fear of riding in car

Question
Hi, my Mini Schnauzer is about 1 yr 4 m old.  Since I got her at about 16 wks she has been in the car at least 3-4 times weekly going to my job with me.  (I'm a vet tech and she loves going to work to hang out with the other staffs pets) She typically will just lay down and sleep in the car, occasionally look out the window.  She has the passenger seat to herself and has been trained not to jump in the drivers seat with me.  For the past couple of months she has been very anxious in the car.  Excessive panting, shaking.  I cannot connect anything to the sudden change.  She is very fearful of semi trucks that go past (they never used to bother her) and the fear has started to happen while at home as well if large trucks/loud noises happen she will go under the kitchen table.  I have tried to make car rides a positive experience by giving yummy treats througout short trips, only giving a peanut butter kong while in the car (she doesn't get it otherwise), and not paying attention to her when she is panting/shaking.  If she stops for some reason I try to make sure to pet her and tell her that she is a good dog.  I really want to make sure that we overcome this so that she is not frightened of the car for the rest of her life because I do travel a lot to and from work, friends, family etc.  I've also tried benedryl, which had no effect, and most recently diazepam which initally I thought helped, but no has no effect.  She has been prescribe alprazolam to be given daily.  She is very attached to me, which I know can be a problem, but is fine to be left home alone either in a crate or out.  I'm trying to tire her out by taking her for walks/dog park trips, but our weather has been extremely cold so we don't get to as much as I would like.  Any suggestions you have would be amazing.

Answer
It takes mere seconds for a dog to develop a fear response, often owners have no clue what may have caused it (something as benign as a shadow can do it).  In this case, your dog has a solid excuse: those semis roaring past a moving vehicle scare ME! She may have been asleep when one whizzed by and caught it in the corner of her eye; it's obviously the sound that bothers her (from your description of her behavior at home.)  Her attachment to you is NOT a problem at all, given her ability to be alone at home.  You seem to have tried everything and you seem to be doing everything right.  Car travel per se doesn't seem the problem but rather the passing trucks.  It's quite difficult to conduct behavior modification while driving and at this point I'm concerned about your attention to the road, for your own safety.

Xanax can be physiologically addictive, meaning the effects wear thin and the dose has to be increased to obtain original efficacy.  I realize the dog is experiencing distress at truck sounds at home and this is why there is a daily dose, but I suggest this medication be given only for a short period of time.  Changing her position in the car (to the back seat with a seat belted harness) may help alleviate her behavior somewhat (change of venue interrupts the conditioned response) but given that she is generalizing the sounds to other places (home), it may do nothing at all.  Avoiding situations where large trucks pass you at high speed (whenever possible) can at least minimize her development of response perseverance; not interacting with her at all (even when she appears not frightened) is a better choice than petting her and praising her when you think she is not fearful.  It's unlikely that she would stop being fearful long enough to connect the reward, she may just appear not to be fearful and you really can't make that observation while driving.  You may have inadvertently rewarded the behavior, rather than simply ignoring it, in an attempt to rehabilitate it.  I can't see that from here.

My only suggestions are: move her to another position in the car, thereby disengaging part of the conditioning and totally ignore her fear responses, even at home.  BUT when you are at home, you can closely observe her and attempt to redirect her.  That's the place to intervene, not in the car when you need to pay attention to the road.  You can attempt this by first hurriedly leaving the room (without looking in her direction) to see if she will follow.  if she DOES, the fear behavior will have been interrupted long enough for you to redirect her into a play training behavior. Such redirection, if done consistently (given the dog continues to rouse from her freeze response under the table) will break the chain of behavior, although it may take a while.  Once she rouses more easily (if she responds to this at all), you may be able to set her up using artificially produced sounds (video or audio), chaining backward from her newly acquired "end result behavior" (play training) to the sound itself.  Desensitizing a dog to a known sound that produces fear (such as thunder) can be done with audio devices, but it must be done very carefully and the dog's body language observed quite closely, or the situation can be made worse.

Since she's already displayed this fear behavior for several months, something is keeping it in place.  Normally, a dog will lose a suddenly acquired fear response, but that involves not forcing the dog into a situation which approximates that which caused it in the first place.  Try the back seat approach and redirecting indoors (if you can interrupt her freeze response).  Also, if you have a friend or relative with an extremely travel wise dog, traveling with that friend and dog may help, but you would have to do this several times a week.  I don't get stumped by many questions, but this one really did stump me.  I wish I could observe the problem and do an in depth interview with you.  Often, the smallest clue (left out of a question initially) is the key to the solution.  You may need to find a behaviorist for an in person evaluation.