US GP: F1 drivers pleased with virtual safety car trial

The FIA ran two tests of the new concept at the end of each of the two Friday free practice sessions at the United States Grand Prix.

It has come as a response to the lessons learned from Jules Bianchi's horrific crash at the Japanese GP, when he ran off the circuit under double yellow flag conditions and struck a recovery vehicle.

At Austin, a sector of the track was deemed to be yellow and drivers had to drive to a specific delta time through it.

The aim of the concept is to slow drivers down without recourse to a safety car.

Although all drivers and the FIA agree that tweaks will be needed before the system can be introduced fully, they were happy with how the first tests had gone.

Sebastian Vettel said: "I think I had a short glimpse at the end there. It does what it is supposed to do. It needs some finetuning, but it works."

Romain Grosjean said that one of the issues that needed perfecting was making it obvious to drivers how slow they needed to be.

The Frenchman said he found it difficult to keep to the delta time during the afternoon test.

"It was very, very difficult," he said. "The delta time goes plus nine tenths, minus six tenths, plus three, then minus two.

"I found it very difficult to follow how you have to open a bigger gap, like two or three seconds, but when it goes green it's lost.

"I only did it in FP2, so I didn't have much training in it, but I found it quite hard."

But Pastor Maldonado said the use of audio tones to inform drivers if they were going too fast meant it was no problem for him to judge his speed.

"You get a dashboard display that you need to follow if you are plus and you are on the target, or you have a tone in the earpieces if you need to drop a little bit.

"It's very easy. If you are plus it's OK and if you are up you just slow down so it is very easy to manage."

The FIA will assess the feedback from Austin and will likely continue testing the system over the final races of this year.