MOTORISTS will have to endure 16 months of traffic chaos when £79m plans to reduce congestion on two M27 bottlenecks get under way next week.

Speed limits on two major stretches - junctions three to four and junctions 11 to 12 - along the motorway connecting Southampton to Portsmouth will be reduced to 50mph.

More than 100,000 drivers who use the road every day have also been warned there will speed cameras to catch anyone who breaks the reduced limit.

Highway bosses say the multi-million-pound schemes will ease frustrating snarl-ups during the morning and evening rush hours.

Work will begin on widening the 1.24-mile (2km) stretch between junction 11, at Fareham, and junction 12, at Portsmouth, next Saturday.

An extra lane will be made in each direction for cars to overtake slow-moving lorries on the hill between the busy junctions.

A Highways Agency spokesman said the climbing lanes, as well as new safety barriers, lighting and drainage will ease snarl-ups on the road which carries 110,000 vehicles a day.

"The main construction work will commence on January 19, which will involve installing the traffic management and 50mph speed restriction, regulated by average speed safety cameras for the safety of road users and road workers," he said.

"There will be minor delays of around ten minutes due to the 50mph limit."

It is expected work on the £27m project will finish in October.

To the west, work on widening the motorway between junction three, at the M271, and junction four, the interchange with the M3, will begin in the middle of next month.

The 2.5-mile stretch (4km) - which carries 121,000 vehicles a day - will be widened in both directions from three to four lanes.

As well as the lower 50mph speed limit, the motorway will be closed for construction on 12 Saturday nights between 10pm and 6am for installation of new gantries.

During the closure of the carriageway, traffic will be diverted at junction three to Chilworth roundabout to either join the M3 or the A27 and the A335 to rejoin the M27 at junction five.

A pre-construction exhibition is being held at Nursling and Rownhams Village Hall, Nursling Street, Nursling, on Friday, February 1, between 12.30am and 8pm and Saturday, February 2, between 10am and 4pm.