Goodchild, Anne VMcCormack, Edward DRowell, Maureen K2020-08-142020-08-142020-08-142020Rowell_washington_0250E_21563.pdfhttp://hdl.handle.net/1773/45906Thesis (Ph.D.)--University of Washington, 2020The violation of the International Regulations for Preventing Collisions at Sea (COLREGS) is a precursor to the majority of collisions. These violations may indicate a poor safety culture within shipping or they may indicate the failure of the COLREGS to capture the modern ordinary practice of seamen. The COLREGS are a mix of rules and regulations. Regulations are a form of explicit, externally applied control; while the text of a rule is ambiguous and requires observing the system it refers to in order to interpret its meaning. In order to observe how Puget Sound mariners interpret the rules of the COLREGS and whether they violate its regulations, their behavior is observed through the use of automatic identification system data. No close encounters are discovered, with cargo vessels safely using the traffic separation schemes and ferries elongating their routes to avoid collision risk with cargo vessels. The uncovered informal rules include ferries crossing traffic separation schemes at non-90 degree angles and passing starboard-to-starboard in head-on encounters. Collision avoidance is a cooperative task and requires a common understanding of the rules. The familiarity between ferry captains and Puget Sound pilots may explain why strict adherence to the COLREGS is not necessary to maintain a safe maritime environment. Changes in the COLREGS, local policy, and navigation technology must account for these informal rules if they are to aid safety. Open source code created and published for this analysis can be used to update the current findings after any change in the local maritime environment or to extend the analysis to other areas and time periods.application/pdfen-USnoneTransportationCivil engineeringThesis