London Black Cabs - fiddling the fares?

[Deleted User]

Hell and thanks for your replies.

I wasn't suggesting that all black cab drivers are fiddling the fares. I was merely pointing out - or rather, questioning, whether there is scope for these devices to be inaccurate, like any other technological device out there. The responses I've got seem to suggest they are totally foolproof and it's impossible for them to lose their accuracy, which I very much doubt given that the device relies on an accurate input from the (tachometer?) or some other component, which in itself is subject to wear and tear.

I've measured the distance in several different ways and it works out as 0.88M. The topography is flat as a pancake. In calculating this 0.88M I walked the distance myself, ensuring that I crossed the road a little bit further away than I needed to, so taking into account a wider turning into the left-hand land (e.g. being over-generous with distance estimates). I also used https://www.walkjogrun.net to compare against with Google Maps. I've also used my own GPS device in four of the cab journeys I've made. The maximum distance I've travelled was 0.9M, well short of the 33% margin of error being suggested here. The average hits 0.88M spot-on.

Like I said, I'm not suggesting that cab drivers are tampering with the devices at all - I'm just questioning the accuracy of devices that may be several years old. The PCO inspects vehicles, but does it inspect/check the devices?

Either way, I've sent a letter to the PCO and I'm going to take the advice on here and ask a cabbie when I next take one.

geordieracer

Deleted_User wrote: »

Hell and thanks for your replies.

I wasn't suggesting that all black cab drivers are fiddling the fares. I was merely pointing out - or rather, questioning, whether there is scope for these devices to be inaccurate, like any other technological device out there. The responses I've got seem to suggest they are totally foolproof and it's impossible for them to lose their accuracy, which I very much doubt given that the device relies on an accurate input from the (tachometer?) or some other component, which in itself is subject to wear and tear. And sat navs cannot be wrong also? They rely on a satellite signal which can also go wrong from time to time


The PCO inspects vehicles, but does it inspect/check the devices? Yes they do check the devices

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so you live 0.88 miles, you have checked all with maps and a sat nav, now again, do some of them charge you because its a secondary tarrif when they pick you up? I.E. After midnight? Or do they add 1 extra on sometimes because you have a large bit of luggage with you, which you have admitted to carrying...

3plus1

Sounds to me that the discrepency is primarily the luggage. Some cab drivers add the charge automatically, others don't always if it's small.

Also, if you're charged a fiver instead of £5.something, it could be a change issue. I've seen cab drivers round down if they're low on coins.

If you know the fare might go over £5, why not carry more than £5?

Personally, I think your discrepency is too small to warrant all this discussion. You are never going to get charged the exact same fare for the same journey. All you can aim for is about the same.

[Deleted User]

I can assure you that the discrepancy is not the luggage.

I can see the meter when I get in. It's £2.20. And as we drive, the counter goes up. There is never anything added on and it's always £2.20 when I get in. The luggage isn't big, but heavy, so I very much doubt they'll add it on.

There's no rounding down either: I'm referring to the fare displayed on the meter.

If you think my discrepancy is too small to warrant this discussion, ask yourself how a 33% margin of error might affect other passengers. A £30 journey (from zone 6 to Gatwick Airport, for example), would cost £40, which is quite a difference.

Anyway, let's see what the PCO say.

BFG_2

No, it would be £30/£32

[Deleted User]

BFG wrote: »

No, it would be £30/£32

No, it would be £40 (ish - just less).

33% of £30 is £10. Add on the discrepancy and it's £40.

How do you get £32?

BFG_2

Because the discrepancy is driven by the shortish nature of jouney. As such it's unreasonable to simply extrapolate this to larger journeys, as the discrepancy will play a lesser role.

Hope that makes sense.

By way of examples
1. You go to newsagent in car, distance 500 yds, one junction - difficult getting out sometimes so time taken is from bottom time of 1 minute [clear run] to 4 minutes [busy and traffic lights against you]. 4 mins is as likely as 1 min, so that's a variation range of 400% of the minimum for 99% of trips.

2. You go to visit relatives, distance 15 miles, several junctions, then dual carriageway.

For your extrapolation to apply the time to visit relatives would have to be from a bottom end of say 20 minutes, up to say 80 minutes. That's patently not the case [except once in 1000 visits when there is a major crash somewhere and snarls up the d/c]. The reality is that the 'typical' time for 99% of trips would be from 20 mins [clear run, inc your junction] to 25 mins [junction slow]. So that's a variation range of only 25% of the minimum for 99% of trips.

So what I'm saying is that 'vagaries' have a much bigger % effect at the 'short' overall journeys. Small changes have a big effect at small sample sizes.

Luggage charge is another example of a 'one off discrepancy' that does NOT extrapolate ie it's 50p for a £5 journey [10% 'extra'] and 50p for a £50 journey [now only 1% 'extra'].

BFG_2

Putting it another way.........

The longer the journey, the narrower and taller the distribution curve for journey times would be.

geordieracer

BFG wrote: »

Putting it another way.........

The longer the journey, the narrower and taller the distribution curve for journey times would be.

Much simpler :T

[Deleted User]

Fair enough, but what I'm suggesting/querying is the source of the discrepancy. It's not - I believe - caused by junctions, traffic, luggage etc which are discrete events that have a disproportionately large impact on shorter journeys than larger ones. I'm querying whether the meter itself is out, which has a proportional impact regardless of the journey length.

If the meter is adding on 20p after, say, 99m rather than 100m, then the length of the journey won't affect the percentage discrepancy.

I get what you're saying, but what I am saying is that the bias occurs because of inaccuracies in the meter (potentially) rather than any kind of intervening act, so actually in this particular scenario the distribution curve would not get taller or narrower (although I accept it would IF they added on luggage charges, which they do not).

So, if the inaccuracy is in the meter, then YES, it would be £40 rather than £32, and it should be £30 (on average).

Or, in other words, your total cost is (X + (X/3)) where X is the 'average' cost of the trip (applies only to smooth journeys where distance is the calculator for the fare - and where it doesn't switch to a time-based fare (e.g. 26.something seconds of 198 metres, whichever comes first). Your point is valid but only applies in the calculation of what X should be in the first place. The meter being wrong is what is responsible for the +(X/3) bit - the calculation of X is a discrete element.

So, example:

Taxi journey of 20 kilometres. Let's say it's totally smooth (I know it's not practical, but let's make that assumption).
Cost = £2.20 for first 200 metres (say) and then 20p for every 200m thereafter.
Total cost = £2.20 + ((19800/200)*£0.2) = £22.00
If the meter is out by 33%, then it's adding on 20p every 133.34m.
Total cost = £2.20 + ((19867/133.34)*£0.2) = £31.99
Margin of error = 45%

Taxi journey of 10 kilometres.
Cost = £2.20 for first 200 metres and then 20p for every 200m thereafter
Total cost = £2.20 + ((9800/200)*£0.2) = £12.00
If the meter is out by 33%, then it's adding on 20p every 133.34m
Total cost = £2.20 + ((9867/133.34)*£0.2) = £16.99
Margin of error = 41%

So, actually, margin of error is pretty similar regardless of distance - and in fact increases over distance (but presumably flattens out to a constant value at a certain distance travelled).