Global warming is the effect of too much greenhouse gases in the atmosphere trapping too much heat. Where do these excess greenhouse gases come from though? It comes from Man. Man produces a lot of greenhouse gases. It comes from the vehicles we use or the power plants that burn fossil fuels for electricity. To help save electricity, we can help individually by doing simple practices like turning off electrical appliances when not used or we could help on a larger scale by finding out which movable bridge is the most energy-efficient as we tried to do. Movable bridges can be very useful in connecting land masses separated by bodies of water. Cars and other land transports can pass over it until a boat arrives, at which point the bridge will move to make way for the boat to cross. This means the moveable bridge allows land transport without hindering water too much transportation, making it very useful in promoting movement . However, certain bridge types might be better than others, and thus should be used more often. Despite this, there are no sources stating the advantages of one bridge type over the others, or if there are even advantages at all.