Cyclists will soon be able to enjoy an uninterrupted and completely off-the-road ride into the city from Perth's northern suburbs, as plans for bridges and underpasses along the Mitchell Freeway come to fruition.

The upgrades will fill a so-called 'missing link' in Perth's Principle Shared Pathway (PSP) network and will feature a first-of-its-kind, separate cyclist-only path.

The works began this week after the first soil was turned on a $32 million project to reduce congestion on the Mitchell Freeway.

Cyclists riding to and from the city from the northern suburbs currently have to cross a number of intersections, navigate paths that are busy with pedestrians and take bridges across the freeway multiple times.

This is set to be eliminated with the introduction of a footpath bridge over the busy Scarborough Beach Road and underpasses at Hutton Street and the Hutton Street freeway ramps.

An artist's impression of the Principal Shared Path bridge over Scarborough Beach Road. ( Supplied: Main Roads WA )

Journey set to be safer and faster for cyclists

WestCycle transport and safety manager Philip Taylor said the changes had been requested by Perth cyclists.

"One of the biggest safety fears for a lot of cyclist is crossing major intersections," he said.

"Just think about the time that will be saved not having to stop and get off your bike, press the request button to cross the road.

"People are going to be saving more than 15-20 minutes I would imagine and it's going to be a lot shorter distance, because you're not having to cross the freeway back and forwards."

WestCycle said the changes and upgrades had been requested by cyclists. ( ABC News: Will Storey )

Cyclists will also now be able to avoid cars when a missing link in the PSP network is filled by a 2.1-kilometre stretch of path between Goody Close, near Glendalough Train Station, and Hutton Street.

Mr Taylor said the new paths and replacement of the old ones had been a long time coming.

"The current paths were probably built back in the '90s and they're in very poor condition, they're dated now," he said.

"The new standards are much better than they have been in previous years.

"I think that particular section at the moment has still got some old concrete.

"For people who are riding bikes, especially on thinner tyres, it's not a pleasant ride, and as it has aged, things like tree roots have lifted up the pavement."

Motorists could also benefit from the upgrades, if more people start to ride bikes. ( ABC News: Will Storey )

In a first for WA, the network between the Glendalough Station footbridge and Roberts Street will feature separated cycle-only and pedestrian-only paths.

The design will cater for high levels of pedestrian traffic around the train station which have long been an obstacle for people riding to work in the city.

The separated sections will consist of a four-metre-wide path for cyclists and a two-metre-wide path for pedestrians.

"Separated facilities exist in other parts of Western Australia's cycle network, such as the Robertson Road Cycleway in Kingsley and the recreational path along the South Perth foreshore, however the Mitchell Freeway facility will be the first-of-its-kind, building parallel separated paths to these dimensions," a Department of Transport spokeswoman said.

Shared walking and cycling sections of the upgraded and new footpaths will be four metres wide.

Construction of the paths will begin south of Glendalough Station and are set to be completed with works at Hutton Street in 2019.

Work to link another gap in the PSP on the Mitchell Freeway between Civic Place and Erindale Road is expected to begin in late 2019 or early 2020.

Freeway congestion could be cut

Mr Taylor said the improved cycle paths could also help to reduce congestion for motorists.

"If we can get a couple more hundred people riding their bikes in the morning that's just a hundred less cars on the freeway and a hundred less car parks we'll need in the city," he said.

The PSP upgrade forms part of a wider 'congestion busting' joint State and Federal project to improve traffic flows on the Mitchell and Kwinana freeways.

Cyclists riding near Glendalough Station will benefit from a separate cycle-only path. ( ABC News: Will Storey )

The Mitchell Freeway is set to be widened by one lane along a seven kilometre south bound stretch between Cedric Street and Vincent Street.

It is claimed the upgrade will reduce travel time for some morning commuters by up to nine minutes by eliminating bottlenecks created by the 180-thousand vehicles which travel the freeway daily.

Along the Kwinana Freeway, a lane will be added heading northbound for eight kilometres between Russel Road and the Roe Highway to create capacity for 1,800 vehicles an hour.

It is estimated this will reduce travel time for some commuters in Perth's south by up to 15 minutes.