Answer:
whoever
Step-by-step explanation:
The "I depend on" threw me off...
without that, we have the dependent cause "___ sits in the front to stay awake and look for police cars"
Now the rule...
whomever= object pronoun; like him, her, them
whoever= subject pronoun; like he, she, they
"She sits in the front..." > "Her sits in the front..."
"Whoever..."
Additional clarification:
object: having something done to it
subject: person/ thing doing something