Composition:
The background takes up more space than the foreground and is unusually detailed for Daumier. The third-class family faces away from the rest of the passengers, which emphasizes its isolation and rejection from the rest of society.
Use of space:
The family figures are drawn in larger proportion than their distance from the rest of the passengers would warrant, which gives them a more commanding presence. The upper-third of the painting is left blank, which suggests a space that is cavernous when it comes to height, but very cramped when it comes to length.
Use of color:
This painting is unfinished, so Daumier's true intent cannot be known.
Use of lighting:
The lighting provides a nice and unexpected contrast to the somber tones. Because the painting is unfinished we have no way of knowing if it would have maintained its sunny character.
Mood:
The mood of the painting is one of transit itself. One is on the move but also resigned and waiting for something to happen, for example, they might be en route to a new job or to a friend's house.
Brushstroke:
As much as possible, Daumier uses economy of line to keep his drawings simple and powerful which is evident in the hands of the mother, for example.