According to records widely used in general knowledge sources, which metro system was recognised as the longest driverless metro network in the world when it first set this record?

Introduction / Context:
Many modern metro systems use automated or driverless trains to improve safety and efficiency. At one point, the Dubai Metro in the United Arab Emirates gained international recognition, including from Guinness World Records, for being the world s longest driverless metro network. General knowledge questions often refer to this fact, asking candidates to identify the city associated with this record.

Given Data / Assumptions:
- The question asks about the longest driverless metro network in the world at the time it set a widely cited record.- Options list Dubai Metro, Vancouver SkyTrain, London Underground, and Delhi Metro.- We are working within the context of standard GK materials that highlight Dubai s achievement.

Concept / Approach:
When the Dubai Metro opened and expanded, it operated fully automated, driverless trains on a large network, earning recognition as the longest driverless metro system. Although other cities, such as Vancouver, have long established automated systems, Dubai was singled out for the combination of its network length and fully driverless operation. The London Underground and Delhi Metro have many lines but are not completely driverless systems in the way described in the record used in general knowledge references of that period.

Step-by-Step Solution:
Step 1: Recall that Dubai Metro was publicised as holding the Guinness World Record for the longest driverless metro network when it opened and expanded.Step 2: Vancouver SkyTrain is also driverless but typically not mentioned as holding the specific record in popular GK sources used for many exams.Step 3: London Underground is one of the oldest metro systems but is not primarily known for full driverless operation.Step 4: Delhi Metro has automated features on some lines but is not commonly cited as the longest driverless network at the time referenced by such questions.Step 5: Therefore, Dubai Metro, United Arab Emirates, matches the record referred to in the question.

Verification / Alternative Check:
Searching for the phrase longest driverless metro network in older news articles and exam notes yields Dubai Metro as the answer, often accompanied by mention of its Red and Green lines and fully automated operation. This supports the selection of Dubai Metro in the context of general knowledge questions.

Why Other Options Are Wrong:
Vancouver SkyTrain, Canada: An important automated system, but generally not the one highlighted in exam oriented content as holding the longest driverless metro network record for the period discussed.London Underground, United Kingdom: Famous as one of the oldest underground railways, but it is not fully driverless and is not associated with this specific record.Delhi Metro, India: A rapidly expanding and modern system, but not recognised in standard GK sources as the longest driverless metro network during the timeframe used in such questions.

Common Pitfalls:
Students may confuse other superlatives, such as the longest metro network overall or the busiest metro system, with the specific phrase longest driverless metro network. Another error is to assume that the oldest or most famous system, like the London Underground, automatically holds every record. It is important to read the qualifier driverless carefully when answering metro related GK questions.

Final Answer:
Dubai Metro, United Arab Emirates was recognised as the longest driverless metro network in the world in the context referred to by this question.