Felipe Massa has labelled a trial of the so-called 'Virtual Safety Car' as a positive step forward for F1 in its efforts to reduce the risk to drivers following Jules Bianchi's accident in the Japanese Grand Prix.

Free practice for the United States Grand Prix saw the FIA trial a new 'speed control' format that sees drivers receive a safety car delta when the "Virtual Safety Car" is deployed.

Drivers must then drive within that time - approximately 35% of race speed - until green flag conditions, with failure to do so resulting in a penalty.

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The trial comes as the FIA considers ways to improve safety following Bianchi's crash in Suzuka when he spun in wet conditions and struck a recovery vehicle. Almost a month on from the accident, Bianchi remains in hospital with serious head injuries.

With this in mind, Massa - who was a staunch critic of race direction's decision to continue racing in the treacherous conditions of the Suzuka race -, feels there is potential in the format.

"I think it's positive, definitely," he said. "Whatever it is they are doing to slow down the cars in a difficult situation, in the difficult weather is positive. It is a difficult thing they need to improve looking at what happened in Japan."

McLaren-Mercedes' Jenson Button also felt there are good points to the system, but admits it is a tricky balancing act for drivers to reduce their speed without losing time to rivals.

"It is very, very tricky," he said "I think when you are wheel-to-wheel and the system comes on, you can't just hit the brakes like we are now to get the speed down. I like the idea but you do spend the whole time looking at the steering wheel.

"With the way the safety car boards are now and the lap we do without the safety car, you can dip below the time and get away with it, because so long as you cross the line as positive you're OK.

"With this system you have to stay positive, but you want to be as close to zero as possible because you could lose two seconds to the car in front. If you drop below and the restart happens, you get a 10secs penalty."

The Virtual Safety Car format won't be used for this weekend's United States Grand Prix, but the trial may determine whether it is used in future races.