Movable Bridges

86

MOVABLE B

ovable bridges are those that canbe lifted or rotated to allow thepassage of marine traffic. Mov-

able bridge technology dates from ancienttimes, with the earliest documented exam-ples represented by simple draw bridgesthat were hinged at one end and lifted atthe other end by an outhaul line. The mov-able bridge remained in its primitive stageuntil the late-19th century after which thebridge type progressed rapidly due to advancesin mechanical, electrical and civil engineer-ing. In the United States, the same need for

LEFT: The Lewes bascule bridge opens for a

ship under way in the Lewes-Rehoboth Canal, ca.

1927. The bridge was one of several Scherzer

rolling lift bridges constructed in the state dur-

ing the 1920s. The bridge on what is now US

Route 9 Business has since been replaced, but

examples of patented Scherzer bascules still

exist in Laurel (State Bridge S-152) and Milford

(State Bridge K-21A).

accommodating greater capacity and spanlengths that spawned the railroad’s great eraof experimentation with metal truss bridgeshad a similar affect on movable bridge tech-nology. In the last quarter of the 19th cen-tury, movable bridge technology enteredthe modern era that was dominated initial-ly by swing span bridges and after the early1890s by bascule (a French word meaningbalance) bridges.

Delaware, with its coastline and numer-ous navigable waterways, has a long histo-ry of movable bridges. In the colonial andearly republic periods, Delaware’s econom-ically important communities were estab-lished on navigable streams because of thereliance on waterborne trade and trans-portation. By the early 19th century, how-ever, increased vehicular traffic justifiedconstruction of bridges over navigablewaterways to replace ferries and circuitous

87

M

BRIDGESDelaware, with its coastline and

numerous waterways, has a long historyof movable bridges. By the early 19th

century, increased vehicular traffic justi-fied the construction of bridges over

navigable waterways to replace ferriesand circuitous roads.

roads around navigable streams. Since bylaw and tradition marine traffic holds right-of-way over roadway traffic, low bridgesover navigable streams had to have mov-able spans to clear the marine channel forthe passage of ships.

One of the first movable bridges inDelaware was built in Wilmington to carrySouth Market Street over the Christina River.Constructed in 1808, it was a wooden “turnbridge” or swing span. Other early movablebridges were located over the ChristinaRiver at Newport, the Nanticoke River atSeaford, and the Broad Creek at Laurel. Theconstruction of the Chesapeake andDelaware Canal from 1804 to 1828 result-ed in several movable bridges to carry oldhighways over the man-made waterway.

Ten movable highway bridges in Delawarethat were built between 1915 and 1957 stillsurvive. Most service crossings that havebeen in use since the 18th or first half of the19th century, and in many instances, theyare the second, third, or even fourth, suc-cessive movable bridge at the crossing.Because all of Delaware’s surviving movablehighway bridges date after 1910, theirdesign was heavily influenced by late-19thand early 20th century engineering andtechnological advances. They are historical-ly significant as examples of period tech-nology. The majority of surviving movablehighway bridges were constructed underthe auspices of the Delaware State HighwayDepartment as part of its program to mod-ernize the state highway system.

Swing Span Bridges

A swing span bridge rotates in a horizo-tal plane around a vertical axis to a

position parallel with the marine channel.When in operation, the movable span issupported in one of two methods; centerbearing on a vertical pin or pivot, or rimbearing on a circular girder called a drum,which in turning moves on rollers. The rimbearing design was used for wider andheavier movable spans. All Delaware exam-ples are the lighter and more easily designed,operated, and maintained center bearingdesign. The superstructure of swing spanbridges can be trusses or girders, and his-torically they reflected the prevailing prac-tices of fixed bridge construction with thespecific type and design matched to thelength and capacity needed at the crossing.

Swing span bridges are rotated by a seriesof reducing gear sets and a rack and piniondrive. The operator houses with the con-

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Swing Span Bridge

Rest Pier Pivot Pier Rest Pier

Rack & Pinnion Drive andBalance Wheels

CenterBearing

Elevation of typical center-bearing swing span bridge.

MOVABLE BRIDGES

trols and machinery are located adjacent toor on the bridge, depending on its size. Manylight swing span bridges were operatedmanually by cranks, but larger ones werefirst powered by steam engines and later bydirect current electric motors.

Swing span bridges were known in Europesince at least the 17th century. Spurred byrailroad expansion and the advances in met-allurgy and bridge engineering, the bridgetype developed most rapidly between 1840and 1890 in this country. Historic pho-tographs show that most swing spans builtin the late-19th and early 20th centuries inDelaware were center bearing and hadpony truss or thru truss superstructures.

Delaware’s oldest surviving movable high-way bridge is the 1915 Poplar Street bridgeover Broad Creek in Laurel, Sussex County(State Bridge S-161). The swing span bridgeis center bearing with a Warren pony trusssuperstructure. Although now fixed so that

89

Fennimore’s New Bridge (above) andFennimore’s Old Bridge (left), swingspan bridges with metal truss super-structures, once carried ThomasCorner Road (State Route 9) overthe Appoquinimink River’s northand south channels at Fennimores,east of Odessa.

The Blackbird Landing bridgeover Blackbird Creek (left)was a variation of swing spanbridge with a center towerand cable stays to supportthe span’s free ends in theopen position. Similarbridges once spanned overCedar Creek at SlaughterBeach and the ChristinaRiver at Newport. None havesurvived.

Late-19th Century Swing Span Bridges

it does not open, the center pivot is still inplace. The technology is also representedby several surviving railroad bridgesincluding the state-owned 1916 bobtail(pivot not centered so that heel and toeportions are different lengths) swing spanbridge on the Georgetown-Lewes line of theformer Delaware, Maryland, & VirginiaRailroad over the Lewes-Rehoboth Canal.This center bearing design bridge is stilloperable.

The demise of swing span bridges inDelaware, as well as elsewhere in thenation, resulted from the basic problemthat the movable span and pivot pier areobstructions to navigation. Across smallerwaterways, this problem was sometimeseconomically solved by a bobtail swingspan where the pivot pier was placed adja-cent to the stream bank rather than the

middle of the channel. The swing span’slonger arm was balanced by a counterweightin the shorter arm. In the 1890s, however,American engineers developed severalalternatives to swing span technology, mostnotably the vertical lift and bascule bridgetypes. By 1910, most engineers preferredthe bascule over all other movable bridgetypes. Historic plans and photographs pre-served in state agencies and historical soci-eties show that most of Delaware’s 20th-century bascule bridges were built toreplace truss swing spans.

Bascule Bridges

Abascule bridge rotates in a verticalplane around a horizontal axis, much

like a seesaw. Although the bascule bridgetype dates to ancient times, it was not untilthe 1890s that American engineers success-

fully developed bridge and operatingmechanism designs that offered rapidity ofoperation and the ability to move long spansvertically achieving unobstructed marinechannels. In comparison to swing spanbridges, bascule bridges did not require aclear turning radius that prohibited theconstruction of docks adjacent to thebridge site, a particular concern in crowdedurban waterfronts.

The beginning of the modern era of thebascule bridge in this country is tradition-ally held to be the successful completion in1893 of the Van Buren Street bridge inChicago, a rolling lift bascule bridge devel-oped and patented by William Scherzer(1858-1893). The bridge was a significantmilestone in bascule technology as it wasthe first movable design that quickly rotat-ed a span of significant length and weight

90

The BroadkillRiver swing span

bridge nearMilton went the

way of manybridges of its

type in the early20th century; itwas replaced bya bascule bridge

in the 1920s.

up and out of the shipping channel. In arolling lift bascule bridge, the center ofrotation continually changes and the centerof gravity of the rotating part moves in ahorizontal line, thereby shifting the point ofapplication of the load on the pier. Themovable leaf rolls back on segmental gird-ers on the heel ends. The girder is matchedto a track affixed to the top of the substruc-ture or approach span. The most commonScherzer design is that with an overheadcounterweight, but it also was built with anunderneathcounterweight.The Scherzer designwas favored greatly by the railroads into thesecond decade of this century, but it alsooccasionally was used for highway bridges.

The Scherzer patents were managed bythe Scherzer Rolling Lift Bridge Companyof Chicago, an engineering firm thatdesigned its bridges but contracted outbridge fabrication and construction. Over175 Scherzer bridges were built nationwide

before World War I. The Scherzer companycontinued to operate until the late 1930s,but by the early 1920s their major patentshad expired, and several employees left thecompany to set up competing firms design-ing Scherzer-type bascules.

Delaware’s two Scherzer rolling lift bas-cule highway bridges are the 1923 CentralAvenue bridge in Laurel, Sussex County(State Bridge S-152) designed by the

Scherzer company, and the 1929 RehobothRoad over Mispillion River bridge inMilford, Kent County (State Bridge K-21A),designed by Charles L. Keller and H. P.Harrington, two former Scherzer companyemployees. The Scherzer rolling lift basculebridge is the only patented type of basculehighway bridge represented in Delaware.

Scherzer was only a few years ahead ofcompetitors such as Thomas E. Brown, Max

91

MOVABLE BRIDGES

Scherzer Rolling Lift Bridge

OverheadCounterweight

SegmentalGirder

Leaf Track

Rack andPinion

Bridge in open position

Elevation of typical Scherzer rolling lift bridge.

G. Schinke, Theodore Rall, and Joseph B.Strauss, who also developed and patentedpopular bascule bridge designs. Each engi-neer patented a movable bridge design thathad advantages and limitations, but accep-tance of one patented design over anotherseems to have been as much a consequenceof local preference, economics, and region-al variation as strict engineering merits. Inthe case of Delaware’s Scherzer rolling liftbascule bridges, state bridge engineerArthur G. Livingston traveled to Chicago in1923 meeting with Charles L. Keller, chiefengineer of the Scherzer Company. TheDelaware State Highway Department hiredKeller as consulting engineer for at least six

bascule bridges from 1923 to 1930.While the patented bascule bridge types

enjoyed a period of success from the 1890sto the early 1920s, they were eventuallyeclipsed by the simple trunnion basculebridge, an unpatented design first advocat-ed by the city of Chicago engineeringdepartment. In 1902, Chicago completedits first simple trunnion bascule bridge.Unlike the rolling lift bascule, the center ofrotation on a simple trunnion basculeremains fixed and is placed near or at thecenter of gravity of the movable leaf. A hor-izontal steel pivot, called a trunnion, sup-ports the entire weight of the bridge whenit is in operation or in the open position.

The counterweight, which serves to bal-ance the long end with the shorter, heelend, is attached at the heel end. The simpletrunnion bascule was a response to some ofthe functional deficiencies of the Scherzerrolling lift type, especially the fact that theshifting of the center of gravity as thebridge operated sometimes caused defor-mation of the segmental girder and tracksystem, as well as increased stress on thesubstructure.

Between 1903 and 1910, Chicago wenton to build eight other highway basculebridges of the simple trunnion design.Frequently featured in period technicalliterature, the terms “simple trunnion bas-cule” and “Chicago Type Bascule” eventuallybecame synonymous.

In Delaware, the simple trunnion bas-cule bridge was the dominant movable typeafter the mid 1920s. Six of the ten surviv-ing movable highway bridges are simpletrunnion bascule bridges built between

92

Doudle-Leaf Bascule Bridge

Trunnion

Leaf Leaf

Counterweight

Elevation of typical double-leaf simple trunnion bascule bridge, illustrated in the open position.

1924 and 1957. Although designed by four different engineering firms,Delaware’s simple trunnion bascule bridges are remarkably similar and veryrecognizable descendants of the original Chicago design. The Delaware StateHighway Department turned to a consulting engineer known nationally forexpertise with movable bridges for each of them. Whether single leaf or doubleleaf, the bridges have deck or thru girder superstructures and fixed concretecounter-weights. Moderne-style operator and mechanical houses are standard, as iselectric-powered operation. The similarityof Delaware’s simple trunnion bascule bridgesis an indication of how pervasive the typewas by 1930, primarily because it was by farthe easiest to design, build, and maintain.

The oldest simple trunnion bascule bridgein the state is the 1924 Front Street bridgein Seaford, Sussex County (State Bridge S-151), a single leaf bascule bridge designedby the Chicago Bascule Bridge Company. Itis followed in age by four bridges in NewCastle County: the 1927 South MarketStreet bridge over the Christina River inWilmington (State Bridge NC-688); the 1929James Street bridge over the Christina River inNewport (State Bridge NC-159); the 1932

93

MOVABLE BRIDGES

The State Route 9 over the Chesapeake & DelawareCanal Channel Branch bridge (above) in DelawareCity is a double-leaf single trunnion bascule bridgebuilt in 1933. Owned by the U.S. Army Corps ofEngineers, it was sealed and rendered inoperable in1971. Larger ships now exclusively use the canal’smain channel, enlarged in 1935. The Broadkill Riverbridge (left) near Milton was a Scherzer rolling liftbridge designed by Keller & Harrington of Chicago inthe mid 1920’s. It no longer exists. Because of the highcost associated with operating and maintaining mov-able bridges, as well as traffic delays caused by bridgeopenings, many of Delaware’s early 20th century mov-able bridges have been fixed or sealed, or replaced byhigh level fixed span bridges.

Early 20th Century Bascule Bridges

North Church Street bridge over theBrandywine River in Wilmington (StateBridge NC-577); and the 1933 State Route9 over Chesapeake & Delaware CanalBranch in Delaware City (State Bridge NC-497), the latter owned by the U.S. ArmyCorps of Engineers. The 208’-long, doubleleaf South Market Street bridge remainsoperable, but the James Street, NorthChurch Street, and State Route 9 bridgesare not operable, having been sealed andmuch of the operating machinery removed.

The newest and longest of Delaware’smovable bridges, the 276’-long WalnutStreet bridge built in 1954-1957 over theChristina River in Wimington (State BridgeNC-687), marks the end of the era of basculebridges. Because of the high cost associatedwith operating and maintaining movablebridges as well as traffic delays caused bybridge openings, high level, fixed spanbridges were preferred after World War II.

In 1954, Delaware’s Chief Highway

Engineer Richard A. Haber commentedthat the state highway department wouldhave rather built a high-level bridge for thenew Walnut Street crossing, but that thehigh price of land acquisition had prevent-ed that option. In the future, the depart-ment pursued replacing movable bridgeswith fixed spans. They also fixed or sealedolder movable bridges across formerly nav-igable waterways when permitted to do soby the U.S. Army Corps of Engineers. Forinstance, in 1975, the Corps permitted thehighway department to close to navigationthe Popular Street (State Bridge S-161) and

94

21

5

6 78

4

3

The Locations of Delaware’sHistoric Movable Bridges

The Central Avenue bridge in Laurel is apatented Scherzer rolling lift bascule bridge,constructed in 1923.

1. Poplar St. over Broad CreekState Bridge S-161Laurel, Sussex County

2. Central Ave. over Broad CreekState Bridge S-152Laurel, Sussex County

3. DM & V Railroad BridgeNumber 38.71Lewes, Sussex County

4. Front St. over Nanticoke RiverState Bridge S-151Seaford, Sussex County

5. Rehoboth Rd. over Mispillion RiverState Bridge K-21AMilford, Kent County

6. North Church St. over Brandywine RiverState Bridge NC-577Wilmington, New Castle County

7. South Market St. over Christina RiverState Bridge NC-688Wilmington, New Castle County

8. Walnut St. over Christina RiverState Bridge NC- 687Wilmington, New Castle County

the Central Avenue (State Bridge S-152)bridges over Broad Creek in Laurel aftershipping on the stream had declined tonegligible levels.

Poplar Street (Road 28A)over Broad Creek

State Bridge S-161Laurel, Sussex CountyDesigner/Builder: Unknown

1915

The Poplar Street bridge is a 112’-long,17’-wide, center-bearing, swing span

bridge with a Warren pony truss super-structure. Constructed in 1915, the PoplarStreet bridge is Delaware's oldest movablehighway bridge. Currently, it is inoperable,although the turning mechanism remainsin place. The bridge was operated manual-ly by turning a capstan to engage the rackand pinion mounted on the center pivotpier. The bridge is listed in the National

Register of HistoricPlaces as a contributing

resource to the Laurel His-toric District, once an impor-tant rural commercial centerwith waterfront warehousesand canneries.

Swing span bridges werethe dominant movable bridgetype in Delaware from the1870s to the 1910s. The PoplarStreet bridge, when built in 1915, was alate example of the movable bridge tech-nology that had been standard for severaldecades and was being rapidly supersededby the new bascule technology.

The bridge pivoted on a center bearingpost with eight balance wheels traveling ona circular rack for stability. The Warren pony

truss superstructure is composed of stan-dard built-up steel angle and channel sec-tions. Warren pony trusses were a popularearly 20th century highway bridge type andwere applied to both movable and fixedspans. Two rail high pipe railings are at-tached to the inside of the trusses. Thebridge is supported on concrete abutments

95

MOVABLE BRIDGES

LaurelBroad Cree

k

BridgeS-152

BridgeS-161

Popl

ar S

t.

Cen

tral A

ve.

➲

N

24 The Poplar Street Bridge(above) is Delaware'sonly remaining pre-1956swing span highwaybridge.

This detail of the pivotpier (left) shows the rackand pinion, balancewheels, and center pivotfloorbeams

and a timber pile center pivot pier.Little is known about the history of the

Poplar Street bridge. Presumably it was con-structed under the auspices of the SussexCounty Levy Court. It was taken over bythe Delaware State Highway Department in1935 as part of its expanded responsibili-ties for all former county roads and bridges.In 1946, the state highway department re-

placed the deteriorated concrete pivot pierwith a timber pile pier. The repair plansnote that the bridge was built in 1915, andthat the swing span was opened about 100times in 1946. The plans also show thatthere was a one-story frame operators houselocated on the northwest embankment.

The Poplar Street bridge was last openedto navigation in 1975. Since that time, ithas undergone alterations that have ren-dered it inoperable but also have resulted inthe preservation of the trusses and operat-ing mechanism in situ. In 1994, the Del-aware Department of Transportation re-moved the trusses to have them cleanedand painted. The beams that support andstabilize the bridge when it is opened werereplaced in-kind. Original riveted connec-tions were replaced by high strength bolts.The operating mechanism including gears,shafting, and center bearing were reset butnot returned to operating condition.

Central Avenue (Old US 13)over Broad Creek See map on page 95

State Bridge S-152Laurel, Sussex CountyDesigner/Builder: Scherzer Rolling LiftBridge Company/Allen S. Fox

1923

The Central Avenue bridge is the oldestsurviving bascule highway bridge in

Delaware and it is one of two survivingScherzer rolling lift bascule bridges in thestate (the other is State Bridge K-21A). Itwas designed by the Scherzer Rolling LiftBridge Company of Chicago and was builtby contractor Allen S. Fox of Dayton, Ohio,under contract with the Delaware StateHighway Department in 1923. The CentralAvenue bridge has all of the characteristicfeatures of the patented Scherzer design in-cluding rounded segmental girders that rollalong steel tracks, thereby raising and low-

96

Excerpts from 1946 repair plans to the Poplar Street bridge.

MOVABLE BRIDGES

ering the bridge. The bridge was lastopened in 1975, and it is currently non-op-erational. It is listed in the National Registeras a contributing resource to the LaurelHistoric District.

The two-span bridge consists of a singleleaf, thru girder bascule span and a 20'-long steel thru girder approach span on thenorth end. The south end of the basculeleaf has a 20 degree skew, measuring 72'-long on the upstream side and 56'-long onthe downstream side to accommodate abend in the creek. The overhead concretecounterweight is supported on built-uptowers. Although the electric motor, opera-tors’ house, and control systems have beenremoved, the open gear train and machin-ery platform over the roadway infront ofthe counterweight remain. The gear trainactivated the pinion gears engaging thestraight open racks mounted on the sta-tionary tower. When opened, the segmen-

tal girders rolled backward alongthe cast steel tracks mounted ontop of the approach span. Thecounterweight moves to a positionjust above the surface of the deck.

The Central Avenue bridge wasfeatured in the 1924 Annual Reportof the state highway department as“the most notable bridge construc-tion of the year.” The account re-ported that the substructure de-sign was prepared in-house, andbids with plans were received forthe steel superstructure. Successfulbidder for the project was the

97

The Central Avenue bridge in Laurel is a patented Scherzerrolling lift bascule bridge, constructed in 1923.

In 1992, DelDOT rehabilitated the Central Avenue bridge.The floorbeams, stringers, and deck were replaced and theconcrete abutments and wingwalls repaired. The electricalcontrols and operators house on the north embankmenthave been removed, and the bascule span currently is non-operational.

The Central Avenue bridge was the featured“Bridge of the Year” in the state highway

department's 1924 Annual Report.

Scherzer Rolling Lift Bridge Company. Thebridge posed no unusual technical difficul-ties, so the company offered one of its stan-dard-configuration rolling lift bascule bridgeswith overhead counterweight, a design that

had been little changed since the early 1900s.The Central Avenue bridge project initi-

ated a fruitful association between the statehighway department and Scherzer chief en-gineer Charles L. Keller, who subsequently

98

General plans for the Central Avenue bridge. Note the dotted lines showing the position of the leafin the open position; the concrete counterweight nearly touches the deck of the approach roadway.

left the Scherzer company to establish hisown consulting firm with H. P. Harrington,another former Scherzer employee. Keller& Harrington designed three other surviv-ing movable highway bridges in Delaware:the 1924 Front Street bridge (State Bridge S-151) over the Nanticoke River in Seaford;the 1929 Rehoboth Road bridge (State BridgeK-21A) over the Mispillion River in Milford,and the 1929 James Street bridge (State BridgeNC-159) over the Christina River in Newport.

Delaware, Maryland &VirginiaRailroad Bridge (Lewes Railroad Bridge)

Number 38.71Georgetown-Lewes railroad line overLewes-Rehoboth CanalLewes, Sussex CountyDesigner/Builder: DM&V Railroad

1916

The Delaware, Maryland & Virginia Rail-road Bridge Number 38.71 carries the

Georgetown-Lewes railroad line over theLewes and Rehoboth Canal, 1/4-mile southof State Route 9 (Business) in Lewes. Thebridge is a center-bearing, bobtail, swing spanwith an over all length of 92' and a deckwidth of about 17'. Constructed in 1916,the bridge is historically significant as a sur-viving example of a swing span railroadbridge.

The swing span bridge has a deck gird-er superstructure composed of two tapered,built-up girders. The design is called a bob-tail swing span because of the unequallengths of its two arms; the longer of thetwo arms measures about 60'-long, and theshorter about 30'-long. The end of theshorter arm is framed with a concrete coun-terweight for balance. Bobtail swing spanscommonly were used for narrow waterwayswhere the off-center pivot pier caused less ofa channel obstruction. The abutments andpivot pier are concrete.

The bridge is operated manually by a

capstan inserted in a drive shaft located inthe deck. The capstan and drive shaft turnbeveled open reduction gears that engagethe pinion gear mounted on the pivot pier.The bridge rotates on its center bearingwith eight balance wheels traveling on atrack. A shaft operates a worm gear thatmoves two end wedges at the abutment endof the swing span’s longer arm. In theclosed position, the wedges lift the arm to

afford a rigid support on the abutment andneutralize the end deflection of the arms.As with all movable railroad bridges, an im-portant consideration is aligning the railson the bridge with those of the approachingrailroad tracks. To accomplish a secure fit,the rails on the ends of the bridge arebowed upwards by rail lift rods. After thebridge is closed, the operator engages alever that lowers the rods, thus lowering

99

MOVABLE BRIDGES

Lewes

DM&V RR. Bridge#38.71

Sava

nnah

Rd.

➲

N

Lewes – Rehoboth Canal

Delaware Bay

Kin

gs H

wy.

9

9 Busin

ess

DM

&V

RR

The Lewes bridge, built in 1916, is an example ofa bobtail, swing span bridge. This photograph wastaken prior to 1996 rehabilitation by DelDOT.

The swing span bridgeis opened manually by

a capstan inserted inthe bridge deck.

the rails into a slotted fit-ting with the approachtracks.

The Georgetown-Lewesrail line was establishedin 1869 as part of theJunction and BreakwaterRailroad (J&B), a short linerunning from the DelawareRailroad at Harrington tothe breakwater at Lewes.In 1883, the J&B wasrenamed the Delaware,Maryland & Virginia Rail-road (DM&V) as part ofthe consolidation of sev-eral smaller Delmarvalines under the control ofthe Pennsylvania Railroad.

The DM&V spurred the development offish oil processing near Cape Henlopen.These factories, located on the eastern sideof the Lewes-Rehoboth Canal, were ser-viced by the DM&V, which made use of theswing span bridge to deliver their products.The line currently is owned by DelDOTand operated by the Maryland & DelawareRailroad.

The 1916 swing span bridge was erect-ed as part of the construction of the Lewes-Rehoboth Canal, begun in 1912. The U.S.Army Corps of Engineers built the 12-milelong canal as part of the inland waterway.In the vicinity of Lewes, the canal followedthe natural course of Lewes Creek, whichwas channelized to meet the canal specifi-cations. In 1915, when the canal reachedthe existing railroad bridge over LewesCreek, the DM&V submitted a proposal tothe Corps to construct the swing spanbridge. It was fabricated by the AmericanBridge Company at its Pencoyd, Pennsylva-nia shops.

100

The rails on the ends of the bridge (above) are bowed upwards by raillift rods, shown here. After the bridge is closed, the operator engages alever that lowers the rods, thus lowering the rails into a slotted fittingwith the approach tracks.

The Lewes bridge (left) is kept in the openposition, and only closed two or three timesper week for passing trains.

The Lewes bridge is one of three extantrailroad swing span bridges in SussexCounty. All are center bearing swing spanswith deck girder superstructures. The oldestis the operational 1890 Delaware RailroadBridge over the Nanticoke River in Seaford.The other is the non-operational 1911Delaware Railroad Bridge over Broad Creekin Laurel.

Front Street (Old US 13)over Nanticoke River

State Bridge S-151Seaford, Sussex CountyDesigner/Builder: Chicago Bascule BridgeCompany (Keller & Harrington)/Allen S. Fox

1924-1925

The Front Street bridge is Delaware’soldest operating bascule highway

bridge. Built in 1924-1925 under the aus-pices of the Delaware State HighwayDepartment, the five span bridge consistsof a 55'-long, single leaf bascule main span

flanked at both ends by two, 33'-longprestressed box beam spans placed in 1992.They replaced the original encased steelmulti girder approach spans. The main spanis finished with pipe railings, andthe approach spans have concretebalustrades. The end posts haveconcrete lamp posts with globe luminaires.At the north end of the bridge is the one-story frame operators house built in 1992to replace the original.

The movable leaf is a built-up thru gird-er with floorbeams. When in operation, theentire weight of the movable span is carriedby trunnions in bearings placed near or atthe center of gravity. They are supported onbuilt up columns or towers that transferloads to the substructure. The counter-weight is attached to the heel end over theconcrete counterweight pit. The counter-weight maintains the leaf in equilibrium,thereby minimizing the amount of powerneeded to overcome the friction and inertiaof the system. The electric motor-driven

operating mechanism of shafting and openreduction gear sets engages the pinion gearand segmental rack bolted to the bottom ofeach bascule girder beneath the trunnion,thereby causing the leaf to pivot on thetrunnion.

The Front Street bridge replaced a met-al truss swing span bridge. In 1923, theDelaware State Highway Department con-tracted with the Chicago Bascule BridgeCompany for the design work, but corre-

101

MOVABLE BRIDGES

Blades

Front Street BridgeS-151

High St.➲

N

SeafordN

anticoke River

Fron

t St

.M

arke

t St.

13

20

20

13

Concord Rd.

spondence in the state’s pro-ject files indicates that CharlesL. Keller and H. P. Harrington,consulting engineers also ofChicago, actually prepared thedesigns. In 1923, Keller andHarrington had left theScherzer Rolling Lift Bridge

Company, and it seems likely that theChicago Bascule Bridge Company simplyhandled the contract for them. Constructioncontractors were Imach-Wozny-McCoy, Inc.of Baltimore for the substructure, and AllenS. Fox of Dayton, Ohio for the superstructure.

In 1992, DelDOT rehabilitated the FrontStreet bridge. Work on the bascule span in-

The main girder for the Front Street bridge from original 1924 drawings.

The 1924 Front Street bridge over the Nanticoke River inSeaford is Delaware’s oldest operable simple trunnionbascule highway bridge. This photo was taken in 1988.DelDOT replaced the approach spans and rehabilitatedthe bascule operating mechanism in 1992.

102

cluded a new concretedeck and repairs to thesteel superstructure. Theoperating mechanism wasoverhauled with new mo-tor, brake, and bearings in-stalled, and most of theoriginal open gear setscleaned and reused in theiroriginal configuration. Theconcrete balustrades on the new approachspans were designed to match the originals.Although much of the bridge’s fabric is re-placement material, the operation, outwardappearance, and function of the simpletrunnion bascule bridge remains as per itsoriginal design.

Rehoboth Road (State Route 1 Business)over Mispillion River

State Bridge K-21AMilford, Kent CountyDesigner/Builder: Keller &Harrington/Bethlehem Steel Company

1929-1930

The Rehoboth Road bridge, a Scherzerrolling lift bascule bridge, was de-

signed in 1929 by Keller & Harring-ton, consulting engineers fromChicago, under contract with the DelawareState Highway Department. The bridge isan example of the rolling lift bridge patent-ed by William Scherzer in 1893, and re-fined in the late 1890s and early 1900s bythe Scherzer Rolling Lift Bridge Companyof Chicago. The Rehoboth Road bridge wasbuilt after the Scherzer company's basicpatents had expired, and former employeesCharles L. Keller and H. P. Harrington hadbranched off on their own.

The three span bridge has a 56'-long,single leaf movable main span, flanked bytwo 26'-long steel thru girder spans sup-ported on concrete abutments and piers.The main span is also a thru girder with

floorbeams. A timber sidewalkwith pipe railings is cantilevered from thewest side. The overhead concrete counter-weight is supported by built-up columntowers. The bridge is a downstate Delawarelandmark, and is recognized by most localresidents as the bridge with the words“Mispillion River” painted on the counter-weight.

The Rehoboth Road bridge is operable,unlike its nearly identical but inoperablecounterpart, the 1923 Central AvenueBridge in Laurel (State Bridge S-152). Theoperating mechanism including electric

103

MOVABLE BRIDGES

MilfordRehoboth Road Bridge

K-21A

➲

N

Rehoboth Rd.

2nd Street

36

14Mispillion River

The Rehoboth Road Bridge is a Scherzer rolling lift basculebridge, constructed in 1929. This photograph was takenafter the bridge's rehabilitation in 1996.

motor, shafting, andopen reduction gear

sets are located onthe machinery plat-

form. The gear train ac-tivates the pinion gear

engaging the straight openrack mounted on the station-

ary steel tower. When the bridgemoves to the open position, the

segmental girders roll along the caststeel tracks mounted on top of the ap-proach span, and the counterweight comes

to rest just above the surface of the deck.The gear train was replaced with all newgears, shafts, and bearings in 1996. Thebridge’s operation has remained the same,although the secondary reduction gears area slightly different arrangement than theoriginal. The frame operator’s house on thenorth side of the bridge was constructed in1996, replacing the original one. The con-trol panel, electric wiring, and automatedtraffic signals are new. Also, as part of the1996 rehabilitation, the floorbeams andstringers were replaced, and the girders werestrengthened.

The bridge was built in 1929 as part ofa Delaware State Highway Department fed-eral-aid project designed to relieve the con-gested streets of Milford’s central businessdistrict. Rehoboth Road bypassed Milfordon the east side of town and offered an al-ternative route for increasing traffic todownstate beach resorts. The bypass pro-ject highlighted the important role federal

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DelDOT rehabilitated theRehoboth Road Bridge in 1996.Here, contractors work toinstall new electrical systems.

The bridge’stoe lock is asimple lever,held in place

with a pin.

Segmental girder from original drawingsfor the Rehoboth Road Bridge, 1929.

financial assistance played inthe state highway department’sprogram of modernization.The Rehoboth Road bridgeoffered no unusual technicalchallenges, and Keller &Harrington provided the state highway de-partment with a design typical of manyshort-span Scherzer rolling lift bridges fromthe mid 1900s through the 1930s. Con-tractor for the steel superstructure fabrica-tion was the Bethlehem Steel Company.

North Church Street overBrandywine River See map on page 21

State Bridge NC-577Wilmington, New Castle CountyDesigner/Builder: Ash, Howard, Needles& Tammen/Seeds and Derham

1932

The North Church Street bridge is asimple trunnion bascule bridge erect-

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The North Church StreetBridge is a single leaf bascule

span built in 1932.

The North Church Street bridge’s operator’s house was built of light-grey brick “to match thecolor of the finished concrete surfaces” of the Moderne-style bridge. Although original windowsand doors have been replaced and operating equipment removed for over 40 years, the operator'shouse still remains an attractive feature of the bridge.

ed in 1932. It was designed by consultingengineers Ash, Howard, Needles & Tammen(AHN&T) of Kansas City and New Yorkand erected by Seeds and Derham ofPhiladelphia, under contract with theDelaware State Highway Department and theLevy Court of New Castle County. Othercontractors for the North Church StreetBridge were the Concrete Steel Company ofPhiladelphia, for reinforcing steel and theAmerican Bridge Company of Ambridge,

Pennsylvania, for structural steel fabrication.The main span of the six-span, 332'-long,

bridge is a single-leaf, simple trunnion bas-cule span. The bascule span is no longeroperable. The bridge features Moderne-stylearchitectural detailing. The concrete abut-ments, wingwalls, piers and balustrades arebattered, stepped, and accented with verti-cal scoring. The operator’s house is built oflight grey brick and has a metal clad hippedroof. The five T-beam approach spans have

arched fascia beams and are supported onconcrete piers with ashlar-faced bases.

The North Church Street bridge re-placed a metal drawbridge dating from1869. The design contract was awarded toAsh, Howard, Needles & Tammen, a con-sulting engineer firm that specialized inmovable bridges.

The North Church Street bridge had ashort life as an operable movable bridge. In1952, twenty years after completion, large-scale shipping on the Brandywine Riverhad ended, and the Delaware StateHighway Department received permissionfrom the U.S. Army Corps of Engineers toclose the bridge. The original wood deckwas replaced by a concrete deck, and thebascule span was fixed in place by removalof the end locks and replacement with fixedbearings. In 1957, the electrical equipment,including motors and controls were re-moved.

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➲

N

Wilmington

Christina River

BrandywineR

iver

13

202

South MarketStreet Bridge

NC-688

Walnut StreetBridgeNC-687

North ChurchStreet Bridge

NC-577

South Market Street overChristina River

State Bridge NC-688Wilmington, New Castle CountyDesigner /Builder: Harrington, Howard & Ash

1927

The South Market Street bridge is adouble-leaf bascule bridge designed

by the prominent consulting engineeringfirm of Harrington, Howard & Ash of KansasCity and New York. The bridge was built in1927 under the auspices of the DelawareState Highway Department. It is an exam-ple of the simple trunnion bascule designthat had become by the mid 1920s themost common bascule bridge because of itsrelative economy and ease of operation andmaintenance. The bridge is one of threepre-1957 simple trunnion bascule highwaybridges that remain operable in Delaware.

The bridge consists of a 208'-long dou-ble-leaf bascule span, flanked by two steel

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Construction photographs of the South MarketStreet Bridge from the Delaware State Highway

Department's 1927 Annual Report.

The 1883 metaltruss swing spanbridge, shown in thebackground of thisphoto, continued tocarry traffic whilethe new basculebridge was con-structed in 1927.The swing span wasdemolished after thenew bridge openedin Fall 1927.

deck girder spans that carry the approach-es over the counterweight pits. The mov-able leaves are built-up thru girders withbuilt-up floorbeams and stringers support-ing an open steel grid deck. The 38'-widebridge has cantilevered sidewalks finishedwith aluminum railings placed in 1982.The approach spans are finished with con-crete parapets. At opposing corners of thebascule span are operator and machinery

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Original plans for the operator's house show the lay out of the operatingmechanism, including motor, brake, and gear train.

When a new South Market Street bridge was pro-posed in 1926, engineers Harrington, Howard &Ash prepared this rendering featured in theDelaware State Highway Department's AnnualReport. Specifications for the design advised that“the design submitted should give careful consider-ation to architectural features as the bridge is usedby all North and South traffic and a pleasing struc-ture to the eye is desired.”

houses constructed of tan brick withpressed metal cornices and hipped roofsbehind plain parapets. The controls are lo-cated in the north operator house.

Each bascule leaf is operated by an elec-tric motor that drives shafting and primaryand secondary open reduction gear sets en-gaging a pinion and rack mounted on theinner curved face of the concrete piers.

DelDOT rehabilitated the bridge in 1982.Work included strengthening the movablegirders and floorbeams; removing the oldoperator’s console, electrical wiring, basculemotors and brakes, and replacing themwith modern components; removing metalbalustrades from the bascule span and re-placing them with aluminum railings; andremoving original center lock bars and re-placing them with a new design center lockbar system.

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The original drawings for the SouthMarket Street bridge include a“Synopsis of Operation” listing thesteps required of the bridge tender toopen and close the bascule.

countryside, Needles bought a farm in NewCastle County, and became a neighbor andfriend of Francis duPont, the state's high-way commissioner. The South Market Streetbridge was the firm’s first major contract forthe Delaware State Highway Department, butnot the last. The firm, which changed its nameto Howard, Needles, Tammen & Bergen-dorff in 1941, has had a significant influ-ence on the course of Delaware’s transporta-tion history. They designed the DelawareMemorial Bridge (1951, 1968) and theDelaware Turnpike/I-95 (1961-1964), alongwith numerous other bridges, turnpikes,and interstate highways across the nation.

Walnut Street overChristina River See map on page 106

State Bridge NC- 687Wilmington, New Castle CountyDesigner/Builder: Parsons, Brinckerhoff,Hall & MacDonald/A. S. Wikstrom, Inc.

1954-1957

The Walnut Street bridge over theChristina River in Wilmington is the

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The South Market Street bridge is a 208'-long double-leaf bascule bridge, constructed in 1927.

Historically, the crossing of the ChristinaRiver at South Market Street has been a vi-tal link connecting Wilmington with pointssouth. In 1808, the Wilmington BridgeCompany received a charter from theGeneral Assembly to raise a private sub-scription of $15,000 to build a bridge to re-place a ferry. The wooden “turn bridge” orswing span was in service until 1883 whenthe City of Wilmington replaced it with ametal truss swing span bridge. In 1926, theDelaware State Highway Department pre-pared a contract to replace the metal trussswing span, which was considered too nar-row and light weight for existing traffic.The grand opening of the new SouthMarket Street bascule bridge was Armistice

Day, November 11, 1927. The bridge open-ing festivities were held in conjunction witha pageant and speeches.

The design of the South Market Streetbridge was awarded to Harrington, Howard& Ash, a consulting engineer firm that spe-cialized in movable bridges. The firm wasfounded in 1914 by John L. Harrington,Ernest E. Howard, and Louis R. Ash. In thelate 1910s, Harrington, Howard & Ash’sbusiness grew rapidly, and the Kansas City-based firm established a branch office inNew York in 1922. Head of the office wasEnoch R. Needles (1888-1972), whose firstlarge contract was to make surveys for a se-ries of bridges over the Chesapeake &Delaware Canal. Enamored with the Delaware

largest of Delaware’s eight extantpre-1956 bascule highway bridgesand is one of only three basculebridges that remains operational. Itis a simple trunnion bascule type. In1955, the Delaware State HighwayDepartment’s Annual Report com-mented that the Walnut Street bridgewas its “outstanding project for1954-55.” The bridge, among the largestbridge projects undertaken by the depart-ment in the decade after World War II, wasdesigned specifically to address Wilming-ton’s congestion problems. It provided analternative route south from the city to US13 and the Delaware Memorial Bridge.

The eight-span bridge consists of a 276'-6" double-leaf bascule main span flankedby three steel multi-girder approach spansto the north and four steel multi-girder ap-proach spans to the south. The bridge has asteep vertical profile, achieving a verticalclearance of over 21' above mean high wa-ter level of the channel. The deck measures64'-wide accommodating four traffic lanesand two sidewalks with three-high rail met-

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The Walnut Street(left) bridge, lookingnorth towardsWilmington.

The Walnut Streetbridge (below), con-structed from 1954to 1957, is a double-leaf bascule bridge.

al railings. The bridge is supported on con-crete piers accented with vertical scoring.Timber pile fenders protect the piers.

Despite its size, technologically speak-ing, the Walnut Street bridge was not in-novative for its time. Rather, it is represen-tative of the bascule bridge technology inwidespread use by the 1910s. The WalnutStreet bridge does, however, make use ofsuch mid-20th century refinements as au-tomated controls and signals, enclosed re-duction gears, and electrically operatedcenter lock bars.

The movable leaves are operated by apinion gear engaging a segmental rackmounted to the bottom of the girders.Shafting and enclosed reduction gear setstransmit power from electric motors locat-ed on the first level of the operator’s hous-es. Each leaf consist of two haunched built-up steel thru girders with built-up floor-beams, steel I-beam stringers, and an open-grid steel deck. The concrete counter-weights are fixed in steel frames at the heelends of the movable spans. The leaves are

locked in the closed position by automatedcenter locks located on the exterior of themain bascule girders.

Moderne-style, flat roofed reinforcedconcrete operater’s houses finished withscoring in a checkerboard pattern are locat-ed at opposite ends of the movable span.They have horizontally pivoted steel sashwindows. The three-story house at thenorthwest corner has a door at roadwaydeck level providing access to the lower lev-el and machinery rooms. The four-story op-erator’s house at the southeast corner con-tains the operator’s console and electricalcontrol equipment. The console is locatedon the top level, which has ribbon win-dows on three sides providing maximumvisibility for the bridge operator.

Planning for the Walnut Street bridgebegan in 1952 when the Delaware StateHighway Department recognized the needfor improved highway access betweenWilmington and points south including thenewly opened Delaware Memorial Bridgenear New Castle. In order to alleviate grow-

ing traffic problems and congestion on theSouth Market Street bridge (State BridgeNC-688), the department advocated for anew river crossing on a 3/4-mile longsouthern extension of Walnut Street. Theproject was to be funded in part by federalaid designated for use on urban highways.The department retained consulting engi-neers, Parsons, Brinckerhoff, Hall andMacDonald of New York to study alterna-tive designs. The firm, chosen because oftheir nationally recognized expertise withurban expressways and large bridges, ini-tially proposed a limited access expresswaywith high-level fixed span bridge over theChristina River, thus eliminating delaysfrom bridge openings. That plan was passedover by the department because of the statelegislature’s unwillingness to supportedlimited-access highway legislation and thehigh cost of land-acquisition associatedwith extending the expressway over thetracks of the nearby Pennsylvania Railroadand into downtown Wilmington. The moreeconomical option, with a movable bridge

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over the river and an underpass beneath therailroad, was chosen.

Construction began in June, 1954, andit was completed in May, 1957. Richard S.M. Lee, was the designing engineer, and J.C. Whiteman, Jr., was resident engineer. Theprimary contractor was A. S. Wikstrom,

Inc. of Skaneateles, New York with theAmerican Bridge Company of Ambridge,Pennsylvania providing the structural steeland the Earle Gear and Machine Companyof Philadelphia providing the bascule ma-chinery and gears. ■

In late 1956, as the Walnut Streetbridge (above) neared completion,the south leaf was raised while con-tractors work on placing the deck ofthe north leaf. This view was takenfrom the Pennsylvania RailroadStation office building.

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