Mr Grayling said it would be a "cheaper and quicker" option rather than building a tunnel for the M25 underneath the new runway.
He indicated the decision would mean the least amount of disruption for drivers commuting along the route during construction periods.
Whilst it is still early to say whether this plan would go ahead, the Transport Secretary said: "It is a cheaper and quicker way of doing it.
"I am, of course, very concerned to make sure that, as this runway is built, it doesn't cause massive disruption on the M25, so I think this is a sensible way.
"It is a very gentle hill up which the planes would take off rather than a flat surface.
"It's what happens at very many airports around the world."
According to the airport's timeline, it is unlikely that any new runway capacity would be operational before 2025.
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West London has remained firmly divided as the decision to expand at Heathrow Airport was backed by Prime Minister Theresa May on Tuesday (October 25).
Andrew Dakers, chief executive of West London Business, said: "This is a milestone announcement for west London’s economy and the wider UK for which we have waited a long time.
"The expansion will unlock significant investment and sends a clear signal as we prepare for Brexit that West London, the UK’s second largest economic powerhouse, remains open for business."
MP for Hayes and Harlington, John McDonnell , labelled the decision "devastating", and vowed to fight for it to be reversed.
He was backed by Uxbridge and South Ruislip MP Boris Johnson and London's Mayor Sadiq Khan , who said: "A new runway at Heathrow will be devastating for air quality across London – air pollution around the airport is already above legal levels of NO2."
The Labour Mayor said City Hall will look into how best they can get involved with legal battles against the decision, despite not pledging any money towards the cause during the last Mayor's Question Time .
Mr Grayling said it would be "difficult for the people living nearby", but added: "Ultimately in politics, you have to do what's best for the whole of the United Kingdom."
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