The Pyatt Tunnel is a historic railroad tunnel in Marion County, Arkansas.
 It is a 660 ft tunnel, hewn through bedrock beneath a ridge north of Crooked Creek and southeast of the city of Pyatt.
 The tunnel's portals are unimproved, and the tunnel itself has no concrete reinforcement, unlike other tunnels on the White Mountain Division of the Missouri Pacific Railroad, which passes through it.
 The tunnel was built in 1903-04, and is one of seven railroad tunnels in the state.
The Portland and Southwestern Railroad Tunnel, also known as the Nehalem Divide Railroad Tunnel, is an abandoned railroad tunnel near Scappoose, Oregon, United States, that is listed on the National Register of Historic Places.
 The tunnel was driven by the Portland and Southwestern Railroad, whose chief business was logging.
 Unusually for a logging railroad, the Portland and Southwestern built tunnels.
 In order to reach the far side of the Nehalem divide in the Northern Oregon Coast Range, the railroad undertook a 1712 ft tunnel.
 Some work was started in 1910, but most work began in 1918 and was completed in 1919.
 Since the tunnel was not through solid rock, the tunnel was lined with timber.
 The tunnel was used until 1945, when it was replaced by a truck road over the divide.
The Byfjord Tunnel (Norwegian: "Byfjordtunnelen" ) is a subsea road tunnel in Rogaland county, Norway.
 The 5875 m long tunnel runs between Grødem on the mainland in Randaberg and the island of Sokn in Rennesøy municipality, running underneath the Byfjorden.
 The tunnel was built as part of the Rennesøy Fixed Link project which opened in 1992 with the goal of connecting all the islands of Rennesøy to the mainland.
 The tunnel was a toll road from 1992 until 2006.
 The tunnel is part of European route E39 highway.
 With a maximum 8% grade, the tunnel reaches a depth of 223 m below sea level at its lowest point.
 The tunnel held the distinction of being Europe's longest and the world's deepest tunnel upon its completion, it was surpassed by a deeper tunnel in 1994 and a longer tunnel in 1999.
 The tunnel had an average daily traffic of 9,675 vehicles in 2015.
The Saverne Tunnel (French: "Tunnel de Saverne" ), also known as the Ernolsheim-lès-Saverne Tunnel (French: "Tunnel d'Ernolsheim-lès-Saverne" ), is a twin-bore, high-speed rail tunnel in western Bas-Rhin, France.
 It carries the LGV Est line of France's TGV high-speed rail network through the narrowest part of the Vosges mountain range, beneath Mont Saint-Michel and adjacent to the Saverne Pass.
 The tunnel consists of two bores, containing one railroad track each, that are connected by passageways every 500 m .
 The LGV Est crosses the 270 m Haspelbaechel viaduct near the western end of the tunnel.
 The tunnel was excavated by a tunnel boring machine between November 2011 and February 2013.
 Civil engineering work on the tunnel ended in April 2014 and it opened with the rest of the second phase of the LGV Est on 3 July 2016.
 The total cost of the tunnel was approximately €200 million.
The Blue Ridge Tunnel (also known as the Crozet Tunnel) is a historic railroad tunnel built during the construction of the Blue Ridge Railroad in the 1850s.
 The tunnel was the westernmost and longest of four tunnels engineered by Claudius Crozet to cross the Blue Ridge Mountains at Rockfish Gap in central Virginia.
 At 4237 ft in length, the tunnel was the longest tunnel in the United States at the time of its completion in 1858.
 The tunnel was used by the Virginia Central Railroad from its opening to 1868, when the line was reorganized as the Chesapeake and Ohio Railroad (renamed Chesapeake and Ohio Railway in 1878).
 The Chesapeake and Ohio routed trains through the tunnel until it was abandoned and replaced by a new tunnel in 1944.
 The new tunnel was named the "Blue Ridge Tunnel" as well, although the original tunnel still remains abandoned nearby.
 The old Blue Ridge Tunnel has since been named a Historic Civil Engineering Landmark.
Of all the seven tunnels on the Lackawanna Railroad's 400-mile mainline, Oxford Tunnel or Van Nest Gap Tunnel would be arguably the most difficult to build.
 The combination of stubborn gneiss, inconsistent funding and American Civil War-era technology caused protracted delays.
 Meanwhile, the construction of the Warren Railroad itself, of which Oxford Tunnel was just a part, caused its chief overseer, John I. Blair, daily headaches.
 The line would require three large bridges, two tunnels (the other tunnel being at Manunka Chunk), and many miles of cutting and filling.
 The terrain was less than ideal for a railroad.
 As such, for over a century, rail historians thought that Tunnel Hill had been initially crossed, prior to the completion of the tunnel underneath, by a switchback or some sort of cheaply built temporary route.
 Neither was true.
 In fact, Blair had built a fairly substantial, albeit circuitous, route over the hill.
 Local inspections during the early 1980s revealed that the actual route taken by temporary track had been partially obliterated by a corn field, misleading previous historians into believing that the route had been configured differently.
The Cricket Tunnel and Crest Tunnel are a pair of railroad tunnels in northern Arkansas, near the city of Omaha in Boone County.
 The Crest Tunnel, at 3500 ft is the longest tunnel in Arkansas, and is its only curved tunnel.
 Both tunnels were built by the White River Division of the Missouri Pacific Railroad in the early 20th century.
 The tunnels were listed on the National Register of Historic Places in 2007.
The Missouri Pacific Railroad (reporting mark MP) , commonly abbreviated MoPac, with nickname of The Mop, was one of the first railroads in the United States west of the Mississippi River.
 MoPac was a Class I railroad growing from dozens of predecessors and mergers, including the St. Louis, Iron Mountain and Southern Railway (SLIMS), Texas and Pacific Railway (TP), Chicago and Eastern Illinois Railroad (C&EI), St. Louis, Brownsville and Mexico Railway (SLBM), Kansas, Oklahoma and Gulf Railway (KO&G), Midland Valley Railroad (MV), San Antonio, Uvalde and Gulf Railroad (SAU&G), Gulf Coast Lines (GC), International-Great Northern Railroad (IGN), New Orleans, Texas and Mexico Railway (NOTM), Missouri-Illinois Railroad (MI), as well as the small Central Branch Railway (an early predecessor of MP in Kansas and south central Nebraska), and joint ventures such as the Alton and Southern Railroad (AS).
The Simpson Tunnel, so named for the Simpson Farm it passed under, was a railroad tunnel originally built in 1903 by U.S. Steel and subsequently used by the Dunlap Creek branch of the Monongahela Railway.
 The tunnel was made of stone with a brick arch construction.
 The line was utilized both to serve coal mines and coke works in the area and to interchange with the Baltimore and Ohio Railroad's Fairmont, Morgantown and Pittsburgh line and the Pennsylvania Railroad's Coal Lick Run branch.
 The last move on that line, and thus through the tunnel, was on November 6, 1975.
 The line was subsequently abandoned by 1976 and the real estate disposed, however the tunnel was not destroyed or blocked at the time.
 At some point between 2008 and 2010 the tunnel was destroyed, likely due to the construction of the Mon-Fayette Expressway.
 It is not clear whether the tunnel was blasted or simply filled in.
The Bellows Falls Tunnel is a railroad tunnel located in center of the Village of Bellows Falls within the Town of Rockingham, Vermont, adjacent to the Connecticut River, and is currently owned and operated by the New England Central Railroad (NECR).
 The Vermont Valley Railroad originally constructed the tunnel in 1851.
 Partially cut through solid rock, the tunnel was built with rough-cut stone blocks, where each portal was decorated with radiating voussoirs around their horseshoe shaped arches.
 The stone blocks average about 18 inches deep as observed at the tunnel portals.
 Record information available from the NECR would indicate that a separate support system exists above the masonry tunnel supporting the hotel building to the north of the Bridge Street roadway which is also directly above, and crosses perpendicular (east/west) to the tunnel below.

Question: What was the common abbreviation for the railroad by which the Cricket Tunnel and Crest Tunnel were built?
Answer: MoPac