The competition seems artificially restricted based on what it's trying to accomplish. Why limit yourself to past data? We have immense sources of data for events months before they actually happen. Why wouldn't you account for a cricket match/product release/concert that's scheduled to happen a month in the future?
"This competition requires participants to predict travel time on Sydney's M4 freeway from past travel time observations". This line seems to suggest that the past travel time is the most important part of the experiment; however, as one other (rrrhys) pointed out, the data is useless, since the road has changed, and the grandparent of this post mentioned sporting events affecting traffic.
All of that said, perhaps a strong model can be generated using just historical data.
