california driving
California: How long does right-of-way persist after a lane change?
<p>Suppose I am driving on a road in California with 2 lanes going in the same direction. My car is 3 car lengths ahead of another car in the adjacent lane, and both cars are going 45 MPH in the same direction. My turn signal has been on for quite some time as I wait for space to enter the other car's lane (and despite this, for whatever reason, the other car isn't slowing down. For the purposes of this question, also assume it's not speeding up either).</p>
<p>Now suppose I change lanes, so I'm in front of the other car, 3 car lengths ahead of it in the same lane, and both cars still going 45 MPH. How long does the other car's right of way last? I.e., how long must I maintain 45 MPH? Initially, I don't know anything about the other car's stopping ability. If the other car remains 3 car lengths behind me for 30 seconds, can I assume that his reaction time is better than 3 car lengths? Does the car behind me, despite having once had right-of-way, eventually need to maintain a safe following distance?</p>
<p>Suppose both cars remain at 45 MPH for 30 seconds, and then I slow down to turn off of the road, and I'm rear-ended. Will the lane change be a potential cause of the accident, even though it occurred 30 seconds before I slowed down?</p>
<p>Now change 30 seconds to 20 seconds, 10, 5, and then just 2 seconds. At what point does the lane change potentially become relevant to a rear-ending case?</p>

<h2>They don't treat right-of-way persistence <em>at all</em></h2>
<p>You are required to follow the car ahead <em>at a distance that is reasonable and prudent</em>, having regard for both speeds, traffic generally, and road condition (i.e. curves, rain).  CVC 21703.</p>
<p>This would apply to the other driver.</p>
<p>You must only shift lanes left or right when possible with reasonable safety and only after signaling.  CVC 22107.</p>
<p>That applies to you.</p>
<p>If you &quot;cut them off&quot; such that they must make adjustments to re-acquire a distance that is reasonable and prudent, then you are guilty of 22107.</p>
<p>If you changed lanes properly, then it is immediately and continuously THEIR duty under 21703 to <em>maintain</em> safe distance despite whichever lawful maneuvering you may need to do.</p>
<p>Note that 22109 forbids you to stop or suddenly decrease speed without first giving an appropriate signal, unless there is no opportunity to give that signal. 22109 is a civil infraction that assumes accidental or negligent braking.  (i.e. me going for the clutch and not remembering the car is an automatic).</p>
<p>Intentionally brake-checking someone is a crime with risk of jail and other more serious consequences than &quot;fine and points&quot;.</p>
