Traffic Law and Crash Investigation
Impaired driving
G.S. 20-138.1 requires operation of a vehicle on a highway, street, or public vehicular area while impaired by alcohol (BAC .08 or more), any impairing substance, or a combination, or while appreciably impaired. Commercial drivers are impaired at .04 (20-138.2); drivers under 21 at any detectable alcohol (20-138.3). Implied consent (20-16.2) applies to anyone who drives on a North Carolina highway; refusal triggers a one-year revocation and is admissible at trial. Breath testing requires a continuous deprivation and observation period (30 minutes) before the sample. Field sobriety tests - HGN, walk-and-turn, one-leg stand - are divided-attention, validated tests that must be administered per protocol.
Crashes
A crash reportable to DMV involves injury, death, or total property damage of $1,000 or more; the investigating officer completes the DMV-349. Hit and run (20-166) is a felony when injury or death results. Also know 20-140 reckless driving, 20-141 speed limits, 20-141.5 felony speeding to elude, 20-157 move-over duties, and 20-217 school bus stop arms.
Crash math
Measure skid marks, debris, and sight lines before anything is moved. Minimum speed from skids uses drag factor and distance; stopping distance rises with the square of speed, so doubling speed roughly quadruples distance.
Traps
Assuming DWI requires a chemical test result; treating refusal as a right without consequence; confusing the driver's duty to report with the officer's duty to forward a report; forgetting that impairment can be proven without a number.
Rule of thumb
Document the driving, the personal contact, the standardized tests, and the chemical analysis as four separate observations - each one independently supports probable cause.