Driving along a dual carriageway, you pass a triangular warning sign showing two vertical black lines that converge into one as they go up the sign. A little further on, you pass a second triangular sign showing two separate vertical arrows, one pointing up and one pointing down. What is the difference between what these two signs are warning you about?
- The first sign warns that the dual carriageway is merging into a motorway; the second warns of a contraflow system that only operates at weekends
- The first sign warns that the physical central reservation dividing the dual carriageway is coming to an end, so the separate carriageways will merge into a single road; the second sign warns that the road you are on is about to carry traffic flowing in both directions on the same carriageway, so you should keep left and expect oncoming vehicles
- Both signs are alternative designs for exactly the same hazard, and a driver should react to them identically regardless of which one is displayed
- The first sign means the road ahead narrows to a single lane in each direction while remaining a dual carriageway; the second means overtaking is prohibited from this point onward
Why B? And why not the others?
Correct answer: B. The first sign warns that the physical central reservation dividing the dual carriageway is coming to an end, so the separate carriageways will merge into a single road; the second sign warns that the road you are on is about to carry traffic flowing in both directions on the same carriageway, so you should keep left and expect oncoming vehicles
The 'end of dual carriageway' sign draws two lines converging into one because it warns that the physical separation between the two carriageways, such as a central reservation or median, is about to disappear, so the road becomes a single, undivided carriageway shared by traffic from both directions. The 'two-way traffic' sign uses two separate vertical arrows, one up and one down, because it warns that the road a driver is already on, which may until now have carried flow in one direction only, is about to carry traffic moving in both directions on the same carriageway, prompting the driver to keep left and watch for oncoming vehicles. The option describing a merge into a motorway and a weekend-only contraflow invents scenarios neither symbol depicts. The option claiming the two signs are interchangeable ignores that a converging-lines symbol and a pair of opposite-pointing arrows are deliberately different designs conveying different physical changes to the road. The option describing a narrowing dual carriageway that remains divided, and a general overtaking ban, misreads both signs, since neither shows a continuing central reservation or an overtaking restriction.
Source: DfT Know Your Traffic Signs — Warning signs: End of dual carriageway / Two-way traffic (GOV.UK)