Inspirations: Gridlock

According to Russell T Davies, one inspiration for Gridlock was childhood memories of being stuck in traffic jams (the same ones where he first had the image of the TARDIS swooping down from the skies over a motorway, which would see light of day in The Runaway Bride).

Another inspiration was the 2000AD comic strip Judge Dredd, with its setting of Mega-City One (a futuristic version of New York).

New New York had been seen in the Series 2 opener New Earth, but the Doctor hadn't actually visited the city. He and Rose had looked at it from a distance, before having an adventure in the self-contained environment of the hospital, which was physically divorced from the rest of New New York.

RTD wanted to get into the city itself, and envisioned the action taking place on three different levels - the subterranean motorway, the ground level Pharmacy Town, and up amongst the vast towers and skyscrapers.

For the latter, RTD specifically gave Coruscant as a visual reference for the VFX designers. This is the planet-spanning city seen as the centre of the Republic, and then of the Empire in the Star Wars franchise. It first appeared in The Phantom Menace (1999). Blade Runner (1982) and The Fifth Element (1997) were also given as visual cues.

In the same way that New Earth was only a loose sequel to The End of the World, so Gridlock would only take some elements of the previous two episodes. As well as the setting, it would feature the Face of Boe once again, and the character of Novice Hame, who RTD had wanted to see more of.

This episode therefore forms the final part of a rough trilogy - known by fans as either the 'Face of Boe Trilogy' or the 'Year 5 Billion Trilogy'.

In creating this trio, RTD was adding to Doctor Who's mythology. Such a thing hadn't really existed in the classic series, other than with the developing Time Lord mythos. Producer Barry Letts had overseen some continuity during his tenure - with the Earth Empire and the Federation, including two visits to the planet Peladon. Note also how many Troughton stories are set in the 21st Century.

RTD wanted his new version of the show to have recognisable settings when away from contemporary Earth, with a sense of continuity in the stories set there. It is notable that many stories are set in the same time zones - the 42nd and 51st Centuries, for instance. This included Torchwood as well, and was continued by Steven Moffat when he took over.

RTD had originally intended the Face of Boe to have died at the conclusion of New Earth, when its message to the Doctor that he was not alone would have been imparted. This was put back when it became known that a third series was guaranteed. RTD had actually already used some of this in the 2006 Doctor Who Annual - written 2005 - where an ancient carving on a rock face had the words "You Are Not Alone" on it.

Brannigan was inspired by a CGI character from Children's BBC - Ratz - who provided links between programmes. He appeared as the floating head of a ginger tom wearing a flying hat, goggles and scarf. He also featured in Saturday morning show Live & Kicking, alongside a certain presenter named John Barrowman...

The bowler-hatted driver in the final car was another Judge Dredd inspiration - a character named Max Normal, who is one of Dredd's informants.

The old man and woman (Ma and Pa) who are attacked in the pre-credits sequence derive from the 1930 artwork American Gothic, by artist Grant Wood. It had also provided inspiration for a scene in The Rocky Horror Picture Show (1975) and episodes of  SpongeBob SquarePants and The Simpsons.

For a monster, RTD considered something from the oceans as New New York had been seen to be sited on a peninsula overlooking the sea. He reasoned that some sort of sea monster would have broken into the motorway tunnels and considered a dinosaur such as those seen in The Beast From 20,000 Fathoms (1953) or Godzilla (1954), or perhaps a giant octopus, such as that from It Came From Beneath The Sea (1955). He eventually settled on giant crabs and, being a fan, recalled that there was a ready-made crab monster in Doctor Who in the form of the Macra.

This just happened to tie in with the idea that an enclosed motorway would be full of noxious gases: the Macra had fed on poisonous gas in their one and only previous outing, 1967's The Macra Terror.

Their presence in the motorway was explained using the urban myth that the sewers of New York are full of alligators which were flushed down toilets when they grew too big for their owners to handle.

RTD reasoned that these Macra escaped from the zoo when the Bliss virus hit the city.

The mood drugs of Pharmacy Town came from a Ninth Doctor novel - Only Human, by Gareth Roberts.

The Doctor's description of Gallifrey comes wholesale from Susan speaking to the First Elder in 1964's The Sensorites.

Two hymns are heard in the story. The Old Rugged Cross is a 1912 gospel song by George Bennard, and Abide With Me dates to 1847 (words by Henry Lyte, tune by William Monk).

The Doctor claims his distinctive long coat was given him by Janis Joplin. Joplin was a rock star who died in October 1970, aged 27. Alcohol and heroin were found in her system.

Next time: from a mention of Daleks in New New York to actual Daleks in the real New York...