
As an American who has lived here for 24 years- yes the speed limits are slow, and no, I don’t think ANYONE “enjoys” driving at the slow speeds they do.
However, I think most people accept this, and there are reasons for the lower limit, although it’s open to debate if these reasons are good.

First- there is literally nothing between Sydney and Melbourne. The only major cities are Abury/Wodonga Border towns. And calling them major cities- for Australian standards.- is 100,000 total between them. Total.
The other major towns (Wangaratta- 29,000/ Goulburn 25,000) there isn’t much there to either of them, and by 4 pm on a Saturday everything but the supermarket and petrol (gas)stations are shut. They are literally country towns.
Wagga Wagga (57,000) is about 40 minutes off the Hume Hwy in the foothills.
Around the exit to Wagga Wagga.
On the morning of our drive, the Bus hit a truck at 2:30 am in the morning, and unfortunately the driver of the bus died and about 35 people were injured. So they closed the Highway. It was still shut at 11:00 am when we arrived in this section.
This added 4 HOURS to our already 10 hour trip. (yes, 14 total hours) To take an exit in this area, sometimes it’s 10 to 30 km BETWEEN exits. So the last thing you want, is for them to close the hwy. Secondly- you’re in the middle of nowhere. There is a LOT of middles of nowhere’s in Australia. It’s pretty much everywhere outside somewhere.
30 minutes outside any major metropolitan area, of which there is only 6 or 7 on a continent the size of the continental United States- and there isn’t much. 1 hour, and there is even less. 2 hours, and it’s rugged country with few roads and basically no people.
To make matters worse on our trip, we got diverted off the freeway, and took a country road waaaay out, meandering around the hills, until we could take a left turn, back towards the freeway and then wondered back in, and finally got back on. That was probably a 45 minute diversion, for what probably should have been 15 minutes on the Hume.
If there is a serious accident like the one we had, at the location we had- these are the facts:
Assuming someone calls in the accident immediately, it’s probably 30 -40 minutes until the ambulance gets to you. A further 5–15 minutes to be assessed and to call for a helicopter. 1 hour for the helicopter to arrive, 5 minutes to load you in, 1 to 2 life flight to the nearest metropolitan (Sydney or Melbourne) trauma centre.
Realistically- you’re probably dead. (No disrespect to the bus driver) Time in that situation is your enemy, and the distances are vast. If you get off the Hume Hwy, your mobile cell cover drops to zero within a couple of kms. (Keep in mind, this may sound remote, but it’s not remote enough to need the world famous Royal Flying Doctors- there are more remote places.)
So, what is the consequences of all of this?
110 km/ hour unfortunately.
What would help?
Does the Hume Highway need a service road running parallel the entire length. Yes. But it doesn’t and it would probably cost several billion dollars to build it, and a lot of it cuts through the mountains between Sydney and Melbourne. It also goes over rivers.
The Hume Hwy is basically 2 lanes each direction, with a divided median strip for the length of it. Should it be more? Yes 4 lanes each direction would probably help. Again more $$$.
Is the hwy engineered for 130 or 150 km/ hour? Probably not. Some corners are too sharp. Gravel on the road. Culverts on the side. Pot holes. The on- ramp that we got back on the Hume, after the accident- had a flaming cattle gate across the road!!!! I’m not kidding. It’s definitely not the autobahn.
Do I wish the speed limit was 150 km/ hour. Yes! Will it ever be? Probably not.
To get the speed limit up, you’d have to re-build the whole hwy. You’d also have to introduce a “basic speed law.” Drive as safe as conditions and your car allows. Australians have no concept of this.
They drive their crappy cars around, like they are Lamborghinis, and they smash into each other or crash off the road. If it rains, everyone slows down to the point where a 15 minute trip turns to a 45 minute trip. It’s one or the other. More people are not killed, because everyone now drives slow…. Everywhere.
A significant amount of driver training would have to be introduced.
However, as several below have pointed out- Australian Governments are are in love with speed cameras. On the Victorian side of the Hume, there are 7 fixed speed cameras each direction. I’m not sure of how many on the NSW side.
And there is “average speed” cameras each direction, so you cannot simply slow down when the camera is coming up, and then gun it again!
And there are mobile speed cameras each direction with unmarked cars on the side of the road.
And there is the occasional “speed trap” with police or highway patrol siting in their car with radar guns.
Can you set your cruise control to 130? Yes, but you’ll get at least 7 tickets, maybe 8, so that’s at least a $2,695.00 ticketed trip, just for Victoria. ($385 each ticket- assuming 110 km/h limit)
In Victoria, if you speed over 26 km/h, it’s an automatic loss of license. (That’s only about 15 mph over the speed limit!) And, if you speed over 15 KH/h you loose 3 demerit points per offense, and you only get 12/ 3 years. So when you get back to Melbourne, go hand your license in at the court, and you’ll have to take out a mortgage to pay the fines.
Here is the other thing. Carry on only flight from Melbourne to Sydney. It’s about 90 minute flight, and $100.00 and if you pre-book a rental car, and you get lucky, you’ll only have to stop at the counter of the rental car company in the airport, for about 3 minutes. The rest of the time, you’re walk from the plane to your car, and you’re on the road. You don’t stop. It’s cheaper, quicker and probably safer than the drive between the two cities.