Traffic Jam

Traffic Jam is a miscellaneous quest in Fallout 4.

Detailed walkthrough
Ask Deb at Bunker Hill for a job. She'll inform the Sole Survivor that some nearby feral ghouls pose a threat to Bunker Hill and that they need to be removed. Go to the National Guard training yard and kill the feral ghouls, then return to Deb to collect the reward.

When the first building is entered, the player character will encounter a few ferals, along with the body of Knight Astlin of the Brotherhood of Steel, which will also start the quest The Lost Patrol. In the second building there will be more ferals, including a glowing one.

If the area had already been cleared previously, the Sole Survivor can directly ask for the reward in the same conversation.

In addition to the caps reward, upon successfully turning in this quest, the caps inventory of the six main Bunker Hill traders (Deb, Kay, Cricket, Doc Weathers, Lucas Miller, and Trashcan Carla) increases by 150 caps permanently. This is cumulative with the similar 300-cap increase rewarded for completing Prep School.

Bugs
If one had previously cleared the training yard without getting this quest, it may be unavailable to accept or turn-in, blocking Prep School. (Despite the in-game console showing it at stage 200, which is "Report back to Deb.")
 * On PC, one can solve this by manually setting the quest stage to 100 using the command . The relevant misc quest entries will be added to the Quests panel. If the first step is not working another option is to advance the quest to the next step by using the command, then the next conversation with Deb will turn the quest in.
 * Another possible workaround is waiting for the cell to reset and getting the quest once ghouls have respawned.
 * Passing all three speech checks for a higher reward (agreeing on 300 caps for the job) has no effect, if the training yard had been cleared previously. Regardless of whether the cell has reset. Clearing it again for the quest or telling Deb that it has already been cleared will only net 175 caps.