Those signs are particularly ambiguous. In keeping with the height limits, they're primarily targeted at trucks. I don't believe those would be understood to prohibit motorcycles, for example. Those signs also aren't in keeping with how the commonwealth prohibits bikes, horses, and pedestrians in other cases, like at entrances to I-93.

I think this is something Mass DoT aught to clarify. Note another example, where Mem Drive passes under Mass Ave: there are the same Cars Only signs, but there is no bike, ped, or horse specific signs, only a sign indicated no trucks. I would not be suprised if the "Cars Only" were not there as a legal restriction, but to remind the uhauls about storrowing 