The Pennsylvania Turnpike, going over and through the Allegheny mountains in the middle of the state, was the nation's first "super highway" and inspired the construction of the interstate system. It was designed to be robust, high-speed, and weatherproof, and was the first of its kind.
The earliest turnpikes
George Washington created the Philadelphia and Lancaster Turnpike Company in 1792 as part of a plan to promote westward expansion by building roads. This company built a 62-mile log-surfaced road near Philadelphia (on the eastern side of the state). Still, the 300-mile trip from Philadelphia to Pittsburgh was a harsh one, largely on dirt roads, and taking up to 35 days to complete.
In 1814 Colonel John Irwin assisted in creating the Pittsburgh-to-Greensburg turnpike (on the western end of the state), which passed through a number of towns and ran right by Irwin's house. A turnpike or pike, it should be mentioned, is the name for the bar across a toll road.
By 1817, the turnpike stretched from Philadelphia to Pittsburgh, and was traveled by foot and horseback. Sheep and hogs were six cents per score; carts and wagons with wheels wider than eight inches were free. This road is thought to have run along what is now Rte 30, Lincoln Highway.
Roads for long-distance travel were largely obsolete by the 1850's due to train travel; the Pennsylvania Railroad (located further north than the Turnpike) was a comfortable and popular alternative. Washington's Philadelphia-Lancaster road was replaced with a canal in 1880.
Vanderbilt does the dirty work
William Vanderbilt, together with Andrew Carnegie, had the idea to build a railroad, the South Pennsylvania Railroad, to connect Philadelphia and Pittsburgh in competition with the Pennsylvania Railroad to the north. He began construction in 1883 and ran out of money sometime around 1885. When the project was abandoned, much of the right-of-way had been cleared, 4.5 miles of tunnels had been dug (there were to be nine tunnels total), $10 million had been spent, and 26 lives lost.
The Pittsburgh, Westmoreland, and Somerset Railroad, a short line (narrow gauge) railroad operating near Pittsburgh, made use of the Quemahoning tunnel from Vanderbilt's project. Otherwise, the abandoned project lay unused until the 1930's.
The "weather proof super highway"
Early in the twentieth century, road travel was difficult because most roads were made of dirt. When the weather was wet, the roads would be so muddy that a car could barely slog through; when it was dry, the dust was so bad that travelers had to wear goggles and makeshift dust masks. As early as 1910, the idea of making a paved road across the state for easy motor travel was being tossed around. There were about 600,000 car owners in the US at that point.
In 1934, three men—Victor Lecoq of the Pennsylvania Planning Board, William Sutherland of the Pennsylvania Motor Truck Association, and State Representative Cliff S. Patterson—thought to propose such a highway along the abandoned South Pennsylvania Railroad that Vanderbilt began. They conducted feasability studies, and Patterson intruduced the bill in the State House in 1935. He was its only sponsor, but support for the bill picked up after reporter David Fernsler started writing about the "weather-proof tunnel highway."
It deserved the epithet; the Turnpike ended up using seven of Vanderbilt's nine planned tunnels. As much of the road as possible was built on the southern and western faces of hills, the better for sunshine to melt the snow and dry the rain. The tunnels and the cuts through mountains kept the road at low altitudes, which also helped the weather.
Even though 155 separate companies were working on various sections of the road, it was considered to be one design project from end to end, a novel idea for the time. Philosophically, the design was driven by the needs of motorists rather than merely being built around the terrain.
Inspired by Germany's autobahns, the Turnpike was designed to be traveled at a speed of 100mph on the straighaways (which made up 70% of its length) and 70mph on the gentle curves. Toll booths were built on downhill grades to give drivers plenty of time to spot them. Even today the Turnpike has one of the lowest traffic fatality rates in the country.
aremmes's writeup has some more details on the Turnpike's design.
Building the Turnpike
In the midst of the depression, banks were not eager to support this unusual highway, but fortunately it was just the sort of project that FDR was looking to promote as part of the New Deal. The Pennsylvania Turnpike Commission was loaned $41 million from the New Deal's Reconstruction Finance Corporation and another $29 million from the WPA. The bonds were to be paid back from the tolls collected.
The Turnpike succeeded financially (they paid back their bonds) and also in terms of road design. It inspired Ohio, Indiana, Illinois, New York, and New Jersey to build major toll roads of their own, and also inspired FDR's Federal Aid Highway Act which paved the way (ha!) for the Interstate highway system.
When construction began, the 15,000 workers built the road at a rate of 3.5 miles per day. All seven tunnels had to be extended, widened, or (in one case) restarted in a different part of the mountain. The workers built 300 bridges and culverts, 10 Howard Johnson/Esso service plazas, 9 interchanges and 11 sets of toll booths.
Opening Day
The turnpike opened on October 1, 1940. Cars were lined up at the toll booths to be among the first to ride it. It stretched 160 miles, from Irwin (just east of Pittsburgh) to Middlesex (near Carlisle, just west of Harrisburg). The highlight of the ten service plazas was Midway, the halfway point and housing the only HoJo's of the bunch that served a full dinner menu. Today the rest stops look exactly the same as in the old photos, except that the little round Esso pumps out front have been replaced with a bigger Sunoco station to the side. Midway in particular has an ice cream stand in the front, and a sign explaining that it was, once, the halfway point on the turnpike.
Today, the turnpike covers a total of 531 miles (including the Northeast Expansion and the Western Expansion). It includes 59 toll booths, 21 service plazas, 2,192 employees, and is traveled by 172.8 million vehicles each year (87% of which are passenger cars, the rest commercial trucks). In the Turnpike's first full year, 1941, 1.3 million cars were expected. 2.4 million ended up driving it.
The tunnels
The Turnpike had been designed as a four-lane highway with a wide grassy median, but the tunnels were only wide enough to fit two lanes of traffic, so cars coming from each direction had to merge into a single lane to pass through the tunnel. The Turnpike Commission had already underestimated the number of cars that would travel on the turnpike; by the 1960's the tunnels (except for the Lehigh tunnel, which was built with four lanes in 1957) were a major bottleneck, causing huge backups of traffic. The Commission took another look at the tunnels. In 1968 they decided to bypass three of them, and bore new "companion tunnels" in the others (Allegheny Mountain was bored slightly earlier, in 1964)..
All of the defunct tunnels are still there, and can be seen if you know where to look. The Quemahoning and Negro Hill tunnels can be seen from the roadside (at mile markers 106.3 and 116.7, respectively); the section of road containing the Ray's Hill and Sideling Hill tunnels can be walked or biked - see trainman's writeup for the details on that. Ray's Hill was the shortest of the tunnels and Sideling Hill the longest. Those who've been inside Sideling Hill say that you can't see the end of the tunnel until you're already a few thousand feet in, and that the middle of the tunnel has icicles on the ceiling even in the middle of summer.
The Allegheny tunnel will soon join their ranks. The Turnpike Commission seems to be distracted with other projects at the moment, but studies in 1996 led to a decision in 1999 that Allegheny should be bypassed.
Tunnel years
Laurel Hill 1940-1964
Quemahoning
Negro Hill
Allegheny Mtn 1940-soon
Ray's Hill 1940-1968
Sideling Hill 1940-1968
Tuscarora Mtn 1940-present
Kittatinny Mtn 1940-present
Blue Mtn 1940-present
Lehigh 1957-present
trainman's writeup has more details on the tunnels and what happened to each.