Can a person shorten his prayer before leaving his city?

If the time for prayer comes when the traveller is still in his city,
then he should pray it in full because he has not yet left his city. If he has left his
city and is on the road when the time for prayer comes, then he should pray two
rak’ahs even if the adhaan came before he left his city. What counts here is the
prayer (not the adhaan). Similarly, if the time for prayer comes whilst you are still
travelling, but you reach your home before you pray, then you have to pray four
rak’ahs, because in this case what counts is the actual prayer. If you pray when you
are travelling, you should shorten your prayer; if you pray when you are at home, you
should pray it in full.