The documentary Freedom Riders begins and ends with a promotional clip for the Greyhound bus company. Shot in the 1960s, the clip — a chirpy musical number — features rows and rows of smiling faces singing the praises of riding with Greyhound as the camera pulls back to reveal the bus, winding its way down a dusty road into a dazzling sunset.

To nostalgia buffs and Mad Men aficionados, at first glance the scene must seem like a snapshot from happier, more vividly hued times, an era in which interstate travel was considered glamorous and no experience was too mundane to be chronicled in a lavish musical number. Yet the scene elicited nervous giggles from audiences in West Lecture Hall during the film’s screening Monday, for one simple reason: Despite the utopian model for bus travel set forth by the beaming Greyhound riders, there was nary a face of color amongst the bus riders.

Directed by Emmy winner and 2002 MacArthur Fellow Stanley Nelson, Freedom Riders illuminates the faces not seen on the bus, offering a far bleaker snapshot of 1960s bus travel. As Nelson himself articulated in a Q&A session following his film, the opening and closing images of Freedom Riders — echoed by repeated shots of the slogan “It’s always a comfort to ride the bus” — directly challenge the reactionary sentiments of those who yearn to hearken back to simpler, happier times.

Slated to premiere on May 16 as part of PBS’s American Experience series, Freedom Riders tells the story of a group of integrated college students who, in 1961, traveled through the segregated South on interstate buses, challenging local Jim Crow laws and sparking national interest in the Civil Rights movement. The film traces the journey of the first Freedom Riders through the Deep South, a journey that ended in brutal mob riots that were sanctioned by segregationist government officials.

Clocking in at just under two hours (but “[feeling] like an hour and 59 minutes,” Nelson quipped beforehand), the expertly paced Freedom Riders uses interweaving narratives to tell the story from multiple perspectives, juxtaposing the surviving Freedom Riders’ firsthand accounts of the events with interviews from state and federal government officials.

Introduced as a “griot,” or storyteller in the West African tradition, by Chair of the African American Studies department Caroline Jackson-Smith prior to the screening, Nelson masterfully fulfills his role as compelling raconteur, relying on expert editing and breathtaking footage (some of which was culled from never-before-seen, FBI-confiscated 8 mm footage of the riots) to tell his story rather than explicit narration. A soundtrack of mostly a cappella gospel tunes beautifully underscores the action, further heightening the audience’s reaction to an already emotionally resonant story.

Nelson also adroitly navigates between his competing narratives, forcing the audience to alternate between feeling inspired by the courage of early Civil Rights heroes and betrayed by the ignorance and complacency of its government. Indeed, one of Nelson’s most effective filmmaking tactics is exploding history’s sacred cows, leveling criticism at such vaunted figures as Martin Luther King, Jr., (who refused to accompany the Freedom Riders on the grounds that their actions would ultimately “do more harm than good”) and then-Attorney General Robert Kennedy, whose insistence that “in many areas of the United States, there is no prejudice whatsoever” drew ironic chuckles from the crowd during one particularly condemning scene.

Most of the film’s ire, however, is reserved for former Alabama governor John Patterson, a proponent of segregationism whose refusal to provide police protection for the Freedom Riders in Birmingham resulted in their brutal beatings, disturbingly represented in the film by close-ups of clubs in fists and sound effects of angry, violent mobs. While many viewers of the film are perplexed by Patterson’s agreement to be interviewed for Freedom Riders, Nelson explained in the post-screening Q&A that Patterson may have “wanted to confess in the same way that people confess to crimes,” citing a deleted scene of Patterson defending his actions by stating that he was up for reelection as evidence of the governor’s repentance.

Ultimately, however, the frustration and ire provoked by the film’s representation of historical atrocities yield to more lingering themes of hope and righteous indignation, with the words of the surviving Freedom Riders serving as a call to arms for audience members to rise up against injustice. “It was like a wave, or wind — you didn’t know where it was going, but you knew you had to be there,” a former Freedom Rider says towards the end of the film, comparing the act of non-violent protest to “putting yeast in bread … like a leavening.”

In light of more urgent trespasses against our individual liberties, it was hard not to leave the film feeling compelled towards revolution, or similarly “leavened.” Jackson-Smith’s post-show comments made this urgency more explicit by drawing comparisons between the Civil Rights movement and protests against the recent House bill slashing public programming, arguing that the legislation represents a “new landscape of struggle.” Nelson (whose film was funded by the National Endowment for the Humanities, which also fell prey to the bill) agreed with this sentiment, warning young people that “history is not this upward movement like we think it is. … If we don’t keep struggling, we’ll slip back down.”

While the success of the Tea Party, the reemergence of the musical and the popularity of Mad Menmay point to a downward-sliding cultural climate (or at least, in the case of Mad Men, a culture of ill-advised nostalgia), what Freedom Riders does most admirably is gently point us in the direction back upwards. Contradictory to what the Greyhound bus slogan tells us in the film’s parting moments, it’s never a comfort to travel. But travel we must, and at least we can find comfort in the fact that there were others trudging down the dusty roads before us.