Registration plates.
Why are the registration plates on cars in the UK black-on-white at the front and black-on-yellow at the back?

There must be a really good reason, because that's the convention that the French adopted when they ditched white-on-black plates a few years ago. (I think they're moving to black-on-white for both now, so there's a secondary question about why that is better yet, and why the UK doesn't do likewise.)
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 15:35, 26 replies)

So you know whether you're looking at the front or back of a vehicle?
...I honestly have no idea
( emvee cruor deo cruoris, Wed 19 Oct 2011, 15:37, closed)

it's so you know which way round the car goes
duh
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:37, closed)

There are people who need different coloured number plates to be able to work out which end of a car they are looking at?

(TheManWithThePlan cussed your mum on, Wed 19 Oct 2011, 15:42, closed)

I wouldn't know which way to face otherwise

(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:42, closed)

^This^

( Enzyme is powered by sunlight, Wed 19 Oct 2011, 15:43, closed)

It might be
an Austin Allegro
( sandettie light vessel automatic New Twitter - @bollocksreally, Wed 19 Oct 2011, 16:17, closed)

but you're not old...

( scarpe We Stole Bikes, Wed 19 Oct 2011, 16:20, closed)

I actually saw one of those the other day.
On the road. Moving, and everything.

I was slightly amazed. It makes me wonder - slightly - whether there're any functional Maestros (Maestri?) or Montegos still around.
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 16:22, closed)

My parents went through a phase of buying Montegos when I was a child.
All second-hand, all in various shades of blue, all estates, and all like driving a grumpy brick. And they all fell apart after a few short years. One in particular seemed to hate me (as much as an inanimate object can): it broke down twice and burst one tyre, all on times when I needed to be somewhere for something very important. I hated that car. It was a git.

But still, they were all better than the vomit-coloured Marina they had when I was really young.
(The Empress it seems you CAN polish a turd!, Wed 19 Oct 2011, 16:41, closed)

Anorak mode on!
There's 12 Austin Allegros still on the road and 17 Maestros.

Base models only - I'm not including the 1.6 Auto etc. in the numbers.
(azgiles, Wed 19 Oct 2011, 17:10, closed)

There's one in Dundee
An Allegro, that is. And this makes me feel really old - I learned to drive in a Maestro!
( K2k6 has a proper job these days, Wed 19 Oct 2011, 23:29, closed)

I can believe it
Having just today encountered an unusually high number of idiots driving cars while apparently being totally unaware of how they work.
(louveciennes , Volvospotter, Wed 19 Oct 2011, 21:49, closed)

What Emvee and the retard said.

( scarpe We Stole Bikes, Wed 19 Oct 2011, 15:39, closed)

that sounds like it could be a new heartwarming sitcom/cop show!
emvee and the retard:back on the streets
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:42, closed)

Naaaah. It's a painfully twee acoustic singer-songwriter duo.
The kind of band that Jo Whiley likes.
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 15:44, closed)

I could be the Meg White of my own shit pretentious rock band?
Sign me the feck up!
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:46, closed)

It's little seen sequel to Freebie & The Bean

( scarpe We Stole Bikes, Wed 19 Oct 2011, 15:48, closed)

blah blah blah....
White and Yellow backgrounds are the clearest distinguishable options for dark letters and you may as well match the number plate with the lights where it can be; white lights at front so white number plate at front; putting the yellow to the rear by default.
(norfolk_is_gay, Wed 19 Oct 2011, 15:47, closed)

So in that case,
the Dutch would have the best convention? (The matching point is one I don't buy, because it doesn't seem that important in comparison to the faff of having different coloured plates by law.)
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 15:51, closed)

so you can tell which way the car is facing, as a pedestrian
in the dark
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:49, closed)

You forgot
"... with poor binocular vision, and when the car has no headlights, but there's sufficient streetlighting to illuminate the registration plate".
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 15:52, closed)

shut up

(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Wed 19 Oct 2011, 15:55, closed)

Reflection.
UK law states that you can't have a white light source on the rear of a vehicle except for reversing purposes. The principle being if you see a white light - the vehicle is coming towards you.

As number plates are reflective a white numberplate is classed as a light source (seriously) and so you can't have a white number plate on the rear of a car.
(azgiles, Wed 19 Oct 2011, 16:03, closed)

I think a proper answer deserves acknowledgement.
And I'm not being sarcastic or mean or anything, for once.
( scarpe We Stole Bikes, Wed 19 Oct 2011, 16:14, closed)

Ah, OK.
Now that does make sense. Though it somewhat leaves open the question of why the front ones are yellow, norfolk's answer at 15:47 notwithstanding.
( Enzyme is powered by sunlight, Wed 19 Oct 2011, 16:20, closed)

That probably is about all there is to it
Black on white is the most clearly legible, but you can't have white at the back so they specify the next most clearly legible, which is presumably black on yellow.
(richardm, Wed 19 Oct 2011, 16:55, closed)

Norfolk is right
Yellow is the next best reflective colour and gives the best contrast with black letters.

This is one reason why military vehicles still use the white on black number plate style - they don't reflect and can't be used for laser targeting.
(azgiles, Wed 19 Oct 2011, 17:00, closed)

Military vehicles
If you look under the back you'll see that the diff housing is painted white. Somewhere up on the chassis is an extra "numberplate light" that can be switched on seperately, so that when they're driving in convoy with all their lights off they can switch on this little 1W light underneath to light up the white paint, so the guy behind can see where they are. Because the wheels are in the way, you can't see it from the sides.
(gordonjcp, Wed 19 Oct 2011, 17:46, closed)

Is that why that is?
I'd often wondered about that.
(richardm, Thu 20 Oct 2011, 9:29, closed)

Until I saw this question, I'd never even wondered about it.
Now, I have a reasonable sounding answer, should it come up again.
( monster munch person, man, woman... camera... TV?, Wed 19 Oct 2011, 21:29, closed)

Secondary question:
Because the French are doing it!
(LongJohnBaldry, Wed 19 Oct 2011, 16:04, closed)

Bof!

( Enzyme is powered by sunlight, Wed 19 Oct 2011, 16:20, closed)

Differences
In most of Canada and the USA the registration plates go only on the rear. It's cheaper that way. The police see only the rear while they are chasing you.
(uncle_bud is not the jelly roll king., Thu 20 Oct 2011, 1:03, closed)