To summarize, you want an Arduino, which is driving around in a car or a bus, to send some data to a sensor.
Firstly, you need to be clear whether you need this data in real time, or whether you can collect it during the drive and send it to the server at the end.
If you need real-time, then we can probably rule out WiFi, unless you are 1000% certain that there is always WiFi coverage (maybe Singapore?).
Which leaves us with the public telephone network. You can decide on cost/battery life (unless you will power the decide from the vehicle), whether to add a SIM / GSM module to an Arduino, or add a temperature sensor to a cheap Android 'phone.
You can ask for recommendations here, but it might be better at Hardware Recommendations Stack Exchange. In either case, please be clear about what it is that you want, and which features have priorities over others.
Your question here is about pushing data from the vehicle to the server. There are plenty of solutions which use SMS, generally because it is cheaper, but you should probably just use HTTPS and a standard CRUD RESTful API of your own design (unless the server has already specified an API).
If you can wait until the end of the trip, then you can just use WiFi when the vehicles get back to base.
Since you speak of buses, you might want to get adventurous. As buses drive around, they might store data until they reach a WiFi point and transmit it then.
OR, until they pass another bus.
Here's a slight rewording of my answer to this question - try to think of zebra as buses :-)
Basically, whereas TCP/IP will drop undeliverable packets, a Delay/Disruption Tolerant Network (Wikipedia version) will store and forward.
Thus, if your bus has no WiFi connectioon, it will wait until it has has, or until it passes another bus, then perhaps send the data packet to the other bus, which might, in turn, have to store until it can has Wifi, then ultimately forward the packet.
Broadly speaking, as the buses pass each other, they say "hey, if you get some WiFi access, can you pass on this data to the server?".
There are already many existing projects using DTN, beginning with the famous zebranet (Google for zebranet wildlife tracking).
I have developed a few such projects myself, but an not allowed to discuss them.
I am sure that a little imagination and a handful of Raspberry Pi Zero Ws would allow you develop an interesting project for your own