As far as being humane goes, it would be kinder to kill a rat outright than to use a live trap and displace it. If you move an animal into the wild, you are putting it into another animal's territory. Every place has enough food to support a certain number of animals. You can't just stick an animal anywhere. Most displaced animals die within a few days of dehydration. Rats would probably survive anywhere, but they would take the place of native animals. In california, it is illegal to displace wild animals.
If you use spring traps, use the big rat traps right away. We thought we had a mouse in our house, and we set lots of mousetraps. In the morning the traps would have snapped shut without catching anything. Eventually we saw that the "mice" had grown into rats. We tried rat traps then, but the rats had learned to avoid the traps altogether. We had been inadvertently training the beasts to stay away from the things.