Transport officials have drawn up an on-road cycle lane running from Henderson Road in Eastney to South Parade Pier. But to keep cyclists safe, diagonal parking on the road will be removed and normal parking will be put in its place – leaving 150 fewer spaces.
The plan is a response to a long-running controversy about whether cyclists should get a route along the promenade, along the road, or none at all.
City leaders say the 354 spaces left will still be ample parking – and Southsea Common can be used for overflow.
But the controversial decision has sparked outrage from people keen to protect the common – and parking spaces.
Tory councillor Linda Symes, ward councillor for St Jude in Southsea, said: 'I'm horrified that the Common is being considered as nothing more than an overflow car park. We should be trying to reduce car parking on the Common to allow people to enjoy a wonderful local amenity.'
The scheme will cost £200,000 and work is set to be carried out next March – at the same time as planned resurfacing works by road contractors Colas.
The plans will see a raised kerb between cyclists and parked cars.
Lib Dem council leader Gerald Vernon-Jackson had already ruled out a cycle lane on the promenade despite a public opinion survey in favour of it.
He said: 'It's on the road because a lot of people think cycling on the promenade is dangerous – particularly disabled people or the elderly or people with small families.
'We did a survey on a busy weekend to see how many spaces there were and there were still spaces available.'
Councillor Lynne Stagg, who is in charge of traffic and transport, added: 'I've got sympathy with people who want to preserve the Common and I do agree, but it's just one small area of the common and only for 17 days a year.
'We have to discourage people from bringing their cars to the seafront - we need to get cars off the road because of climate change.'
Cyclists have welcomed the move, which is meant to be the first stage of a new route running along the whole seafront.
But no plans are yet in the pipeline for the second phase, from South Parade Pier to Clarence Pier.
John Holland, chairman of Portsmouth Cycle Forum, said: 'We welcome the plans and look forward to them being implemented as soon as possible – hopefully in time for next summer.
'It's good to see the safety improvements as a result of the removal of the echelon parking – and we look forward to phase two.'

A cycle lane running alongside parked cars in Twyford Avenue, Stamshaw
COMMITMENTPortsmouth's Cycling Strategy includes a commitment to provide a cycle route along the seafront.
It would complete National Cycle Network, Route 2, which is a long distance cycle route which will link Dover in Kent with St Austell in Cornwall when it is complete.
It is sometimes referred to as the South Coast Cycle Route.
It is fully open and signed between Dover and Brighton, but is still under development between Brighton and St Austell.
Portsmouth has also promised to increase the number of cyclists in the city by four per cent by 2010 in a bid to tackle obesity and health problems.
ANOTHER TWIST IN THE GREAT CYCLING DEBATE
Sketch by Alex ForsythSo the great seafront cycle debate has taken another twist.
First, the pedestrians fought off hordes of riders threatening to descend on the promenade – with a little help from team coach Gerald Vernon-Jackson.
Then the Lib Dem leader back-pedalled after an opinion poll showed support for the idea of a prom cycle lane and loudly declared: 'It's too dangerous.'
So now it's motorists who look set to be saddled with the cycling problem.
A safe on-road route? Fine – at the expense of parking spaces in one of the most popular parts of the city.
And where can motorists park instead? Why Southsea Common of course, a much-loved open space. Clad in her yellow jersey, cycle supporter Councillor Lynne Stagg is out in front.
She wanted riders on the prom, but now her Tour de Southsea will see bikes on safe road routes and cars be damned. But could it be that someone is cleverly steering this seafront cycle twister from behind the scenes?
If you make the solution controversial enough, suddenly the option of doing nothing looks more attractive.
And perhaps when it comes to the crunch, cyclists will be told to get on their bikes after all.
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