even temporary tall walls (the ones you seem to be describing) are often better than guard rails, as they usually have steel wires running through them so they don't separate. Continuous pour tall walls are obviously preferred, but the sectioned ones are still more effective than a guard rail.
The worst kind of barrier is this one, employed on the 400 and highway 11 in Ontario. Every time I drive on the two roads I honestly feel unsafe, it feels like there is almost no seperation between the two directions of traffic. MTO has been mulling over rebuilding and widening the 400, and I can't wait until they do to get rid of this, as well as the only at grade intersection on a 400 series highway. (11 is also planned to be rebuilt and to be upgraded to full freeway standards for its entire length)