Some theory test topics are hard because there is a lot to learn. Others are hard for a different reason: you think you know them. A number you half-remember, or a rule you have absorbed as a passenger, can feel right and still be wrong. These are seven areas where precise numbers and precise wording matter, with the Highway Code rule behind each one so you can check it for yourself.

1. Following distances and stopping distances

Two different ideas get mixed up here. The two-second rule is about the gap you keep to the vehicle in front. Rule 126 says to allow at least a two-second gap on high-speed roads and in tunnels where visibility is reduced, and that the gap should be at least doubled on wet roads and up to ten times greater on icy roads.

Stopping distance is how far you travel from seeing a problem to stopping. It is thinking distance plus braking distance, and it grows much faster than speed. The Highway Code's typical stopping distances show 23 metres at 30mph (9 metres thinking, 14 braking) but 96 metres at 70mph (21 thinking, 75 braking). Rule 227 adds that in wet weather, stopping distances will be at least double those needed on dry roads.

2. Speed limits, including Wales

Rule 124 sets national speed limits for cars and motorcycles: 60mph on single carriageways and 70mph on dual carriageways and motorways. In built-up areas the limit is 30mph in England and Scotland but 20mph in Wales, unless signs say otherwise. A limit is a maximum, not a target, and many theory questions test whether you would drive below it in the conditions described.

3. The hierarchy of road users

The Highway Code's introduction sets out rules H1 to H3, which learners who studied older material sometimes miss. H1 says those in charge of vehicles that can cause the greatest harm have the greatest responsibility to reduce the danger they pose to others. H2 says that at a junction you should give way to pedestrians crossing or waiting to cross the road you are turning into or from, and that you must give way to pedestrians on a zebra crossing. H3 says you should not cut across cyclists, horse riders or horse-drawn vehicles going ahead when you turn into or out of a junction or change lane.

If a question involves a pedestrian waiting at a side road you are turning into, the answer reflects H2: you should give way.

4. "MUST" versus "should"

The Highway Code uses wording deliberately. Rules with MUST or MUST NOT are legal requirements, and breaking them is a criminal offence. Rules with should or should not are advice. Breaking them is not an offence in itself, but the Code can be used in court as evidence when deciding liability. Some theory questions ask what the law requires rather than what is good practice, and this wording is how you tell the difference.

5. Sign shapes and colours

Traffic signs follow a system, and learning it lets you work out signs you have never seen. Signs with red circles are mostly prohibitive: they tell you what you must not do. Blue circles with no red border mostly give a positive instruction, telling you what you must do. Triangles mostly give warnings, and rectangles give directions and information. The Stop and Give Way signs are exceptions, each with its own distinctive shape.

DVSA lists Know Your Traffic Signs as one of the three books the multiple-choice questions are based on, so it is worth working through properly rather than relying on recognition from the road.

6. Mobile phones, including when supervising

Rule 149 says you MUST NOT use a hand-held mobile phone, or a similar device capable of interactive communication such as a tablet, for any purpose when driving. The detail people miss is that the same rule applies when supervising a learner driver. The exception is calling 999 or 112 in a genuine emergency when it is unsafe or impractical to stop.

7. Headlights and fog lights

Rule 226 says you MUST use headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres. You may also use front or rear fog lights, but you MUST switch them off when visibility improves. Questions often test the second half. Rule 236 explains why: fog lights dazzle other road users and can obscure your brake lights, so you must not use them unless visibility is seriously reduced.

How to make these stick

  • Learn the reason, not just the number. Wet roads reduce tyre grip, so distances double. A reason is easier to recall under pressure than a bare figure.
  • Check the source. When you get a question wrong, find the rule in The Highway Code. Seeing the official wording once is often enough to fix it.
  • Revisit weak topics on purpose. Getting a topic right once does not mean it is secure. Come back to it a few days later.
  • Read every word of the question. "Must", "should", "not" and "at least" change answers.

TheoryIQ shows an explanation after every practice answer, so a wrong answer turns straight into the rule you need, and progress tracking highlights the topics you keep dropping marks in. You can try the example question on our home page, see how the practice tools work, or read our mock test strategy for how to turn mistakes into marks.