At the early stage of bridge design, many factors are considered before determining the bridge's geometrical alignment and length of spans, which have great influence on the construction method and costs. Traditionally, the alignment and spans are determined based on the design engineer's experience. However, the resulting design, though feasible, may not necessarily be the most economical, due to the nature of the numerous possible combinations of span lengths. This paper presents an integrated, automatic system (Automatic Bridge Planning System, ABPS) for preliminary bridge design. In ABPS, relevant site data, such as hydrological and geological conditions, as well as existing obstacles, are computerized into an objectoriented environment. In addition, code requirements for bridge design, common bridge construction methods, and expertise elicited from experts, are represented as various knowledge bases. The input to the system is a set of start/end positions of the bridge marked by the designer on a Geographical Information System (GIS) map on the computer screen. The output of the system is a set of the most feasible solutions that not only meet the site conditions and code requirements, but also bear minimum construction costs. The output solution consists of geometrical alignment and span lengths, structural units, and major beam sizes, which can serve as basic criteria for the detailed design of the bridge.