From coast to coast, an engineering marvel

Motorists were tearing along Route 1 in their gas-guzzling '56 Chevies when construction first began on the massive asphalt web that makes up the nation's Interstate highways.

Since then, the system some have called the greatest public-works project in history has changed America's landscape. Not only has it made travel easier, some estimate that Interstates, which cost more than $129 billion to build, have returned $774 billion in added economic productivity.

The system was declared finished in 1991, but there are still a few small stretches on the drawing board or under construction. Today it spans almost 43,000 miles, a distance that would circle the earth nearly twice.

A strategic defense

Although the first rumble of bulldozers breaking ground was not heard until 1956, plans for the Interstate system began much earlier when Congress called for a feasibility study in 1938. Six toll-financed superhighways were proposed: three to run north-south and three east-west. In 1947, state highway agencies along with the Defense Department mapped out the first 37,700 miles of the present system.

It was not until the Eisenhower administration pushed through the Federal-Aid Highway Act in 1956, however, that construction could begin.

President Eisenhower, a former general, believed the highway system would be an important part of the nation's strategic defenses, allowing efficient troop and equipment transport. So he made its construction a priority.

With passage of the Highway Act, the federal government agreed to pay 90 percent of the Interstate system's construction costs, instituting gasoline and motor-vehicle user taxes as a "pay-as-you-go" financing strategy. The project was later named the Dwight D. Eisenhower System of Interstate and Defense Highways.

A new kind of highway

The Interstate system began a new kind of highway, introducing nonstop traffic as well as new safety standards. Unlike the old US highways, Interstates could have no intersections and no traffic signals. To accomplish this, engineers had to build more than 55,000 bridges or overpasses for intersecting roads and railway tracks.

The new safety standards also required that all Interstates be divided, have at least four extra-wide lanes, and wide shoulders. All curves were to be engineered to accommodate banking at high speeds, and blind spots at the peaks of hills were to be eliminated.

Did you know?

*Routes with odd numbers run north and south, while routes with even numbers run east and west.

*For north-south routes, the lowest numbers begin in the West, while for east-west routes, the lowest numbers begin in the South. For example, I-5 runs along the West Coast, but I 10 lies along the southern border.

Making connections

One objective of the system is to connect cities of 50,000 or more people. Accoring to the latest census figures, Interstates actually links 286 of 366 cities that size. It also links 45 of the nation's 50 state capitals.

Bumper to bumper across the USA

Surprise. The busiest highway is not in Los Angeles. It's not even in New York or Chicago. The busiest stretch of Interstate is I-75 in Atlanta, one of the widest paved surfaces in the US, with 13 lanes for horn-honking traffic.

Here's a list of the most-traveled stretches of the Interstate system.

(c) Copyright 1999. The Christian Science Publishing Society