I did say that no one on either side of this argument had presented statistics, didn't I?
If no one can document the accident rate claims, however, I'd err on the side of public safety, not excessive accommodation that privileges some people with exemptions others don't enjoy. Freedom of religion remains regardless, people just have to accept that not all of their religious choices are free of personal costs, that they don't always get to spread the costs of their choices onto other people.
If the reflective markers don't produce any benefit at all, no one should have to use them, Amish or not. If different forms of markers are effective, everyone should have those options, Amish or not. I shouldn't have to be Amish to use a lantern or gray tape if those work just as well bright orange triangles.
In fact, the only way for religion to really be an important issue here is if you think there's a fundamental right for religious believers to make other people with differing beliefs bear a burden for their choices. If you argue that the law has no safety merit, then the law is a bad law for all people, regardless of their beliefs.
I felt the same way about a court case a few years ago when a Muslim woman was insisting that her driver's license photo be taken with her veil on. That makes the photo worthless as a form of ID, of course. She did not win the case, and I'm glad she didn't. If photo IDs aren't really that important, no one should be required to carry them. If they are important, no one should have a special privilege of being exempt that other people don't enjoy.