You might enjoy taking your dogs out in the car with you on short or long haul journeys. Stop for a break anywhere and just remember that your dog needs a break too perhaps.
Being couped up in a stationary vehicle can be fatal, especially on a hot sunny day. If you've ever tried it yourself, even with the window down, you start to feel uncomfortable very quickly. At least we can sweat - DOGS CAN'T!
Although the temperature outside a parked vehicle may be constant, the temperature inside very quickly begins to rise and may be more than 10 degrees hotter in as little as 15 minutes. Please watch this short video in which a short experiment illustrates just what your own dog might have to endure. Winding down the windows slightly really won't make a great deal of difference!
Have you tried it lately?