Greenwich Mean Time was introduced in 1675, in conjunction with the opening of the Royal Observatory, but it was introduced as a navigational aid for mariners, not to govern timekeeping practice, which remained highly localized. The development of railway travel accelerated the need for standardization; the accelerated pace of travel meant that local time discrepancies posed a practical problem. Britain adopted Greenwich Mean Time as standard in 1848 (although this was not legally formalized until 1880), with railways taking the lead in implementation. North America resolved to follow, with the railways again to the fore. Four time zones were proposed: Eastern, Central, Mountain and Pacific. Their borders were based on solar noon at respectively 75, 90, 105 and 120 degrees of longitude west of Greenwich. The rigid lines of longitude were subsequently amended to keep existing railroads within the same time zones. Standard time took effect at midday on 18 November 1883, but again legislation lagged behind transportation: Congress would not enact Standard Time Zones until March 1918.
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