Traffic and Crash Investigation
Traffic Stops and Authority
A traffic stop is a seizure requiring reasonable suspicion of a traffic violation. Once lawfully stopped, officers may order occupants out, request license and registration, and conduct a limited inquiry. Prolonged detention beyond the stop's purpose requires independent reasonable suspicion. Know when a stop becomes an arrest and when a search is lawful (consent, probable cause, inventory, incident to arrest).
Crash Investigation Basics
Crash investigation requires systematic scene management: protect the scene, render aid, identify witnesses, photograph and diagram, and measure. Understand the concepts of perception-reaction time, stopping distance, and speed estimation from skid marks (using the drag factor and the skid formula). Document road conditions, weather, lighting, and vehicle damage patterns to reconstruct what happened.
Impairment and DUI
DUI investigations follow the three phases: vehicle in motion, personal contact, and pre-arrest screening. Field sobriety exercises-horizontal gaze nystagmus, walk-and-turn, one-leg stand-are standardized and must be administered per protocol. Know the implied consent framework and when a warrant is required for a blood draw. Document observations that support impairment: odor, slurred speech, bloodshot eyes, and driving behavior.
Traps and a Rule of Thumb
Questions blur the distinction between a consensual encounter at a crash and a formal stop. They also test whether you know that standardized field sobriety tests are divided-attention tests and that HGN is not a balance test. Watch for DUI questions that assume a breath test is always required-refusal carries administrative consequences, not automatic criminal liability.
Rule of thumb: For any traffic encounter, ask: What justified the stop, what justified any extension, and what justifies any search? Each step needs its own legal basis.