Triboro Bridge

The Triboro Bridge connects Manhattan, the Bronx and Queens through a complex sequence of three long-span bridges plus elevated viaducts and interchanges over Randall's Island.

Initial plans for the bridge were announced in 1916 but the bridge did not receive initial funding until 1925. Groundbreaking occurred on October 25, 1929 (one day after Black Thursday), but the subsequent depression caused suspension of work soon the following year. Parks Commissioner Robert Moses convinced Mayor LaGuardia to form an independent agency (the Triboro Bridge Authority) to handle construction of the bridge (and circumvent the corrupt patronage system of the time). Moses then secured a $37 million loan from the Federal Public Works Administration to resume construction in 1933. Port Authority chief engineer Othmar Ammann was brought in to complete and coordinate design of the structure based on earlier work by Gustav Lindenthal and Arthur I. Perry. The bridge was officially opened by Presiden Franklin Roosevelt on July 11, 1936. (reference)

Draw Span

The western segment closest to Manhattan is a 310-foot-long single-deck lift span over the Harlem River at 125th Street. The deck hangs from two 210-foot towers and is flanked by two 230-foot-long fixed truss spans.

3/12/2005 02:12 PM
Draw span view from the South

3/12/2005 02:15 PM
View from the south

3/12/2005 02:18 PM
West tower closeup

3/12/2005 02:19 PM
West tower closeup

3/12/2005 02:19 PM
Under the draw span

Suspension Span

The eastern segment connecting the Wards Island viaduct with Astoria, Queens was envisioned by original designer Arthur I. Perry as a dual-deck, 16-lane roadway supported by four suspension cables. When Amman came on board, he scaled back the design to a single eight-lane, truss-stiffened deck with two 3,104-foot long suspension cables hanging from two 315-foot-tall, 5,500-ton steel towers. Amman's modifications permitted use of foundations that had been constructed in the initial phase of construction while shaving $10 million off the budget.

The 1,380-foot main span hangs 135-feet over mean high water. The two 20-inch diameter cables each contain 37 strands, with each strand composed of 248 galvanized steel wires around 1/5th of an inch thick. The structure is unique in that the cables bend an unusually high 45 degrees at the anchorage bent posts, placing more of the load downward on the anchorages than is customary. The 20-foot-deep stiffening trusses surround the roadway on the main deck and obscure motorist views of the river and city, but the pedestrian walkway hangs over the river from the top outer edge of the truss, providing both exceptional views of the river and comforting separation from the traffic whizzing by below.

Lamp posts and other ornamental features (such as the tiered tips of the towers) reflect the Art Deco aesthetic of the 1930s. The four vertical posts between the legs of each tower are ornamental and have no structural purpose. When I visited in 2008, the bridge was undergoing a much needed dehumidification and renovation of the anchorages and a reanchoring of the cable strands.

3/12/2005 01:40 PM
Suspension span view from the South

7/2/2008 08:12 PM
Flagpole on the east approach in Astoria

7/2/2008 08:13 PM
Flagpole on the east approach in Astoria

7/2/2008 08:14 PM
Flagpole on the east approach in Astoria

7/2/2008 08:15 PM
Aluminum bas relief map in Astoria of the Triboro Bridge

7/2/2008 08:16 PM
East approach pedistrian walkway to Wards Island

7/2/2008 08:20 PM
Astoria just north of east approach

7/2/2008 08:23 PM
Lamp post on east approach

7/2/2008 08:25 PM
Temporary walkway hanging of north side of eastern anchorage

7/2/2008 08:26 PM
Concrete repair on eastern anchorage

7/2/2008 08:26 PM
Northeast cable anchorage eyebar

7/2/2008 08:26 PM
Repair of eastern anchorage

7/2/2008 08:27 PM
Pedstrian walkway and eastern tower

7/2/2008 08:29 PM
Eastern tower

7/2/2008 08:30 PM
Northeast joint of main span and east pier

7/2/2008 08:30 PM
Lamp

7/2/2008 08:31 PM
East tower

7/2/2008 08:31 PM
Hell Gate rail bridge viewed from the Triboro Bridge at sunset

7/2/2008 08:31 PM
Astoria Park viewed from the Triboro Bridge

7/2/2008 08:33 PM
Main span roadway viewed from the east

7/2/2008 08:33 PM
East tower viewed from the west

7/2/2008 08:34 PM
Hell Gate rail bridge

7/2/2008 08:35 PM
Anemometer on weather station

7/2/2008 08:36 PM
Ward's Island construction

7/2/2008 08:36 PM
West tower viewed from the east at sunset

7/2/2008 08:37 PM
Suspender cable attachment to main span

7/18/2008 06:12 PM
Lighting angle scale

7/2/2008 08:38 PM
Old unused sign display?

7/18/2008 06:08 PM
Northwest eyebar

7/18/2008 06:10 PM
Suspender cable

7/18/2008 06:20 PM
Joint

7/18/2008 06:20 PM
Air duct in tower

7/2/2008 08:38 PM
West tower viewed from the west

7/2/2008 08:39 PM
West tower and roadway coming off main span

7/2/2008 08:41 PM
Pedestrian walkway at west pier - note degraded concrete waiting to be replaced

7/2/2008 08:42 PM
Pedestrian walkway at west pier

7/18/2008 06:07 PM
Northwest cable

7/18/2008 06:07 PM
North pedestrian walkway, west tower

7/2/2008 08:42 PM
Renovated pedestrian walkway down to Wards Island with enclosed cage to prevent jumping or dropping of projectiles

7/2/2008 08:47 PM
Pedestrian walkway down to Wards Island

7/2/2008 08:51 PM
Construction equipment under Wards Island viaduct

7/2/2008 08:51 PM
West approach to the suspension span with walkway down to Wards Island

7/2/2008 08:53 PM
Pre-cast roadbed sections awaiting installation

7/18/2008 05:57 PM
Pre-cast roadbed sections

4/2/2008 09:07 PM
Night view from the Northeast in Astoria Park

4/2/2008 09:38 PM
East approach by night

4/2/2008 09:39 PM
East approach by night

Fixed Truss Span

Perhaps the least glamorous part of the Triboro Bridge is the truss section connecting the Bronx with the main interchange on Randalls Island. The main span over Bronx Kill is a 383-foot-long subdivided Warren Truss span with a clearance above mean high water of 55 feet. The approach truss spans are 1,217 feet giving a total anchorage-to-anchorage length of 1,600 feet.

At the time of construction, Bronx Kill was not navigable and the Corps of Engineers permitted use of a fixed span with the proviso that it be built in a way that would permit conversion to a lift span at a later time. Subsequently much of Bronx Kill has been filled in to expand parkland, leaving the tidal estuary little more than a shallow canal. The Kill can be navigated by canoe between the Harlem River on the west and East River on the east at high tide.