One involves widening 67 miles of Britain's busiest motorway, the M25, from three lanes to four – a scheme that could take a decade to complete.
The other is for improvements to the M1, including the widening of a 50-mile stretch from three to four lanes between junctions 21 to 30 and a bypass through Kegworth, east Midlands.
Combined, the cost of the programmes will exceed £3.5 billion. The M25 work, which would start in 2006, is in addition to the widening of five lanes now under way to the west of London near Heathrow.
A spokesman at the Highways Agency, which is responsible for major roads in England, explained the Government's plans for the M25.
He said: 'We propose to widen almost all of the current dual three lane sections to four lanes in each direction, except between Junction 3 (M20) and Junction 5 (M26) and at a number of junctions.
The proposed widening will cover about 67 miles and will generally be within the boundaries of the existing motorway. Our aim is to tackle congestion on London's orbital motorway and improve safety and journey times for traffic.'
By upgrading the motorway network, the Government is hoping to eventually slash journey times and eliminate congestion.
Archie Robertson, chief executive of the Highways Agency, said: 'These plans will enable road users to enjoy safer and less congested journeys when these schemes are completed.
'Upgrades on these vital routes will tackle congestion on the M25 and M1, improving journey time reliability for road users and supporting economic growth.'
Before fully implementing the schemes, the Government is to assess the impact the roadworks will have on local areas.
Robertson explained: 'The agency will now develop the design, programming and procurement arrangements for the schemes.
During design, we will be investigating any impact on the landscapes and communities that might be affected by the works. Specific issues such as lighting, noise, air quality will be carefully considered, along with appropriate mitigation measures.'