Here are 13 reasons why...
1. "Are we nearly there yet...?"
It's the classic line, handed down through generations of kids and responsible for parents tearing out so much hair that the clumps could collectively thatch a Cotswolds cottage. No, we're not nearly there yet. Nor will we be there in 30 seconds, when you ask again. We're in gridlock on the M25. We may never be there.
2. The car seats
A process that requires you to clamp the seat belt slack between your teeth like a dressage pony, then weave it over and under to resemble the world's most complicated naval knot. To make life a little easier, your children will flex themselves into the 'rigor-mortis' position, and smack your unguarded face repeatedly with a plastic dinosaur.
3. Traffic lights - lots of them
It's true: one major perk of road travel is that it knocks hyperactive kids out for the count. But there's a dangerous caveat: this only works as long as the vehicle is in motion. And so, your car becomes a bit like the booby-trapped bus from Speed: if it ever slows below 20mph, your child will go off like a tiny, red-faced atom bomb. And God help us, here comes a red light...
4. The seat-kicking
Thud. Thud. Thud. All the way from Calais to the Pyrenees (and back). You feel demeaned, like a high-school nerd in an '80s screwball comedy with a sign pinned to his back saying 'Kick Me'. In the end, defeated, you'll roll your seat full-forward and hunch in the brace position for the rest of the journey, just to make it stop.
5. The music
It's bad enough that Now That's What I Call A Pre-School Mega-Mix! has bumped Arctic Monkeys from your car stereo. But what's worse is that your kids will demand one specific song to be repeated on an endless loop. After seven hours of Gangnam Style or What Does The Fox Say?, you will want to pull onto the M1's hard shoulder and run shrieking into the night, your brain having finally liquidated in your skull.
6. The screaming
"Muuuum, daaaaad, he's annoying me." Listen up, car designers: what we really want is one of those soundproof glass partitions, as used by limo drivers to block out the screeches when ferrying hen parties through Liverpool at 3am.
7. The toy-dropping
Regular as clockwork, at three-minute intervals, the passenger seat parent will be called upon to demonstrate their skills as a contortionist. Yep, there you go again: twisting in your seat, eyeballs bulging, pelvic-floor muscles weeping, fingertips straining for a stray Moshi Monster in the footwell.
8. The travel sickness
You've slapped so many studded wristbands on your child's arms that they resemble that bloke who flogs dodgy watches down the pub – but after the third consecutive mini-roundabout, they'll still hit the back of your head with a flume of partially digested Pom-Bears. Just grit your teeth, push on to South Mimms services and clean yourself up with napkins in the Little Chef toilets.
9. The games
At some point in the journey, misty-eyed parents pining for a more innocent time will turn off the head rest DVDs and call for a game of I Spy. Bad move. Your kids will either choose something forehead-slappingly obvious from the car's interior ("Is it the steering wheel – again?") or a cooling tower that you passed 12 miles back outside Sheffield. Back to Chipwrecked it is, then...
10. "I need a wee..."
You've got three options when that urgent little voice pipes up. You can hang on for the services and risk the car upholstery. You can neck the 2-litre family bottle of Evian and hand it back. Or you can swing onto the hard shoulder, hide your child behind a shrub and sob inwardly when the wind changes direction and streaks your new Diesel jeans with piddle. There is no right answer here.
11. The memories of your sports car
Pre-kids, your pride and joy was a two-seater that cornered on wheels and had bhp to burn. (Or, at least that's what you dreamt of.) Now, you're driving a dull parentmobile whose criteria for purchase was that it had Isofix car seat points and generous boot space. Periodically, you will pull up at the lights and see your former selves in the next lane, driving a Boxster, wearing Ray Bans and howling with laughter.
12. The awkward questions
In the car, you're a captive audience, and your kids will take full advantage, grilling you on the specifics of the 'special kiss' that Daddy gave Mummy to put them in her tummy, and the logistics of how Father Christmas crosses seven continents in a single night. Your only hope may be to distract them by pointing out roadkill.
13. The debris
You finally arrive at your destination at 3am, crick-necked and bloodshot-eyed. At this point, the kids will be carried off to bed, leaving you to inspect the back of the car: a bombsite of biscuit crumbs, crisp packets and soiled wipes that suggests a fox let loose in a tuck shop.
More on Parentdish: Are we nearly there yet? Top tips for car journeys