The population growth of Germany fitted with two single cycle curves.

UPPER ASYMPTOTE 119.552

GERMANY (General Curve).

40

FIG. 5. The population growth of Germany, fitted with the general curve

(equation (i)).

It is obvious that this procedure describes the known facts regarding Germany's population growth in an entirely satisfactory

manner.

Can we do as well or better with the general curve (i)? The answer to this question is given by Fig. 5.

The equation of the fitted curve is

= y

119.552

I + el.9416.0331x+.00038x2-.000000213

(viii)

Plainly the fit of theory to observations is as close as could be desired.

Taking all the available evidence into account, of which only a fraction has been presented above, I believe that it is justifiable to regard equation (i) as constituting a descriptive law of population growth. By its instrumentality we can describe how populations grow, and predict their future growth over reasonable periods of time with a degree of accuracy not attainable by any other method hitherto discovered.

THE NATION'S TRANSPORTATION PROBLEM.

BY EMORY R. JOHNSON,

(Professor of Transportation and Commerce and Dean of the Wharton School, University of Pennsylvania.

It is a somewhat paradoxical fact that as the transportation facilities of any country are developed and made more efficient economic prosperity and social well being become increasingly dependent upon adequate, prompt and economical carriage of persons and property and transmission of ideas. Transportation is one of the principal determinants of social organization and social progress.

In a country such as the United States, the demand for transportation services grows with surprising rapidity, and the capital required to keep transportation facilities abreast of demand has already reached large figures and must necessarily continue to increase at a corresponding rate. Every nation has its transportation problem and always will have. The United States, having a more extensive transportation system than any other country possesses, may be said to have the greatest transportation problem of any nation.

The truth of this is evidenced by the facts as to the present and prospective traffic upon steam and electric railways and upon highways and the capital required for the development of railroad and other transportation facilities. The purpose of this paper is to state those facts briefly and to consider with equal brevity some of the principles that should control the government's relation to transportation.

PRESENT VOLUME OF TRAFFIC.

Figures of traffic that run into billions are too large to give the human mind a definite impression, but they at least indicate in a general way the magnitude of the service rendered by railroads and other transportation agencies in the United States. In 1923, the railroads in this country had a revenue-paying traffic amounting to 413,562,000,000 tons one mile. If the non-revenue or company

freight be added the total becomes 457,589,000,000 ton miles. This is the largest freight traffic ever handled by the railroads in any

year.

The passenger services of the railroads in 1923 amounted to 38,000,000,000 passengers one mile. This, however, was not so large a traffic as the railroads handled during the unusual period of the participation of the United States in the World War.

The electric railways of the United States in 1923 carried more than 16,000,000,000 passengers. Records are not kept of the distances that passengers travelled on electric railways and, for that reason, it is not possible to give figures for passenger miles.

It is not definitely known how many passengers were carried by motor busses in this country, but it is estimated that approximately 1,000,000,000 passengers ride in motor busses annually. The traffic is large and is increasingly rapidly. The Fifth Avenue Coach Company of New York City carried 56,000,000 revenue passengers in 1923. It is said that 3,500,000 people daily ride upon the busses operated on the streets of London. The motor busses in London are now transporting a billion and a quarter passengers annually. It has been roughly estimated that in 1923 passenger automobiles carried nearly ten billion passengers, and that the average ride was about eleven miles in length. This would make the motor passenger miles over one hundred billion or two and one-half times the railroad passenger miles.

Only very partial information is known of the volume of freight handled by motor trucks which are now being largely used both by organized carriers and by large shippers using their own trucks. An estimate based upon data presented by the Automobile Chamber of Commerce indicates that motor trucks in 1923 carried 2,220,000,000 tons of freight, the average haul being less than five miles. The total ton-miles was approximately ten and one-half billion.

FUTURE INCREASE IN TRAFFIC.

A careful estimate has been made of the volume of traffic that will be moving upon American railroads ten years hence or in 1933The estimate was made for the Bureau of Railway Economics by the railroad companies of the United States. The companies re

porting information operated two thirds of the railway mileage in the country and handled over two thirds of the traffic. On the basis of these reports, it is evident that there will be an increase of at least one third in the freight traffic of American railroads during the decade ending in 1933. This is a much smaller rate of increase than has prevailed in the past. But even that growth will bring the revenge freight traffic of American railroads in 1933 up to 550,000,000,000 ton miles. The passenger traffic will probably increase somewhat slower than the freight business, but the increase during the decade ending in 1933 can hardly be less than 25 per cent. Even that conservative estimate brings the passenger traffic of American railroads in 1933 up to 47,500,000,000 passenger miles, which is not much more than the total reached during the war period.

It takes imagination as well as information to picture the economic development of a country such as the United States. The increase of large scale production accelerates industrial activity. Capital accumulates with augmented speed, the country goes ahead faster than most people realize. An indication of the economic growth of the country is given by a statement made by the Pennsylvania Railroad that upon the lines of that company's system 513 new industries were located in 1923 developing freight traffic estimated at more than 6,500,000 tons annually. These newly established enterprises on the Pennsylvania System will expect to load 186,000 cars annually.

In spite of the enormous travel by private automobiles and the rapid increase in the use of motor busses, the electric railways in the United States have a constantly expanding traffic. The increase in their traffic in the decade ending in 1922 was 60 per cent.

Although it seems somewhat paradoxical, it is none the less a fact that the increase of the use of motor busses tends to supplement rather than to supplant the service of electric railways. The busses bring traffic to the railroads and electric railways and thus complement, as well as compete with, the carriers by rail. Undoubtedly the most rapid increase in traffic is that of the motor busses, but figures are not available to show the actual rate of increase in this traffic.

CAPITAL REQUIRED ANNUALLY.

This ever enlarging work of transportation cannot be performed without large expenditures of capital. The railroad companies in