One development that has not made the road safer is that humans are idiots, and no amount of engineering short of creeping darwinian evolution will change that.
I offer as my first piece of evidence the use of cruise control. Over long distances, cruise control is very useful. It allows concentration on the road and ones surrounds, instead of focussing on the speedo. In the hands of idiots however, the cruise control can lead to accidents.
Idiot behaviour 1:
When entering the highway, the cruise control overtaker studiously sets the cruise control to 100 kmh and there it stays. When coming up behind a slower vehicle, the cruise control overtaker will swing out into the right lane, blithely unconcerned that a person traveling at 110 in that lane has just had to apply the brakes to avoid a collision.
Idiot behaviour 2:
Just as in Idiot behaviour one, when entering the highway, the cruise control overtaker sets the cruise control to 100 kmh and when overtaking a slower vehicle, even if that vehicle is doing 99.5 kmh, the cruise control overtaker slowly, oh so slowly, crawls past almost defying the laws of physics. This is particularly annoying when the vehicle being overtaken is a triple trailered road train. No amount of passive aggressive tail-gating will make this idiot drive at say 105 kmh. Thats dangerous speeding.
Idiot behaviour 3:
With the cruise control set to 110 kmh, the cruise control idiot comes up behind your car traveling at 100 kmh and moments before ramming your rear bumper, suddenly brakes. Causing a near bowel evacuation as you stare bug eyed in your rear view mirror imagining the crew of the SS Idiot behind you getting ready to board after ramming.
Sadly, I cant see that any amount of technology will help change idiot behaviour. Im not sure if crash reports are made public, but I would like to know if variables like 'cruise control on' are reported upon when the causes of accidents are being investigated. I recall speaking to a policeman 20 years ago at a party, he told me that at many road accidents he had attended, a cassette was found floating about the car interior obviously being ejected or inserted by the driver moments before the accident. This was never reported in the stats either.