Roofs Over Rivers

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Despite all the work that went into it, this record-holding bridge stood for only three years; it was destroyed in an ice jam and never replaced. But although the inventor died in 1822, his arch bridges lived on. His boss-carpenters became contractors themselves and bridged countless lesser streams in New York, Pennsylvania, Ohio, and Indiana. Their sons and apprentices took the tried-and-true Burr arch even farther afield, using it for railroad spans in New England and highway bridges from Nova Scotia to California.

The big timbers that went into the elaborate structures of Palmer, Wernwag, and Burr took considerable manpower to put together. There was a crying need for a simple bridge that could be erected by a common carpenter’s gang. Ithiel Town, an architect from New Haven, Connecticut, filled the bill in 1820 with the patenting of his “Town lattice truss” bridge, an all-wood arrangement of planks crisscrossed like a garden fence and pinned together with big two-inch wooden pegs. Weight placed on it only tightened its framework.

Town promoted the bridge throughout the eastern states while carrying out his main work of designing churches and public buildings. The lattice truss caught on slowly, but eventually it became the favorite type of construction in New England. Town received a royalty of one dollar per foot for patent rights, and two dollars a foot if one of his sharp-eyed agents discovered a bridge erected on the plan without prior permission. New England emigrants took the Town lattice truss with them to Ohio and Michigan, and there was even one built (without a roof) over the Jordan River in Salt Lake City.

In these early years, bridge engineering was a matter of trial and error. In 1829, Colonel Stephen H. Long of the U.S. Army Topographical Engineers devised the first scientific wooden-truss bridge in America. It was essentially a series of crossed beams pinned into square frames. The Colonel called it the Jackson Bridge, in honor of the President, and built the first one as a highway overpass over the B&O Railroad outside Baltimore. It was the first railway grade-crossing separation in America.

Since Colonel Long, famed for his western explorations, was primarily a railway engineer, many of his bridges were built on the new rail lines of the 1830s. The first railroad drawbridges—over the Passaic and Hackensack rivers in New Jersey—followed his plans, as did the first combined railroad and highway bridge, over the Raritan River at New Brunswick, New Jersey. It is recounted that, when caught in the inky interior of the New Brunswick bridge while a train rumbled across the roof, more than one horse died of sheer fright!

Long’s bridges enjoyed a popularity of ten years, during which they vied with Ithiel Town’s lattice trusses for use by the growing rail network. The rival promoters exchanged polite notes via the newspapers, waxing eloquent in praise of their respective designs. Colonel Long, busy with army matters, finally left his share of the battle to his brother and “General Agent,” Dr. Moses Long of Warner, New Hampshire. Dr. Long, who was also the town postmaster, used his free franking privilege to blanket the East with advertising broadsides extolling the virtues of the “Long patent bridge.” Ithiel Town countered by appearing in person at bridge contract-lettings to plead the merits of his “mode,” sometimes—if the bridge were to be large or to stand in a prominent location—offering to waive his royalties.

After 1840, both the Town and the Long patent bridges were almost totally eclipsed by another design, using wooden cross-frames and iron rods and invented by William Howe of Spencer, Massachusetts. Howe came from a family of inventors: his brother Tyler devised a spring bed, and his nephew Elias achieved lasting fame for his sewing machine.

The Howe truss had a lot of the features of Long’s bridge, and the Colonel cried “infringement” long and loud, but to no avail. The basic difference was in the introduction of the iron rods and turnbuckles with which the Howe bridge could easily be trued up by tightening a few nuts. This ease of erection and maintenance made the Howe truss a special favorite of the railroads, and enabled them to span a stream quickly during the period when they were hastily laying new track in all directions. All the pieces for a wooden Howe truss bridge could be pre-cut and loaded on a brace of flat cars. Add the iron rods, plus a crew of husky Irish laborers, and the cars could be pushed out to a pair of waiting abutments at the end of the track. Twenty-four hours would usually see a 100-foot bridge in place; it could be roofed and sided while it was in service.