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Hot Weather and Summer Driving: The Complete UK Guide

Hot weather and summer driving in the UK can increase vehicle stress, driver fatigue, dehydration risk, glare, tyre problems and breakdown exposure, particularly for professional delivery drivers who spend long periods on the road. The safest approach is to prepare the vehicle before setting off, monitor the driver as carefully as the vehicle, and adapt speed, route planning and rest breaks to the conditions.

Extreme heat is no longer exceptional on UK roads. The Met Office recorded 40.3°C at Coningsby, Lincolnshire, on 19 July 2022, which remains the UK’s highest officially recorded air temperature.

For courier drivers, the effect is cumulative. A working van may spend hours in stop-start traffic, repeatedly heat up while parked, carry a substantial load and operate with air conditioning, navigation equipment and other electrical systems running throughout the day.

That makes summer vehicle preparation part of road safety, not just vehicle maintenance.

Drivers who use a van professionally should combine the precautions below with regular vehicle maintenance for delivery drivers and normal manufacturer service schedules.

What Does Hot Weather Do to a Car or Van?

Hot weather increases thermal stress on tyres, cooling systems, batteries, air-conditioning systems and the people travelling inside the vehicle.

The principal vehicle-related risks are:

• Cooling-system problems — high ambient temperatures reduce the temperature difference between the radiator and surrounding air, making effective cooling more important.
• Tyre problems — tyre temperature and pressure increase during driving, particularly on long, heavily loaded or high-speed journeys.
• Battery deterioration — high under-bonnet temperatures can accelerate internal battery corrosion and deterioration.
• Air-conditioning demand — keeping the cabin cool consumes energy, whether that energy comes from a combustion engine or an EV traction battery.
• Reduced visibility — strong sunlight, windscreen contamination and low-angle glare can make hazards substantially harder to see.
• Driver heat stress — excessive cabin temperature and inadequate hydration can reduce concentration and increase fatigue.

A properly maintained vehicle should still operate safely in hot weather. If the temperature gauge rises abnormally, coolant is repeatedly lost or warning lights appear, heat should not simply be blamed on the weather. Those symptoms can indicate an underlying fault requiring investigation.

GOV.UK states that drivers are responsible for ensuring their vehicles are roadworthy and specifically identifies tyres, oil, coolant, battery condition and screenwash among the items that should be checked at appropriate intervals.

Check your vehicle is safe to drive — GOV.UK

What Counts as a Heatwave or Extreme Heat Warning in the UK?

A UK heatwave is defined by location-specific temperature thresholds, while Met Office Extreme Heat Warnings are based on expected impacts rather than one fixed temperature.

This distinction matters.

A heatwave occurs when a location records at least three consecutive days on which the daily maximum meets or exceeds the threshold for that area. Those thresholds vary geographically.

A Met Office Extreme Heat Warning, by contrast, is based on impact. Forecasters consider the probability and likely consequences of the heat rather than simply waiting for one national temperature to be reached.

Heat-Health Alerts are another system. In England, these are issued by the UK Health Security Agency in partnership with the Met Office and are specifically concerned with health impacts.

Drivers should therefore pay attention to the warning level, expected impact, overnight temperatures and local forecast, not simply the headline daytime maximum.

Met Office heatwave definition

Met Office weather warnings guide

Why Hot Roads Can Affect Tyres and Vehicle Handling

Road surfaces can become substantially hotter than the surrounding air because dark asphalt absorbs solar radiation, increasing heat exposure for tyres and softening some road surfaces during prolonged hot weather.

This does not mean that every warm road suddenly loses grip. The practical risk comes from heat interacting with tyre condition, loading, inflation pressure, speed and existing road-surface defects.

Drivers should pay particular attention to:

• visible tyre damage
• bulges or cuts in sidewalls
• abnormal vibration
• incorrect cold tyre pressure
• insufficient tread
• heavy vehicle loading
• unusually soft or damaged road surfaces

For cars and light vans, the UK legal minimum tread depth is 1.6mm across the central three-quarters of the tyre and around its circumference.

The legal minimum should not be treated as a maintenance target. Professional drivers should monitor tyre condition throughout its usable life rather than waiting until a tyre reaches the statutory threshold.

What Vehicle Checks Should Drivers Make Before a Hot-Weather Journey?

Before a summer journey, drivers should check fuel or charge, oil, tyres, coolant, electrics, lights, screenwash and overall vehicle condition.

A useful memory aid is the FORCES approach:

The Highway Code says a vehicle must be legal and roadworthy before setting off, while route planning, adequate fuel or charge and appropriate breaks should also be considered.

For delivery work, a short pre-route inspection is particularly valuable because a multi-drop driver may complete dozens or hundreds of individual stops before returning to a depot or home base.

Drivers considering running their own vehicle commercially can also read Pegasus Couriers’ guide to becoming a delivery driver with your own van.

How Does an Engine Cooling System Control Heat?

The cooling system transfers heat away from the engine through coolant circulation, the radiator, thermostat, water pump, expansion tank and cooling fans.

During normal operation, coolant absorbs heat from the engine. The water pump circulates it through the cooling system, and the radiator transfers that heat to the surrounding air.

At higher vehicle speeds, air flowing through the grille assists this heat transfer. At low speeds or while stationary, electric or mechanically driven cooling fans become particularly important.

Most modern vehicles use an antifreeze/coolant mixture rather than plain water. Ethylene glycol is common, but drivers should use the exact coolant specification and mixture recommended by the vehicle manufacturer rather than increasing the antifreeze concentration simply because the weather is hot.

A typical 50:50 coolant mixture provides both freeze and boil-over protection, but the performance of the complete cooling system also depends on system pressure and vehicle design. One major coolant manufacturer, for example, specifies boil-over protection of approximately 129°C for its 50:50 formulation.

The practical rule is simpler:

Do not improvise coolant ratios. Use the correct specification for the vehicle.

Repeated coolant loss, visible leaks, overheating or pressure problems require diagnosis rather than repeated topping-up.

Does Stop-Start Traffic Make Engines Overheat?

Stop-start traffic increases cooling-system demand because the vehicle receives less natural airflow through the radiator, but a healthy modern vehicle should not normally overheat simply because it is stationary in summer traffic.

At low speed, radiator fans compensate for reduced airflow.

If the temperature gauge climbs abnormally while stationary but returns to normal at speed, possible causes can include:

• a defective radiator fan or relay
• low coolant
• a thermostat fault
• blocked radiator airflow
• water-pump problems
• leaks or pressure loss

Summer traffic can also lengthen routes significantly.

For professional couriers, effective software de planificare a traseelor can therefore have a safety and efficiency benefit as well as a logistical one. Reducing unnecessary mileage and prolonged congestion can reduce driver fatigue, fuel or energy consumption and the amount of time a vehicle spends operating under high thermal load.

Does Hot Weather Increase Tyre Pressure?

Tyre pressure normally rises as the tyre becomes warmer, which is why pressures should be checked when tyres are cold and set to the vehicle manufacturer’s specification.

Do nu reduce pressure simply because a hot tyre produces a higher reading after a journey.

The Highway Code states that tyres must be correctly inflated according to the vehicle manufacturer’s specification for the load being carried.

For a working courier van, load matters. The appropriate pressure may differ between an empty vehicle and one operating near its permitted payload.

Before a long journey, inspect:

• cold inflation pressure
• tread depth
• cuts and cracking
• sidewall bulges
• embedded objects
• uneven wear
• valve condition

A bulge or structural defect should not be treated as a minor cosmetic problem. It can indicate internal tyre damage requiring professional assessment or replacement.

Why Can Summer Heat Damage Vehicle Batteries?

High temperatures can accelerate chemical deterioration and corrosion inside lead-acid batteries, which can shorten battery life even though battery failure is commonly associated with winter.

Cold weather often exposes a battery that has already lost capacity, while high under-bonnet temperatures may have contributed to that deterioration months earlier.

Possible warning signs include:

• slower-than-normal starting
• intermittent electrical faults
• corrosion around terminals
• battery or charging-system warnings
• repeated flat-battery incidents

Battery age alone is not a sufficient reason to replace an otherwise healthy battery. Testing the battery and charging system provides better evidence than using an arbitrary age threshold.

Delivery vehicles deserve particular attention because frequent stopping and starting, electrical accessories, refrigeration or communication equipment, and short urban journeys may create a demanding duty cycle.

Is Air Conditioning or Opening the Windows More Efficient?

Air conditioning uses energy, while open windows increase aerodynamic drag, so the most efficient option depends on vehicle speed, temperature, vehicle design and driving conditions.

There is no reliable universal rule such as “AC always adds 10%” or “windows are always more efficient below a particular speed.”

For safety, cabin comfort matters.

If excessive heat is making a driver tired, uncomfortable or unable to concentrate, avoiding air conditioning purely to save a small amount of fuel is a poor trade-off.

A sensible approach is to:

• ventilate a very hot parked vehicle before setting off
• use air conditioning to establish a comfortable cabin temperature
• use recirculation where appropriate to cool the cabin efficiently
• keep the system serviced if cooling performance falls
• park in shade where practical

Electric vehicles use traction-battery energy for cabin cooling, so heavy climate-control use can reduce available driving range. The exact reduction varies significantly with ambient temperature, vehicle efficiency, journey length and HVAC technology.

How Should Drivers Use TPMS in Hot Weather?

A tyre-pressure monitoring system can warn about significant pressure problems, but it does not replace routine manual inspection and cold-pressure checks.

Two broad TPMS designs are used:

Direct TPMS uses pressure sensors associated with individual wheels.

Indirect TPMS generally detects differences in wheel behaviour through systems such as ABS wheel-speed sensing rather than measuring tyre pressure directly.

Drivers should not assume that the absence of a dashboard warning means every tyre is correctly inflated.

The authoritative figure remains the manufacturer’s recommended cold inflation pressure for the relevant vehicle load.

How Does Summer Sun Glare Affect Driving?

Low-angle sunlight can temporarily reduce a driver’s ability to see vehicles, cyclists, pedestrians, road signs and braking traffic ahead.

The Highway Code specifically says drivers should slow down and, if necessary, stop if dazzled by bright sunlight.

A clean windscreen is particularly important because dust, smears and insect residue scatter light and can make glare worse.

Useful precautions include keeping the inside and outside of the windscreen clean, maintaining screenwash, using the sun visor and wearing suitable sunglasses that do not restrict vision.

The wider principle is visibility: if glare prevents you from seeing the road clearly, reduce speed rather than attempting to maintain normal progress.

This is part of the same defensive-driving approach covered in Pegasus Couriers’ broader guide to road safety for drivers.

Can Hot Weather and Dehydration Affect Driving Performance?

Yes. Heat, dehydration and fatigue can impair concentration, increase discomfort and contribute to driving errors.

An often-cited Loughborough University study examined mild hypohydration during a two-hour simulated driving task. Participants in the fluid-restricted condition had an average body-mass reduction of around 1.1% and made significantly more minor driving errors than when adequately hydrated.

The researchers compared the magnitude of the increase in driving errors with effects reported elsewhere at around 0.08% blood alcohol concentration. That does nu mean dehydration literally produces the same physiological state as alcohol intoxication, nor should it be presented as a universal BAC equivalence.

It is also important to distinguish UK drink-drive limits.

The legal blood-alcohol limit is:

For professional drivers, the practical conclusion is straightforward: do not deliberately restrict fluid intake to avoid toilet stops.

How Much Should a Driver Drink in Hot Weather?

There is no single fixed hourly water requirement that is correct for every driver; fluid requirements depend on temperature, activity level, body size, diet and individual health.

NHS guidance says most people should generally aim for 6–8 cups or glasses of fluid per day, but more may be required in hot environments or during prolonged physical activity.

Courier drivers can require additional fluid because delivery work combines driving with repeated walking, lifting and exposure to outdoor temperatures.

Useful hydration indicators include:

• drinking regularly rather than waiting until the end of the shift
• increasing fluids during hot or physically active periods
• keeping water readily available in the vehicle
• watching for thirst, dizziness, tiredness and headache
• using urine colour as a rough indicator, with pale urine generally suggesting better hydration

Dark yellow, strong-smelling urine, dizziness and unusual tiredness can be symptoms of dehydration.

Tea and coffee can contribute towards normal daily fluid intake. Caffeine can have a mild diuretic effect, but it is inaccurate to claim that ordinary caffeinated drinks automatically dehydrate the body more than the liquid they provide.

Nutrition matters too. Drivers spending long periods on the road can use Pegasus Couriers’ guide to healthy eating for professional drivers alongside sensible hydration planning.

NHS hydration guidance

How Should Drivers Protect Themselves From the Sun?

Drivers who spend long periods outside the vehicle should protect exposed skin and eyes from strong summer sunlight.

The NHS recommends sunscreen of at least SPF 30 cu at least four-star UVA protection, alongside shade and suitable clothing rather than relying on sunscreen alone.

For delivery drivers this is especially relevant because a working day can involve hundreds of transitions between the van and outdoor delivery points.

Protect:

• față
• ears
• neck
• arms
• hands
• other exposed skin

Sunscreen should be reapplied according to its instructions, particularly after heavy sweating.

NHS sunscreen and sun-safety guidance

How Can Drivers Keep Children and Pets Safe in Hot Vehicles?

Never leave children or animals unattended in a hot parked vehicle simply because the stop is expected to be short.

Vehicle interiors can heat rapidly in direct sunlight, and opening a window slightly does not make a parked vehicle reliably safe.

Young children, older people, people with certain medical conditions and animals can be particularly vulnerable to heat stress.

For pets, the relevant legislation differs across the UK.

În England and Wales, the Animal Welfare Act 2006 makes it an offence to cause unnecessary suffering to a protected animal.

În Scoția, animal welfare is governed principally by the Animal Health and Welfare (Scotland) Act 2006. Scottish Government guidance identifies unnecessary suffering under Section 19 and places welfare responsibilities on those responsible for animals.

If an animal appears to be in immediate danger inside a hot vehicle, contact the police. Do not assume that breaking a vehicle window automatically carries legal immunity; the circumstances and justification for any damage can matter.

Is It Illegal to Drive After Taking Hay-Fever Medication?

Taking an antihistamine is not automatically illegal, but driving while the medicine makes you unfit to drive can be an offence.

Chlorphenamine, found in products including Piriton, is a sedating antihistamine. The NHS warns that it can cause sleepiness, dizziness, blurred vision and difficulty concentrating and says not to drive if those effects occur.

UK drug-driving law makes it illegal to drive when you are unfit because of legal or illegal drugs. Police may conduct a field impairment assessment where impairment is suspected.

The correct semantic relationship is therefore:

medicine → possible impairment → unsafe driving → potential offence

not:

medicine → automatic driving offence

Anyone unsure whether a medicine affects driving should check the patient information leaflet and speak to a pharmacist, doctor or healthcare professional.

GOV.UK drug-driving law

Can You Drive in Flip-Flops or Bare Feet in the UK?

There is no blanket UK law saying that driving in flip-flops or barefoot is automatically illegal, but footwear must not prevent safe control of the vehicle.

Highway Code Rule 97 says drivers should ensure that clothing and footwear do not prevent them using the controls correctly.

That distinction matters.

Rule 97 does not create a standalone “flip-flop offence”. However, inappropriate footwear could contribute to unsafe vehicle control and become relevant if a driver’s actions amount to a road traffic offence.

For professional driving, secure footwear that allows predictable pedal operation is therefore the sensible standard.

How Should Drivers Overtake Tractors and Agricultural Vehicles in Summer?

Drivers should overtake agricultural vehicles only when the road ahead is sufficiently clear and the manoeuvre can be completed safely and legally.

Agricultural traffic becomes more common on many rural routes during harvesting and other seasonal work.

There is no universal Highway Code rule requiring exactly 300 metres of clear road before overtaking.

Instead, Highway Code Rules 162–169 require drivers to assess visibility, available space, other road users and the characteristics of the vehicle being overtaken. Rule 164 specifically warns that large and agricultural vehicles can restrict the driver’s view of the road ahead.

Rule 169 deals with slow-moving vehicles allowing traffic to pass when safe; it is not the rule prohibiting overtaking on bends or near junctions.

The safest principle is simple:

If you cannot clearly see enough road to complete the entire manoeuvre safely, do not begin the overtake.

What Should You Do if an Engine Starts Overheating?

If the temperature gauge rises abnormally or an overheating warning appears, reduce vehicle load and find a safe place to stop before serious engine damage occurs.

If safe to do so:

1. Switch off the air conditioning.
2. Reduce engine load.
3. Move to a safe stopping place.
4. Switch the engine off if the vehicle is overheating.
5. Allow the cooling system to cool before inspection.
6. Never remove a pressurised coolant or radiator cap while the system is hot.
7. Seek breakdown assistance if the cause is unclear or coolant has been lost.

Turning the cabin heater to maximum can sometimes transfer additional heat from the engine coolant through the heater matrix and may help temporarily while reaching a safe stopping location. It is not a repair and should never be used to justify continuing a journey with a failing cooling system.

Repeated overheating requires diagnosis.

What Should Be in a Summer Breakdown Kit?

A useful summer breakdown kit should help occupants remain visible, hydrated, contactable and protected from the weather while waiting for assistance.

Consider carrying:

A warning triangle can be useful on suitable ordinary roads, but the Highway Code says it should be positioned at least 45 metres behind a broken-down vehicle where appropriate and must never be used on a motorway.

What Should You Do if You Break Down on a Motorway?

On a motorway, the priority is to get the vehicle and occupants away from live traffic whenever that can be done safely.

Highway Code Rule 277 says that if a vehicle develops a problem, drivers should leave at the next exit or reach a service area if possible.

If that is not possible:

• move left
• use an emergency area or hard shoulder where available
• stop as far left as possible
• switch on hazard warning lights
• exit on the side furthest from traffic if safe
• move well away from the vehicle and traffic
• get behind a safety barrier where one is available and safe to use

If the vehicle cannot reach the left-hand side or occupants cannot safely leave it, the Highway Code says to remain in the vehicle with seatbelts and hazard lights on and call 999 immediately.

Never place a warning triangle on a motorway.

Emergency areas are identifiable by blue signs carrying an orange SOS symbol.

Highway Code motorway breakdown guidance

Does Summer Weather Change the Risks for Courier Drivers?

Yes. Courier drivers experience summer risks more intensively because they combine prolonged driving with repeated stops, manual activity, route deadlines and frequent transitions between air-conditioned vehicles and outdoor heat.

That creates a connected risk chain:

heat → physical fatigue → lower concentration → slower hazard recognition

At the same time:

heat → greater vehicle thermal load → component stress → higher breakdown exposure

And operationally:

summer congestion → longer routes → greater driver exposure → more fatigue and energy consumption

The solution is not one isolated precaution. Effective summer delivery work requires vehicle maintenance, route planning, hydration, realistic workloads, safe stopping behaviour and driver awareness to work together.

Drivers operating in Scotland should also remember that delivery stopping and parking remain subject to local road restrictions. Pegasus Couriers has a separate explanation of the pavement-parking ban in Scotland for drivers who regularly make urban and residential deliveries.

How Can Route Planning Reduce Summer Driving Risk?

Good route planning can reduce unnecessary mileage, congestion exposure, missed delivery windows and the amount of time a driver spends operating in peak heat.

For courier businesses, summer route planning should consider:

• forecast temperatures
• known congestion
• lucrări rutiere
• seasonal tourist traffic
• suitable rest locations
• charging or fuelling requirements
• delivery density
• vehicle range
• customer time windows

Route optimisation is therefore connected not only to productivity but also to driver fatigue, vehicle thermal load and fuel or battery use.

Read more about software de planificare a traseului și de ce funcționează.

What Is the Best Summer Driving Routine for a Delivery Driver?

The safest summer routine combines a pre-route vehicle inspection, adequate hydration, weather awareness, planned breaks and continuous monitoring of tyres, warning lights and driver condition.

Before the route:

Weather → vehicle → driver → route

Check the forecast and warnings.

Check tyres, coolant, oil, fuel or charge, lights and screenwash.

Take adequate drinking water and sun protection.

Plan the route and likely breaks.

During the route: Monitor → adapt → stop when necessary

Watch warning lights and temperature readings.

Drink regularly.

Use air conditioning when needed to maintain a comfortable driving environment.

Slow down where glare or visibility becomes problematic.

Take a break if concentration deteriorates.

Do not allow delivery pressure to override road safety.

For drivers interested in professional courier work, Pegasus Couriers provides information on current opportunities and the application process through its courier driver application page.

Frequently Asked Questions About Hot Weather Driving

What tyre pressure should I use in hot weather?

Use the vehicle manufacturer’s recommended cold tyre pressure for the load you are carrying.

Do not deliberately lower cold pressure because warm tyres will increase in pressure during driving.

Check the vehicle handbook, fuel-filler information or pressure label provided by the manufacturer.

Tyres should also be inspected for tread depth, cuts, bulges and other defects.

Should I let air out of a tyre because its pressure rises when it is hot?

No. Do not normally bleed pressure from a tyre simply because a reading taken after driving is higher than its cold pressure.

Tyre manufacturers specify pressures on a cold basis.

Allow the tyre to cool and compare the cold reading with the vehicle manufacturer’s specification.

Can hot weather alone make a healthy engine overheat?

A correctly functioning cooling system should normally control engine temperature even in hot weather, although high temperatures and heavy operating conditions increase the demand placed on it.

An abnormal rise in temperature may indicate a cooling-system problem rather than simply “hot weather”.

Persistent overheating needs investigation.

Can dehydration make driving less safe?

Yes. Research indicates that even relatively mild hypohydration can increase minor driving errors during prolonged monotonous driving.

A Loughborough University study found significantly more driving errors in its fluid-restricted condition than in the adequately hydrated condition.

Drivers should drink regularly and increase fluid intake appropriately during hot or physically demanding work.

Is 0.08% the drink-drive limit in Scotland?

No. Scotland’s legal blood-alcohol limit is 50mg per 100ml of blood, equivalent to 0.05%.

England, Wales and Northern Ireland use the higher limit of 80mg per 100ml, equivalent to 0.08%.

Can I drive after taking Piriton or chlorphenamine?

Only if the medicine is not impairing your ability to drive safely.

Chlorphenamine is sedating and may cause sleepiness, dizziness, blurred vision or impaired concentration.

The NHS specifically advises drivers not to drive if they experience those effects.

Are flip-flops illegal for driving?

Flip-flops are not automatically illegal, but footwear must allow proper control of the vehicle.

Highway Code Rule 97 says clothing and footwear should not prevent correct use of the controls.

How much water should a courier driver drink in summer?

There is no universal quantity that every driver must consume each hour.

NHS guidance recommends drinking regularly and increasing fluid intake when you are hot, sweating or physically active.

Delivery drivers should keep fluids accessible and watch for signs of dehydration rather than following an arbitrary one-size-fits-all hourly target.

What should I do if sunlight makes it difficult to see the road?

Slow down and stop if necessary until you can see safely.

Highway Code Rule 93 specifically addresses being dazzled by bright sunlight.

Keep the windscreen clean, use the vehicle’s sun visor and wear suitable sunglasses when appropriate.

Should I use a warning triangle after breaking down on a motorway?

No. The Highway Code specifically says never to use a warning triangle on a motorway.

Where appropriate on other roads, it advises placing one at least 45 metres behind the vehicle.

What is the safest response to an animal trapped in a hot vehicle?

Contact the police if the animal appears to be in immediate danger, and provide the vehicle location and the animal’s condition.

Do not assume that damaging somebody else’s vehicle is automatically lawful. Emergency circumstances may be legally relevant, but the safest first action is to involve the emergency services.

Animal-welfare legislation also differs between Scotland and England/Wales.

What is the main summer-driving rule for professional couriers?

Prepare the vehicle, manage the driver and adapt the route to the conditions.

Summer road safety is not one issue. It is the interaction between:

weather + vehicle condition + driver condition + road conditions + workload + journey planning.

Treating those factors as one connected operating system reduces avoidable breakdowns, fatigue and risk while helping professional drivers complete routes safely and efficiently.

Phil West

Pegasus Couriers is a leading UK delivery partner for major eCommerce brands such as Amazon, Evri, and Yodel. Founded in 1988, the company is directed by Phil West, a UK military veteran who advanced from a Pegasus delivery driver to Director. Operating across multiple UK depots with a fleet of more than 500 drivers, Pegasus Couriers prides itself on exceptional service and a strong culture of internal career advancement.