In your study on box culverts, I have some questions:
Standard severities from RSAP were used to describe the box culvert hazard. Although these culvert severities probably were not intended to include water, all severities incorporated into RSAP have proven to be excessive. And it is reasonable to regard RSAP culvert severities to be representative of having some water in the box.
Adding two or three box culverts in a row would essentially create a longer hazard. Our sensitivity analysis showed that longer hazards create higher cost/benefit ratios for any given safety treatment. Further lengthening the hazard would make moving the culvert farther from the roadway more beneficial relative to the other two treatment options.
With regard to the clear zone offset requirements, the MsRSF had no intention to indicate that the clear zone should or should not be adjusted for 3R work relative to new construction. We chose clear zone limit its used by our sponsor, Iowa, in this study.
Many DOT's have expressed concern over culvert grates becoming clogged and leading to flooding. In a study conducted many years ago, TTI explored this problem and found no evidence of clogging. Unfortunately TxDOT chose not to publish that report. Recall that great bars are 30 inches apart and can span lengths of 20 feet or more. TTI's findings indicated that 2-1/2 foot wide by 20 foot long openings are difficult to clog, even in heavily wooded areas. Iowa has been using grades for a number of years. Perhaps you could contact them to see if clogging has been a problem.
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