Vessel shipments, entrances, and clearances.-Shipments by dry cargo vessels comprise shipments on all types of watercraft, except tanker vessels; shipments by tanker vessels comprise all types of cargo, liquid and dry, carried by tanker vessels. A vessel is reported as entered only at the first port which it enters in the United States whether or not cargo is unloaded at that port. A vessel is reported as cleared only at the last port at which clearance is made to a foreign port, whether or not it takes on cargo. Army and Navy vessels entering or clearing without commercial cargo and vessels touching at a United States port in distress, or for other temporary causes without discharging cargo, are not included in the figures.

Units of measurement.-Cargo tonnage and shipping weight both represent the gross weight of the cargo including the weight of containers, wrappings, crates, etc. However, shipping weight excludes lift and cargo vans and similar substantial outer containers. Other tonnage figures generally refer to stowing capacity of vessels, 100 cubic feet being called 1 ton. Gross tonnage comprises the space within the frames and the ceiling of the hull, together with those closed-in spaces above deck available for cargo, stores, passengers, or crew, with certain minor exceptions. Net or registered tonnage is the gross tonnage less the spaces occupied by the propelling machinery, fuel, crew quarters, master's cabin, and navigation spaces. It represents substantially space available for cargo and passengers. The net tonnage capacity of a ship may bear little relation to weight of cargo. Dead-weight tonnage is the weight in long tons required to depress a vessel from light water line (that is, with only the machinery and equipment on board) to load line. It is, therefore, the weight of the cargo, fuel, etc., which a vessel is designed to carry with safety.

Historical statistics.-Tabular headnotes provide cross-references, where applicable, to Historical Statistics of the United States, Colonial Times to 1957. See preface.

No. 937.

SCHEDULED AIR CARRIERS-NUMBER, OPERATING REVENUES, AND
EXPENSES: 1955 to 1970

[In millions of dollars, except number of carriers. 1955 not exactly comparable with later years. See also headnote,

table 941]

Includes all cargo carriers. Each airline counted only in group in which greater portion of its operations prevailed.

Source: U.S. Federal Aviation Administration, FAA Statistical Handbook of Aviation, annual. Data from U.S.

Civil Aeronautics Board.

Transportation-Air and Water

565

FIG. XXXVIII. DOMESTIC SCHEDULED AIR CARRIERS-REVENUES, MILES FLOWN, AND PASSENGERS CARRIED: 1957 TO 1970

Source: Chart prepared by U.S. Bureau of the Census. Data from U.S. Federal Aviation Administration.

Source: Chart prepared by U.S. Bureau of the Census. Data from U.S. Corps of Engineers.

No. 920. Bus CARRIERS-REVENUE AND EXPENSES, BY TYPE OF SERVICE: 1967 [Money figures in thousands of dollars. Covers carriers with payroll not subject to Interstate Commerce Commission economic regulation. Excludes carriers operated by municipalities or other governmental bodies]

Represents zero. 1 Includes unclassified carriers, not shown separately.
Source: U.S. Bureau of the Census, U.S. Census of Business: 1967, Misc. Subjects, BC 67-SS8.

No. 921. CLASS I INTERCITY MOTOR CARRIERS OF PROPERTY: 1950 TO 1971 [Carriers subject to ICC regulations. Prior to 1960, excludes Alaska and Hawaii. See text, p. 536, for class limits]

Source: U.8. Interstate Commerce Commission, Transport Statistics in the United States, Part 7, annual.

5,676

No. 922. TRUCK CARRIERS-REVENUE AND EXPENSES, BY TYPE OF CARRIER: 1967 [Money figures in millions of dollars. Covers only carriers with payroll not subject to Interstate Commerce Commission regulations. Based on a probability sample of all carriers with payroll in the "trucking, except with storage," industry; for details, see source]

Source: U.S. Bureau of the Census, U.S. Census of Business: 1967, Misc. Subjects, BC 67-SS8.

Railroads

No. 923. RAILROADS-SUMMARY STATISTICS: 1940 TO 1971

557

[As of December 31. 1950 excludes Alaska and Hawaii. Covers class I and II railroads, excluding switching and terminal companies, except as noted. Includes intercorporate duplications. See also Historical Statistics, Colonial Times to 1967, series Q 44-124]

1 Includes unofficial companies and, through 1960, circular companies; see text, p. 536.
Includes lessors, proprietary, unofficial and, through 1960, circular companies.
Includes mileage in Canada.

Includes switching and terminal companies, except average tractive effort and average capacity.
For 1950, steam locomotives of class I railroads; beginning 1960, all locomotives of class I railroads.
Represents horsepower. 7 Excludes caboose cars. Class I railroads only. Includes lessors.

10 Increase in investment over a period of years cannot be obtained accurately by subtraction of 1 year's investment from that of another owing to reorganization, sale or abandonment, reclassification, etc. Also includes proprietary companies. 11 Includes amortization applicable to proprietary companies.

12 Comprises common stock, preferred stock, and funded debt unmatured.

13 After extraordinary and prior period items. 14 Includes highway grade crossing casualties.

Source: U.S. Interstate Commerce Commission, Transport Statistics in the United States, Part 1, annual, and Accident Bulletin, annual. Beginning 1969, accident data from U.S. Federal Railroad Administration, Accident Bulletin, annual.

494-660 O-73-37

No. 924. RAILROADS, CLASS I LINE-HAUL-REVENUES AND EXPENSES: 1950 TO 1972 [In millions of dollars, except percent. See text, p. 536, for explanation of class limits. See also Historical Statistics, Colonial Times to 1957, series Q 103-117]

No. 925. RAILROADS, CLASS I LINE-HAUL-SELECTED PASSENGER STATISTICS: 1950

TO 1972

[See text, p. 536, for explanation of class limits. See also Historical Statistics, Colonial Times to 1957, series Q 87-89]

No. 926. RAILROADS, CLASS I LINE-HAUL-SELECTED FREIGHT STATISTICS: 1950 TO

1972

[Excludes switching and terminal roads. Tons of 2,000 pounds. See text, p. 536, for explanation of class limits. See also Historical Statistics, Colonial Times to 1957, series Q 93]

Source of tables 924-926: U.S. Interstate Commerce Commission, Annual Report and Transport Statistics in the United States, Part 1, related monthly and quarterly reports, and Financial and Operating Statistics, Class I Railroads, Statement No. 100, semiannual; and unpublished data.