Exactly why drivers are facing 16 months of disruption on the busy Penryn bypass has been revealed.

On Tuesday the Packet reported how a speed restriction is to be put in place on the entire stretch of the A39 between Antron Hill at Mabe and Union Road, off the Hillhead Roundabout to Falmouth, starting in less than a fortnight.

Now the reason why motorists will be slowed to 40mph for almost a year and a half has been explained by the company involved.

South West Water said it was due to a £10.5 million upgrade to College Water Treatment Works, which supplies Falmouth and the surrounding area.

A South West Water spokesperson said: “As part of the project we are installing new granular activated carbon filters at the works, which remove natural and manmade organic matter sometimes present in Argal and College reservoirs, which supply the treatment works.

“We are also making some modifications to the works to increase its capacity.

“Normal access to the treatment works is through a nearby residential area. The use of these roads by a large number of construction vehicles would have a negative impact on the residents and small businesses in that area. “For that reason, we have agreed a temporary access with the highways authority and to ensure vehicles can access the site safely a temporary speed restriction will be in place during the project.”

Motorists have been warned that long delays are likely during the period of work, which is scheduled to begin in less than two weeks, on Monday, May 27, and not end until September 27, 2020.

Between these dates a 40mph speed limit will be in place, 24 hours a day, including at weekends.

It is yet more disruption for weary motorists, who over the last 18 months have faced regular delays in this area due to the construction of first the Persimmons Homes development opposite Falmouth Town Football Club, which resulted in eight months of traffic lights at Union Hill Corner that only came down just before Christmas.

This was followed by the construction of the business park further along Bickland Water Road and most recently the Chy An Dowr housing development opposite Mongleath Road, for which three-way traffic lights were installed for many weeks.