You might encounter a single lane bridge, even on the main road (indicated by this sign).  The rule is that you have to slow down and the car which approaches first, crosses the bridge first.

Driving in Iceland can be tricky - but if you listen carefully to Elfis, you should be fine  "Take a look at the Video." 

There are many single lane bridges on the Ring Road. The actual rule is that the car closer to the bridge has the right-of-way. However, it is wise to stop and assess the situation, i.e. attempt to see what the other driver plans to do. This sign indicates that a single lane bridge is ahead.

Top ten tips on driving in Iceland

1. Everyone in the car needs to wear seatbelt
2. Do not stop or park the car on the road except in a case of emergency.
3. Lower your speed when you approach and drive on a gravel road.
4. Choose the speed in accordance with the road surface.
5. Check the weather and road surface in advance on www.road.is and www.safetravel.is.
6. Make sure you get enough sleep in summer when there are daylight 24 hours.
7. Be sure that you have the driving lights always on - night and day.
8. The car that approaches a single lane bridge first, crosses first.
9. Sheep and other livestock you see near the road can suddenly run across the road
10. Don‘t risk your life and safety by driving into a CLOSED road.