The recommended highway network in the Final Report of the North East Lancashire Project Study (NELPS), published in 1969, included a 'Fast Route' as its backbone. From the intersection of the M6 and the M61 the proposed route for a dual three-lane motorway ran eastwards to the heart of Blackburn to be integrated into the future plans for the town. Beyond the town centre it passed through to Whitebirk, and further east, along the Calder Valley as far as Colne.

In 1972, the firm of Consulting Engineers, of Howard Humphreys and Partners, was appointed to carry out the design of the route between Riley Green and Whitebirk, which included the section through Blackburn. The Lancashire Sub-Unit of the North Western Road Construction Unit (NWRCU) assumed responsibility for the detailed design of both the section between M6/M61 and Riley Green, and that from Whitebirk to Burnley.

It was intended that the preparation, design, statutory procedures, and construction would be completed by 1978, but this optimistic programme did not reckon with the implications of new requirements for public participation in road planning. It was decided, therefore, by the Department of the Environment, that there should be extensive Public Consultation into a number of possible routes, between M6/M61 and Hyndburn.

Of the six routes examined, the Sub-Unit carried out the initial route location and assessment for four of them, identified by the colours, Red, Yellow, Purple and Green. The Consulting Engineers concentrated on the complex Blue and Brown routes passing through Blackburn Town Centre. Whereas, it was intended that four of the routes would be constructed to motorway standard, the Yellow and Green routes would be all-purpose roads only.

The first of its kind in the UK, the Consultation Exercise, which took place in Spring 1975, involved the distribution of several thousand copies of a document inviting participants to complete a Questionnaire commenting on the alternatives. An exhibition was held for several days at six different locations.

The County Council as the local Highway Authority, together with all the District Councils in North East Lancashire, except Blackburn Borough Council, supported the motorway standard Brown route. It was feared, however, that the majority of the members of the public would opt for the Green route, as it affected the least number of properties and avoided the urban parts of Blackburn.

The Secretary of State did not announce his decision that the all-purpose Green route had been selected until the Autumn of 1977. This route to the south of Blackburn had been rejected in the NELPS at an early stage, and did not feature in the Report of the Study. With a relatively low economic rate of return, the scheme was removed from the National Roads Programme in 1980, when design work was suspended.

Strong representations continued to be made against these decisions, which culminated, in late 1983, in a major deputation to the Minister of State for Transport led by the County Council and supported by Members of Parliament, and representatives of all the local authorities in North East Lancashire. By that time sections of the Calder Valley Route beyond Whitebirk had already been completed or were under construction to motorway standard.

In 1984, the Secretary of State accepted the case that had been made and, in due course, design work was resumed for a motorway standard road on an alignment similar to the Green route. With the abolition of the Sub-Unit, Howard Humphreys and Partners assumed design responsibility for the whole of the section, which became known as the Blackburn Southern By-pass.

Detailed design work began in 1989 for the 13 mile long route, and Public Inquiries were held in February 1990 and November 1991.

The section of motorway was to have mainly dual two-lane carriageways, with some sections to be constructed with three-lane carriageways. All the structures were, however, to be designed to allow for future widening without alteration.

There were to be two major three-level interchanges connecting with the M6 and the M61, and a free-flowing junction with the completed section of the M65 to the east of Whitebirk. Of the four other junctions providing links to major roads, three were to be located on radial routes to the southwest and south of Blackburn. It was envisaged that the improvement in communications would enhance the opportunities for developing major industrial sites on the southern periphery of Blackburn, and in nearby Darwen.

The works were to be undertaken under two main construction contracts to the west and east of Stanworth, starting in March 1994 and March 1995 respectively. However, alterations to public utility services were carried out under advance contracts involving major items such as the Thirlmere Aqueduct, and 440kV National Grid and other high voltage overhead lines.

In an area where there had been no malicious objection to the motorway, the arrival of 'protestors' at the start of the first main contract affected progress. They established bases in abandoned buildings and trees, and caused delay and disruption to both contracts. The provision of security guards also involved considerable additional costs.

In carrying out the earthworks there was a massive shortfall of site-won filling material, with the main deficit at the eastern end of the project. In all, over 3 million cubic yards of imported fill were needed for the two contracts, the main source being a borrow pit near Brindle, which raised considerable opposition from local residents.

There were three major rock cuttings, near Stanworth Farm, at Guide, and at Stanhill. The motorway passed between a line of 440kV pylons and the listed building of Stanworth Farm. Forming the almost vertical sides of the cutting, presented a particular challenge. Elsewhere, it was necessary to cap two old mineshafts, and an ancient tramway tunnel, last used in 1850, was found while excavating a cutting.

Where the motorway passed through an area known as Earcroft an underground system of stone soughs was encountered. These carried water to nearby cotton mills and a system of thrust-bore tunnels was installed to pick-up and discharge the flow. At Feniscowles, special measures were necessary to prevent the water supply to a paper mill drawn from the River Roddlesworth from being contaminated by run-off from the motorway.

A large number of structures was required. Of the total of 46 bridges, there are four major viaducts. Two carry the motorway over the M6 and the M61, within the interchanges, and the others cross steep-sided valleys. At Stanworth Woods, the spectacular 1000 feet long structure is over 100 feet above the valley floor. It was incrementally launched by the Contractor in order to reduce the damage to trees in the valley below. In addition to a further 15 underbridges, there are 20 overbridges, one of which carries the Blackburn-Manchester railway line. Of the four footbridges which were constructed, a unique lattice girder bridge at Brimmicroft carries both a public footpath and a stream over the motorway.

Throughout both the design and the carrying out of the construction, particular attention was given to environmental matters. These included the pre-contract relocation of plants, and extensive planting on the completion of the works.

In addition to the extensive use of mounding, the first use in the UK of transparent screens on two overbridges, had the effect of reducing traffic noise on adjacent property.

The Blackburn Southern By-pass section of the M65 was opened to traffic in December 1997.