In 1850 the United States had about 9,000 miles of railroad track. The first transcontinental railroad across the United States was finished at Promontory Summit, Utah, on May 10, 1869.

Union Pacific crews built the railroad west from Omaha, Nebraska, while Central Pacific crews built east from Sacramento, California, until the two lines met in Utah.

In 1862 Congress passed the Pacific Railroad Act, which gave the Central Pacific and Union Pacific companies land and government bonds for each mile of railroad they built. The two companies built miles of track side by side past each other, so Congress had to name Promontory, Utah, as the place where the lines would join.

The Central Pacific dug its Summit Tunnel in the Sierra Nevada on four faces at once: two teams worked inward from the two ends of the tunnel, and two worked outward from the middle.

The winter of 1866-67 was a fierce one in the Sierra Nevada, where the Central Pacific was tunnelling. It brought forty-four storms.

In that tunnel, switching from black powder to nitroglycerin raised the average progress in the headings from 1.18 to 1.82 feet a day, and at the bottom of the tunnel from 2.51 to 4.38 feet a day.

California banned the transport of nitroglycerin, so to keep using it the Central Pacific hired a chemist, James Howden, to make it on site in the mountains instead of shipping it.

The golden spike was only ceremonial: the track was finished with ordinary iron spikes in an ordinary tie.

When the last spike of the first transcontinental railroad was driven, a one-word telegram, "Done.", was sent across the country.

Before railroad time zones, most U.S. towns kept their own local time based on the sun, which made train schedules confusing. On November 18, 1883, American railroads began using four standard time zones to replace the many local times used in schedules. In 1918 Congress passed the Standard Time Act, which made time zones the law of the United States 35 years after the railroads began using them.

New York City's first subway line opened on October 27, 1904, and it was about nine miles long. On its first day it carried more than 100,000 riders, each of whom paid a nickel (five cents).

Words to know

• transcontinental: across a continent
• ceremonial: for show
• bonds: government IOUs
• telegram: wire message