Tragic for those involved, but bloody rare considering the massive amounts used. Id be more concerned about how fatigue and inexperience or road conditions contributed. There's more chance of people being injured due to the road or inexperienced or fatigued drivers of heavy vehicles carrying feather pillows than by AN transport explosions.
Those reminiscing fertiliser use, this AN is minimum 99.5% AN 3mm 'coated' non porous prill (vs fertiliser grade around 40%,non-coated and larger diameter porous  prill), its coating reduces water absorption thus increasing shelf life as AN is naturally hygroscopic (absorbs water), the water acts as a desensitizing agent. And diluting/washing away with water is actually one of the emergency response or clean-up procedures for any spill. But that doesnt mean the fertiliser grade stuff didnt work very well :angel: it just isnt as efficient, but is/WAS cheaper. Even the 40% grade is restricted as it has been used in 'dirty' ANFO bombs. The only fertiliser grades available at the nursery are sub 20% (if at all).
Yes AN by itself is very safe unless boiling and contained as this may have been, if this was a MMU (hard to tell from photo remains) then it may have had a mixing tank of diesel, but it would not have been mixed as ANFO during transport, that's not how its done, only mixed when loading holes (OK for the experts, bagged ANFO is shipped on pallets and isn't as popular nowadays, even still, requires an explosion to detonate it - number 8 det sensitive). The accident may have allowed the two to mix by rupturing the compartments, but its all speculation until the investigation is published. 
Alternatively it may have been AN emulsion for wet holes and greater density, even still, this would not have had a sensitiser added until being loaded into drill holes, again, a rupture may have occurred, still to be investigated.
There are some comments from other shotfirers/blast crew/mine rescue/knowledgeable workplace types -  that are factual, any overreactions at this stage (before incident investigation results) are not helping the public perception of the true hazard on the roads. Should we discuss the amount of cyanide and sulphuric acid that gets trucked around? LPG and BLEVE blasts (Boiling Liquid Expanding Vapour Explosion)...I wouldn't want to live near a petrol station with an LPG bullet, even though they have venting valves, which are mechanical and could fail to vent quickly enough...or at all.
But best wishes to those injured for a quick recovery.
Download the relevant code here: 
Australian Code for the Transport of Explosives by Road and Rail - 3rd edition - Safe Work Australia