 The December 1990 amendment changed the car order to a separate contract, the M6 series cars (9000-series).Similar to the change with the proposed purchase of M2 cars, the decision was made to purchase improved models following a reassessment of fleet requirements.The contract called for 39 cars, with an option for 9 more cars, and was awarded to Morrison Knudsen in August 1990 for $91.5 million.