"Gridlock" completes a loose trilogy that began with "The End of the World" and "New Earth" (2006), and contains hints at the series' story arc.

The Tenth Doctor takes Martha to an alleyway in the city-state of New New York on New Earth where street vendors are selling addictive mood drugs in the form of sticky patches to help people deal with their emotions.

The Doctor chases after Martha's kidnappers and arrives at the Motorway, a completely enclosed highway filled with thousands of hover vans stuck in gridlock.

[2] Head writer and executive producer Russell T Davies wanted to visit the same world each year to maintain a sense of continuity, something that could be hard to do with Doctor Who's formula.

[1] Producer Phil Collinson remarked that "Gridlock" displayed Davies' tendency to write about "topical" issues; it is set in a dark dystopian future, but is also a satire on the common traffic jam.

[3] The episode also displays the Doctor's growing attachment to Martha; he feels guilty for lying to her and bringing her to New New York just to show off and realises that he misses her when she is taken.

[4] Also in the online commentary, Davies noted that Brannigan's appearance was based on "Ratz", the CGI disembodied cat's head that was a "virtual presenter" of CBBC's Live & Kicking in the early 1990s.

[4] Ma and Pa at the start of the episode are based on the farming couple in the painting American Gothic, both having identical hairstyles, glasses and fashions.

[1] "Gridlock" also contains important hints about the story arc of the series as it reveals the "great secret" promised to the Doctor by the Face of Boe in "New Earth" – "You are not alone".

[1] Will Cohen, The Mill's Visual FX Producer, revealed in Radio Times that the films Blade Runner, The Fifth Element and Star Wars, specifically the planet of Coruscant influenced the look of New New York.

[1] The production team shot for four days in the "6-foot by 6-foot" car, which Davies called a "nightmare" because not many camera angles were available and only one crew member could adjust the props and lighting at a time.

[11] The undercity where the Doctor and Martha arrive was filmed at the Cardiff Bay maltings and the Ely Papermill,[citation needed] which were designed to look in disrepair.

He praised the attention to detail of the props department, the appearance of the Macra, and the concept of the traffic jam, but felt there were many plot holes.

[16] Mark Wright of The Stage was positive towards calling back to "The End of the World" and "New Earth", and praised Agyeman and the visual look of the episode.

Despite finding the ending "life-affirming", he found a possible plot hole: "one wonders why the Face of Boe didn't just open the roof in the first place".

He stated that the "fun, fast-paced story with lots of comedic set pieces" worked to its advantage, and the appearance of the Macra was a "treat" for long-time fans.

[19] Despite the popularity of the later series episodes "Human Nature"/"The Family of Blood" and "Blink", Burk felt that "Gridlock" was the "worthiest candidate for this season's best story".