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Kimley»>Horn A. General: The bridge length, height and pier locations are subject to vertical and horizontal design clearance requirements such as those for clear zone, navigation, and hydrology. After these considerations are met, span lengths are governed by economics and aesthetic considerations. Superstructure depths (grade separation structures in particular) shall be kept to the minimum that is consistent with good engineering practice. Recommended span/depth ratios for steel superstructures are shown in AASHTO. The length of the bridge will be affected by: a. Opening required by Hydraulic requirements. b. Environmental Considerations. c. Width of waterway and/or width of cross section of roadway being spanned including the use of retaining walls. B. Statical System: The economic and engineering advantages of both simple span and continuous spans shall be addressed. C. Superstructure: Some superstructure types that could be considered are prestressed concrete girders, reinforced or prestressed concrete slabs, steel rolled sections or plate girders and post tensioned slabs. D. Substructures: Some substructure types that could be considered are pile bents and multi -column or hammerhead piers. Variations of column shapes may be appropriate for aesthetic or economical requirements. E. Foundations: Some foundation types that could be considered are steel and concrete piles, drilled shafts and spread footings. G. Temporary Traffic Control: Show how traffic will be maintained during construction for each of the bridge alternates considered. Consider all major overhead work items such as bridge demolition and girder placement. H. Quantity estimates: For minor bridges rough quantities (such as reinforcing steel based on weight per volume of concrete) may be sufficient. keeping in mind that the intent is to establish relative and equitable costs between alternates and not necessarily to require the accuracy of the Final Estimate 4 of 10 254