How It's Made - Traffic Signals

traffic signal polls must be strong

enough to bear the weight of road signs

street lights and of course traffic

signals the poles are also built to

withstand extreme weather conditions

such as high winds and heavy snow

accumulation traffic signal poles are

made of high-strength steel years of

weather exposure can cause corrosion so

the poles are galvanized on both sides

for protection each pole has a welded

plate to connect it to a perpendicular

pole the poles are made out of these

steel sheets the steel arrives at the

factory in one large roll they use a

decoy ler to unwind the sheet and

flatten it out then a shear cuts it to

the correct length

a computer-guided plasma cutter mark

short lines on both ends of the sheet

these lines indicate were to bend the

flat sheet to form a round pole

the machine cuts the sheet into a

rectangular shape or a trapezoid shape

if the pole will taper at the top

workers number the Machine lines with

chalk giving lines directly opposite of

each other the same number then they

transfer the sheet to a bending machine

called a press break

the press break bends the sheet along

the marked line to a pre-programmed


workers use a digital measuring device

to make sure the first Bend is accurate

if it is they continue bending along the

remainder of the lines transforming the

flat sheet into a multi-sided round pole

now the pole moves to a welding station

or hydraulic rollers apply pressure from

both sides

this forces the edges of the sheet

together so that a welding head confused

the scene with molten steel at the same

time the head deposits a granular powder

called flux which prevents air from

penetrating the weld and weakening it

workers place the pole in a hydraulic

press so it doesn't warp as the seen

weld cools and shrinks


next a computer-guided plasma machine

cuts a connection plate out of thick


the machine also drills holes for the

high strength bolts needed to attach the

plate to the traffic signal poll workers

Center the connection plate on support

place they've already welded to the pole

then they weld everything in place

next workers weld a baseplate to the

bottom of the pole it has holes for the

anchor bolts which are used for securing

the traffic signal to the street workers

inspect the welds with a testing device

it uses an electric current to

magnetically draw coloured powder into

any defective area the factory ships the

finished poles to a galvanizing plant

where they're dipped in a series of wash


the plants tanks are deep enough to

fully submerge the poles so they can

treat both the inner and outer surface

at the same time

now the polls go into a vat of sulphuric

acid this baths dissolves the more

stubborn contaminants that washing can't

remove the next tank contains a chemical

that weakens the surface of the polls

this allows the galvanizing metal to

penetrate the steel rather than sit on

the surface

the final tank contains molten zinc

as the poles bathe in the 842 degrees in

workers and fire protection suits skim

the surface to remove iron oxide and ash

that floats to the top this keeps the

freshly galvanized surface clean as the

poles are hoisted out of the tank and

set aside to cool

because they're galvanized rather than

painted these poles are able to support

traffic lights signs and street lamps

for 40 years or more