Labs not afraid of vehicles

I have a problem with my two labs. We live at the end of a gravel road on 10 acres. 5 of these acres are enclosed with "Invisible Fence" to keep my labs from roaming the neighborhood. Whenever a vehicle comes to our house or leaves my dogs don't know to stay out of the path and I'm afraid they're going to get hit. I went out the road this morning to get the paper and Hokie ran right across in front of me and he was so close that I lost sight of him. I live in fear that the UPS or FedEx trucks are going to run over them. Can anyone make some suggestions? Honking the horn does nothing.
Thanks,
Labmomma (Donna) :)

Maybe build them a dog run ? i have one and there in it when im not out in the yard when i am they are all with me Dont take the Chance!!!

Move the fence so that it does no go in the path of the vehicles.

Move the fence, build a run when for when you can't supervise them, and/or keep them indoors when you aren't outside or when you aren't home.

Really, we have had one PT member in a similar situation, with dogs that didn't pay attention to cars, and one of her girls was run over by a car (she's fine, thankfully). It would be HORRIBLE if that happened to one of your pups!

Yup, either more "invisible fencing" or a real fence to keep them of the driveway. You cannot be sure they'll be safe any other way.