Police don’t have a magic tool that can detect intoxicated drivers instantly. Law enforcement must look for visual clues to give them a reason to pull a car over. Traffic violations are the most prominent signs. When you see someone constantly swerving in and out of incoming traffic, there is likely something wrong with either the car or the driver.
Police can’t assume someone is driving while intoxicated, especially if the driver has done nothing wrong. In today’s world, the driver would be quick to uphold his rights. The National Highway Traffic and Safety Administration (NHTSA), therefore, enumerates 24 visual cues, divided into four categories. Police have a reasonable suspicion if the probability factor (p) is 1 or more.
Problems in maintaining proper lane position (e.g. weaving, swerving, drifting) – p = 0.5 to 0.75
Speed and braking problems (e.g. stopping too far, driving too slow) – p = 0.45 to 0.70
Vigilance problems (e.g. driving without headlights, driving in opposite lanes) – p = 0.55 to 0.65
Judgment problems (e.g. tailgating, unsafe lane change or turn) – p = 0.35 to 0.90
Weaving, in addition to a specific visual cue, warrants a factor of at least 0.65. Spotting two clues deserves at least 0.50. Police can stop a driver with a factor of at least 0.35. Visual cues during stops also count. Signs like slurred speech, difficulty in leaving the car, or excessive swaying call for at least 0.85.
If you’re stopped for visual signs of DWI, consult an attorney in Raleigh, NC.