average of 14 days during those seasons of the year when traffic might most nearly represent the normal. Blanchard’s method[177] contemplates taking the census in four periods of three days each, one in April, May, or June, one in July, one in August, and one in September or October, as local conditions may dictate. The days selected should include Sunday in order to include the heavy automobile traffic on that day. If further information is desired additional three-day periods could be taken during the winter season. Most of the authorities seem to think that the daylight hours from 5 A.M. to 9 P.M. are sufficient. But in the light of the tests being conducted by the Illinois Highway Commission which show alternate convex and concave warping of pavements from day to night it might be well to take account of night traffic. Some of the latest censuses, namely Iowa and Connecticut, placed scales on the highways and actually weighed the vehicles. In Connecticut road scales were used which weighed the individual wheel loads. The observers are supplied with cards on which is printed the classified list of vehicles and animals likely to pass with columns for tallying them during the separate hours. The in-and-out-of-town vehicles are recorded separately, and, if actual weights are not taken, whether loaded or unloaded. Information relative to the weather and condition of the roads is also noted, and there are blank spaces for the station, the date, and the signature of the observer. The station, or stations, should be so placed that the road or district will be fairly represented, since it will not be practicable to get exact data on every portion of a highway, for every turn-out, branch line, or tributary will alter results. Each station should be established in some place where a good view of the road for some little distance may be had, and where the observers may be reasonably comfortable. The number of observers will depend upon the amount of traffic and the detailed information desired. With considerable traffic it may be necessary to divide up the work, giving one set of observers the in-traffic and another the out-traffic, one man to observe passenger automobiles another trucks and delivery wagons, or one man to jack up and weigh front wheels and another rear. System will result in more accurate results, and in less loss of time for the drivers, and less congestion of traffic. It is customary to take the census over the entire system on the same days although that is not absolutely necessary. =Classification of Traffic.=--The object of a classification is to obtain: (_a_) the maximum loads and average number of heavy loads per day. (_b_) The lighter loads, whether horse drawn or motor driven, iron, solid rubber or pneumatic tire, trailers, traction engines, animals, harnessed and unharnessed, and any other load which might affect the wear of the roadway. (_c_) Any other interesting data regarding the traffic, such as, local or through, cars belonging within or without the state or county, camping parties, and so on. Maximum wheel loads are required, primarily, to see if state regulations regarding them are being complied with. In the Connecticut census it was found that a majority of trucks were loaded beyond their rated capacity and many of them beyond the legal maximum wheel loads. Again heavy loads stress a pavement near to its elastic limit every time they pass over it. It is well established that any structural material when stressed near, to, or beyond the elastic limit will become fatigued with repeated stresses. The higher the stress the quicker they will fail by fatigue. It is not considered good practice to stress a material, especially a brittle material, repeatedly to a point half-way to its elastic limit. (The elastic limit is that stress that may be given to a body without producing a permanent set; below which it will return to its original shape upon the removal of the stress.) A walnut may not crack at the first blow but with a sufficient number of no harder repeated blows will crack. The higher the stresses the sooner the crack occurs. So it is important to know how many loads daily are stressing a pavement near to its elastic limit. From all the loads it has been the endeavor of road engineers to work out “importance factors” that will measure the relative damage done by the several classes. The Road Board of Great Britain has adopted the British ton as a unit and calculations are based on the traffic in tons per yard of width per year or per mile.[178] The British Road Board Unit Weights are as follows: -------------------------------------+--------------- |Assumed Average Classification of Vehicles |Weight in Tons. ------------------------------------+--------------- Ordinary cycles | 0.09 Motor cycles | .13 Motor cars (including motor cabs and| any other motor vehicles) | 1.6 Motor vans (covered) | 2.5 Motor omnibuses | 6.0 Motor lorries (rubber tires) | 6.0 Trailers to rubber tired lorries | 5.0 Motor lorries (steel tires) | 10.0 Trailers to steel tired lorries | 5.0 Light tractors | 5.0 Trailers to light tractors | 5.0 Traction engines | 12.0 Trailers to traction engines | 8.0 Light vehicles (one horse) | 0.4 Light vehicles (two or more horses) | 0.6 Heavy vehicles (one horse) | 1.25 Heavy vehicles (two or more horses) | 2.5 Omnibuses (two or more horses) | 3.0 Tram cars (electric, steam or horse,| as the case may be) | .... Horses (led or ridden) | 0.5 Cattle | 0.3 Sheep and pigs | 0.1 Hand carts and barrows | .... Horses drawing vehicles (to be | calculated from number of vehicles) | 0.5 ------------------------------------+--------------- The French unit of traffic is technically known as the “collar,” a draft animal harnessed to a wagon being counted as 1.0. The metric ton, 1000 kg., is also sometimes used. The French, feeling that the dead weight of a vehicle or animal did not truly measure its effect as to wear on a road surface, classified the traffic and assigned importance factors to the several classes. From 1882 to 1903 the classification consisted of: 1st, Trucks and farm wagons, loaded; 2d, Public vehicles designed for transporting passengers and their baggage; 3d, Light vehicles, such as private vehicles, and empty farm wagons; 4th, Larger animals, such as horses, mounted or not, mules, and large cattle; 5th, Small beasts, such as sheep, goats, and pigs. In 1903 motor vehicles were separately listed; they were divided into five classes: 1st, Metallic-tired automobiles, “which in general are heavily loaded, have a slow movement and produce the effect of wearing away the road surface”; 2d, Elastic tired automobiles licensed to make a speed of not more than 30 km. per hour; 3d, Automobiles whose speed was less than 30 km. per hour; 4th, Bicycles or velocipedes propelled by the feet of the rider; and 5th, Motor cycles, whether having two, three, or four wheels. The report of the second international road congress further states that “it is necessary to attribute to each element of the traffic an importance which belongs to it from the viewpoint of the destructive effect exercised on the road crust.” Consequently the numbers of vehicles or animals in the several classes were modified by multiplying them by importance factors arbitrarily assumed. Importance Classification factors An animal harnessed to a loaded vehicle 1 collar Loaded trucks and farm wagons 1 Public vehicles for transporting passengers 1 Light vehicles, and empty farm wagons ¹⁄₂ Harnessed horses to light vehicle or empty wagon ¹⁄₄ Mounted horses or with load on back ¹⁄₄ Unharnessed horses ¹⁄₅ Cattle ¹⁄₅ Small beasts (sheep, pigs, goats) ¹⁄₃₀ Automobiles with metallic tires, weight in metric tons times 1¹⁄₄ = No. of collars Automobiles with elastic tires Motor cycles ³⁄₁₀ Vehicles licensed to make a speed over 30 km. per hour 3 Vehicles licensed to make a speed of less than 30 km. per hour 1 From this it was possible to reduce all traffic to the unit “collar,” which was used as a comparative measure of the use of the several roadways. The tonnage was calculated by multiplying the numbers by average weights obtained by weighing a sufficiently large number of the units in each class. Consideration was also made of the weight of the useful load as separate from the weight of the vehicle itself. Animals not harnessed were considered as a part of the useful load. In Italy traffic censuses followed practically the same classification and methods as in France. In the United States some of the states have used coefficients of reduction, or importance factors, while many others have contented themselves with a count of vehicles only. In 1910 Maryland used the following: