Vehicles have crossed lanes including heavy vehicles. But the intent is more to keep people from running off the shoulder, especially on bridges.
I think you missed the mark on this one. No way cable barriers in the middle of a median keep people from running off the shoulder. They'd be 15yds off the shoulder to contact the cable barriers.
They are also intended to prevent crossing the medium to opposing traffic and in such cases are well off the shoulder. It depends on what the traffic engineer believe the site calls for as to what gets installed along with available funding.
Below a quote from a study of Missouri.
Eliminating
Cross-Median Fatalities
Statewide Installation of Median
Cable Barrier in Missouri
http://onlinepubs.trb.org/onlinepubs/trnews/trnews248rpo.pdf
[/QUOTE
Below are the old fashion barriers that are being replaced with strung steel cable on the shoulders near davis for the on and exit ramps. Notice these barriers keep the cars on the shoulder. But I suspect you did know that.