National Highways has fully opened two new stretches of all lane running (ALR) smart motorway, including completion of a 32-mile section of the M4.
The eastern section of the M4 between junctions 3 and 8/9 has now moved to 70mph, which means that the whole scheme from junctions 3 to 12 is now fully open.
The government-owned company has also opened a small stretch of the 23-mile scheme to convert the M1 between junctions 13 and 16 to ALR.
The full opening of both schemes at the national speed limit has been delayed by the need to retrofit and calibrate stopped vehicle detection (SVD).
As Highways has reported, although National Highways said it had brought forward a programme of retrofitting SVD to ALR schemes from next March to September of this year, this meant retrospectively excluding schemes in construction, such as the M4 and M1 schemes, both of which missed the accelerated target.
Construction of both schemes also began before National Highways implemented a new standard for the spacing of places to stop in an emergency.
National Highways said that although the western section of the M4 scheme – from junction 8/9 to junction 12) was fully opened to traffic at national speed limit last year and cones and temporary signs on the eastern section had previously been removed, it was running at 60mph while systems were tested and commissioned.
The company said there is a place to stop in an emergency every 1.3 miles on average between junctions 3 and 12, which is worse than its new standard of a maximum of one mile apart and ideally every three-quarters of a mile.
National Highways said the scheme includes purpose-built 34 emergency areas, approximately one every two miles. The Transport Select Committee has called for these to be fitted on all ALR schemes at a maximum of 1.5km (approximately one mile) apart.
Mike Grant, National Highways delivery director, said: ‘All construction work is now complete on the eastern section between junctions 3 and 8/9 and with the successful calibration of the technology, including stopped vehicle detection, we are now able to restore the national speed limit.
‘A maximum 60mph limit remains in place between junctions 3 and 4 to help improve air quality in Hounslow and to smooth traffic flows into London.’
National Highways is also converting the M1 between junctions 13 and 16 to ALR, with the upgrade opening in three ‘main’ sections. The first section opened earlier this year.
This week the company opened a 4.2-mile stretch north of junction 14 part of, which is one half of the second section. It said a further 4.5-mile section to Junction 15 is set to open ‘in early 2023’.
The third section of the overall scheme, between junctions 15 and 16, began its phased opening last month, with four lanes in each direction at 60mph, and is expected to fully open by March 2023.
Again the reduced speed limit remains in place while SVD is tested, along with other technology, such as calibrating MIDAS traffic sensors for the new lane one.
A National Highways spokesperson told Highways that the overall scheme comprises 46 emergency areas, an increase of eight on the original design. This represents approximately one every mile on the 23-mile, two carriageway scheme.
