I did it a lot. I started at 3:00 am, went back out at day light. Marked the spots on a map with the locations and approximate numbers...
Stop the truck.
wait for 3-5 minutes
Interogation Howl
Wait 5 minutes after they quit howling to leave. If you don't get an answer, drive 5 more miles down the road, mark the stops on your map.
If you get out of your truck, don't slam the truck door when you howl.
I took the light out of my truck that comes on when I open the door.
I have a toggle switch in the cab for the brake and back up lights. You can put the inside lights on a toggle switch also.
You can mount two large outdoor PA speakers underneath your truck availale from Radio shack. You can have a toggle switch put on your inside tape deck for inside or outside speakers.
In some states,this method of doing a census count is illegal, check your regs.
I also had a Siren before I learned to howl, but it has to be set outside on the ground, fully self contained to be legal....can not be attached to the vehicle in any way. The siren can not be blown in an area close to houses where it will disturb people, if they complain, you get a ticket. Good Siren's are very expensive.
Using a set of electronic ear muffs works wonders, you will hear coyotes howling off in the distance that you would otherwise would not have heard.
I'm not excessive compulsive, just extremely well focused.