Having been through that tunnel several times, all I can say is: Without lights? ARE YOU NUTS?

I usually think the NPS is overdoing the safety rules. For this and for requiring RVs to have an escort, I agree with them. Getting an RV through this tunnel undamaged with two way traffic requires a very good & experienced driver. Bicycles with lights would have traffic backed up until they reached the other end. IIRC there aren't any places where you can see far enough to be able to pass bicycles. There are several ventilation windows but I don't remember if you could use them for a bicycle turnout.