May/june 1990 | Volume 41, Issue 4
Fifty years ago the builders of the Pennsylvania Turnpike completed America’s first superhighway—and helped determine the shape of travel to come
Most American motorists take for granted the concrete and asphalt web of interstate highways that has penetrated so deeply into the nation’s economy and thinking. The 43,000-mile system of fouror-more-lane divided, limited-access roads reaches from the canyons of California to the beaches of Florida and the urban bustle of the Northeast Corridor. But of course there was a time when the superhighway idea was brand-new. In the United States, it all began with the Pennsylvania Turnpike—a road that, fifty years ago this October, profoundly changed the way Americans perceived time and distance. Not only was the Pennsylvania Turnpike the nation’s first major toll road, it was also, more significantly, our first long-distance, highspeed, limited-access, four-lane divided road —the direct conceptual predecessor of the interstate system. It was built with four 12-footwide lanes and wide, safe shoulders; long, level straightaways and gentle curves; and grades of no more than 3 percent (a three-foot rise for every hundred feet of forward travel). Even more striking was its seamless, gradeseparated design: no cross streets, traffic lights, business entrances, railroad crossings, trolley cars, or pedestrian access. All local and state roads were realigned to pass over or under the turnpike, and the only commercial concessions allowed on the highway were ten gas-station-and-restaurant plazas with their own entrance and exit ramps. Most remarkable, the highway did all this while running virtually at right angles to the ridges of the rugged 2,900-foot-high Allegheny Mountains. By using six uncompleted tunnels left over from an abandoned nineteenth-century railroad project and one new tunnel, the turnpike kept its climb to a minimum.
The original section extended for 160 miles from Middle-sex, about 15 miles west of the state capital at Harrisburg, to Irwin, about 20 miles east of Pittsburgh. Previously, motorists traveling between these cities had had to contend with one of two narrow two-lane roads: the Lincoln Highway (U.S. Route 30) or the William Penn Highway (U.S. Route 22). Both were built with sharp curves and steep grades (as high as 9 percent) because of the mountainous terrain, which made them hazardous in winter. Long-haul trucking companies so dreaded the mountains that many of them routed East-to-Midwest shipments hundreds of miles out of the way, taking either U.S. Route 6 across northern Pennsylvania or the lakeshore route through Buffalo, New York. When the turnpike opened, it reduced the accumulated climb from 13,000 feet, via Route 30, to less than 4,000 feet. It also cut 5 to 18 miles off the distance of a trip between Pittsburgh and Harrisburg, and the length of time for such a trip, dropped from six hours in good weather to less than three. Many motorists covered the 160 miles in two and a half hours.
Pennsylvania’s statewide speed limit at the time was 50 miles an hour, but with trucks sharing the mountainous two-lane roads, motorists were lucky to average much more than half of that. (Of the 3,000,000 miles of highway in the United States in 1940, only 11,070 miles were wider than two lanes.) The turnpike’s four-lane divided configuration allowed faster traffic to overtake slower vehicles wherever necessary, except at the tunnels, which were constructed as two-lane sections in the interest of economy. Speeds were limited only by common sense, and in fact, the turnpike had no speed regulations during its first six months of operation. (In April 1941 a 70-mile-an-hour limit was imposed.)
Today certain elements of the turnpike’s design standards are considered obsolete—primarily the narrow 10-foot median strip separating opposing lanes of traffic. But when it opened, the turnpike design was so radically different, and ultimately so successful, that it altered the course of national transportation policy.
The story of the Pennsylvania Turnpike’s impact on Americans’ driving habits and highway design really began a decade before the invention of the automobile, because large stretches of its original right-of-way were laid out over the abandoned roadbed of the stillborn South Pennsylvania Railroad. In the 188Os, when railroad barons wielded even more power and influence than do today’s corporate traders and raiders, William H. Vanderbilt, owner of the New York Central system, believed that the Pennsylvania Railroad was supporting a competitor to his line between New York City, Albany, and Buffalo. In retaliation he aligned himself with the Pittsburgh industrialist Andrew Carnegie in a scheme to build a Pittsburgh-Harrisburg railroad, thirty miles south of and virtually parallel to the Pennsylvania’s main line. Other allies were prepared to handle traffic between Harrisburg, Philadelphia, and New York, completing Vanderbilt’s plan to short-circuit the Pennsylvania and siphon off its lucrative coal and steel traffic. As a youth Carnegie had worked as a Pennsylvania Railroad telegrapher and later even named one of his steel mills after a Pennsylvania president, J. Edgar Thomson; but now he was angry with the line over what he thought were excessive rates for shipping his steel to Eastern markets.
Vanderbilt’s $15 million syndicate put surveyors to work conducting one of the most exhaustive railroadline location studies ever undertaken in the United States, covering nearly 1,0OC square miles with some 5,000 miles of survey lines. Beginning in the fall of 1883, the first of about twenty-five hundred laborers went to work blasting nine mile-long tunnels, carving out deep cuts, and building huge earthen fills. Vanderbilt’s line crossed the mountains at an elevation some 300 feet higher than the Pennsylvania’s, but it had two advantages: It was about 30 miles shorter between Harrisburg and Pittsburgh than the 249-mile Pennsy, and its route was a highly refined one.
Engineering News and American Contract Journal published a report on October 4, 1884, titled “An Editorial Jaunt over the Line of the South Pennsylvania Railroad.” An excerpt reads: “One of the striking features . . . presented to the mind of the engineer in considering the adopted location is that it is a ‘summit line’ for a large portion of the way and instead of following the devious windings of the mountain streams as does its older brother, the Pennsylvania Railroad, it cuts through the mountain ranges which cross it at right angles and seeks the crests of the water sheds. This is so much the case that through the region between the Tuscarora Mountain and Sideling Hill, and again between the Allegheny Mountain and the Chestnut Ridge . . . we failed to discover a single water-way passing under the road bed for which a 12 ft. opening was not more than ample. There is not an iron bridge on these crest lines for more than 40 miles. This simple fact speaks for itself as a measure of economy and locating skill.”
But when the line was about 60 percent completed with less than a year’s work remaining, the financier J. Pierpont Morgan crafted a truce between Vanderbilt and the Pennsylvania. Morgan had gotten warning signals from London investors who considered the South Pennsylvania project emblematic of the wildcat speculation in American railroads. Its completion, they told Morgan, could only hurt investors in both companies and, in the end, all the railroads in the United States.
Some $10 million had been poured into the project, but it was shut down in September 1885 and became popularly known in hindsight as Vanderbilt’s Folly. None of the tunnels were completed all the way through, but excavation had been conducted from both ends of all of them, and in one the crews were only 394 feet apart—and could hear each other—when the project was halted.
Civil engineers who had worked on the South Pennsylvania took the cancellation as a personal affront to their profession, and this epitaph appeared in the final edition of South Pennsylvania Rail Road Transit , a journal they had produced for their own consumption during the height of the construction activity: “And here for the time being, and probably for a long time to come is smothered the best line of railroad between the Ohio Valley and the Atlantic that has ever been or can be projected, built or operated.”
Since almost nothing is forever, as early as 1910 a proposal was floated, albeit tongue in cheek, to convert the roadbed and tunnels into a high-speed motoring boulevard illuminated by electric lights. A few snippets of the right-of-way were used briefly for short-line and logging-railroad operations, but nothing substantive occurred until the Depression threw thousands of Pennsylvanians out of work.
With an epidemic of unemployment, each state government was given the task of searching for projects to take advantage of President Franklin D. Roosevelt’s New Deal employment programs. In Pennsylvania that job fell to the State Planning Board, which made an inventory of economic and social indicators and land-use patterns. An employee of the board, Victor LeCoq, and a trucking lobbyist, William A. Sutherland, discussed the idea of reusing the roadbed and tunnels for a highway with Clifford S. Patterson, an engineer who had just been elected to the state legislature from western Pennsylvania. Early in 1935 Patterson introduced a resolution in the legislature calling for a feasibility study. Officials of the federal Works Progress Administration liked the idea, and the state secretary of highways, Warren Van Dyke, applied for, and won, a WPA survey grant.
Beginning in January 1936, engineers and surveyors again swarmed in southern Pennsylvania. They found the Vanderbilt roadbed and uncompleted tunnels in surprisingly good condition. The idea gained momentum, and on May 21, 1937, Gov. George H. Earle signed Act 211 into law, authorizing creation of the Pennsylvania Turnpike Commission. The act gave the commission broad powers to construct and operate a turnpike, impose tolls, and issue revenue bonds but did not award it a dime of state money. The state’s constitution prohibited incurring more than $1 million of debt without a referendum, and the estimated cost of construction was on the order of $60 to $70 million. The commission’s task was to raise that amount in private capital or federal funding—no easy job even in normal times, and much harder during a depression—and build the road. A $60 million bond offering in early 1938, received coolly on Wall Street, was canceled.
The reason was that although investors had seen and backed many bond issues for major toll facilities (this was, after all, the era of the Holland Tunnel and the Golden Gate Bridge), they had difficulty envisioning the equivalent of a 160-mile-long toll bridge. Nobody, it seemed, argued with the engineering concept, but neither did many people believe that a market existed to make the road financially self-supporting. With the clamor of the European conflict growing ever louder in Washington, however, President Roosevelt became convinced of the highway’s military value for keeping steel moving, and he authorized funding through two New Deal agencies: a $29.25 million outright grant from the Public Works Adw-10 ministration and a $40.8 million purchase of bonds- in effect, a loan- by the Reconstruction Finance Corporation.
Meanwhile, engineers and others kept busy out in the field. The state High-way Department provided interim technical support, with the understanding that it would be reimbursed when funding materialized, and the Turnpike Commission awarded a contract for the removal of water that had seeped into the tunnels.
Engineers began to map out a highway alignment that generally followed the Vanderbilt roadbed, using six of the nine tunnels and about 40 miles of the graded roadbed. (At Allegheny Tunnel the old excavation was considered unstable and unsafe, and a new tunnel was laid out 85 feet south of the original.) Much as a military strategist might chart an invasion, the engineers developed these plans as a contingency, ready to be uncoiled when the funding became available.
When final approval came from Washington, on October 10, 1938, the commission had to move with lightning speed to comply with a federal requirement that the project be under construction by the end of that very month. The preliminary engineering work hadn’t been in vain: just four days later a contract was advertised for site grading for a 10-mile stretch of roadway in the gently rolling farmland west of Harrisburg. Bids were opened on October 26, a contract awarded that day, and groundbreaking held the next day. Roads and Streets , a trade magazine, commented, “It should be noted that only four days were allotted for the completion of plans, the design of structures, the preparation of contract documents, and the actual advertising of the first contract. . . .”
From the start the commission chairman, Walter A. Jones, a millionaire oil executive from Pittsburgh who was a confidant of President Roosevelt, exhibited a stubborn faith in the concept. His conviction kept him pursuing financing for month after month in the face of ridicule and well-meaning advice that he was aiming too high. Once the project was set in motion, however, there seemed to be no single personality or guiding figure energizing the push to build the turnpike. Increasingly Jones’s health began to fail, and he was out of the public eye for weeks at a time. When in August 1940 a caravan of VPs got an inaugural look at the road on the eve of its opening, Jones was too sick to attend. (The entourage, which included U.S. senators and representatives, at times grew in length to ninety-three cars.)
As Jones’s energies waned, a group of engineers and technicians who almost instinctively knew the value of teamwork tackled the job. The immensity of the task and the shortness of deadline, combined with the certainty that it was a privilege to work on the nation’s first superhighway, may have kept egos in check. In any event, Samuel W. Marshall of Norristown, who had been the state’s chief highway engineer, became the turnpike’s chief engineer. At the time of groundbreaking, his staff numbered 115 engineers. One year later it had ballooned to more than 1,100. “It was, in my opinion,” he wrote in a paper presented to the American Society of Civil Engineers, “the fastest moving, hardest hitting engineering organization with which I have ever been associated.”
If the time for beginning the project had seemed short, the amount of time allotted to finish it was even more startling: the road had to be substantially complete by May 1, 1940, later amended to June 29 of 1940—a mere twenty months. A job of this magnitude normally would take three or four years to complete. It resulted in 155 contracts’ being awarded to 118 firms, and before long ten thousand employees and $12 million worth of roadbuilding equipment were at work around the clock.
The design and safety standards for the roadway were unprecedented in the United States, although they were similar to those of Adolf Hitler’s hundred-mile-an-hour autobahns, which had been built for military and ideological purposes beginning in 1933. Just ten years before work started on the turnpike, many American highways had been built with a total double-lane width of 16 feet. To keep down the cost of right-of-way acquisition and excavation, the turnpike’s engineers considered using a 20-foot-wide design (that is, two 10-foot-wide lanes in each direction), but because they expected a mixture of heavy truck and auto traffic, they instead agreed on a 24-foot standard. In the tunnels the pavement narrowed to two lanes, each 11.5 feet wide. Engineers also considered, then rejected, another cost-cutting plan to pave two lanes with reinforced concrete and two with asphalt; they used concrete for all four lanes. Concrete has a higher first cost but is cheaper to maintain in the long run. A narrow, 4-foot median strip was scrapped in favor of a 10foot-wide divider.
Of the 160 miles of roadway, 110 miles was on straightaway. Superelevation, or banking, was built into the curves to a very specific end. Many contractors on the job had worked on early paved roads whose curves had been deliberately constructed without banking to discourage higher speeds. This had contributed to skidding and overturning accidents. The superelevation on the turnpike was a carefully chosen compromise: Curves were banked, but not so steeply as to encourage speeds greater than those that would allow a driver to stop within the turnpike’s standard 600-foot minimum rear-end-collision sight distance, which generally assumed a typical top speed of 70 miles an hour.
Another feature related to superelevation was a technique that had been used in railroading for many years: the transition, or spiral, curve. With this alignment design, the highway eased gently from straightaways into curves, so that the sharpest part of any curve was at its midpoint. The practice, reported Roads and Streets in October 1939, “has ... only recently been adopted for state highway work, and has been used by comparatively few states.”
Where curves were required, the sharpness was matched to adjacent highway sections to account for the psychological tendency to maintain a speed once it has been attained. Thus the longer the tangent, or straight stretch, the milder the curve allowed at either end of it. Although straight segments of the autobahns had been built with slight curves designed into the alignment every few miles to stimulate driver awareness, no such rule applied on the turnpike; for most of the distance none was necessary, for the rugged countryside required curves anyway. But some motorists still complain today about the boredom of a nearly 40-mile stretch west of Carlisle that is relieved by just one gentle curve. Later highways have been built to avoid such long straightaways.
Grades were limited to 3 percent to ensure that trucks and, if necessary, military vehicles could use the highway as easily as pleasure cars. The Vanderbilt railroad had been designed for long, heavy freight trains, and its maximum grade was only 2 percent. As a result, the turnpike often diverged from the railroad alignment to strike out on the shorter course permitted by a slightly steeper grade. The transitions from level highway to grades, and over the summits, were designed, like the curves, with minimum daylight and headlight sight-distance standards in mind.
In addition, to give the highway all-weather availability, the route was, where practicable, laid out on the southern exposures of hills to take the fullest advantage of solar heating to clear snow and wet pavement. Some of the excavation required was of heroic proportions. Planners originally envisioned an eighth tunnel near Everett but at the last minute decided to make it an open cut, necessitating the removal of 1.1 million cubic yards of earth and rock. The result was Clear Ridge Cut, which was, at 153 feet deep, the largest highway cut in the nation at that time.
The turnpike’s nine intermediate interchanges, each having its own tollbooths, were built with 1,200-foot-long entrance and exit lanes, always located in the middle of a straight stretch of roadway; at a “sag,” or long, gentle dip; or both. Moreover, the ramps and tollbooths were placed to give motorists leaving the turnpike the advantage of always looking down on the tollbooth - and - interchange layout and getting a bird’seye view of it before entering it, rather than being surprised by coming over the top of a hill and suddenly being confronted with a splitsecond decision. Tollbooths were built across the highway itself at Irwin, the western terminus, and at Carlisle, near the eastern end.
The synergy of all these elements was summarized by Charles M. Noble, a turnpike engineer who wrote in Civil Engineering , in July 1940: “Unlike the existing highway systems of the United States, in which design standards fluctuate every few miles, depending upon the date of construction, the Turnpike will have the same design characteristics throughout its entire 160mile length. Every effort has been directed towards securing uniform and consistent operating conditions for the motorist. In fact the design was attacked from the viewpoint of motor-car operation and the human frailty of the driver, rather than from that of the difficulty of the terrain and methods of construction.”
Before the opening of the turnpike, there were only a few places in the country where this concept could be visualized. One was the nation’s first parkway—the Bronx River Parkway, in New York City and Westchester County, which had been built in the 1920s as a fourlane limited-access highway but was only 15 miles long and was considered a 35mile-an-hour road. The other was in a miniature diorama at the General Motors Futurama exhibition at the New York World’s Fair of 1939 and 1940. Designed by Norman Bel Geddes, it purported to show American life in 1960 and was uncannily accurate in its depiction of multiple-lane high-speed expressways.
When the turnpike finally opened, on Tuesday, October 1, 1940, neither the commission nor the motoring public knew quite what to expect. The bravest motorists reported covering the 160 miles in a shade over two hours, with no interference by state troopers. Toll attendants, when asked what the speed limit was, responded, “Drive carefully.” The fare was $1.50 from end to end for passenger cars, or roughly a penny a mile. Truck tolls were higher, based on weight, but the method of determining the rate was primitive: It was up to the attendant’s visual inspection. For the first few days traffic was somewhat heavy, obviously augmented by one-time curiosity seekers, but not uncontrollable. Then on October 6, the first Sunday, miles-long traffic jams formed at every tollbooth, as fall foliage and sunny weather attracted thousands upon thousands of motorists to the brand-new road. Attendants ran out of tickets and hand-wrote their own. Some people spent four hours waiting in line to pay their tolls. The jams finally eased at about 10:30 P.M. Turnpike officials estimated the volume at 10,000 vehicles but later revised it to 27,000—a number equal to the amount of traffic expect- ed in about a week of operation. Overflow exit lanes were quickly added to accommodate the expected crowd for the second Sunday. Even more cars and trucks used it then—about 30,000—but the preparations prevented a recurrence of the first weekend’s nightmare.
With temporary problems discounted, the turnpike seemed to live up to the “dream highway” image that its promoters had been pushing. Gov. Arthur H. James drove from Pittsburgh to Harrisburg in its first week and called it a “peach of a road.” Fortune magazine termed it the “first American highway that is better than the American car.” Reginald M. Cleveland of The New York Times wrote: “Underfoot is a continuous ribbon of smooth pavement crossed by bridges of simple beauty. Overhead are the hawks of the Kittatinny [Mountain], their flight scarcely more swift or effortless than that of the driver of the new super-road.”
Traffic planners expected 1.3 million vehicles in the turnpike’s first year of operation; in fact the tally was 2.4 million. This success disproved the critics, some of them at the highest levels of the U.S. Bureau of Public Roads, who had favored improved urban highways but not intercity expressways. President Roosevelt and Congress liked the long-distance superhighway concept, and in 1944 the precursor to the Interstate Highway Act was passed. The turnpike chairman, Walter A. Jones, had already issued his own proposal for an 1,800-mile $860 million system of toll superhighways stretching from Boston to Richmond, Virginia, and from Philadelphia to Chicago, Indianapolis, and St. Louis. A turnpike engineer in the Somerset field office, J. M. Kantner, had written in the Somerset Daily American soon after the road’s opening, “The completion may well mark the driving of the golden spike in the first link of America’s future chain of super highways....”
After World War II the Pennsylvania Turnpike expanded both in mileage and in popularity. A 100-mile extension costing $87 million was built east toward Philadelphia in November 1950, and a 67-mile western extension costing $77.5 million reached the Ohio border in December 1951. Traffic and revenue had been depressed during the war, with gasoline and tire rationing in effect, but now civilian prosperity began to show itself. Traffic rose from 2.4 million vehicles in 1946, the first postwar year, to 11 million in 1952, the first year both major extensions were opened.
More extensions followed —a 33-mile $65 million stretch eastward to the Delaware River in November 1954 and then over the river to connect with the New Jersey Turnpike in May 1956. This completed a continuous expressway link from New York through Indiana, which soon extended to Chicago.
The few engineering changes that had been made since the design of the original 1940 highway mainly involved providing improved drainage beneath the nineinch-thick concrete roadway slab. The entire east-west turnpike stretched for 360 miles, and a 110-mile branch from the Philadelphia area to Allentown and Scranton opened in November 1957.
The financial success of Pennsylvania’s turnpike inspired the creation of toll-road authorities in Colorado, Florida, Indiana, Illinois, Kansas, Maine, Maryland, New Hampshire, New Jersey, New York, and Ohio. But by 1954 toll roads were in political trouble, and the coming of the free interstate system in 1956 headed off the formation of any national toll-road network. Throughout Pennsylvania other extensions were planned and even in advanced stages of design. In whole or in part, sections of Interstates 79, 80, 81, 90, and 95 within the state all were originally envisioned as Pennsylvania Turnpike projects. In the end the $118 billion national interstate system, with its nontoll operation and its 90 percent federal funding guarantee, won out. The interstate system was what the author Phil Patton, in his 1986 book Open Road , termed the “last program of the New Deal and the first space program.”
As the turnpike’s routemileage growth ended, its internal improvements became more important. A rising fatality rate in the early 1950s resulted in the installation of a steel guardrail in the median strip. Crossover accidents had become notorious, the number of highway deaths rising from 5 in 1940 to 91 in 1953. The worst year, by rate, was 1950, with 12.4 fatalities per hundred million vehiclemiles. (In the 1920s, with minimal safety engineering, the national average was 18 per hundred million vehiclemiles; today it is just 2.6.) The speed limit was adjusted several times, according to the geography and the accident rate along particular sections, and then in 1956 a uniform 65-mile-an-hour limit was imposed. More state troopers were added, and by 1957 the rate had fallen to 3.3 deaths per hundred million vehicle-miles.
By 1960 traffic volume had ballooned to more than 31 million vehicles, and the seven two-lane tunnels were choked. A $100 million investment program lasting through most of the 1960s was considered necessary to meet the competition of more recent superhighways, specifically Interstate 80 and the combination of the New York Thruway and Interstate 90, all of which were built to more contemporary design Standards, with much wider median strips. The program allowed the commission to close three tunnels and reroute traffic over new bypasses, which were built to interstate specifications. New two-lane tunnels were bored parallel to the remaining four existing tunnels, providing uninterrupted fourlane travel across the state.
By 1970 the volume of traffic had risen to 51.1 million vehicles, and the Turnpike Commission considered a billion-dollar proposal to modernize the original 160 miles. The plan would have created an eight- to ten-lane expressway with eighty-milean-hour capability and cars separated from truck traffic. It was dropped as too expensive. The oil embargoes of 1973-74 and 1979 cut into traffic ,volume and revenue, putting the financing of major new projects on shaky ground anyway, and like all highways, the turnpike soon found itself with a federally imposed 55-mile-an-hour speed limit.
By 1980 traffic volume was 63.9 million vehicles and rising, and legislation was enacted in 1985 to allow the commission to embark on several major improvements. Last year the turnpike carried more than 97 million vehicles—270,000 a day—and officials greeted a ceremonial two billionth traveler.
Of course, to finance improvements to keep up with the rising traffic volume and to maintain the roadway in good condition, the tolls have had to rise. The initial penny-a-mile price remained unchanged for twenty-nine years; it was first raised in 1969 and now stands at 3.1 cents a mile.
Were the turnpike built today, it would look substantially different in some details. The 200-foot-wide right-of-way would be 300 feet wide. The median would be 60 feet wide, not 10. (Still, the fatality rate on the turnpike is one of the most favorable in the nation—0.6 deaths per hundred million vehicle-miles, less than a quarter the national average.) For greater safety, service and restaurant plazas would be set back farther from the roadway than the 1940-built plazas, as are all new or relocated plazas. The original service-plaza buildings were built of gray stone to replicate native Pennsylvania architecture, a feature too expensive to duplicate on any new one. The cloverleaf curves at interchanges would be much broader than their original 100-footradius corkscrew design; it was specifically aimed at slowing down motorists leaving the highway.
But time has hardly passed the Pennsylvania Turnpike by. Since 1987 the toll-collection system has been computerized. A segment near Philadelphia was widened to six lanes to handle the congestion resulting from commuter traffic in that area. Any realignments or bypasses are designed to current-day interstate standards, as are several route expansions under way in western Pennsylvania: the 16-mile Beaver Valley Expressway, the 13-mile Greensburg Bypass, and the Mon Valley/Fayette Expressway (which will connect Pittsburgh with Morgantown, West Virginia). All are designed to improve access and stimulate economic development in a region afflicted by the decline of steel and other durable-goods industries. A system of emergency call boxes installed every mile in the mountainous region as a trial is being expanded systemwide. Fast food has replaced the original Howard Johnson’s restaurants at the service plazas. A new seventeen-lane interchange, which will be the turnpike’s largest, is being installed near Philadelphia to provide direct connections with the last uncompleted segment of interstate highway in Pennsylvania: 1-476, the north-south “Blue Route” through the city’s western suburbs.
On the Northeastern Extension the turnpike is currently marking another first, the first American highway use of the New Austrian Tunneling Method (NATM), which the turnpike is employing to eliminate the last remaining section of the two-lane road —the Lehigh Tunnel—by boring a second two-lane tube. Used to build rail tunnels for the Washington, D.C., Metro system and the light-rail system in Pittsburgh, NATM eliminates the need to erect steel superstructures inside a tunnel after each blast and clearing of rock. With NATM, a concrete mixture known as shotcrete is sprayed on the tunnel roof and walls soon after each blast. The fast-setting solution stabilizes the rock, preventing rock falls as well as eliminating the need to assemble a supporting structure.
In Pennsylvania the tollsuperhighway concept, whose obituary has been written several times, is still alive.