The east side of the City has more undeveloped land and contains many newer subdivisions with much younger trees. So the west side of the City has more mature/older trees than the east side. This leads to more yard waste collection volume on the west side which can take longer to collect.
DPW is aware of this difference and makes efforts to schedule crews to complete the same number of collection rounds on both sides of the City each season. For example, if a round of yard waste collection on the east side is completed ahead of a round on the west side, then crews are shifted west to help complete that collection round before moving to the next round. Also depending on the time of the season, more crews may be assigned west than east to balance the collection process on both sides of the river.