Jamie Chadwick completes W Series title double

Ricciardo takes Earnhardt Sr.'s car for a spin ahead of US GP (0:41)

Daniel Ricciardo drives Dale Earnhardt Sr.'s 1984 Chevrolet Monte Carlo at the Circuit of the Americas. (0:41)

Britain's Jamie Chadwick retained her W Series title on Sunday after winning back-to-back races at Austin's Circuit of the Americas.

The 23-year-old earned a $500,000 prize for the winner of the all-female single-seater series and collected 15 points towards a Formula One super-licence.

Drivers need 40 points to race in Formula One but Chadwick now has the 25 that allow her to take part in Friday practice.

She already had 10 from finishing fourth in last year's Asian F3 championship.

Chadwick and compatriot Alice Powell had arrived in Texas level on 109 points, but with the latter leading 3-2 on wins.

The Williams F1 development driver won Saturday's first race to go 10 clear and on Sunday led every lap from pole position, with Powell finishing sixth.

The races in Texas were on the U.S. Grand Prix support programme and marked the first time the Formula Three level series had ventured outside Europe. All eight races this year were on the F1 undercard.

Chadwick took her first title in 2019, with the series cancelled last year due to the COVID-19 pandemic.

W Series is aimed at helping women climb the motorsport ladder to Formula One, which has not had a female race driver since Italian Lella Lombardi in 1976.

Chadwick will be able to race in W Series again next year but only without being eligible for further super-licence points.