RF or RFID Vehicle Tracking System

I have been tasked by my boss to look into development of an inexpensive vehicle tracking system for our test fleet. To start, we will just be tracking them in our parking annex, which is about 800 m2 , but will eventually be expanded to twice that size and possibly to an outside test track. I've begun looking into both RF and RFID systems, but I need help/advice.

RF:
There are RX/TX modules readily available for Arduino, and I know you can triangulate position with RF. My concern is that the 300-400 MHz modules won't reach far enough, and also how am I supposed to read the data from all the modules to a central computer (I assume over Wifi, which will probably require a second controller if both the RF and WiFi shields won't play nice on one board).

RFID:
There is an NFC/RFID Arduino shield readily available, but I haven't figured out if this one shield works as both the Tag and the Reader, and how the system would work to triangulate position and once again, send all this data back to a central computer.

Any and all advice is much appreciated, thank you everyone.

For distance reading you need a big aerial.
Look at the security loops in a supermarket.
Its been succesfully used for herd control i believe although i think that 125 khz tags were used for that.i think you need to look at an rf solution rather than tags.

Inexspensive, thats the tricky bit.

Here is a thought though.
Could you bury cheap tags throughout the area, poddibly drill holes and use pet implants.

Then have the cars report back as they drive over.

Several wifi equipped arduinos operating as a mesh may give you the required coverage.

http://forum.arduino.cc/index.php?topic=241881.0

Couldn't you just do this?

GPS is not an option. Any cellular/GPS signal in the warehouse is horrible. We are looking at an RF system because it can operate indoors.

I've done some more research into RFID, and from what I've found RFID doesn't do triangulation, so will put that idea on the back-burner.

Cost way maybe put receiver at the entrance which will tell you what car went in and out. If you want to see where car is park then maybe at the parking spot. Put receiver in front and transmitter in bumper. When car come in it will light up and you will know where car is. Will work for security that way too

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