That time of the morning, the Tullamarine freeway inbound (to the east and south) would have been full of commuter traffic, while the outbound side would have been full of traffic going to MEL.
Atmospheric conditions were cool and still with very little air movement. Mt alexander road to the south may have been a better option.
I know that Vic Roads have a response plan to bypass a crash at the trumpet (intersection of tulla and calder freeways) through essendon airport but I don't think it works the other way.