The Messenger of Allah (salAllahu alayhi wasalam) said; Three supplications will not be rejected (by Allah (Subhanahu wa Ta’ala)), the supplication of the parent for his child, the supplication of the one who is fasting, and the supplication of the traveler. [al-Bayhaqi, at-Tirmidhi - Sahih]
During travel supplication is heard by Allah (Subhanahu wa Ta’ala) if the trip is for a good reason, but if the trip is for a bad intention or to perform illegal things (making sins) this will not apply to it.