The Outer Drive Bridge, also known as the Link Bridge, is a double-deck

bascule bridge A bascule bridge (also referred to as a drawbridge or a lifting bridge) is a moveable bridge with a counterweight that continuously balances a span, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- or ...

carrying

Lake Shore Drive Lake Shore Drive (officially Jean Baptiste Pointe du Sable Lake Shore Drive, and called DuSable Lake Shore Drive, The Outer Drive, The Drive, or LSD) is a multilevel expressway that runs alongside the shoreline of Lake Michigan, and adjacent to ...

across the

Chicago River The Chicago River is a system of rivers and canals with a combined length of that runs through the city of Chicago, including its center (the Chicago Loop). Though not especially long, the river is notable because it is one of the reasons for ...

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

, United States. Construction was started in 1929 and was completed in 1937 as one of the

Public Works Administration The Public Works Administration (PWA), part of the New Deal of 1933, was a large-scale public works construction agency in the United States headed by Secretary of the Interior Harold L. Ickes. It was created by the National Industrial Recove ...

's infrastructure projects in Chicago. The bridge is officially named the Franklin Delano Roosevelt Memorial Bridge to honor the centennial anniversary of the birth of Franklin Delano Roosevelt.Chicago’s Bridges
/ref> It was planned by the

Chicago Plan Commission The Chicago Plan Commission is a commission implemented to promote the ''Plan of Chicago,'' often called the Burnham Plan. After official presentation of the Plan to the city on July 6, 1909, the City Council of Chicago authorized Mayor Fred A. Bu ...

, using Hugh E. Young as the consulting engineer, was designed by the Strauss Engineering Company, built by the

American Bridge Company The American Bridge Company is a heavy/civil construction firm that specializes in building and renovating bridges and other large, complex structures. Founded in 1900, the company is headquartered in Coraopolis, Pennsylvania, a suburb of Pitts ...

, and erected by Ketler and Elliot Company. It crosses near the mouth of the Chicago River.

Significance/purpose

Outer Drive Bridge and Chicago Harbor Lock (2009)

The building of this

bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

was meant to create many jobs for Chicagoans and ease traffic flow on Michigan Avenue and in the

Loop Loop or LOOP may refer to: Brands and enterprises * Loop (mobile), a Bulgarian virtual network operator and co-founder of Loop Live * Loop, clothing, a company founded by Carlos Vasquez in the 1990s and worn by Digable Planets * Loop Mobile, an ...

. In 1937 this structure was the longest, widest, and heaviest

in the world. The Outer Drive itself, now known as Lake Shore Drive, links the south side to the north side of the city, running along the western shore of

Lake Michigan Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and the third-largest by surface area (), after Lake Superior and Lake Huron. To the east, its basin is conjoined with that o ...

. It extends from its origin in Jackson Park on the South Side of the city to the Loop, across this Outer Drive Bridge over the

, to its eventual terminus at Hollywood Avenue and Sheridan Road in Edgewater on the city's North Side.

Funds

While the completion of the Outer Drive was considered one of the most important projects in the PWA it took many years to complete. A main issue was

funding Funding is the act of providing resources to finance a need, program, or project. While this is usually in the form of money, it can also take the form of effort or time from an organization or company. Generally, this word is used when a firm uses ...

. Due to a lack of provided security by

Chicago Park District The Chicago Park District is one of the oldest and the largest park districts in the United States. As of 2016, there are over 600 parks included in the Chicago Park District as well as 27 beaches, several boat harbors, two botanic conservatories ...

s, the allotment for the bridge was revoked until the districts were all in position to comply. The total cost of the Outer Drive is estimated at $11,563,000.

Economic justification

Calculations based on a

traffic flow In mathematics and transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devi ...

of 40,000 vehicles per day on a saving of eight minutes between Oak Street and Seventh Street, made possible by the use of the bridge rather than Michigan Avenue. The delay cost estimated to be one cent per car per minute (60 cents per hour for the value of time or the value of fuel saved) resulted in a savings in vehicle operation of $584,000 per annum; that amount capitalized at 5% would indicate that $23,360,000 could properly be spent to eliminate this delay, in the eyes of the decision makers at the time of the construction. From the perspective of

engineering economics ''For the application of engineering economics in the practice of civil engineering see Engineering economics (Civil Engineering).'' Engineering economics, previously known as engineering economy, is a subset of economics concerned with the us ...

, this savings calculation justified the Outer Drive bridge project, showing a possible saving of $11,797,000.

Bridge operation

According to

Engineering News-Record ''Engineering News-Record'' (widely known as ''ENR'') is an American weekly magazine that provides news, analysis, data and opinion for the construction industry worldwide. It is widely regarded as one of the construction industry's most authori ...

, "Each leaf is to be operated by two sets of

gear train A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...

s, consisting of four sets of

gear reduction Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differ ...

s. Each gear train is connected to two 100-horsepower main operating motors, only one of which is to be used at a time. The time required for opening or closing the bridge against a wind is stated to be 57.6 seconds, of which 10 seconds is for

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the ...

and 2.86 seconds for

deceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the ...

. The main operating racks are bolted to the underside of the outside trusses, the pitch radius being . The operating pinion, with a pitch diameter of , is mounted on a shaft of the gear train. Outer Drive Bridge Chicago - opened for sailboats 2011

Outer Drive Bridge Chicago - opened for sailboats 2011

Heavy locking devices are provided at the center of the bridge and at the rigid in its closed position. The center lock in addition to holding the leaves together in their closed position, also transmits

live load A structural load or structural action is a force, deformation, or acceleration applied to structural elements. A load causes stress, deformation, and displacement in a structure. Structural analysis, a discipline in engineering, analyzes the effe ...

shear from one leaf to the other. This center lock consists of a set of four female castings bolted to the river end of one leaf, and a second set of four male units bolted to the river end of the other leaf, all castings being on the centerlines of the trusses. The male unit consists of two castings forming a

toggle Toggle may refer to: *Toggle mechanism *Toggle switch *Toggling harpoon, an ancient weapon and tool used in whaling to impale a whale when thrown *A type of textile closure, like an elongated button *Toggle (Doonesbury character), a character in t ...

. Heel or rear locks are necessary to prevent the leaves from opening when live loads pass over the part of the bridge between the trunnions and the rear break in the floor. Each leaf is provided with two pairs of rear locks, each pair being placed between the inside and outside trusses. The four locks of a leaf are connected by shafting, and operation by means of two 15-horsepower motors set either side of the centerline of the bridge" (April 22, 1937).

References

*"A Record Size Bascule," Engineering News-Record, v. 118 (April 22, 1937): 583-587. *"Chicago Gets Added PWA Funds for Outer Drive Completion," Engineering News-Record, v. 115 (December 5, 1935): 795-796. *"Continuous Girders Top Rigid Frame Viaduct Bents," Engineering News-Record, V. 118 (May 6, 1937): 671-673. *"Lakefront Boulevard Link Forms Milestone in Chicago Plan," Engineering News-Record, v. 118 (April 15, 1937): 546-548.

External links