Fifteen Idaho bridges are listed in the National Register of Historic Places for their cultural and historical significance. The two in Boise could hardly be more different from each other.
The 1931 Oregon Trail Memorial Bridge on Capitol Boulevard, which we wrote about last week, is a graceful four-arched reinforced concrete span designed by Charles A. Kyle, bridge engineer for the Idaho Transportation Department. It was listed in the register on Nov. 5, 1990.
The Ninth Street Bridge, built in 1911, is a two-span steel truss bridge across the Boise River, located just downstream from the Memorial Bridge. Its 322 feet are supported by a concrete abutment at either end and a concrete pier at the mid-point. It served for many years as the southbound lane of the Capitol Boulevard couplet. It had a 19-foot-wide, steel-reinforced concrete roadbed and a 6-foot-wide pedestrian walkway. It was in use until the present southbound span was built beside it. In 1988 the roadbed and walkway were removed and rebuilt with wood planking to accommodate use by pedestrians and bicyclists.
Like most truss bridges of the period in Idaho and elsewhere, the bridge has dedication plaques. Those on the crossbars at each end of the Ninth Street Bridge identify the builder as the Missouri Valley Bridge and Iron Works. Others list the Ada County commissioners of both 1910 and 1911, and Lapointe & Fox of Boise as consulting engineers.
News stories in the Idaho Statesman about previous bridges that had crossed the river at or near 9th Street, all owned by private citizens rather than government entities, always referred to them simply as "the Boise Bridge." In January 1876, owner H.P. Isaacs sold the bridge to his brother, J.C Isaacs, for $6,000. Most of that bridge was swept away by high water that spring. New owner William B. Morris contracted with Dowling Brothers to supply the lumber needed to build a new bridge at the site.
The Statesman reported that "William B. Morris, manager and builder, fully understands what kind of a bridge is needed, and we are satisfied it will be a much better bridge than the old one. The cost of the new work is $5,000. It is done in the most substantial manner, and every precaution has been taken to secure it against the effects of future freshets." When Morris died in 1878, his nephew, Will Ridenbaugh, inherited his estate, including the bridge.
In January 1884, the Ada County commissioners wanted to buy it from him and make it toll free, but they didn't have the money. The Boise City Council then voted to buy it from Ridenbaugh with money raised from a special tax of three-fourths of 1 percent on all taxable property in Boise City, and then give it to the county. Mayor James Pinney and council members John Lemp, Nathan Falk and John Broadbent thereby created the first public ownership of a Boise bridge.
A unique feature of the work done on the bridge in 1884 was to add a steel cable suspension span, surely making it the first suspension bridge in Idaho. The Statesman reported on May 29, 1894, "The suspension span at the Boise City Bridge proves to be a grand success. Teams are crossing regularly with good loads of freight, and the stages are also crossing with passengers, mails and freight without interruption. The structure is perfectly safe for all the weight that need go upon it. There will be no further interruptions to travel."
The span got its first real test on June 1, 1884, when a band of 70 heavy horses was driven across it at a gallop, their total weight estimated at 25 tons. No damage was done to a bridge designed to carry 12 tons.
Arthur Hart writes this column each Sunday. Email firstname.lastname@example.org.