PVC or Pex should be buried into a sand bed surrounding the pipe( for a cushion effect ). Pipe should not be buried with natural earth ( including rocks ).. My Sister ran about 2000 lf of PVC to access the water at the main road ( no problems), Metal pipe sleeves under any roadway is an excellent suggestion. I have Used Pex for long runs with no problem in crushing ( school district requirement),coiled plastic tubing. - that red stuff. PEX is soft and will collapse. Put some wire in the trench with it so you can find it later. Couple feet deep and in a pipe where it goes under road. Heavy equipment will break it. Freeze isn't the problem.