California has—and for decades has had—more motor vehicles than any other state, and ranked second only to Texas in interstate highway mileage in 2000. An intricate 8,300-mi (13,400-km) network of urban interstate highways, expressways, and freeways is one of the engineering wonders of the modern world—but the traffic congestion in the state's major cities during rush hours may well be the worst in the country. In 2000, California had a total of 168,076 mi (270,492 km) of public roads, streets, and highways.

In pioneer days, the chief modes of transportation were sailing ships and horse-drawn wagons; passage by sea from New York took three months, and the overland route from Missouri was a six-week journey. The gold rush spurred development of more rapid transport. The state's first railroad, completed in 1856, was a 25-mi (40-km) line from Sacramento northeast to Folsom, in the mining country. The Central Pacific–Union Pacific transcontinental railroad, finished 13 years later, was financed in part by several Sacramento business leaders, including Leland Stanford, who became governor of the state in 1861, the same year he assumed the presidency of the Central Pacific. Railroad construction crews, mostly imported Chinese laborers, started from Sacramento and dug and blasted the route through the solid granite of the Sierra Nevada and then across the Nevada desert, linking up with the Union Pacific at Promontory, Utah, on 10 May 1869. Stanford himself helped to drive the golden spike that marked the historic occasion. The Southern Pacific completed a line from Sacramento to Los Angeles in 1876 and another to Texas the following year. Other railroads took much longer to build; the coastal railroad from San Francisco to Los Angeles was not completed until 1901, and another line to Eureka was not finished until 1914. The railroads dominated transportation in the state until motor vehicles came into widespread use in the 1920s.

As of 2000, California had 7,710 rail mi (12,408 km) of track, with Class I track constituting 75%; Class I railroads operating within the state in 2000 included Burlington Northern and Santa Fe Railway and Union Pacific. Amtrak passenger trains connect the state's major population centers with an average of 38 intercity trains and an additional 170 commuter trains every day.

Urban transit began in San Francisco in 1861 with horse-drawn streetcars. Cable-car service was introduced in 1873; a few cable cars are still in use, mainly for the tourist trade. The 71-mi (114-km) Bay Area Rapid Transit System (BART) was completed in the 1970s despite many mechanical problems and costly delays. BART connects San Francisco with Oakland by high-speed, computerized subway trains via a 3.6-mi (5.8-km) tunnel under San Francisco Bay and runs north-south along the San Francisco peninsula.

Public transit in the Los Angeles metropolitan area was provided by electric trolleys beginning in 1887. By the early 1930s, the Los Angeles Railway carried 70% of the city's transit passengers, and in 1945 its trolleys transported 109 million passengers. Competition from buses—which provided greater mobility, but aggravated the city's smog and congestion problems—forced the trolleys to end service in 1961. During the late 1980s, plans were developed for a commuter rail transportation system in the Southern California region. In 1992, the first three lines of the Metrolink system began operation. By 1995, six Metrolink lines were serving the counties of Los Angeles, Orange, Riverside, San Bernardino, and Ventura.

California's extensive highway system had its beginning in the mid-19th century, when stagecoaches began hauling freight to the mining camps from San Francisco, Sacramento, and San Jose. In the early 1850s, two stagecoach lines, Adams and Wells Fargo, expanded their routes and began to carry passengers; by 1860, some 250 stagecoach companies were operating in the state. The decline of stagecoach service corresponded with the rise of the railroads. In 1910, at a time when only 36,000 motor vehicles were registered in the state, the California Highway Commission was established. Among its first acts was the issuance of $18 million in bonds for road construction, and the state's first paved highway was constructed in 1912. The number of automobiles surged to 604,000 by 1920; by 1929, about 1 of every 11 cars in the US belonged to a Californian. Ironically, in view of the state's subsequent traffic problems, the initial effect of the automobile was to disperse the population to outlying areas, thus reducing traffic congestion in the cities.

The Pasadena Freeway, the first modern expressway in California, opened in 1941. During the 1960s and 1970s, the state built a complex toll-free highway network linking most cities of more than 5,000 population, tying in with the federal highway system, and costing more than $10 billion. Local, state, and federal authorities combined spent over $9.3 billion on California highways in 1997, nearly $2 billion of that amount for maintenance. Also in 1997, federal aid to California from the Federal Highway Administration fund totaled about $2 billion.

By providing easy access to beach and mountain recreation areas, the new freeways—in combination with the favorable climate and low price of gasoline—further encouraged the use of the automobile and led to massive traffic tie-ups, contributed to the decline of public transit, and worsened the coastal cities' air-pollution problems. Los Angeles County claims more automobiles, more miles of streets, and more intersections than any other city in the US. The greatest inducement to automobile travel in and out of San Francisco was the completion in 1936 of the 8-mi (13-km) San Francisco–Oakland Bay Bridge. The following year saw the opening of the magnificent Golden Gate Bridge, which at 4,200 ft (1,280 m) was the world's longest suspension bridge until New York's Verrazano–Narrows Bridge opened to traffic in 1964.

In 2000, California had 168,076 mi (270,492 km) of public roads. Included in this total were 83,428 mi (134,264 km) of roads classified as rural and 84,648 mi (136,227 km) classified as urban. Also in 2000, the state registered 28,146,424 motor vehicles, first in the nation—including 17,321,413 automobiles, 10,329,198 trucks, and 47,312 buses. California also leads the nation in private and commercial motorcycle registrations, at 448,501. There were 21,243,939 California drivers' licenses in force in 2000.

The large natural harbors of San Francisco and San Diego monopolized the state's maritime trade until 1912 when Los Angeles began developing port facilities at San Pedro by building a breakwater that eventually totaled 8 mi (13 km) in length. In 1924, Los Angeles surpassed San Francisco in shipping tonnage handled and became one of the busiest ports on the Pacific coast. In 2000, the port at Long Beach handled 70.1 million tons of cargo. The port at Los Angeles handled 48.2 million tons in 2000. Other main ports and their 2000 cargo quantities include Richmond, 19.5 million tons; Oakland, 12.2 million tons; and San Diego, with 3.7 million tons.

In 2002, California had nearly 935 aircraft facilities, including 539 airports, 383 heliports, 11 seaplane bases, and 2 stolports. California's most active air terminal—and one of the nation's most active—is Los Angeles International Airport, which handled enplaned 32,167,896 passengers in 2000. Also among the nation's 20 busiest air traffic control towers in 2000 were those at San Diego, Oakland, San Jose, Sacramento, Santa Ana, and San Francisco.