TWA has confirmed it's order for 50 A318s and 25 A320s, in addition to 75 A320 options. The A320 order/options can be any combination of A319/320/321.
This order along with the 50 Firm/50 Option 717 order has been used by TWA as a trade in against it's order for 10 RR Trent powered A330-300s which are now cancelled.
This could be another reason for the Airbus A318/Boeing 717 order split. The airbuses offset the A330 loss to Airbus and the 717's Rolls Royce GmbH BR715 engines offset the loss of the Trent order.
TWA is also said to be interested in ordering PW2040 powered 757-300s to replace it's ageing 767-200s on domestic routes.
Well, the uncertainty over the A330 order has finally ended, I would have liked to see the TWA livery on an A330