Whilst travelling, what are the rules for praying salah? If a person for instance is praying Zuhr and knows he will miss the time to pray Asr whilst travelling, can he combine Asr prayer with Zuhr?
بسم الله الرحمن الرحيم
In The Name Of Allah, The Most-Gracious, The Most-Merciful
For the one who is considered a musafir (traveller), it is waajib for him to shorten the four-unit prayers to two units. There is no combining of prayers in the Hanafi madhhab while travelling.
There is no excuse for missing the obligation of salah while travelling. You must either stop off and pray if you are able to. If you are not able to do that, it will be required to pray on the vehicle that you are travelling on.
For more details on praying on a vehicle or plane, please see the following link: http://daruliftabirmingham.co.uk/salah-on-an-aeroplane/
Only Allah knows best
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Ibn Abideen, Raddul Muhtaar, Volume 2, Page 123-124