The M6 northbound is closed in both directions between junctions J14 and J15, due to a serious accident, the Highways Agency have said.
Northbound traffic is being diverted leaving at J14 and rejoining J15 following the 'Hollow Triangle' symbol signed diversion, via the A34 and A500.
The road expected to re-open from 5:30 pm.
The M1 is closed in both directions near Watford in Hertfordshire due to a serious road traffic collision, the Highways Agency has said.
The northbound carriageway is closed between junctions J1 and J5
The southbound carriageway is closed between junctions J5 and J4
Motorists have been advised that the closures are likely to be in place through the morning peak period and to consider alternative routes for their journeys into London or to delay where possible.
Transport Secretary Justine Greening has told ITV News that the repair work done on London's M4 motorway has been "significant", as the city prepares for the London 2012 Games this month. The M4 was closed last week after a crack was found in a "sensitive" area.
Labour MP John Woodcock described the reopening the M4 motorway in London today as a a "huge relief", but said ministers needed to come out and confirm they were totally happy that the road is safe to use.
The Shadow Transport Minister told BBC Breakfast: "The whole country wants the Olympics to be a huge success so it is a huge relief that the road is open because of the chaos it would have caused with athletes arriving on Monday to travel to the Olympic Village."
"Given the scale of the problem, ministers need to come out and say they are completely confident the crack is fixed."
The Highways Agency have said in a statement:
The road, which is expected to be one of the busiest routes during the Olympic Games, was shut last Friday between junctions 2 and 3 after cracks were discovered on a viaduct.
But it was reopened to traffic just after 5.30am after engineers completed the "complex" repairs, officials said.
The works to the bridge supports of the Boston Manor Viaduct were due to be completed yesterday.
The Highways Agency has confirmed that the M4 has been re-opened.
There are still weight restrictions.
The BBC are reporting that the M4 has re-opened between junction 2 and 3. The motorway had been closed after cracks found in a bridge.
Repair work on the M4 in west London, the main route from Heathrow to the capital, is progressing well and the motorway should open in the next few days, the Highways Agency said tonight.
Downing Street revealed this afternoon that David Cameron is taking "very close interest" in the M4 maintenance works.
Downing Street has revealed that David Cameron is taking "very close interest" in the M4 maintenance works. He is focused on it.
"The PM wants the M4 to be repaired as soon as possible," they say, adding that he is getting regular updates on the the progress.