How does one pray on a bus or train, and is ablution (Wudu') required for it?

Prayer is obligatory whether one is traveling or at home, and it is not valid without ablution (wudu') or dry ablution (tayammum (definition)) when water cannot be used. Islamic law has eased conditions for the traveler by permitting the shortening of the four-rak'ah prayers and combining the Dhuhr prayer with Asr, and Maghrib with Isha. If the time for an obligatory prayer overtakes someone on a vehicle, and they are unable to perform ablution or dry ablution, or disembark, and they fear the prayer time will expire, then they should pray on the vehicle, observing the direction of the Qiblah and the pillars of prayer as much as possible. Otherwise, they should pray in their current state, because Allah the Almighty says: "Allah does not burden a soul beyond its capacity" and "So fear Allah as much as you are able," and the Prophet, peace and blessings be upon him, said: "What I have forbidden you, avoid; and what I have commanded you, do of it as much as you are able." However, the prayer must be repeated when one is able to do so.