Up here in God's Country (Northern New England = Maine, New Hampshire, Vermont) Jersey barriers caused a real problem ... small animals trying to cross the roads would come up against them and were usually killed when trying to get back across. Now the barriers have small hole in the bases, gouged out by construction workers, so little critters can safely get through.
I imagine this might be true in other areas where there is still enough forestation to give homes to woodland critters. When in other states I always check to see if the barriers have similar escape-through holes.