When a person drives after using drugs or alcohol, vision can be affected and it becomes especially difficult to judge which aspect of what they see?

Introduction / Context:
Safe driving depends heavily on clear vision and the brain's ability to judge speed and distance. Drugs and alcohol interfere with the nervous system, slowing reaction times and distorting perception. Traffic safety education often stresses that one of the most dangerous effects is poor judgement of distances between vehicles, which increases the risk of collisions. This question focuses on which visual task becomes especially difficult under the influence of these substances.

Given Data / Assumptions:

• The driver has consumed drugs, alcohol or both.
• We are considering which visual judgments are most affected for driving.
• The options include light intensity, colour, distance and shapes.

Concept / Approach:
Alcohol and many drugs depress the central nervous system. They can cause blurred vision, reduced peripheral vision and impaired depth perception. Depth perception is the ability to judge how far away objects are. When depth perception is affected, a driver finds it harder to estimate stopping distances, overtake safely and position the vehicle correctly on the road. While colours and brightness can also be affected, especially at night, the most critical and commonly emphasised danger is poor judgement of distances and speeds. That is why traffic safety campaigns say that even small amounts of alcohol can seriously affect driving judgement.

Step-by-Step Solution:
Step 1: Identify the key driving tasks that depend on accurate vision, such as judging how far away another car is and how fast it is moving. Step 2: Recall that alcohol and many drugs slow brain processing, which makes depth perception and distance estimation less reliable. Step 3: Recognise that misjudging distance can lead to late braking, unsafe overtaking and failure to maintain safe following gaps. Step 4: Compare this with colour recognition and shape recognition, which are usually less critical than distance judgement for moment to moment driving safety. Step 5: Choose the option that refers directly to difficulty in judging distance between the driver's vehicle and other road users.

Verification / Alternative check:
If you read driving manuals or road safety pamphlets, you will often see statements like alcohol reduces your ability to judge speed and distance. They may also mention blurred vision and reduced side vision, but depth perception is given special emphasis because it directly influences decisions about braking and overtaking. This consistent message supports the choice that focus on distance judgement as the main difficulty.

Why Other Options Are Wrong:
Option A, light intensity, can be affected in terms of glare sensitivity, but it is not described as the main judgement problem in most safety materials. Option B, colours, can be harder to distinguish at night or when vision is blurred, but colour confusion is less central than misjudged distances for crash risk. Option D, shapes, are usually still recognisable even if vision is slightly blurred, so shape recognition alone is not the primary problem. Option E, the number of lanes, is determined more by road markings and is not typically the visual judgement emphasised in relation to alcohol and drugs.

Common Pitfalls:
Some learners think first about colours because of traffic lights and signs. While colour vision is important, a driver who misjudges how far away another car is can cause severe accidents even if colours are seen correctly. To avoid this confusion, remember that road safety campaigns focus strongly on judgement of speed and distance as key abilities affected by alcohol and drugs. Linking this message to exam questions will help you choose the correct option.

Final Answer:
When driving after using drugs or alcohol, it becomes especially difficult to judge The distance between their vehicle and other road users.