Arch is nowadays the most popular type of bridges being suitable in mountainous areas as well as in flat terrains. Arches are sometimes above the deck and are called tied arch bowstring. Also, arches may be positioned completely under the deck which is supported on spandrel columns over arch ribs. The configuration of superior deck is particularly suitable for bridging large or deep valleys and canyons, while the bowstring with inferior deck may suit best large water ways of flat valley crossings.Arch geometry can be either circular, parabolic or inverted catenary and rarely elliptic, all with hinged or fixed end connections. Arch form can also be unusual or irregular geometry such as the Sheikh Zayed Bridge designed by the late Zaha Haddid in Abu Dhabi, U.A.E.Arch shape should be chosen to ensure that the arch is working predominately in compression, under permanent load. In all cases however, it is worthy to note that the bending moment and shear forces are hardly equal to zero due to permanent loading conditions, although the magnitude of these straining actions will be small even under asymmetric loading cases or support end conditions .This study investigates the optimum configuration of spandrel arch ribs and tied bowstring arch bridges. For a bridge of given material and a known span, there should exist an optimum geometry. Two steel arch bridges were analyzed and comparison made between the optimum geometric configurations during the in-service condition. The study provides useful data for bridge engineers while designing this type of bridges. An extensive parametric study has been conducted in order to arrive at some reliable conclusions.