In some areas, the mountain roads through the fjords are very desolate - no one around for miles. Although I drove it alone, I would recommend driving in pairs. Or if you do go alone, make sure someone knows your path of travel and when to expect you back.
Also, while I was making my way through the mountains, there was a strech of road where there were no road signs for miles. I became concerned that I might have missed a turn or made a wrong turn. I stopped at a sheep farmer's place and talked to the farmer. He assured me that I was on the right track. He said a lot of people stopped and asked him where they were in relation to Rekyvik. He wasn't sure why there were not many road signs, but he had heard that more signs were going to be put up some time in the future.
In some of the higher elevations, there are rescue cabins for emergencies. They are little orange cabins that have water, food and blankets inside. There is a radio with direct connection to emergency crews. Each cabin has GPS system operating so the emergency crews know exactly where to send help. These cabins are for true emergencies ONLY
Before you enter the fjords, fill up your gas tank, and better yet, if you have an extra tank, fill that too. There were not many gas stations once you get into the fjords. I did find one, but I had no cash, and the station owner did not take credit cards. He was extremely generous and gave me 10 liters of gas! Incredible! He was worried that I may not have enough gas to make it to the next gas station. If I ever make it back to the fjords, I know exactly where to go to repay his generosity. (Sorry I can't tell you where it is. I would just know it when I see it)
Keep in mind, if you have an extra gas can, by Icelandic law, it must be transported on the outside of the vehichle. It must be secured tightly. There is a big fine if you are caught with a gas can inside your car or in your trunk.