one way ticket，round trip ticket，single ticket，return ticket

[japanjapan]

Dear Teachers，
If I am in city A, I want a ticket to go to city B. In American English, I can use "one way ticket", in British English, I can use "single ticket". If I want a ticket to go to city B and come back to city A, In American English, I can use "round trip ticket", in British English, I can use "return ticket". This is what Collins Dictionary tells me.
Now, My question is: Suppose I am in city A now, and I am going to city B, my friend offers me a ride, so I needn't a ticket from A to B. But when I go back to city A, I have to use a ticket and I want to buy it in city A now before I set out. What should I say to the salesperson? Is there a parlance for this kind of ticket too?
I look forward to your help. Thanks a million！

 

[maoyueh]

Dear Teachers，
If I am in city A, I want a ticket to go to city B. In American English, I can use "one way ticket", in British English, I can use "single ticket". If I want a ticket to go to city B and come back to city A, In American English, I can use "round trip ticket", in British English, I can use "return ticket". This is what Collins Dictionary tells me.
Now, My question is: Suppose I am in city A now, and I am going to city B, my friend offers me a ride, so I needn't a ticket from A to B. But when I go back to city A, I have to use a ticket and I want to buy it in city A now before I set out. What should I say to the salesperson? Is there a parlance for this kind of ticket too?
I look forward to your help. Thanks a million！

I think it is simply called a ticket from city B to city A.