The city had invested heavily in a new light-rail line, projecting that it would draw riders away from congested highways within its first…

The second sentence reports what actually occurred, in direct contrast to the optimistic projection named in the first sentence, and in reality signals precisely that shift from forecast to actual outcome. As forecast would mean the outcome matched the prediction, the opposite of "fell well short of projections." Similarly would suggest agreement between the two sentences, but the sentence describes a shortfall, not a match. In addition would frame the second sentence as a separate, compatible point instead of a contradiction of the projection.