Is it necessary to delay the evening adhkar until after the Asr prayer, or is it permissible to recite them before the prayer, knowing that the reason for the delay is transportation?

The time for evening remembrances begins at noon (Dhuhr) and ends at midnight. There is no harm in reciting them before the Asr prayer, although it is better to delay them. If you fear that the time for the Asr prayer will expire while you are on the bus, then pray on it according to your ability, whether standing or sitting, and facing the Qibla (definition) if possible.