Is Combining Prayers when Travelling Permissible?
Question

I work in Cairo and I live in Tanta (86 km away). In Ramadan I do the following. When I pray Dhuhr, afterwards I intend to pray `Asr shortened, because when I leave work the Adhan is about to be called for `Asr, and I am in a hurry to catch my train. 
Is it permissible for me to join my prayers and shorten them as I am doing? 
Or should I wait to pray `Asr and then go back to my town? In this case I will be late and will arrive as the sun is setting, which causes a great deal of hardship as I will not be able to rest, especially as I want to pray Tarawih. 
Is it permissible for me to pray `Asr in the train while sitting down?
Praise be to Allah.Can you combine prayers when travelling?
It is permissible to join Dhuhr and `Asr prayers , and Maghrib and `Isha’ for one who is travelling. That is indicated by many hadiths, such as the following: 

Al-Bukhari (1108) narrated that Anas ibn Malik (may Allah be pleased with him) said: The Prophet (peace and blessings of Allah be upon him) joined Maghrib and `Isha’ prayers when travelling. 
Ahmad (3178) narrated from Ibn `Abbas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) joined two prayers whilst travelling. Shaykh Ahmad Shakir (3288) said: Its Isnad  (chain of narration) is authentic. 
Muslim (706) narrated that Mu’adh (may Allah be pleased with him) said: We went out with the Messenger of Allah (peace and blessings of Allah be upon him) on the campaign of Tabuk, and he used to pray Dhuhr and `Asr together, and Maghrib and `Isha’ together. 

Types of traveller 
A traveller may be of two types : 

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

It is permissible for any traveller to join prayers , whether he has made a stop or is on the road. 
Is it better for the traveller to join the prayers?
But is it better for the traveller to join the prayers or to offer each prayer at its proper time? 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said in his essay on the times of the prayer (Mawaqit As-Salah, p. 26): 
It is better for the traveller 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 traveller who is on the road, it is better for him to join Dhuhr 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 Dhuhr and `Asr at the time of Dhuhr , because this is easier for you. The Messenger of Allah (peace and blessings of Allah be upon him) 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 and Muslim, 2327)
In this case you have to strive to pray `Asr in congregation and look for someone to pray with you. 
Can you pray in the train sitting down?
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 Fatawa Al-Lajnah Ad-Da’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 Allah says (interpretation of the meaning): 
“So keep your duty to Allah and fear Him as much as you can.” [At-Taghabun 64:16]
And the Prophet (peace and blessings of Allah be upon him) said: “If I tell you to do something, do as much of it as you can.” (Al-Bukhari and Muslim )
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 Dhuhr 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 Allah with obedience.” [Al-Baqarah 2:238]
And the Hadith of `Imran ibn Husayn (may Allah be pleased with him) which was narrated by Al-Bukhari (may Allah have mercy on him): that the Prophet (peace and blessings of Allah be upon him) said to him: “Pray standing, and if you cannot, then sitting, and if you cannot, then on your side.” An-Nasa’i added, with an authentic Isnad: “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 ‘Uthaymin (may Allah have mercy on him) said in Fatawa Arkan 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 Dhuhr at the time of Dhuhr, as stated above.
And Allah knows best.