DISCLAIMER: I am no lawyer, so this is for informal reference only.
Necessity defense is to justify otherwise unlawful action to avoid greater harm. For example, as Section 1252 of the Vehicle and Traffic Law in New York State forbids non-police to lane-split on motorcycles without regard to the speeds of 5 vs. 55 or http://www.nhtsa.gov/people/injury/pedb ... cle51.html conditionally supporting lane splitting, ultra-slow lane splitting may qualify for non-automatic necessity defense when considering the choice of evils. Once the speed of lane splitting is too fast for condition, it is no longer necessity defense.
See also https://en.wikipedia.org/wiki/Necessity ... ew_York%29 for more state information.