How can one perform the Asr and Dhuhr prayers when ablution is unavailable and it's difficult to find a place to pray due to crowding or the nature of travel (such as riding a train), leading to the prayer time expiring?

Prayer must be performed on time, and one should beware of missing it or delaying it. If someone fears missing prayer due to transportation, they should pray before boarding or immediately after disembarking. If a person boards before the prayer time begins and cannot stop the vehicle, and he thinks that he will miss the prayer, then if the prayer is one that can be combined (like Dhuhr and Asr, or Maghrib and Isha), he should delay it until the time of the second prayer, even if he is not traveling. However, if the prayer cannot be combined (like Asr with Maghrib), he should pray it while riding by gesturing, and perform tayammum (definition) if he cannot find water. It is not permissible for him to delay the prayer beyond its time. It is permissible to combine two prayers, whether at home or traveling, when there is a need, to alleviate hardship. A traveler prays four rak'ahs if he is in his residence.