The scheduled start of Free Practice 1 was delayed by 40 minutes by the unexpected arrival of dense fog over the Circuit of the Americas in the unusually cold early morning.

The 90 minute session had been expected to get underway at 9am local time (3pm GMT) but as the time approached the fog only grew heavier, forcing officials - including race director Charlie Whiting - to delay the start of the session.

They initially placed the track under an indefinite red flag until the visibility improved, but the red flag was quickly withdrawn with race control then issuing updates every ten minutes regarding the state of the track and the likelihood of getting the session underway, while the sun got to work burning through the fog cover.

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The main problem for the race officials is that in such limited visibility, the medical helicopter would have been unavailable in the event of a serious accident that required a driver to be airlifted to hospital, making the fog a potentially serious safety matter.

The track finally went green at 9.40am local time, but the session length was reduced to 60 minutes. That meant that despite the chilly conditions, teams were quick to send their cars out for installation laps as they got to work on their morning test and development programs.

However a new red flag was shown 15 minutes into the curtailed session, seemingly again a result of the absence of a medical helicopter at the track.

The session saw Heikki Kovalainen get his first run in the Lotus replacing Kimi Raikkonen, who has been having back surgery in Strasbourg. Raikkonen's 2014 team mate mate Fernando Alonso has also been suffering from back pain in the last two weeks since Abu Dhabi after a high speed off that took him over some aggressive kerbing at the Yas Marina Circuit, but the Spaniard has been passed fit and cleared to race this weekend.

FP1 saw three test and reserve drivers in action, with Rodolfo Gonz?lez replacing Jules Bianchi at Marussia and Alexander Rossi getting a home outing at Caterham in place of regular driver Giedo van der Garde.

The session also saw the F1 Grand Prix weekend d?but for GP3 champion Daniil Kvyat, who has successfully qualified for his superlicence and will now make his first laps in the Scuderia Toro Rosso that will be his office for 2014. Kvyat's team mate next year, Jean-Eric Vergne, is the man who will step aside for him for today's FP1 session.