On a late autumn evening in 1887, a man stood on a wooden platform one hundred sixty feet above the Hudson River in Dutchess County, New York, fitting the pin that would connect two halves of a cantilever structure reaching toward each other from opposite directions over the fourth span of the river. The platform had no railing on the river side. It did not need a railing to perform its function. The man fitting the pin needed to reach the bolt hole, and he was on the correct side of the platform to do so.
Beneath him, the river moved toward the sea at the speed of the tide running that evening. In autumn, the Hudson runs with the tide in both directions at Poughkeepsie. The river at the bridge site lay two hundred twelve feet below the level of the track he was helping to build. A fall from the work platform would not have been two hundred twelve feet.
The distance was exactly his height above the water surface. When the Poughkeepsie Railroad Bridge opened to traffic on January 1, 1889, it was the highest railroad crossing of the Hudson River and among the longest railroad bridges in the United States. It crossed the Hudson through five main cantilever spans between six stone piers, with iron girder approach spans extending from the river spans to the west bank at Highland in Ulster County and the east bank at Poughkeepsie in Dutchess County. The total length from abutment to abutment was 6,767 feet.
The track elevation above high water at the main channel span was 212 feet. The depth of the river beneath the middle span in its natural state was 68 feet. There was a swing span, demanded by the Army Corps of Engineers as a condition for allowing the bridge to be built, located in the third opening from the east bank. It was 525 feet long and rotated around a central pier to open a navigable channel for river traffic when the mechanism was operated.
The bridge was the answer to a problem that had limited freight movement in the northeastern United States since the beginning of railroad construction. The men who built it—the compressed-air workers in the caissons beneath the river and the iron gangs on the structures above—were documented in the records of the Poughkeepsie Bridge Company only to the extent those records required. To understand the problem the Poughkeepsie Bridge was built to solve, one must see the Hudson River as an obstacle. The Hudson runs from north to south through the geological center of New York State, separating New England from the continental interior.
At its southern end, it empties into New York Harbor. The railroads of southern New England—those serving the industrial cities of Connecticut, Massachusetts, and Rhode Island, the textile mills of the Connecticut River valley, and the foundries and machine shops of Springfield, Providence, and Worcester—reached the Hudson at its tidewater mouth, which was also the mouth of New York Harbor, to move goods between the industrial interior of New England and the coal fields of Pennsylvania, and between the mills of the Connecticut River valley and the grain elevators of Chicago and ironworks of Pittsburgh. The freight had to cross the Hudson. In 1870, it crossed the Hudson by ferry.
In 1880, it still crossed the Hudson by ferry. The terminal facilities and freight transfer operations at New York Harbor were among the busiest points on the American railroad network. Every freight car moving from New England to the Pennsylvania coal fields or the industrial cities of Ohio passed through the New York Harbor terminals and was switched at least twice. It was loaded onto a car float, moved across the water, then unloaded from the float at a terminal on the opposite shore, sorted, and coupled into a departing train.
Time, damage, cost, and delay piled on delay in a terminal system processing more cars than it was designed to hold because the manufacturing economy of New England had outgrown the capacity of the ferry that served it. The bottleneck was structural. This was not a temporary inconvenience. It was the physical consequence of the Hudson River existing at a point where geography forced all east-west freight traffic through a single river mouth that could not be bridged at its opening.
The harbor was a seaport. The lower Hudson was a navigation channel. A railroad bridge over the lower Hudson in the 1880s would have been an obstruction to one of the busiest commercial waterways in North America. The Corps of Engineers would not allow it.
The navigation requirements of the harbor could not accommodate it. Ferry crossing at New York Harbor was the only option because no alternative existed above the Hudson Highlands. The Hudson narrows as one moves north. Above the harbor, above the wide reach of Tappan Zee, and through the Hudson Highlands at West Point, where the river cuts through a mountain range the glaciers did not remove, the valley walls slope down to the water and the river runs between hills of Precambrian gneiss and granite.
Above the Highlands, the valley opens again into the flat farmland of the mid-Hudson, the river valley the Dutch had farmed in the seventeenth century and that had been occupied by the Hudson Valley manor estates since before the Revolution. At Poughkeepsie, the river was wide, but not too wide to cross. Rock on both banks was available for pier foundations. The valley walls on both sides offered approach grades a railroad could climb without extraordinary engineering.
The city of Poughkeepsie on the east bank already lay on the main line of the New York Central and Hudson River Railroad. A crossing at Poughkeepsie would connect existing railroad infrastructure on both sides of the river, and it would lie north of the Highlands where the navigation requirements of the lower harbor did not apply with the same absolute force. The Poughkeepsie Bridge Company was organized precisely to build that crossing, incorporated by railroad interests that wanted an independent connection across the Hudson above the New York terminals—a route that would allow freight to move directly between the New England connections and the main lines west and south of the Hudson without entering the New York Harbor freight system at all. The economic case was the avoidance of costs.
Every ton of freight passing through Poughkeepsie instead of the New York terminals saved the transfer charges, the time cost of the transfer operation, the congestion delays the terminals imposed on everything passing through them, and the damage to goods from repeated handling. For freight moving between the manufacturing cities of Connecticut and the coal fields of Pennsylvania, the Poughkeepsie crossing was the removal of an obstacle that had added cost to every ton since the beginning of railroads. The company received its charter. It appointed an engineering staff.
The survey located the crossing on the river at Poughkeepsie where geology and valley engineering permitted. Design work began. The engineering problem posed by the Hudson at Poughkeepsie differed in kind from the problems at the Susquehanna at Rockville or the Patapsco at Relay. The Susquehanna at Rockville was a wide, shallow, braided river with a gravel and boulder bottom, easily reached for the construction of temporary cofferdams with a working depth that horse-powered pumps could maintain.
Forty-eight elliptical stone arches of seventy-foot span, built in cofferdams dewatered during the construction seasons between the fall of the spring flood and the rise of the autumn flood, were the structural answer to a crossing where materials, depth, span requirements, and construction method permitted stone. The Hudson at Poughkeepsie was not that river. The main channel at the crossing site reached 68 feet in depth at ordinary stage. The river was tidal.
The tidal variation over the course of a working day changed water levels in ways a construction plan had to absorb. The bearing rock beneath the river sediments lay at depths that temporary cofferdam construction could not practically reach with the methods available in the mid-1880s, and the Corps of Engineers had determined in the bridge permit that the river must remain open to commercial navigation throughout construction. Any temporary dam extending across part of the main channel during construction would close navigation. That was not permitted.
Therefore, the structural form of the Poughkeepsie crossing could not be a stone arch. A stone arch required falsework—temporary guiding structures supporting the arch ring until the keystone was placed and the mortar cured to full strength. Falsework in a navigable tidal river 68 feet deep was not the answer. The form had to be assemblable from above without support from below.
The form that could do that, that could span several hundred feet over a navigable channel and be built out from the pier tops without supports from the river surface, was the metal cantilever truss. The cantilever principle had been proven in long-span American railroad bridges during the 1870s and 1880s. The Kentucky River Bridge of the Cincinnati Southern Railroad, completed in 1877, had used cantilever construction to cross a gorge where falsework from below was impractical. The cantilever method allowed the truss to grow outward from each pier in both directions, balanced about the pier top without any support from below.
From each pier, truss arms extended outward over the adjacent spans. When the arms from adjacent piers approached each other at mid-span, a shorter suspended truss was installed between them, hung from the ends of the arms by pin connections. The suspended span carried its weight to the cantilever arms. The cantilever arms carried that weight through compression in the top chord and tension in the bottom chord to the pier tops and thence down through the stone masonry to the foundations.
The load path was continuous from the track surface to the river bottom. The river stayed open throughout construction. The navigation channel remained navigable. The bridge was assembled entirely in the air above the water it crossed.
Five such main cantilever spans would cross the Hudson between six stone piers. The pier foundations posed the construction problem the cantilever truss design ignored. The problem of how to establish six stone piers in 68 feet of tidal river water on a rock bottom that could not be reached by cofferdam. The solution was the pneumatic caisson.
Pneumatic caissons had been used in major American bridge foundations since the East River caissons of the Brooklyn Bridge in the early 1870s, and before that at the Eads Bridge in St. Louis beginning in 1869. The principle was the same at Poughkeepsie in 1886 as at Eads Bridge seventeen years earlier. A steel working chamber was placed on the river bottom at the pier site.
The chamber was sealed and pressurized with compressed air pumped from the surface. The compressed air, at a pressure sufficient to balance the hydrostatic pressure of the water above, kept river water from entering the working space within the chamber. Men entered the working chamber through an airlock, a small chamber between the pressurized interior and the atmospheric surface that allowed pressure equalization in both directions, to work in the chamber at the base of the pier being constructed. They excavated river bottom material by hand with picks, shovels, and wheelbarrows, removing it through a separate debris outlet that allowed excavated material to be raised to the surface under pressure.
As excavation deepened, the pier structure above the caisson forced it downward under its own weight toward the founding level. When the working face of the caisson reached the bearing stratum, the rock beneath the river sediments, the foundation excavation was complete. The working chamber was filled with concrete. The pier column was built up above it in stone masonry.
Thus the foundation was made. The men who worked in the caissons at Poughkeepsie in 1886 worked in compressed air at pressures dictated by the depths of water above the caisson roof. At the depths encountered in the main channel, the air pressure in the caissons reached levels at which the medical literature of the 1880s was beginning to study the physiology of nitrogen absorption under high pressure, linking it to the condition caisson workers called “the bends. ” The relationship between decompression sickness and the formation of nitrogen bubbles in blood and tissue was not yet understood in the mechanical terms that later physiological research would produce.
What was understood, empirically and incompletely, was that men who left the airlock too quickly, reducing pressure on their bodies too rapidly on exiting the working chamber, suffered symptoms ranging from severe joint pain that could double a man over, to paralysis, and even death. What was understood was that the required decompression time—a specific duration of pressure reduction in the airlock on exit—reduced the incidence of the condition but did not eliminate it entirely. Whether the decompression time set by the construction management was the same time the men actually spent in the airlock was the gap between specification and application that existed on every pneumatic caisson project of the period. The men working in the compressed-air chambers at Poughkeepsie were paid by piecework where piece rates applied, or by the day at a premium wage above surface labor that the nature of compressed-air work commanded.
This premium was the recognition of risk in the terms the labor market of 1886 used to acknowledge risk. A man spending the required time in the airlock for decompression was a man spending that time without working, and therefore without earning. The man who could not afford to spend time without earning money was the man who moved through the airlock faster than the specified rate. The consequences of that choice fell unevenly across the workforce, concentrated among the men most economically pressed to take the risk, and were recorded in the construction medical records to whatever extent the records required recording.
The caisson excavation at the Eads Bridge in St. Louis between 1869 and 1874 killed twelve men from decompression sickness and permanently disabled many others. The caisson excavation at Poughkeepsie proceeded with better empirical understanding than the Eads Bridge foundations, but under the same underlying conditions: compressed air, excavation under pressure, the airlock as the only link between working environment and surface, and workers making decisions about decompression time in the chamber that construction management could not fully determine or enforce. The men who emerged from the airlocks at Poughkeepsie bent over by the condition called “caisson disease” appeared in the construction records to the extent that 1886 record-keeping required documenting an injured worker.
Many of them never appeared in the records at all. The workers who performed the caisson work at Poughkeepsie came from the pool of men available to the heavy construction labor market of the Hudson Valley in the mid-1880s. Irish immigration in the 1840s and 1850s had left a labor density in the Hudson Valley and northeastern cities that, by the 1880s, had partly settled into the crafts and political structures of port cities while still partly working in mobile construction labor. Irish-born workers and American-born sons of Irish immigrants provided the general labor and part of the skilled excavation and construction trades in the caisson foundations at Poughkeepsie.
Italian immigration to the northeastern construction labor market was growing during the decade but had not yet reached the scale it would achieve in the 1890s, when Pennsylvania Railroad construction would draw Italian workers from the south and Sicily through the padrone system in numbers later employed at the Rockville Bridge construction a decade later. The Poughkeepsie caisson workers of 1886 were the generation before that shift, the end of the Irish construction workforce and the beginning of the Italian workforce, working in compressed-air chambers beneath a Hudson River crossing that neither group would have chosen to build had the wages been otherwise. The wages for compressed-air work at Poughkeepsie were the wages set by the Hudson Valley construction labor market of 1886 for men willing to work under the river in conditions the medical understanding of the age could not fully explain and the engineering management could not entirely control. They were higher than surface labor wages.
They were the rate the contractor agreed to pay and the men agreed to accept. The difference between the agreed wage and the wage actually received—after the contractor deducted for lodging, provisions, and any advances against future earnings—was a difference a worker could verify only if he could read the contractor’s books, which most of the tunnel diggers at Poughkeepsie in 1886 could not. The iron gangs that erected the cantilever trusses over the Hudson were different in makeup from the diggers in the river bottom. They were specialists in a trade that the expansion of American railroading had created continuous demand for since the beginning of major iron bridge construction in the decades after the Civil War.
Bridge gangs moved from one major structure to another across the railroad network as work required. They went where the iron was being raised. The Poughkeepsie crossing in 1886 was where the iron was being raised, and the men capable of working at height on iron structures came to it as members of a specialized trade that followed jobs through internal communication passing word of upcoming work and wages. The riveting gangs closing the connections of the Poughkeepsie cantilever trusses worked in crews of four.
The heater kept the rivets in a portable forge at the temperature that made the iron workable. If too cold, the rivet stiffened before its head could be fully driven. If too hot, the metal was soft at the moment it needed to be tight. The passer caught the hot rivet thrown by the heater with tongs or a metal can, placed it in the hole, and stepped back.
The holder-on held a bucking bar against the manufactured head of the rivet on the back side of the connection, providing opposing pressure that allowed the head to be formed properly against the other side, while the riveter drove the head with a hand hammer, or a pneumatic hammer if compressed-air equipment was used, drawing air from a hose connected to a compressor at the pier top or on a boat in the river below. The process required coordination among four men on a platform that might consist of wooden planks tied to the structure members with rope, secured by nothing more than the strength of the rope lashings themselves. The platform one hundred sixty feet above the Hudson in the autumn of 1887 was adequate to support the riveting crew, their tools, and the weight of the work they performed. “Adequate” was what the construction schedule required and the project budget provided.
The railing on the river side of the platform was not part of the equipment required to close the pin connections in the fourth cantilever arm over the Hudson. The man fitting the pin on the river side of the scaffold was fitting it there because that was where the connection point was located. He had been making such connections at height on iron structures for his entire time in the iron bridge building trade. The risks were not unknown to him.
This was the essence of the work. The fabricated truss members that the iron gangs installed over the Hudson—chord sections, web members, pin plates, and lattice connections—were produced in a specialized bridge shop and delivered to the site by the existing railroad network. They arrived by train or barge, then were lifted from the delivery point by construction derricks positioned atop the pier caps, and placed into position for the connection crews by men operating the derrick ropes and guiding the swing of the loads. A chord section weighing several tons swinging from a derrick head two hundred feet above the Hudson was not a load that could be controlled the way a hand tool could be controlled.
It was a manageable load. The difference between “controllable” and “manageable” was what the men running the derricks and the men receiving the loads on the scaffolds understood through their daily experience and expressed in habits of motion and positioning that enabled them to do the work without being struck by the loads they handled. These habits were not written down in any records. No law of New York State or regulation of the federal government in 1886 required them to be written down.
They were professional practices passed among crew members who had learned them from the men who came before. The five spans of the cantilever bridge grew outward from the tops of the six piers over the five river bays through 1886 and into the 1887 construction season. As the cantilever arms from adjacent piers reached toward each other at mid-span, the erection engineers managed the sequence of member installation to control the stresses within the structure that was not yet complete. A cantilever arm weighing several hundred tons of steel and extending over the Hudson without a matching arm on the approach side would have imposed moments on the pier foundations that those foundations were designed to resist only in the completed structure, not in the structure still under construction.
The erection sequence was the engineering document that turned design intent into physical reality on the site. The foremen executing that sequence above the pier tops read the erection drawings produced by the engineering staff and made the daily decisions about which member to install next based on the requirements of the drawings and what construction conditions permitted. The approach bridges extending the structure from the river spans to both banks were built on stone abutments and iron trestles mounted along the valley walls at each shore. The west bank approach climbed the hills of Ulster County from river level to the bridge deck elevation on iron trestles rising from the hillsides below track level.
The east bank approach descended from the bridge deck to the railroad connections in the city of Poughkeepsie through shorter truss bridges carried on stone piers. The approach structures were not the real engineering challenge of the river crossing. They were the work that had to be done before the river spans became useful, the connections that turned the 6,767-foot structure into a railroad crossing rather than a self-contained bridge over the Hudson. The swing bridge in the third opening from the east bank was an acknowledgment built into the structure that the river it crossed had commercial users whose interests preceded the railroad.
The Hudson River steamboat trade between New York City and Albany had operated since Robert Fulton’s first commercial voyage in 1807. The brick factories of the Hudson Valley had shipped their products from river wharves since before the canal era. The ice harvest that supplied Manhattan with refrigeration before mechanical systems replaced it was taken from the winter ice of the Hudson above the Highlands. The swing bridge at Poughkeepsie was 525 feet of the bridge that rotated around its central pier to open a navigation channel when river traffic required it.
The right of river navigation in the channel was older than the bridge itself. The swing bridge was the form that right took in compliance with the federal permit requirements. The bridge opened to railroad traffic on January 1, 1889. The first revenue trains to cross it were the through freights between the New England railroad connections and the main lines west and south of the Hudson that the Poughkeepsie Bridge Company had been organized to serve.
The route ran from the Connecticut and Massachusetts railroad systems through connecting lines to the east end of the bridge, across the Hudson at Poughkeepsie 212 feet above the river, and from the west end through the Central New England and Western Railroad to junctions with the Erie Railroad and other western lines. The bottleneck was not eliminated. The New York Harbor terminal system continued to handle shipments that could not reach the Poughkeepsie crossing economically or for which the connecting routes made the Poughkeepsie path impractical. But the shipments the route served, and that economic feasibility favored, crossed the Hudson at Poughkeepsie instead of passing through the ferry terminals, and the costs saved were the revenue basis the bridge company had anticipated.
The New York, New Haven and Hartford Railroad acquired the Central New England Railroad in 1904, and with it the trackage rights and connection arrangements that had used the Poughkeepsie crossing since its opening. Under New Haven control, the bridge became part of the through freight route the New Haven used to move coal from the Pennsylvania fields to the industrial market of New England. Coal from the Pennsylvania mining regions moved west and north over Pennsylvania Railroad connections, crossed the Hudson at Poughkeepsie, and reached New England through New Haven connections in Connecticut. The coal traffic was the pillar on which the viability of a through freight route creating a crossing over the Hudson north of New York had always rested.
And still the coal moved across that bridge 212 feet up, for decades. Penn Central acquired the New Haven Railroad’s properties in 1968. Penn Central went bankrupt in 1970, the largest corporate failure in American history at that time. The Poughkeepsie Bridge and the through freight route it enabled passed, after the Penn Central bankruptcy, to the Conrail operating entity in 1976.
The bridge had carried railroad traffic for eighty-seven years. The cantilever arms, riveted together by iron workers over the Hudson in 1886 and 1887, had carried commercial freight trains since January 1889, through the entire development of railroad motive power, from the steam locomotives of the New Haven and its predecessors to the diesel power that replaced steam during the 1950s. The pier foundations, sunk by caisson workers into the rock of the Hudson riverbed in 1886, had been continuously in the river since they were poured. On May 8, 1974, a fire broke out in the middle section of the Poughkeepsie Bridge.
Welding operations on the deck, performed by a maintenance contractor, ignited the creosote-soaked timber decking and walkways in the middle spans. The fire spread through the combustible material in the deck of the main spans over the river before it was controlled. The structural steel elements of the cantilever trusses did not burn. Steel does not burn.
But steel, at the sustained temperatures of a creosote-and-timber fire, loses a significant portion of its structural strength. The load-bearing and tensile capacity of a steel member heated to the temperatures of the 1974 fire and then cooled is not the same as that of a member that was never heated. The inspection conducted after the fire concluded that the thermal damage to the structural steel in the affected spans was sufficient to require major repairs before the bridge could safely return to commercial service. The cost of repair compared to the revenue the through freight route was generating in 1974 was the calculation Conrail made.
The calculation did not favor repair. The bridge was closed to railroad traffic and remained closed. The structure stood over the Hudson for the next thirty-five years carrying no traffic at all. The pier foundations were in the river.
The cantilever arms were in the air. The swing span mechanism sat on its central pier without rotating. The tidal river continued to run beneath the six stone piers in its natural cycle, the cycle it had followed before any crossing existed over it. The caisson foundations sunk by compressed-air workers into the riverbed rock in 1886 continued to support the pier columns.
The pier columns continued to support the cantilever arms. Those arms continued to extend over the river. The structure had been designed to last, and it did last. It simply no longer carried trains.
In 2009, the Poughkeepsie Bridge was reopened as a walkway over the Hudson River Historic State Park. The damaged structural steel was repaired. The deck was rebuilt for pedestrian use. The swing bridge was inspected, fixed in place, and preserved as it stood.
The piers, founded by men who worked under compressed air beneath the Hudson in 1886, carried pedestrian traffic on the reopened walkway in the same way they had carried New Haven Railroad freight for eighty-five years before the fire. The foundations were sound. The pier proportions were correct. The stone masonry had stood in the tidal river for 123 years and continued to perform the function assigned to it by the 1884 engineering design.
Two million people have crossed the walkway over the Hudson since 2009. They cross 212 feet above the river on the steel. The iron gangs connected the bridge over the Hudson in 1886 and 1887. The Hudson moves beneath them in the tidal cycle it has always followed.
Looking south from the walkway on a clear day, the river disappears around the bends of the valley and continues toward the harbor, eighty miles to the south. No freight train crosses at Poughkeepsie anymore. The direct freight route the bridge was built for no longer operates as the Poughkeepsie Bridge Company organized it to provide. The goods the bridge carried between New England and Pennsylvania through eighty-five years of railroad service now move by other means over other routes.
There are interpretive signs on the walkway above the Hudson. They identify the bridge and its engineering history. The signs record the length, the height, the opening date, and the significance of the cantilever construction. The Poughkeepsie Bridge Company and its engineering department are represented in the terms historical interpretation uses to represent them.
The bridge is classified as an engineering achievement. The iron gangs who walked the members of the cantilever arms two hundred feet above the Hudson in the construction seasons of 1886 and 1887 are not named on the signs. The riveting crews—the heaters, passers, holder-ons, and riveters who closed the field connections in whatever weather the Hudson Valley produced during two years of construction—are not named on the signs. The men who worked in the pneumatic caisson chambers beneath the river surface, in air pressure dictated by the depth of water, and who left the airlocks at rates the physiology of 1886 could not fully protect them from, do not appear on the interpretive panels.
The compressed-air workers appear in the medical records of the construction period, to the extent record-keeping required documenting a worker injury. Many of them are not in those records at all. The payroll records of the Poughkeepsie Bridge Company document labor costs for the caisson work, the iron work, the masonry, and the approach bridges, to the extent the financial accounting of 1886 required. The workers appear in those accounts as part of the cost of the work.
The iron gangs appear at the crew level, where timekeeping tracked crew productivity. The individual members of those crews—the heater who maintained the proper temperature, the holder-on who braced the bucking bar against the rivet shank, the man who fitted the pin on the river side of a work platform without a railing in the autumn of 1887—appear in those records to the extent required to track the cost of the connection. They do not appear to the extent required to track the identity of who did the work. The cantilever arms are still there.
The piers are in the river. The foundations are in the rock beneath the river. The tidal Hudson continues to flow through the space occupied by the six pier columns in its course. The swing bridge rests on its central pier as it has rested since the last time it swung, sometime before 1974.
The structure built by compressed-air workers and iron gangs in 1886 and 1887 over the Hudson at Poughkeepsie now carries pedestrian traffic over the same river it was built to carry trains across. The record of how it got there exists in the engineering drawings, the cost accounts, and the corporate records of the company that built it, operated it, and finally closed it to railroad traffic. The engineering drawings are precise. The cost accounts are complete to the standard the accounting of that period required.
The men who did the work are in those records as costs, crew counts, daily wage rates, and total expenditures presented by the contractor and paid by the bridge company. They are not in those records as individuals who worked in the pressure chambers, raised the iron sections, drove the rivets, and fitted the pins two hundred feet above the Hudson. The work was done. The record of the work is the record the system required to be kept.
The men are in that record as the cost of the work. The bridge is still there. And the river still moves beneath it.
