Laws for pet safety during travel protect the well being of the animal. Having a dog is an expensive venture that comes with serious responsibility. Even dogs just being driven to the vet need to be safely transported. Keeping a dog restrained is easiest in a crate, and when a dog is crated it causes less of a distraction for the driver. Also, in an accident, the crate protects the dog from projectiles moving throughout the car and from becoming a projectile itself -- just make sure the crate is stationary to begin with.
Measure the width of the van on the inside where the rear doors open. The inside panels of the van are wider than the opening at the rear doors. In order to get more than one crate in the back of the van, the crates need to measure less in width than the rear-door entry.
Draw a plan of how you want the dog crates to line up in the van. Once you have a design for crate placement, you can focus on making sure the crates are stationary.
Purchase ratchet straps from your local moving company or hardware store. Industrial vans come with D-rings and tie downs already installed in the floor and walls. Thread the ratchet straps through the D-rings and tie downs before you place the dog crates in the van, but keep the straps loose.
Arrange the crates in the van by size placing the larger ones father into the van and the smaller ones closer the rear of the van. To keep your field of view unobscured when driving, do not stack the crates. Also, there can only be one row of dog crates.
Place the ratchet straps in front of the crates with the buckle over to one side to protect the buckle from getting banged and coming loose. Take the handle on the ratchet buckle and move it left to right. You can hear the belt tighten with each click. Keep moving the handle back and forth until the tension in the ratchet strap is snug against the dog crates, thus securely strapping them in place.
Travel with dogs that are similar in personality. A calm dog travels better with other calm dogs.
If the dog is aggressive move it from location to location by itself in a single crate. Cramped quarters can make and aggressive animal more ferocious.