A dual carriageway is a road with two (or sometimes three) lanes running in each direction separated by a central barrier, the speed limit on which can vary between 30 and 70 m.p.h. depending on location. Unlike motorways, dual carriageways may be used by learner drivers, cyclists and 50 cc mopeds. Also unlike motorways, there is no law to prevent pedestrians walking alongside the road. The intention of a dual carriageway is to keep traffic flowing. When approaching a dual carriageway it will be clearly signposted with the applicable speed limit. Please remember that this limit is the absolute maximum at which you may travel if it is safe to do so. When joining it is essential to follow the MSPSL routine and after joining you should be prepared to travel at about the same speed as the other vehicles.
Once on the dual carriageway, you should remain in the inside lane unless you are overtaking one or more vehicles, or you intend to turn right off the dual carriageway. In the latter case early planning is required to ensure you are correctly positioned. When travelling on the dual carriageway, you should be a safe distance from the vehicle in front of you. So at 30 m.p.h. you should allow a minimum of six car lengths, but at 40+ m.p.h. you would need to apply the 2 second rule. This means that as the vehicle in front passes a fixed object such as a lamp post or a bridge, you should be able to count “one thousand, two thousand” before you reach that fixed object. Please remember that in rain you would need to double this distance and in snow and ice it would be up to ten times the distance to give you sufficient time to stop in an emergency.
When travelling on dual carriageways good observation and early planning are essential. You may be looking for an exit or direction signs for an exit. Remember: you may be in heavy traffic so you need to plan your drive. As an example, you may need to take the next exit which could be half a mile away but, if you are travelling in the outside lane when the exit or filter lane is first sign posted, you would need to return to the inside lane in good time to ensure a safe exit without disrupting other traffic. Likewise, if your exit is to the right you would need to do the same and plan early. You should also be on the lookout for signs indicating a change of speed. For example, if you are travelling at 50 m.p.h. and you can see that the limit is coming down to 40 m.p.h. you must ensure that you are travelling at that lower speed as you pass the sign. Conversely, if you are travelling at 40 m.p.h. and a sign indicates an increase to 60 m.p.h. you should ensure you have passed the sign before you start to accelerate. With the higher speeds allowed on dual carriageways in rural areas, you will get count down markers to indicate an exit. There will be green countdown markers, three, then two, then one, 100 metres apart ahead of the slip road. This should be used as a deceleration lane so that you can adjust your speed to that of the new road. When exiting a dual carriageway with a lower speed limit in town, exits will generally be via a normal turn or set of lights.