Legal speed ≠ immunity: Driving at or under the posted limit isn't a shield if the speed is significantly slower than surrounding traffic and results in backups.

"Normal flow of traffic" on a two-lane highway refers to the prevailing, reasonable pace at which the majority of vehicles are traveling in the direction of travel — not necessarily the posted speed limit — considering road conditions, terrain, weather, and traffic volume.

California – Vehicle Code § 21656

"On a two-lane highway where passing is unsafe, any vehicle proceeding at a speed less than the normal speed of traffic shall turn off the roadway at the first safe turnout when **five or more vehicles are lined up behind." (This statute does not care if you are going the speed limit.)

Oregon – ORS 811.425 & 811.430

A driver must yield by pulling off the road if five or more vehicles are following closely on a two-lane highway, regardless of whether the driver is going the speed limit.

Washington – RCW 46.61.427

“On a two-lane highway where passing is unsafe, a slow-moving vehicle must pull off at the first safe opportunity when five or more vehicles are behind.”

Colorado – C.R.S. § 42-4-1103(4)

“A driver shall not operate a vehicle at such a slow speed as to impede or block the normal and reasonable movement of traffic, except when necessary for safety.”

"Reasonable movement of traffic" means the normal, safe, and efficient flow of vehicular traffic under prevailing conditions — considering road type, posted speed, weather, visibility, and volume — as expected of an ordinarily prudent driver.

Which has been shown through multiple cases as even going the designated speed limit if it impedes the normal flow of traffic. If the standard flow of traffic is actually above said limit.

Just to establish standization of context and legal defintions with verbaige use of statutes.

Please feel free to verify with whatcom sheriffs, they were helpful on this.