Slip Road On
The slip road provides space for you to accelerate up to a speed that roughly matches the other vehicles already on the dual carriageway.
Look for the speed limit sign on the slip road. Although speed limits should not generally be thought of as targets, in this situation the speed limit can provide a good indication of the speed that other vehicles are likely to be travelling. So you can merge safely with the other vehicles, it makes sense to use the slip road to get close to this speed if possible. This means you will be accelerating more rapidly than you are used to in normal driving.
As always, you should know what is going on behind you before accelerating.
Some slip roads are divided into lanes, in which case the usual rules regarding lane discipline should be applied.
Many slip roads consist of a single, wide lane. In this case, it is normal to proceed in the middle of the available space. If you need to overtake someone on the slip road, this should always be done on the right. Similarly, if another road user wishes to overtake you, move to the left and allow space for them to pass on the right.
Signal right to indicate your intention to join the main carriageway. This should be done nice and early to attract the attention of traffic already on the dual carriageway. By getting yourself noticed early, you will make it easier for everyone to facilitate a safe merge. This is especially true at night, when it can be very difficult to tell if another vehicle ahead is joining from a slip road or already on the main carriageway. An early signal makes all the difference in this situation.
As you get close to the main carriageway, you should already have your speed well up and your right signal on.
Use your right mirror to get an idea of how much space is available for you to merge into. If there appears to be plenty of space, all you need to do is have a quick glance into your right blindspot and, if definitely clear, ease into the left lane of the main carriageway.
If there are many other road users on the dual carriageway, you should find that they will do whatever is necessary to enable you to join. This may mean moving over to the right lane (look out for anyone giving a right signal), or they may simply adjust their speed a little to create space for you. It is at this point that you will be glad you got your speed up nice and early on the slip road. If you are travelling too slowly at this point, it can be difficult to get your speed up quickly enough to keep up with the other vehicles you are trying to merge with. If, however, the other vehicles are travelling more slowly than you are, it is a simple matter to adjust your speed down a little. Once your speed is matched to the other vehicles, you should find it is fairly straightforward to identify a gap and move into it.
Try to get as much information as possible using your mirrors, especially your right mirror. While it is important to check your right blindspot before committing yourself onto the main carriageway, it is also very important that you have your eyes on the road in front of you as much as possible, especially when travelling at higher speeds.
Only in vary rare circumstances, when the dual carriageway is very busy, might you find yourself unable to merge from the slip road without stopping and waiting for a gap.
On the dual carriageway
Once you have joined the dual carriageway, it is important to cancel your signal straight away so it does not mislead others into thinking you are about to change lanes. Focus on staying in the centre of your lane. As always, keep an eye on your mirrors so you know what is happening behind you, and try to maintain a safe, sensible speed for the conditions. Use the “two second rule” to keep a safe gap in front of you and ensure that you can stop safely at any time. If another road user gets too close behind you, increase the space in front of you so you have even more reaction time available. Remember to at least double stopping distances for wet weather, and increase them even more for icy or foggy conditions.Get animated examples with the interactive Dual Carriageways app for iPad