The doctor shakes his head and begins to chuckle lightly to himself. I am nothing if not thorough. By now, the Doctor is giggling uncontrollably with Kirk not far behind. He says between gulps of air. Undaunted by their jocularity, he continues.
Chickens are of lower intelligence in comparison to other fowl of similar physiology.
It is therefore unlikely that they had any 'reason' for crossing the asphalt. However, a gravel or dirt road hold some possibility's that they may have confused the road with familiar territory but the percentage is low. Kirk asks covering his mouth with his hand in a undisguised attempt to appear serious. About 4,998.7 to one depending on the variables. The Doctors voice warbles slightly as half a giggle gets caught in the question.