[MUSIC PLAYING] NARRATOR: Traffic signal poles 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. [MUSIC PLAYING] 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 decoiler to unwind the sheet and flatten it out. Then, as shear cuts it to the correct length. A computer-guided plasma cutter marks short lines on both ends of the sheet. These lines indicate where 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 of 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. [MUSIC PLAYING] The press break bends the sheet along the marked line to a pre-programmed angle. 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 multisided round pole. Now, the poll moves to a welding station where hydraulic rollers apply pressure from both sides. This forces the edges of the sheet together so that a welding head can fuse the seam 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 seam weld cools and shrinks. Next, a computer-guided plasma machine cuts a connection played out of thick steel. The machine also drills holes for the high strength bolts needed to attach the plate to the traffic signal pole. Workers center the connection plate on support plates they've already welded to the pole. Then, they weld everything in place. [MUSIC PLAYING] Next, workers weld a base plate 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 colored powder into any defective area. The factory ships the finished poles to a galvanizing plant where they're dipped in a series of wash tanks. 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 poles go into a vat of sulfuric acid. This bath dissolves the more stubborn contaminants that washing can't remove. The next tank contains a chemical that weakens the surface of the poles. This allows the galvanizing metal to penetrate the steel rather than sit on the surface. The final tank contains molten zinc. [MUSIC PLAYING] As the poles bathe in the 842 degree zinc, workers in 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. [MUSIC PLAYING] Because they're galvanized rather than painted, these polls are able to support traffic lights, signs, and street lamps for 40 years or more. [MUSIC PLAYING]