I'm obviously not a road engineer, but I had no difficulty in recognizing that a small bush and a patch of grass were insufficient "barriers" to prevent a car, truck or bus from crossing the divide on a motorway. Every time I drive along the M11 I consider how flimsy that hedge is.
In the region of the US where I grew up (NY, NJ, MA - probably the same everywhere), no highway would be built with a small "grass and bush" divide. Most new roads (by new, I mean post World War II) have a much bigger gap and generally the central divide has a significant dip so that anyone leaving the road will not find their way into the on-coming lanes.
By the way, wasn't this issue settled in favor of crash barriers after the accident on the Chapelizod by-pass 7 or 8 years ago? That was the one where a bus full of school children had a very lucky escape. I guess the fact that no one died meant that there was no reason to do anything about it.
