I'm currently staying in Portland and yesterday I had a free day so I spent the day travelling on the city's light rail system. I have to say that it beats anything I've experienced in the UK hands down. Unlimited travel for the day is just $4.75 and it is valid during the rush hour too. One thing I have to ask is are there any conductors or ticket inspectors? I must have used a dozen trams and not once did I see anyone checking tickets, even outside the free central area. I might as well have saved $4.75 and not bother buying a ticket :hmmm:
I've ridden MAX about a dozen times and have only been asked to show my ticket twice. I get the impression checking is a random occurrence, so you could roll the dice and try to ride free but given the low price for a ticket it isn't worth the risk.