So many drivers are going so slow, in the merging slip lane, after they have past the 100 km/h sign as they approach the freeway, that traffic on the freeway has to slow as they enter the freeway lane to avoid a collision or to let them in.
The whole purpose of the slip lane is to allow you to match the speed of the traffic on the freeway. If it is slower than 100 km/h due to congestion then match that.
As you approach the area of merging use your right hand indicator and safely enter the freeway traffic flow. Remember it is you that is entering the freeway, the freeway traffic is not entering your lane, it is their lane and you are entering it!
If you use this approach sensibly most drivers will adjust their speed to allow you to merge either in front of them or behind them or shift to the right hand lane if it is available to them.
There are a couple of places along the freeway that have on and off ramps where some drivers really hold up traffic because they can’t be bothered to speed up because they are exiting at the next off ramp. For example: Cedric street entrance to Osbourne Park Hutton Street exit is one. Traffic trying to get into the left hand lane to exit at Hutton Street are sometimes having to slow down below 70 km/h to enter the left lane. This then slows all the traffic behind them and the knock on effect of this congestion a kilometer back.
Or the vehicle behind the the slow vehicle can’t go fast enough to safely merge right onto the freeway.