The hills on either side of where the M1 Princes Motorway crosses Cataract Creek have long been known by Illawarra motorists as the Big Dipper.

But planned work that will add an extra lane in each direction will also create the need to come up with a new name for this section.

The state and federally funded work also involves realigning the curves at either end of this stretch, by constructing new road sections.

As part of this construction the plan is to lop a few metres off the hills at either end, according to a spokesman for Roads and Maritime Services.

“Through the two crests the road will be lower by around six to eight metres,” the spokesman said.

“At Cataract Creek, the road will be at the existing level.”

Reducing the steepness of the hills is designed to assist heavy vehicles in maintaining a more consistent speed.

At present, heavy vehicles slow down on the upward sections, while some also travel over the speed limit on the downhill section to build momentum for the uphill run.

According to Review of Environmental Factors, the extra lanes, smaller hills and improved curves will shorten travel time for both light and heavy vehicles.

By the time the first stage is finished – which is expected to be by 2020 – the travel time northbound is predicted to be cut by just under a minute and just over a minute for those heading south.

It’s a similar story when it comes to average speeds, which the review notes are below the posted 100km/h speed limit.

“The data indicates that travel speed for heavy vehicles are substantially lower than the posted speed,” the review states.

“In peak period, the travel speed is about 80 to 90 kilometres per hour for light vehicles and about 50 to 60 kilometres per hour for heavy vehicles.”

After the first stage is finished cars are predicted to travel around 22km/h faster on the Picton Road to Bellambi Creek stretch, while heavy vehicle speeds could improve by between 7km/h and 13km/h.