Complex sentence: Two additional round trips between Seattle and Portland were added on December 18,2017; an early morning departure from each city and a late evening return, enabling same-day business travel between the two cities.
Split into simpler sentences: Two additional round trips between Seattle and Portland will be added on December 18,2017. A new early morning departure from each city will be matched by an evening return, to enable same-day business travel between the two cities.