Is it permissible to recite Surahs while walking?

My educational institution is at a distance of about 1.5 KM from Bus stop. I usually cover this distance while reciting Surahs. What I want to ask is, Is it permissible to recite Surahs from Qur'an while walking, or Is it against the grace of Holy Book?. It also helps me to memorize Surahs easily. I intend to do so in a voice only audible to me of course.