Highland Driving

During wintertime the Icelandic highlands are impassable/closed for anyone not in a modified vehicle (super jeep). Timing of these closures depends on weather and conditions, see here.
To visit the highlands you will need a modified vehicle along with an experienced driver.

Highland driving is very different from normal driving. Conditions can change more rapidly than on lowlands and you are often required to cross unbridged rivers. Roads can be rough and you need to drive slowly, often 40 km/h or less. Planning is extremely important, leave your plan here.

Start by check if roads are open on road conditions and the weather forecast and keep in mind weather can change rapidly.
Information Centers in the area, rangers and wardens are good sources for detailed information.
Make sure that you have a 4×4 (4WD) car with good ground clearance and proper experience for driving in the highlands.

River Crossing:

The risk is always yours, no insurance covers any damage caused by crossing rivers (damages can cost thousands of euros/dollars).
The current and depth of the rivers are constantly changing and rivers often become impassable.
If you’re unsure of crossing a river then don’t do it, just turn around.
Plan the route you are going to take before entering the water and drive slowly (5 km/h) and steady – do not switch gears while in the water!
Always try to go down stream as going against the current will increase the risk of water going into your engine.
Do NOT enter the river where it seems calm – this is a sign of depth.
Some rivers have signs like this and a stick in the river. Study the sign until you understand it:
Here is a video showing proper form for crossing a river.