Early History of the Tunnel

The Hoosac Tunnel (Figure 1) was constructed by the Troy & Greenfield Railroad, which eventually became part of the Boston & Maine Railroad line. Today, the tunnel is owned by Guilford Transportation Industries and is used exclusively for freight.

The surveying for the tunnel utilized four stone lining towers as well as two backsights located to the east and west of the mountain. Two of the lining towers were at the portals of the tunnel, and the remaining two were located on the mountain over the tunnel alignment. All six towers were equipped with transits (theodolites), and the alignment was carried into the tunnel by means of plumb bob lines suspended from the tunnel roof. When the tunnel bore was complete, the bore from the east met the bore from the west within 9/16 in of the planned alignment.

Very early in the tunneling effort, attempts were made to utilize an innovative type of boring machine. Unfortunately, the device progressed only a short distance before it became hopelessly frozen in the rock. It remained stuck in place for many years until it was eventually scrapped. The machine's failure was mainly due to the fact that, at the time, only cast iron was available for its construction. The concept of the machine was sound, however, and it was the ancestor of modern-day tunnel boring machines constructed of steel.

Subsequently, a second tunnel bore was begun next to the disabled boring machine, and air-powered drills were used. In 1866, a water-powered air compressor plant was built along the Deerfield River, which runs near the eastern portal of the tunnel. This facility contained four compressors, which provided air for the drills at 65 psi (pounds per square inch) by means of an 8-in-diameter cast iron pipe. Steam engine backup was provided for the compressor in the event of severe icing on the river in winter.

The pneumatic drills used were Burleigh drills built in the town of Fitchburg, Massachusetts. These drills later became the basis for the design of Ingersoll-Rand rock drills that were used in the construction of such notable structures as the Hoover Dam.

Blasting had been tried early in the project, but the black powder available then could not shatter the veins of quartz prevalent in the rock which composed Hoosac Mountain. However, in 1867, Prof. Mowbray of Titusville, Pennsylvania, offered the use of his newly developed form of nitroglycerin, which he called tri-nitroglycerin (dynamite, which is a combination of nitroglycerin and rottenstone had not yet been developed). Near the west portal of the tunnel, Mowbray concocted this explosive in a structure that became known as the Acid House.

A fascinating incident occurred one winter that revealed a safe method for the transport of tri-nitroglycerin. One very cold day, the project's chief engineer assumed the task of delivering tri-nitroglycerin to the east tunnel portal using a horse-drawn sleigh over the mountain. The horses lost their footing in the snow, and the sleigh tumbled into a ravine. Despite his expectations, the chief engineer was not blown to bits. The incident first showed that tri-nitroglycerin was safe to transport when frozen.

The Hoosac Tunnel was ultimately a complete success. However, the necessity for the use of steam locomotives during its early history caused a great deal of inconvenience and discomfort due to the large quantities of smoke in the tunnel. For drainage purposes, the tunnel slopes downwards slightly from its center to both portals. Thus, the locomotives had to "pour on the steam" for the first half of their trip through the tunnel. Occasionally, a locomotive would actually lose traction but, because of the smoke and noise, this fact would not be apparent to the engineer or fireman. If they became suspicious, the fireman would have to stick a shovel handle out of the side of the cab to touch the tunnel wall in order to see if they were really moving or not.

The Electrification

Then, in 1910, the operation of the Boston & Maine Railroad was taken over by the New York, New Haven & Hartford Railroad of Connecticut, which had just completed a pioneering electrification of its main line into New York City. This was the first use of a high-voltage ac overhead catenary to supply power to electric locomotives. The installation was designed by the Westinghouse Electric Company, and the power house was located in the town of Cos Cob, Connecticut. The catenary was energized at 11,000 V, and this was stepped down by means of transformers on the locomotives. A low frequency of 25 Hz had to be used (rather than 60 Hz) because of commutation difficulties experienced when attempting to operate the series-connected traction motors on higher frequencies. This electrification of the New York, New Haven & Hartford Railroad main line was designated an IEEE Milestone in Electrical Engineering and Computing in May 1982.

The management of the New York, New Haven & Hartford Railroad immediately ordered the installation of exactly the same type of system (11,000 V, 25 Hz) for the Hoosac Tunnel in order to allow the use of electric locomotives. These locomotives would pull not only the trains themselves but also the coupled steam locomotives. The latter would operate through the tunnel with their fires banked so as to minimize the smoke nuisance.

Five electric locomotives (called electric motors) were built by the Baldwin Locomotive Company and were then equipped by the Westinghouse Electric Company. Two of these were designed to pull passenger trains through the tunnel at a reasonable speed, and the other three (Figure 2) were geared lower in order to handle heavier freight trains at slower speeds.

In order to supply this electrification, a power house was constructed about 2.5 mi south of the tunnel's west portal in the village of Zylonite (this odd name resulted from the manufacture there of an early plasticlike material of the same name that was similar to celluloid). This generating station was actually built by the local interurban streetcar company, the Berkshire Street Railway, which had coincidentally also come under the ownership of the New York, New Haven & Hartford Railroad. The streetcar operation had been powered by an 1889-vintage direct current (dc) power house at the same site that provided 550-V dc to the overhead trolley wires. The plan was to use the new power station to supply both the streetcar line and the new Hoosac Tunnel electrification.

The new Zylonite generating facility was completed in 1911. It utilized steam-turbine-driven generators to produce the 11,000-V ac power for transmission to the Hoosac Tunnel. By 1913, a substation had been added, which contained three rotary converters to convert the 25-Hz power into dc power to operate the streetcar line. Then, the old dc streetcar power house adjacent to the new station was shut down.

The Zylonite power house contained four Bigelow & Hornsby 500-hp water-tube boilers to supply steam to two Westinghouse 11,000-V, 25-Hz turbine-driven alternators. The boilers were equipped with automatic stokers, economizers, and superheaters as well as both forced and induced draft. The coal was delivered by the Boston & Albany Railroad (which was actually a competitor of the Boston & Maine Railroad) via a track connection from the city of Pittsfield, Massachusetts, to the south.

The Hoosac Tunnel electrification was single-phase, with the 11,000-V ac power applied between one overhead catenary conductor and the grounded track rails. The two Westinghouse alternators in the power house were each rated at 3,750 kVA (3,000 kW) on a single-phase basis, even though they were wound as three-phase generators. Figure 3 shows an overhead catenary bracket during installation on the roof of the tunnel.

The three-phase outputs from the alternators fed into three station buses which were called the trolley bus, the power bus, and the ground bus. The trolley bus fed the overhead catenary wire, the ground bus ultimately connected to the track, and the power bus served as a single-phase supply for auxiliary equipment. A series resistance was incorporated in the trolley bus connections to limit the short-circuit current to a level of 600 A to be compatible with the capabilities of the circuit breakers.

The main high-voltage transmission line running north from the Zylonite Station terminated just west of the western portal of the tunnel at a small brick structure called the West Portal Switch House (this building still stands today but is totally derelict).

At that time, the Hoosac Tunnel had two railroad tracks (the roadbed was changed to a single track in 1957). From the West Portal Switch House, two overhead catenary wires ran through the tunnel, one for the eastbound track and one for the westbound track. Both of these wires were fed from the same trolley bus in the power house.

The electrification extended for only a very short distance beyond the eastern portal of the tunnel. However, there was a small repair shop at that location which tapped the catenary and ground (track) connections for single-phase power to supply lighting and an air compressor (with a single-phase motor) via a step-down transformer.

At the western end of the tunnel, however, the electrification extended for some distance beyond the west portal (Figure 4) to a yard and repair shop facility in North Adams. Interestingly, in the repair shop, taps from the catenary, the grounded track, and the power bus connection from the Zylonite Station were all used to obtain a supply of three-phase power (via step-down transformers) for use in the shop.

An elaborate overhead arrangement of insulated conductor crossings at a point just west of the North Adams railroad station was necessary to allow the 550-V dc trolley wire of the Berkshire Street Railway to cross the high-voltage catenary wires of the Hoosac Tunnel electrification. Aerial switching devices were used so that the crossing could only be energized from one of the two power systems at any given time.

The tunnel was originally equipped with a 1,000-ft-long vertical ventilating shaft at its center (called central shaft). Following the electrification, the fan located at the top of the shaft was replaced to decrease the presence of smoke and fumes in the tunnel even more. As a result of these improvements, it became possible to stand at the location of the central shaft and see both tunnel portals as "pinpricks of light." To this day, a shanty located at the central shaft for use by trackwalkers is known as the Hoosac Hotel.

Later Developments

The original intention had been to eventually construct a hydroelectric facility on the Deerfield River at the eastern end of the tunnel to supply the catenary and, then, to use the Zylonite Station exclusively for the streetcar operation.

In 1913, the New England Power Company began construction of a hydroelectric plant on the Deerfield River near the east portal of the tunnel. This facility was actually one of a series of such hydroelectric stations, and it became known as Deerfield No. 5.

The equipment provided for this station was rather unique. Each turbine was designed to drive two generators. One was a conventional 60-Hz generator, and the other was a 25-Hz generator for the Hoosac Tunnel catenary. Both were three-phase machines, but the latter was operated single-phase like the generators at Zylonite.

There were three such turbine-generator units, and each of the six generators was rated at 3,000 kVA. The amount of 60-Hz power that could be provided by the station was, of course, determined by the 25-Hz catenary load at any given time. The 25-Hz generators were designed to feed no more than 15 times normal current into a dead short circuit, and they were each capable of providing up to 4,300 kVA for a 20-min period in order for the electric locomotives to handle heavy freight trains in the tunnel.

Rail traffic in the Hoosac Tunnel had become so heavy by 1913 that the three machines at Deerfield No. 5 were actually used as 60/25-Hz frequency changers until the necessary water handling facilities were completed to allow for the operation of the turbines themselves. Power for the operation of the 60-Hz generators as synchronous motors was provided by a 66-kV transmission line from the Vernon, Vermont, hydroelectric plant of the Connecticut River Transmission Company. Eventually, this same transmission line would be used to convey the 60-Hz power output of the Deerfield No. 5 Station in the opposite direction.

Thus, after the Deerfield River No. 5 hydroelectric station was completed in 1915, the station at Zylonite was held in reserve as a power source for the catenary. By 1928, however, the Zylonite Station was totally shut down since the streetcar system had entirely yielded to the automobile by that year. Today, no trace of the station remains.

The Hoosac Tunnel electrification remained in use until 1946 (supplied with 25-Hz power from Deerfield Station No. 5) when diesel locomotives completely replaced steam locomotives and there was no longer any need for the electric locomotives to haul the latter through the tunnel. The only remaining evidence today of this electrification are the crumbling remains of the West Portal Switch House.

For Further Reading

O.R. Cummings, "A history of the Berkshire street railway," Transportation Bulletin No. 79, Connecticut Valley Chapter, Nat. Railway Historic. Soc., Warehouse Point, CT, 1972.

H.K. Hardcastle, "The Hoosac tunnel electrification," Electric J., pp. 830–846, 1911.

"Single-phase generating, transmitting and distributing systems for the Hoosac tunnel," Elect. World, pp. 741–745, Sep. 23, 1911.

"Electric development in New England," Elect. World, pp. 1365–1372, Dec. 28, 1912.

"Note re early tunnel lighting," Elect. World, p. 97, Feb. 23, 1889.

M. Howes, HoosacTunnel.net Web site [Online]. Available: http://hoosac.franklinsites.com/