The Freeway Numbers Game

The noted British architectural historian Reyner Banham once dubbed the Los Angeles freeway system the city’s “fourth ecology”--an “Autopia” every bit as much a part of the landscape as the beaches, the flatlands and the foothills that define the region both physically and psychically.

“The actual experience of driving on the freeways prints itself deeply on the conscious mind and unthinking reflexes,” Banham wrote in his 1971 book “Los Angeles: The Architecture of Four Ecologies.”

“As you acquire the special skills involved, the Los Angeles freeways become a special way of being alive.”

Yet for all their mystique--and their often intimidating effect on newcomers--the freeways follow a fairly logical layout as they stitch together a disparate metropolis. And the jumble of numbers and names actually makes sense once drivers understand the basics.

The rules are pretty much the same nationwide.

For instance, the 27 east-west national highways such as Interstate 10--the Santa Monica and San Bernardino freeways hereabout--have even numbers. And the 31 north-south highways such as Interstate 5--the Golden State and Santa Ana locally--have odd numbers.

The lower the number, the farther south or west the highway is. North-south routes take higher numbers as they move east. The same goes for east-west routes as they move north.

So it’s not hard to figure out that Interstate 90--which, at 3,081 miles, is the longest route in the country--is also among the farthest north in the Lower 48 states. It connects Boston and Seattle. The second longest at 2,907 miles, Interstate 80, connects New York City and San Francisco.

The shortest route is Interstate 878, which runs just seven-tenths of a mile in New York City. Three digits though? Routes posted with three digits such as the 878--or the 405, the San Diego Freeway--are offshoots of the main routes. Like their big brothers, the offshoots are numbered according to where they are and where they go.

If the first of the three numbers is even, the route is considered a beltway and connects to an interstate at both ends, generally to avoid the traffic congestion of the main road. The 405, for instance, veers away from Interstate 5 in the north San Fernando Valley and loops back in Irvine, although anyone who’s ever driven the 405 knows it fails to avoid much congestion.

Attentive readers probably have already figured out that the second and third numbers denote the freeway from which the beltway route splits. So it follows that the 210 splits from the 10 in Pomona and then joins the 5 near Sylmar.

The 878, by the way, is part of the Nassau Expressway near John F. Kennedy International Airport in Queens.

If the first number is odd, the route is a spur that does not connect back to an interstate. The 710, for example, splits from the 10, but never rejoins an interstate. The same goes for the 110, or Harbor Freeway.

But all of this applies only to interstates. Before 1956, the nation’s first effort at comprehensive roads was the United States Highway System. Among the most famous: Route 66. Most of the same rules apply, but are reversed. North-south routes take higher numbers as they move west and east-west routes get higher moving south. The intent was to prevent any state from having the identical U.S. Highway and interstate numbers.

State routes, such as the 170 or the 118, don’t follow the same rules.

Despite all the care and thought that go into numbering the freeways, few locals ever use most of the numbers. Even fewer ever use some of the names bestowed upon ribbons of concrete by the state and local bureaucrats.

Almost nine years after it was named, few people call the 105 by its proper moniker: the Glenn M. Anderson Freeway, after the Long Beach congressman who helped round up funding for local transportation projects. Many still call it the Century Freeway.

In the same way, most drivers heading through the Santa Susana Pass refer to the route as the Simi Valley Freeway, not the Ronald Reagan Freeway. In fact, most freeways get their handles from the places they go to.

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The Harbor Freeway. The Ventura Freeway. The Hollywood Freeway.

Or they are named for where they are.

The Foothill Freeway. The Marina Freeway. The Glendale Freeway.

This the locals know, although it can be maddening to newcomers. Sometimes we know neither the number nor the name, just where it goes, as if by instinct.

As Banham wrote more than a quarter-century ago: “The freeway system in its totality is now a single comprehensible place, a coherent state of mind, a complete way of life, the fourth ecology of the Angeleno.”