Risk Evaluation on Low Water‐Crossing Structures

Highway engineers occasionally face the dilemma of either constructing a regular high bridge so that traffic would not be interrupted by floods or using a low water-crossing structure so that traffic would be interrupted by floods at certain time intervals. The low water-crossing structure (LWCS) is usually much cheaper but has strong negative social and political impacts. A public-opinion survey was conducted and analyzed for the thoughts from various engineers from state highway departments, forest services, and other institutes on this issue. The most important intangible factors for the selection of LWCS were (in order of importance): possible damage to human life, amount of daily traffic, frequency of possible floodings, legal considerations, and the location as part of an emergency route. Availability of an alternate route, duration of traffic interruptions, and possible property damage form the second most important group. Certain absolute constraints were concluded from these questionnaires. A warning system is an important ingredient for the selection of LWCS also. Respondents overwhelmingly (more than 85%) indicated that they would be willing to consider changing their criteria for the selection of LWCS if a great majority (more than 75%) of other designers have criteria different from their own.