Nothing like it had ever been built before. A highway with no intersections, no grade crossings, no traffic lights and no speed limit. A highway with a center parkway, a highway completely fenced in and lighted at night.

The Pennsylvania Turnpike was a wonder of its time when it opened 40 years ago. A "dream highway", the Philadelphia Record called it. And so it was.

Until that time, highways were ribbons of asphalt or concrete that mostly took the route of least resistance through the countryside -- up, down and around. Auto tunnels were rare. Steep grades were common. Few highways were fenced, and you were as likely to meet a cow on the road as another vehicle.

Limited access was unknown to American motorists. Every highway crossed other roads, not to mention cow paths, tractor ruts and home driveways. When there wasn't a slow truck groaning ahead of you, there were innumerable curves and intersections. A straight stretch where you could maintain constant speed was a joy, usually short-lived.

Getting to your destination in those days was often an adventure and sommetimes a feat of mind over matter. Then came the Pennsylvania Turnpike. sIt electrified the American car-traveling public. Imagine a strip of road 160 miles long on which you could fly like a bird! No speed limit then; if you wanted to tool along at 120 -- and some did -- no one would stop you. (Today the limit is 55 miles an hour.)

"Nobody had ever seen a road without stoplights, intersections, steep hills and sharp curves," one of the turnpike's original engineers, Harry Lundy, is quoted in "Vanderbilt's Folly," by William H. Shank. "That first Sunday it opened, it was so crowded they couldn't get off at the interchanges."

So popular was the turnpike that it became the model for all the expressways to come, including the nation-wide interstate system. It is, in a very real sense, the grandaddy of the expressway system.

Today, there are 39,500 miles of interstate highways in use, with another 8,000 miles a-building. There are 62 toll roads in the United States spanning 4,616 miles. Both the interstates and the toll roads owe much to the Pennsylvania Turnpike, their prototype.

"When they built it, with its tunnels, its safety features, its 3-percent grade, scenie routes and its limited access, it was hailed as the eighth wonder of the world. And it still is," said Jack I. Greenblat, chairman of the Pennsylvania Turnpike Commission.

"It took the rest of the United States years to start duplicating Pennsylvania's four-lane, limited-access invention, and they're still copying us, here and all over the world -- everything from our tickets to the precast roadway we're putting in on the turnpike's 5,000-foot bridge near Scranton."

In an age when the dollar was a lot of money, the Pennsylvania Turnpike cost $70 million to build over a partially completed railroad roadbed, the South Penn.

Years before the idea of the turnpike was born, construction of a cross-state railroad line through the Allegheny Mountains in the southern part of the state had been started by the New York Central's William Vanderbilt. Enraged by the rival Pennsylvania Railroad's incursions into what he considered his territory in the Northeast, he sent thousands of workmen into Pennsylvania to build a competing line parallel to the Pennsy's.

But through the intervention of financier J.P. Morgan, peace was made between the two railroads and the South Penn project, then 60 percent complete, was abandoned. It became known as Vanderbilt's Folly and remained unused and neglected for 50 years.

In the Depression days of the 1930s, however, the idea of creating an all-weather superhighway over the abandoned route took hold. The Federal Works Progress Administration approved the project as a way to create jobs. With the help of federal agencies, bond financing was obtained, and the first spade of earth was turned on Oct. 27, 1938.

Though much work had been done on the rail route, workmen had to convert a right-of-way intended for trains into one for cars. They had to clear, complete and widen abandoned tunnels. In a few cases, they had to reroute the roadway. But at last, two years later, on Oct. 1, 1940, the first cars drove through the toll gates and onto the turnpike.

"There was no other toll road [of this scale] at that time," said Lee Rischel, who was in charge of the toll collectors, "so this was an original operation. We decided to classify cars by axle and tire size." Thus was born the present fee system used on many toll roads.

Toll roads, of course, were nothing new. Kings and satraps throughout history had often charged fees to travelers using roads under their control, particularly if they thought they could get away with it. Tolls were charged on early wooden roads in the Northeast to defray maintenance costs. Indeed, the term "turnpike" derives from the hinged pole (or pike) placed as a barrier across the road at the toll gates and raised or moved inside when the toll was paid.

"Toll highways were common throughout the 19th century and even in the early days of the 20th," Shank writes in "Vanderbilt's Folly." But the Pennsylvania Turnpike was the first modern toll road.

Though it marked its 40th birthday on Oct. 1, 1940, some 26,000 vehicles used the turnpike daily; today, the figure is close to 200,000. It is also a much longer road. Today, after several extensions, it measures 470 miles and runs from the Ohio state line to the New Jersey line, with a spur north to Scranton. The original road extended 160 miles from Carlisle (near Harrisburg) to Irwin, 15 miles east of Pittsburg.

After a decade of operation, it became obvious that the original two-lane tunnels were becoming a bottleneck. So new parallel tunnels or by-pass roads over the mountains were constructed. It was not until 1968 that the entire route of the turnpike was four continuous lanes.

An army of specialists serves the turnpike. The roadway operates 200 trucks, all with radios, capable of notifying central headquarters of disabled vehicles and accidents. Turnpike officials boast that a tow truck will reach a disabled vehicle anywhere on the road within 15 minutes.

Along with resurfacing and snow-removal vehicles, each of the 19 maintenance stations has an ambulance on call 24 hours a day with two men manning it. Three hundred state troopers are assigned to the turnpike, with 100 on duty at any one time.

At turnpike headquarters near Harrisburg, a communications room is manned day and night to keep track of accidents and traffic flow, and to inform travelers of snow and other weather conditions. "We guarantee a clear road," said H.R. Haratine, a turnpike spokesman. Only once since the road opened has it been forced to close, he said; that was early in the 1970s, when a severe snowstorm forced the turnpike to shut down for three hours.

Ten percent of the roadway is resurfaced every year, so there is a completely new surface every 10 years. Driving on the turnpike -- at the least the original portion of it -- is a pleasant experience. The road takes you through pretty farm country, and the tunnels add an interesting element to the journey. Few billboards mar the scenery on the original route until you approach Pittsburg.

The turnpike also provides access to a number of interesting sites. Maps are available at all toll booths, giving brief description of off-turnpike historic sites and tourist points of interest. Most service plazas have a large fixed map showing nearby points of interest.