The USD Index is calculated against the following mix of currencies -
Euro (EUR), 58.6% weight Japanese yen (JPY) 12.6% weight Pound sterling (GBP), 11.9% weight Canadian dollar (CAD), 9.1% weight Swedish krona (SEK), 4.2% weight and Swiss franc (CHF) 3.6% weight
The Euro makes up 58% of the calulation so as this currency keeps falling, due to the Euro crisis, the USD will keep rising. How far the USD goes up depends mainly on how much the Euro goes down.