One issue is you can put the thing in a lead box or whatever until you need it for a toll. there is no requirement that it be available. so its easily thwarted

One issue is you can put the thing in a lead box or whatever until you need it for a toll. there is no requirement that it be available. so its easily thwarted as an enforcement mechanism. one could also envision equal protection lawsuits or what not related to this as well.