The Highways Agency has launched a consultation today to discuss the speed limit on a part of the M3 in Surrey for London commuters.
Rush-hour traffic slows to an average 45mph on the busy route in the morning and an average of 56mph in the evening.
The planned £174 million upgrade will transform a 13.4 mile stretch into a 'smart motorway' by adding an extra lane in both directions between Junction 2 and 4a.
This will increase capacity, reduce congestion and boost average speeds for motorists to cut 4 minutes per vehicle from a morning commute.
Due to the capacity increase however, emissions from the extra traffic are predicted to breach local air quality limits on a short selection of the route, unless it's limited to 60mph during certain times of the day.
Roads Minister Robert Goodwill said:
Variable speed limits on our motorways are nothing new and have been used for many years to cut congestion and keep vehicles moving.Introducing speed controls for air quality reasons is proposed for less than 1% of the strategic road network. Peak time speed limits on the M3 are currently below 70mph. However let’s be clear, no decisions have been taken yet but the risks need to be managed responsibly, with any proposed limit removed as soon as air quality levels improve.