(a) A person commits the crime of obstruction of highways if the person knowingly


(1) places, drops, or permits to drop on a highway any substance that creates a substantial risk of physical injury to others using the highway; or


(2) renders a highway impassable or passable only with unreasonable inconvenience or hazard.


(b) It is an affirmative defense to a prosecution under (a)(1) of this section that


(1) the defendant took reasonable steps to remove the substance from the highway; and


(2) no person suffered physical injury as a result of the presence of the substance on the highway.


(c) Obstruction of highways is a class B misdemeanor.