Note: I will keep my comments to passive RFID (non-battery powered tags) and leave aside active RFID commonly used for toll roads, shipping containers, etc.
RFID is actually a family of technologies, typically defined by ISO standards, and operating over several distinct frequencies: 134kHz (LF), 13.56MHz (HF), and 900MHz (UHF). LF and HF use inductive coupling between the tag (transponder) and reader (transceiver) while UHF uses capacitive coupling. Theses technologies do not allow one to know a specific distance, but rather when a tag is in the field or not. So, when Wal-Mart uses UHF tags on their pallets, they don't know where the pallet is exactly in their warehouse, they simply know when the pallet has passed through their loading dock. I've seen some triathlon timing systems use UHF RFID, but they still use cameras in case of close finishes.
Thanks! I've seen some timing systems that are used in triathlons but the main problem was making a field that was 25-30 feet width but a tight spread (1 foot). Do you think active would fair better in that respect? Last time I checked it seemed so but it also jacked up the price a bit. I know that for Olympic BMX they are using some type of active transponders but I can't think that any commercially available solution would be accurate enough. I assume they have to be doing camera checking too but for .000 second split times even a foot spread seems like a wide margin of error.
Given the granularity in timing (i.e. 0.000 sec) you are looking for, I don't think active would help; and, the tags are certainly more expensive, though reusable.
RFID is actually a family of technologies, typically defined by ISO standards, and operating over several distinct frequencies: 134kHz (LF), 13.56MHz (HF), and 900MHz (UHF). LF and HF use inductive coupling between the tag (transponder) and reader (transceiver) while UHF uses capacitive coupling. Theses technologies do not allow one to know a specific distance, but rather when a tag is in the field or not. So, when Wal-Mart uses UHF tags on their pallets, they don't know where the pallet is exactly in their warehouse, they simply know when the pallet has passed through their loading dock. I've seen some triathlon timing systems use UHF RFID, but they still use cameras in case of close finishes.
Hope that helps.