US Grand Prix listed as provisional on 2016 Formula 1 calendar
The 2016 United States Grand Prix has been listed as provisional on a record 21-race calendar confirmed by Formula 1's governing body the FIA.
The Austin race is in doubt because of a 20% cut in Texas state funding.
Meanwhile, FIA president Jean Todt and commercial boss Bernie Ecclestone have been given a mandate to make changes on "pressing issues".
The FIA has also allowed in-season engine development and increased tyre choices for next season.
A record calendar
The longest season in the history of F1 starts in Australia on 20 March and features a new race in the Azerbaijan capital Baku on 19 June.
The Mexican Grand Prix has been moved forward seven days to 30 October, a week after Austin.
Among other changes from this year, the Russian Grand Prix moves from October to 1 May, with Malaysia moving from its previous slot after Australia to 2 October.
The British Grand Prix is on 10 July.
The FIA World Council has taken the unusual step of giving Todt and Ecclestone the right to "make recommendations and decisions regarding a number of pressing issues in F1 such as governance, power units and cost reduction".
This move follows the rejection of a plan by the pair to introduce a low-cost 'alternative engine', after opposition from Mercedes and Ferrari.
F1's two bosses are locked in a fight with the major teams over power and control of the sport, with engines the main battle ground.
Ecclestone wants to re-establish his authority, while Todt's main aim so far has been to persuade the engine manufacturers to lower the cost of the power-units they supply to customers.
A statement by the FIA said Todt and Ecclestone had "expressed their intention to establish conclusions on these matters by 31 January 2016".
That is two weeks after the engine manufacturers have agreed to present a proposal on engines, including ways to reduce costs, increase availability and simplify their design.
Big engine rule changes
Major steps have been made by the FIA to free up engine development in an attempt to allow rival companies to catch up with the dominant Mercedes team.
All manufacturers will have 32 development 'tokens' available next season, ascribed to parts of the engine depending on their influence on performance. That is an increase from the previous number of 25 for next year.
The amount of tokens available in succeeding years has also been increased, to 25 in 2017, 20 in 2018 and 15 in 2019.
The rules governing potential new entrants have also changed.
Honda had to fight to be allowed only nine tokens in its first season this year and was scheduled to then move into step with the restrictions on its three rivals, Mercedes, Ferrari and Renault, all of whom have had one more year's racing with their engines.
But now any new manufacturer will be allowed 15 tokens in its first season, and then 32, 25 and so on in succeeding years.
In another change to the engine rules, manufacturers will now be allowed to supply more than one specification of engines to customers.
The FIA has agreed to allow Ferrari make a supply of 2015 engines to a team which it did not specify, but which is known to be the Red Bull junior team Toro Rosso.
More tyre freedom
Teams will be allowed to choose from three tyre types at each race next year, compared to the current two.
This is an attempt to introduce more strategic variety and uncertainty into the races.
Teams will still have to use at least two different types in each race, unless there is wet weather.