Most drivers know the obvious rules: speed limits, seatbelts, no phones. What tends to catch people out are the rules sitting just outside the Highway Code's greatest hits, the ones nobody mentions in lessons and which only come up when someone gets a fine. Here are ten that regularly surprise people, including drivers who have held a licence for decades.
1. Smoking in a car with under-18s
It has been illegal since 2015 to smoke in a vehicle carrying anyone under 18, and that applies to the driver and passengers alike. Opening a window does not make it legal. The driver can be penalised for allowing it, not just the person smoking, and the fine is £50 each. Vaping is not covered by the same law, though it is still a poor idea with children in the car.
2. Sounding your horn when you should not
The horn is a warning device, not a greeting. Legally you should not use it while stationary, or in a built-up area between 11.30pm and 7am, except to warn of immediate danger from another moving vehicle. Leaning on it out of frustration can be treated as inconsiderate driving, and repeated use in a residential street at night is exactly the sort of thing that attracts a fine.
3. Splashing pedestrians
Driving through a puddle and soaking someone on the pavement is not just rude, it can be prosecuted as driving without reasonable consideration for other road users. It has resulted in fines, and in cases where it has clearly been done deliberately, penalty points. Slow down near standing water when there are people about, which is also better for your brakes and your visibility.
4. Sleeping in your car
Pulling over when you are tired is the right call, and the Highway Code encourages it. The complications are around where and how. Sleeping in a vehicle parked illegally, or on a hard shoulder, can land you in trouble, and if you have been drinking you can still be considered in charge of the vehicle even with the engine off and the keys in your pocket. If you need to stop, use a service area or a proper car park.
5. Carrying pets safely
Rule 57 of the Highway Code requires animals to be suitably restrained so they cannot distract you or injure anyone if you stop suddenly. That means a harness, a carrier, a dog guard or a boot divider. It is not a fixed-penalty offence in itself, but an unrestrained dog can lead to a careless driving charge, and plenty of insurers will query a claim if a loose animal contributed to a crash.
6. Driving with snow or ice still on the car
Clearing a small porthole in the windscreen and setting off is illegal. You must have a full view of the road, and that includes all windows, mirrors, lights and number plates being clear. Snow left piled on the roof is a specific problem, because it slides onto your windscreen when you brake or into the path of the car behind you. Give yourself the extra five minutes.
7. Flashing your headlights to warn other drivers
Officially, headlights are for letting others know you are there, not for signalling. Flashing to warn oncoming traffic about a speed camera or a police check can be treated as obstructing an officer in the course of their duty, which carries a fine. Flashing to let someone out is common courtesy but has no legal standing either, so if you accept the invitation and there is a collision, the responsibility is still yours.
8. Mobile phones, including when stationary
Everyone knows handheld phone use while driving is illegal. Fewer people realise the law covers any handheld use of the device, including at traffic lights, in stationary traffic, or while queuing at a drive-through, and it covers scrolling, filming and picking a song as well as calls. The penalty is six points and £200, which for anyone within two years of passing means an automatic revoked licence. Use a proper cradle, set your route before you set off, or pull over somewhere safe with the engine off.
9. Leaving the engine idling
Sitting with the engine running while parked is an offence under the Road Traffic (Vehicle Emissions) Regulations, and many councils actively enforce it with fixed penalties, particularly outside schools. Warming the car up on the driveway on a cold morning counts, and leaving it running unattended can also invalidate your insurance against theft. Turn it off if you are going to be more than a minute.
10. Pedestrian crossings and priority
At a zebra crossing you must give way once someone has stepped onto it, and following the 2022 Highway Code changes you should also give way to anyone waiting to cross. The same update gave pedestrians priority when you are turning into or out of a side road. Plenty of experienced drivers have not caught up with these changes, so it is worth reading properly, particularly if you learned before 2022.
None of these are obscure technicalities, they are the rules that quietly generate a lot of fines every year. Most exist for a sensible reason: keeping your view clear, keeping your attention on the road, and not making life harder for people walking. If you are learning now, you have the advantage of studying a current Highway Code. It is genuinely worth a proper read rather than skimming for the theory test, because it stays useful long after you pass.