The signal will go for miles. Make sure each bus is on it's own channel and you use encryption on the WiFi.
The base station should also have an amplifier and one of these antennas.
Edit: The amplifier and antenna both use "N" connectors, which is a good thing. You should use LMR-400 coax between the amplifier and antenna for better results, and of course, the antennas get mounted on the roof of the buses.
Please tell me if the wifi booter amplifier has got to be installed in each bus or its only the antenna required.
Since the thread isn't locked yet...
Try just the antenna. It may make the difference you need. The amplifier is quite powerful, especially when connected to one of these antennas.
Each bus needs the equipment.
Remember... This setup (using the amplifier) may be illegal to use in the U.S. (and probably most of Europe).
It may be legal in some South American countries.
I'm rather certain 'anything goes' in Paraguay and Bolivia.
The use of just the antenna is legal just about everywhere.