classification merely because artificial aids must make the highway suitable for use before commercial navigation may be undertaken," provided there must be a "balance between cost and need at a time when the improvement would be useful. * * * Nor is it necessary that the improvements should be actually completed or even authorized. The power of Congress over commerce is not to be hampered because of the necessity for reasonable improvements to make an interstate waterway available for traffic. * * * Nor is it necessary for navigability that the use should be continuous. * * * Even absence of use over long periods of years, because of changed conditions, * * * does not affect the navigability of rivers in the constitutional sense."[365] Purposes for Which Power May be Exercised Furthermore, the Court defined the purposes for which Congress may regulate navigation in the broadest terms, as follows: "It cannot properly be said that the constitutional power of the United States over its waters is limited to control for navigation. * * * That authority is as broad as the needs of commerce. * * * Flood protection, watershed development, recovery of the cost of improvements through utilization of power are likewise parts of commerce control."[366] These views the Court has since reiterated.[367] Nor is it by virtue of Congress's power over navigation alone that the National Government may develop super-power. Its war powers and power of expenditure in furtherance of the common defense and the general welfare supplement its powers over commerce in this respect.[368] Congressional Regulation of Land Transportation EARLY ACTS; FEDERAL PROVISION FOR HIGHWAYS The acquisition and settlement of California stimulated Congress some years before the Civil War to authorize surveys of possible routes for railway lines to the Pacific; but it was not until 1862, in the midst of war, with its menace of a general dissolution of the Union, that more decisive action was taken. That year Congress voted aid in the construction of a line from Missouri River to the Pacific; and four years later it chartered the Union Pacific Company.[369] First and last, litigation growing out of this type of legislation has resulted in the establishment in judicial decision of the following propositions: _First_, that Congress may provide highways for interstate transportation (earlier, as well as today, this result might have followed from Congress's power of spending, independently of the commerce clause, as well as from its war and postal powers, which were also invoked by the Court in this connection); _second_, that it may charter private corporations for the purpose of doing the same thing; _third_, that it may vest such corporations with the power of eminent domain in the States; and _fourth_, that it may exempt their franchises from State taxation.[370] BEGINNINGS OF FEDERAL RAILWAY REGULATION