I think that lovud only works vertically. Am I wrong about that?
Also, there is a difference depending on what the mechitza is for. For example, a glass mechitza does not work for ervah (you cannot daven if there is a wall of glass between you and someone dressed inappropriately). So the bus mechitza should be all the way closed, if you need it at all. It would work for tzoieh (excrement).
Now that brings to mind the famous ma’aseh with a choshuver yungerman (happened long time ago, and he is a very chashuva person) and his R”Y. Out of the clear blue, he goes over to the R”Y and asks him, “Is the Rosh Yeshiva considered tzoieh or ervah?” He was asking regarding the chiyuv to stand for an adam gadol – and if a mechitza between them of glass makes a difference (I believe the correct answer is that it does not). The R”Y was the type to appreciate such sharfness, so he readmitted the talmid after kicking him out of the yeshiva.