HGV theory test questions explained

The LGV multiple-choice test asks 100 questions, and the ones candidates go looking for afterwards are nearly always about the vehicle: its blind spots, its load, its air system and its paperwork. Each question below has the correct answer, the reason behind it and a note on the distractor that catches people. You can meet all of them in the free HGV mock tests.

Seeing around the cab

You’re driving a lorry with a sleeper cab. When would a quick sideways glance be helpful?

Answer: when traffic is merging from the right or left.

A sleeper cab is longer behind the driver’s door, and the extra bodywork widens the blind area beside and just behind the cab. Mirrors do not cover all of it. At a slip road or where lanes join, a car can sit alongside in exactly that space, so a brief look to the side confirms what the mirrors seem to show. The other options (after a pedestrian crossing, on sharp bends, before a steep hill) are not situations where something arrives next to you unseen. The linked question, why a sleeper cab makes driving harder, has the answer “it increases your blind spots”. Both are in LGV practice test 3. For the full picture of where a lorry driver cannot see, read blind spots and vulnerable road users.

Loads and containers

You’re making several deliveries. What problems may the decreasing payload cause?

Answer: you might overload an axle.

It sounds backwards: the lorry is getting lighter, so how can anything be overloaded? Multi-drop loads usually come off the rear first. What remains sits towards the front, and the share of weight carried by the front axle goes up even though the total has gone down. Gross weight can be legal while one axle is over its limit. The cure is to redistribute what is left. “Exceeding kerbside weight” is the trap answer: kerbside weight is the empty vehicle and has nothing to do with payload.

How should an ISO container be secured to the trailer?

Answer: using the locking levers.

ISO containers are built with corner castings that drop onto matching securing points, usually called twist locks, on a skeletal or container-carrying trailer, and the levers lock them in. Ropes cannot restrain a steel box of that mass, sealing the doors is about security and not restraint, and pushing it against a headboard does nothing for sideways movement. A container should only travel on a vehicle that has the proper securing points.

You’re part-loading a lorry with an empty ISO container. Where should it go on the trailer?

Answer: over the rear axles.

A part load placed over the trailer’s rear axles keeps weight on the trailer wheels, which improves stability and reduces the chance of those wheels lifting in a turn. Close to the fifth wheel leaves the back of the trailer light; close to an edge puts the load off centre.

A related question asks when an articulated lorry is most likely to jack-knife. The answer is when it is unloaded, for the same reason: with no weight pressing the trailer tyres onto the road, they lose grip under heavy braking.

When must you notify telephone companies that you’re moving a high load?

Answer: when the load’s height exceeds 5.25 metres (17 feet 6 inches).

Overhead telephone lines cross roads at a lower height than most people expect. Above 5.25 metres you should tell the telephone companies your intended route in good time before the journey. The distractors are all lower heights (4.00, 4.30 and 5.00 metres), so the thing to remember is that the notification figure is the highest one offered.

Brakes and tyres

Moisture can freeze in your air storage tanks in very cold weather. How do you help prevent it?

Answer: drain the tanks daily.

Compressing air squeezes water out of it, and that water collects in the reservoirs. In freezing weather it can turn to ice in the tanks and pipes, cause a loss of pressure and lead to brake failure. Draining removes it. Most modern lorries have automatic drain valves and air dryers, so the daily job becomes checking that those are working. Pumping or “using the brakes frequently” moves air, not water. This one is in LGV practice test 9, and the air system as a whole is explained in daily checks and heavy vehicle braking.

Your brake-system warning lights are not operated by the ignition switch. How do you check them?

Answer: look for a check switch on the dashboard.

On many vehicles the warning lights come on briefly with the ignition as a bulb check. Where they do not, there is a separate test switch. Asking someone to look at your brake lights checks different lamps altogether, and leaving it until the end of the journey defeats the purpose.

Which of these would be illegal: different makes of tyre on one axle, a recut tread, a tread depth of 1.3 mm, or exposed ply or cord?

Answer: a tyre with exposed ply or cord.

Three of the four are legal on a large goods vehicle, and that is what makes the question hard for car drivers.

• 1.3 mm of tread is legal because the minimum for large vehicles is 1 mm across three-quarters of the tread breadth, in a continuous band around the tyre. The 1.6 mm figure applies to cars and light vans.
• Recut tread is not an offence on a large goods vehicle.
• Different makes on one axle is not an offence either.

Exposed ply or cord means the structure of the tyre is damaged, and that is an offence on any vehicle.

Your tractor unit has three air lines and the trailer has two couplings. Which line do you not connect?

Answer: the blue line.

Red is the emergency line and yellow is the service line; both are present on two-line and three-line systems. Blue is the auxiliary line, which a two-line trailer has no coupling for. Follow the manufacturer’s instructions for stowing it. The reverse question, a two-line unit and a three-line trailer, has the matching answer: the trailer’s auxiliary line is left unconnected.

Incidents and records

What does a plain orange rectangle on a vehicle at an incident mean?

Answer: it is carrying dangerous goods.

Vehicles carrying dangerous goods display orange plates. A plain one tells you only that hazardous material is on board; panels with numbers and symbols identify what it is. At an incident, keep your distance, note any markings you can read safely and pass them to the emergency services when you call.

An enforcement officer keeps one of your tachograph charts. Who signs the back of the replacement?

Answer: the officer.

When a chart is retained, ask the officer to sign the back of the chart you continue with, adding their name, telephone number and the number of charts kept. That signature is your evidence of why the original is missing. Two neighbouring questions follow the same logic of keeping one continuous record: if you change to another vehicle with the same type of tachograph, take your chart with you and use it there; and one chart covers 24 hours. The rules behind the records are in drivers’ hours for lorry drivers.

Using explanations well

For lorry questions, “what could go wrong, and to whom?” usually finds the answer even when the wording is new: an overloaded axle, a frozen brake line, a car hidden beside the cab. After each practice test, write that sentence for every question you missed. The questions are based on DVSA’s guide to driving goods vehicles as well as the Highway Code; the tyre rule above is in the Highway Code’s annex on vehicle maintenance, safety and security.