Your opportunities occur only if you have selected a suitable location and are extremely patient. Using your vehicle as a blind allows you to have an important advantage - mobility. Instead of waiting for your subjects to move into range of your lens, you can move yourself closer to them. If you use the right technique combined with a concern for safety and ethics, your vehicle is a highly effective way to get close to wild birds. One more advantage - I find photographing from my truck much more enjoyable than crouching in an overheated, airless blind for hours.
Nothing can totally replace the great feeling of walking or hiking in a natural environment.
However, if you want to get close to a variety of wild bird species along the roadside, try using the blind you already own. This hawk allowed my truck to approach close enough for a photograph because he had spotted a field mouse in the grass right below this fencepost. Shortly after this shot was made he jumped down and captured the mouse and flew off before I could get my eye back to the viewfinder. Canon A2 and 300MM F4 IS with 1.4x extender, AV mode at F5.6. This cheerful little bird inhabits open fields and meadows in the Midwest.