The blue reflector
s in the midst
of the road are trapezoidal prism
s; that is, an isosceles trapezoid
projected along the axis normal
to the trapezoid. The reflectors are not
placed in the middle of the road; rather, they are placed offset
to one side of the road.
Located on that side of the road is a fire hydrant.
In very snowy areas, the blue reflector may be supplemented by a 3 to 4 foot tall stake adjacent to the hydrant, topped with a circular red reflector. The stake identifies the location of the hydrant for fire departments (who shovel our hydrants after every storm), and for snow plows, to warn them not to plow through the hydrant.