Safe is not a quantifiable term.
QFT
Sometimes (I reckon anyway) speed limits are set as part of a revenue raising exercise. Put up a sign where it's very easy to 'speed' like the intersection of Stock Rd and Winterfold Rd. The speed limit changes from 80 to 60, the sign is on a downward slope just as you go around the corner so all of a sudden you have to drop 20kms an hour with little warning. This is a very busy road with a lot of trucks. Almost every other intersection till you hit Rockingham in the south is 80 kms. Even northbound the the speed limit through most intersections is 70.
Agreed man... I used to drive down Stock Rd frequently for rehearsal with one of my old bands... always shitted me. After several intersections (closer to Freo) there are no speed signs what so ever. Tha fuck?
Also, here's an example of (imo, what is) justified speeding... and it happens all the time. You're on a two lane road, all cars traveling close to the speed limit. One car directly behind you, one right next to you in the other lane. The car right next to you starts drifting or changing in to your lane, somehow unaware of your presence. What do you do?
1. Do nothing, the car next to you slams in to you, and all three of you are in an accident.
2. Slam your brakes in hope that the car next to you wont hit you... the car behind you fucks you up.
3. Speed up quickly (break the law, omgz) to get ahead of the car next to you, so you can avoid a collision altogether.
Options 1 and 2 play by the book, and both involve you being fucked.
Option 3 breaks the sacred, arbitrary laws that blatantly dictate what is right and what is wrong, but result in you not being fucked.
But of course, according to the law, Option 3 is the irresponsible and unsafe choice. Yeah... makes sense.
I've had to take Option 3 countless times in my driving journeys... if I have to bear some kind of guilt for it, so fucking be it... at least I am still alive (and not a quadriplegic), with a working car.