Firstly: 

It is permissible to join Zuhr and ‘Asr prayers, and Maghrib and ‘Isha’, for one who is traveling. That is indicated by many ahaadeeth, such as the following: 

1 – al-Bukhaari (1108) narrated that Anas ibn Maalik (may Allaah be pleased with him) said: The Prophet (peace and blessings of Allaah be upon him) joined Maghrib and ‘Isha’ prayers when traveling. 

2 – Ahmad (3178) narrated from Ibn ‘Abbaas that the Messenger of Allaah (peace and blessings of Allaah be upon him) joined two prayers whilst traveling. Shaykh Ahmad Shaakir (3288) said: Its isnaad is saheeh. 

3 – In Saheeh Muslim (706) it was narrated that Mu’aadh said: We went out with the Messenger of Allaah (peace and blessings of Allaah be upon him) on the campaign of Tabook, and he used to pray Zuhr and ‘Asr together, and Maghrib and ‘Isha’ together. 

A traveler may be of two types: 

1 – When he is actually on the road

2 – When he has made a stop, i.e., he is not on the road; either he has reached the place to which he is traveling, or he has made a stop on his journey and stayed there for a while. 

It is permissible for any traveler to join prayers, whether he has made a stop or is on the road. 

But is it better for the traveler to join the prayers or to offer each prayer at its proper time? 

Shaykh Ibn ‘Uthaymeen said in his essay on the times of the prayer (Mawaaqeet al-Salaah, p. 26): 

It is better for the traveler who has made a stop not to join the prayers, but if he joins them there is nothing wrong with that, unless he needs to join them because he is tired and needs to rest, or because it is hard for him to find water each time, and so on, in which case it is better for him to join the prayers and avail himself of the concession. But for the traveler who is on the road, it is better for him to join Zuhr and ‘Asr, and Maghrib and ‘Isha’ – in the way that is easier for him, either praying them at the time of the earlier prayer or the time of the later prayer. 

Based on this, it is better for you to avail yourself of the concession, and join Zuhr and ‘Asr at the time of Zuhr, because this is easier for you. The Messenger of Allaah (S) was never given the choice between two things but he would choose that which was easier, so long as it was not a sin, in which case he would be the most careful of people to avoid it. Narrated by Muslim, 3560; Muslim, 2327. 

In this case you have to strive to pray ‘Asr in congregation and look for someone to pray with you. 

Secondly: 

With regard to praying ‘Asr in the train whilst sitting, this is permissible according to the majority of scholars, if you cannot pray standing. 

It says in Fataawa al-Lajnah al-Daa’imah (8/120): 

If the time for prayer comes and the plane is still in the air and there is the fear that the time for prayer will end before it lands, then the scholars are agreed that the prayer must be offered in whatever manner one can, bowing, prostrating and facing the qiblah if possible, because Allaah says (interpretation of the meaning): 

“So keep your duty to Allaah and fear Him as much as you can”

[al-Taghaabun 64:16]

And the Prophet (peace and blessings of Allaah be upon him) said: “If I tell you to do something, do as much of it as you can.” Agreed upon. 

But if it is known that the plane will land before the time for prayer ends, and there will be enough time to offer the prayer or the prayer is one which can be joined with another – such as Zuhr which may be joined with ‘Asr, or Maghrib which may be joined with ‘Isha’ – and it is known that the plane will land before the time for the second prayer ends and there will be enough time to offer the prayers, then the majority of scholars are of the view that it is permissible to offer the prayers in the plane, because it is obligatory to offer them when the time for prayer begins, in whatever manner one can, as stated above. This is the correct view. 

And it also says (8/126): 

It is not permissible to pray sitting down in a plane or elsewhere if one is able to stand, because of the general meaning of the verse (interpretation of the meaning): 

“And stand before Allaah with obedience”

[al-Baqarah 2:238]

And the hadeeth of ‘Imraan ibn Husayn which was narrated by al-Bukhaari: that the Prophet (peace and blessings of Allaah be upon him) said to him: “Pray standing, and if you cannot, then sitting, and if you cannot, then on your side.” Al-Nasaa’i added, with a saheeh isnaad: “And if you cannot, then lying on your back.” 

Some of the scholars are of the view that it is not permissible to pray in planes, trains or cars because it is not possible to offer the prayer as it is offered when standing on the ground – unless there is the fear that the time for the prayer will end. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in Fataawa Arkaan al-Islam (p. 380): 

It is obligatory to pray in a plane if one does not know the time of the prayer, but if he cannot offer the prayer in the plane as he offers it on the ground, then he should not offer obligatory prayers in the plane if the plane will land before the time for prayer is over, or the time for the following prayer if it is a prayer that may be joined with another. For example, if a plane takes off from Jeddah just before sunset and the sun sets whilst it is in the air, he should not pray Maghrib until the plane lands and he disembarks. But if he fears that the time will end and he intends to join it to ‘Isha’ at the time of the latter, he can pray them when he lands. But if the plane keeps on flying and there is the fear that the time for ‘Isha’ will end, which is at midnight, then he should pray them in the plane before the time ends. 

Based on this, in order to be on the safe side, you should not pray ‘Asr in the train, rather you should join it with Zuhr at the time of Zuhr, as stated above.