Perth's road network is going through a period of major transformation with a number of freeway upgrades and extensions underway.

The $1 billion NorthLink project is building 42 kilometres of new freeway, the city's two major expressways are being widened, and there are major road upgrades in Perth's growing southern suburbs.

Road design has become more sophisticated and complex in the 66 years since the city's first traffic lights were switched on.

Seen from the air, some of Western Australia's most unique intersections are a curious tangle — ranging from engineering masterpieces to just plain confusing.

Dave Landmark, the road and traffic engineering manager at Main Roads WA, explains the way some of these interchanges came about.

Going in all directions

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 29 seconds 29 s Traffic engineer Dave Landmark says NorthLink will include Perth's first full-systems interchange.

When it opens to traffic in the weeks ahead, the NorthLink interchange in Malaga will be Perth's first high-speed, free-flowing, full-movement freeway-to-freeway interchange.

Mr Landmark said motorists would be able to turn left, right or go straight from any direction and barely have to slow down, let alone stop at a traffic light.

Dave Landmark has overseen many major projects during his 18 years at Main Roads WA. ( ABC Radio Perth: Gian De Poloni )

"There are no traffic signals at all. It caters for all movements.

"It's the interchange between two major highways and it would be what we call a full-systems interchange."

The larger NorthLink connection will allow vehicles to travel 1,800 kilometres between Port Hedland and Bunbury without being interrupted by a red light.

Loops link north and south

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 29 seconds 29 s The Narrows Interchange has been altered many times since it was built in the early 1970s.

When the Narrows Interchange was completed in the 1970s, it changed Perth's foreshore forever.

A large section of the river around Mounts Bay Road was reclaimed, providing several access points to the CBD for motorists coming from the south.

"It was a pretty impressive engineering feat," Mr Landmark said.

"You've got all these loops and strands of spaghetti, so to speak, trying to make it free flowing."

The original form of the Narrows Interchange in 1964, feeding traffic into huge city car parks. ( Supplied: Main Roads WA )

Mr Landmark said the Kwinana Freeway originally led traffic into a huge riverside car park.

"It's quite interesting that you had these massive car parks and the main focus was just to feed traffic into the car parks and into the city," he said.

"At the time, there was a lot of road building happening certainly in America and the automobile was the way to go."

The tennis ball

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 29 seconds 29 s Australia's first and only 'tennis ball' intersection is the junction of the Roe Highway and Berkshire Road.

Berkshire Road in Forrestfield is one of WA's most peculiar drives because of its unique intersection with the Roe Highway.

"I've never seen any interchange which has been designed like this," Mr Landmark said.

"We call it a tennis ball — it's almost as though the turning movements simulate those join lines that you have on a tennis ball."

Mr Landmark said he could understand if some motorists found the WA-engineered design confusing.

"It certainly was innovative and I'm certainly not aware of anything similar in Australia.

"But there's nothing counter intuitive here because it works exactly the same as any conventional interchange."

The goal, he said, was to slow vehicles while keeping all the necessary traffic movements intact.

"So that way you get the safety benefits but you also still maintain the operational efficiency."

Triple-lane trouble

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 30 seconds 30 s Bunbury's Eelup Rotary is the biggest roundabout in WA and the only one controlled by traffic lights.

The huge triple-lane roundabout at the gateway to Bunbury, 175 kilometres south of Perth, is the largest in the state.

It is WA's only signalised roundabout, with traffic lights installed at each corner of the junction in 2012 in a bid to reduce congestion and boost safety.

Mr Landmark said Main Roads considered building a freeway interchange or a smaller roundabout in the centre before it opted for traffic lights.

"We looked at it and said it's a shame to throw away all the bitumen you've got there," he said.

"It had horrendous crash history.

"It had real problems from a congestion point of view, particularly during the long weekends because you had a lot of traffic coming down from Perth to Margaret River."

Mr Landmark said tow truck drivers had lamented the roundabout's improvements out of fear they would lose revenue.

"This was a huge success; the number of crashes really dropped significantly."

Five kinds of confusion

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 30 seconds 30 s Albany is home to the only five-way roundabout in WA, which often confuses tourists and locals alike.

The dual-lane Chester Pass roundabout at the entrance to the port city of Albany has five exits, making it a logistical headache for locals and tourists alike.

Main Roads has even taken the unusual step of producing a how-to-use guide for the roundabout.

"If I had to design a roundabout from the start, I wouldn't design it this way, that's for sure," Mr Landmark said.

"There can be some confusion in terms of which lane you need to go in, which can result in sideswipe-type of crashes — it's not an intuitive thing."

Compounding the problem is a busy stop sign-controlled meeting of two major highways just 100 metres north of the roundabout.

"It's starting to reach that stage where maybe as a roundabout it is not performing as well as it should be," Mr Landmark said.

Main Roads had considered installing traffic lights or bridges but land constraints made it difficult, he added.