Many people do not know the difference between a single and a dual carriageway. It is particularly important when driving on a national speed limit road.
A single carriageway road is a road where there is no separation between yourself and oncoming traffic. It could be one lane each way or more.
A dual carriageway is a road where there is a separation between yourself and oncoming traffic. This could be in the form of a central barrier or raised kerbs or a grassed area or some other separation. It could be one lane or more in each direction .
Speed limits can vary from road to road from 20mph right up to national speed limit.
These rules are particularly important when thinking about national speed limit roads.
National Speed Limit
When you see the national speed limit sign the actual speed limit depends on the type of road. For cars on a single carriageway the speed limit is 60mph. For cars on a dual carriageway the speed limit is 70mph.For other road users there are different limits. See this link for more details https://www.gov.uk/speed-limits
Lanes and Lane Changing
On a road with more than one lane going in your direction the usual rule is to use the left hand lane. Any lanes on the right would normally be used for overtaking slower moving vehicles or for getting into position for example turning right. If you have been overtaking you should then return to the left hand lane when safe to do so. How should you change lanes?
If you need to change lane, first use your mirrors and if necessary take a quick sideways glance to make sure you will not force another road user to change course or speed. When it is safe to do so, signal to indicate your intentions to other road users and when clear, move over. Staying in an overtaking lane for too long can disrupt the flow of traffic and you should return as soon as it is safe to do. Remember that changing lanes increases your risk of being involved in an incident so you should only overtake when necessary.
When overtaking cyclists motorcyclists and horses give plenty of clearance and beware they may change direction suddenly to avoid uneven road surfaces.
Undertaking i.e. passing on the left should be avoided. If you are in the left hand lane in slow moving traffic you may undertake traffic in the right hand lane if it is going slower than you. If a vehicle is signalling to go right you may undertake if it is safe to do so.
For more information please follow the following link to the highway code https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158#multi-lane-carriageways-rules-133-to-143