From: ahk@chinet.com   
      
   John Levine  wrote:   
      
   >>>>We're talking about transit fares. All that has to be done in real   
   >>>>time is validate the fare media. The rest of it doesn't have to happen   
   >>>>immediately.   
      
   >>>Transit fares can be pretty complicated.   
      
   >>You gave an example in which you were billed in arrears.   
      
   >The credit card pseudo-Oyster is billed in arrears, but I'd guess that   
   >they get approval for the price of a travecard (the most you can spend   
   >in one day) the first time you tap in.  Or they may figure that the   
   >risk that the charge will bounce is worth it for the value of not   
   >having to produce and manage cards for a million casual users.   
      
   We're not talking about buying jewelry here.   
      
   >The Caltrain examples are prepaid.  There are several chunks of   
   >prepaid value, in this case an eight-ride ticket and cash, and it   
   >needs to debit the right one when you tap out.   
      
   I was referring to your Oyster card example.   
      
   >Smartcard systems go to considerable effort to allow offline   
   >operation, with info stored on the card and clever crypto to   
   >authenticate cards and terminals to each other.  If it'd really be   
   >easy to do it all offline later, why do it the hard way?   
      
   That's the crux of it, isn't it? I'm suggesting it's not worth the expense.   
      
   The other day, my Ventra account failed to perform the auto-reload;   
   it's linked to my credit card. I had to make a transfer. When I   
   boarded rail, the card went into deficit (in leiu of referring me to   
   the vending machine at which I could have reloaded value). The system   
   is supposed to be set up so that it never goes into deficit, given a   
   $10 cushion I'm required to maintain. On the bus, I learned about the   
   $1 deficit. The card was shut off. I can't add value to the account   
   at the bus, but the driver allowed me to board.   
      
   Checking later, the card had been read on the bus, so there was no   
   reason for the system to shut the card down. There's never an explanation   
   as to why the credit card auto load failed and why they didn't tell me.   
      
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