Automatic vehicle notification

Project theme :

Within a large UNIVERSITY there are so many vehicles (carts) are assigned for the teachers to go from one place to the another place but the problem is CART doesn't know from where it has to pick a teacher. suppose there are 10 CARTS and there are 10 stations in the UNIVERSITY. Any teacher reaches 3rd station then he will press a button there so a NOTIFICATION will be sent to the NEAREST CART to the corresponding station.

What is exactly need :

A mechanism is attached on each station ( a button ) if anybody press that button , the nearest CART get notified that anybody at that station need the cart to be reached there.

Problems :

How to make such a button which can simply send any kind of notification that you have to go at that place?
How to find the location of the CART so that the nearest cart will only be notified?
How to process the data so that I can find the nearest CART?
How to connect all the devices wireless so that it can detect all info from anywhere in the UNIVERSITY??