Like a protracted trek on Route 66 — whose John Steinbeck-endowed nickname supplies the title — “Mother Road” is ambitious, unwieldy, conspicuously significant and uncomfortably long. But this play, a sequel to “The Grapes of Wrath,” does boast humor. Preparing to drive from California to Oklahoma in his Dodge pickup, the play’s Mexican American protagonist, Martín Jodes, tells his travel companion William Joad that the truck’s name is Cesar.

“As in the labor leader?” William asks.

“No,” Martín shoots back sarcastically, “the salad.”

Martín’s zinger lands with snap in director Bill Rauch’s burnished and powerfully acted production, now running at Arena Stage after originating at the Oregon Shakespeare Festival. But other aspects of this work by Octavio Solis (“El Paso Blue”) are less satisfying. Through the lens of Martín and William’s present-day road trip, “Mother Road” aptly ponders looming current concerns, including racism, immigration, economic inequality and environmental crisis, issues that both echo and diverge from the realities captured in Steinbeck’s 1930s-set novel. But the play’s episodic structure creates diffuseness, certain plot twists are strained, some psychological epiphanies are too tidy, and the narrative treads an uneasy tightrope between realism and symbolism.

At the start, William (a persuasively crusty Mark Murphey) seeks an heir for his Oklahoma farm. Akin to the Joad family seen fleeing the Dust Bowl in “Grapes,” William finds his relative Martín (a vibrant Tony Sancho), a sometime migrant worker. After a testy first meeting that recalls an odd-couple buddy movie, the men set off for the Sooner State, connecting en route with migrant worker Mo (Amy Lizardo, irresistible), whose ebullience generates delightful comedy. After the group picks up others, including James (Cedric Lamar), an African American farmer of a mystical bent, the journey begins to seem less a naturalistic story arc than a high-concept, if admittedly heartwarming, vision of healing the nation through diversity.

Solis seeds the script with poetry, including a chorus’s incantatory lines conjuring up Southwestern vistas, glimpses of ­migrant-worker hardship and more. In Rauch’s lively production, which deftly sinews the in-the-round Fichandler Stage, chorus members execute resonant stylized movement and also take cameos, such as a diner cook and waitress (Lamar and Kate Mulligan). They also embody inanimate objects, donning antennae to depict a motel TV, for instance; it’s a device that adds humor while fittingly evoking a haunted landscape. (Jaclyn Miller is movement consultant. Paul James Prendergast created the original music and sound design, which encompasses stirring chorus song.)

William and Martín are haunted, too. In a not very convincing scene that strains to riff on “Grapes,” the fundamentally reasonable William lashes out at the waitress, an ex-Okie, for romanticizing the Dust Bowl migration. Afterward, the cook consoles her: “They’re just strangers passing through.”

Mother Road by Octavio Solis. Directed by Bill Rauch; set designer, Christopher Acebo; costumes, Carolyn Mazuca; lighting, Pablo Santiago; projections, Kaitlyn Pietras; fight director, U. Jonathan Toppo; associate director, Kareem Fahmy. With David Anzuelo, Natalie Camunas, Ted Deasy and Derek Garza. 2 hours and 40 minutes. Tickets: $41-95 (subject to change). Through March 8 at Arena Stage, 1101 Sixth St. SW. 202-488-3300. arenastage.org.