During the journey, Sunnaĥ Ṣalāĥ are not shortened but rather will be offered completely. If the traveller is in the state of fear or anxiety, he is exempted from offering Sunnaĥ Ṣalāĥ but he is required to offer it when in peace.
(‘Ālamgīrī, vol. 1, pp. 139)
صَلُّوۡا عَلَى الۡحَبِيۡب صَلَّى اللّٰهُ تَعَالٰى عَلٰى مُحَمَّد
1. [For a traveller who has travelled] outside the city, (‘outside the city’ refers to the place from where Qaṣr becomes Wājib for a traveller), one can offer Nafl Ṣalāĥ while riding a conveyance (e.g. a moving car, bus, or van. In this condition, facing the direction of Qiblaĥ is not a pre-condition) and the traveller must face the direction towards which the conveyance is moving. If he does not face this direction, then the Ṣalāĥ will not be permissible. Facing the Qiblaĥ is not a condition even at the time of the beginning of Ṣalāĥ. He is required to face the direction towards which the conveyance is moving, and to perform Rukū’ and Sujūd by gestures. (It is also necessary that) the