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Question on unmet demand surveys
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Author:  StuartW [ Sun Oct 22, 2017 10:58 am ]
Post subject:  Question on unmet demand surveys
Regarding rank observations in an unmet demand survey, if it's stated:

"The survey suggests 5,000 passenger departures occur per week from ranks in the area, involving 6,000 cab departures."

What precisely is meant by "passenger departures" and "cab departures"?
Author:  bunny [ Sun Oct 22, 2017 11:43 am ]
Post subject:  Re: Question on unmet demand surveys
Passenger departures = Cabs with passenger
Cab departures = Cabs leaving rank without passengers. Either giving up or on radio jobs
Author:  StuartW [ Sun Oct 22, 2017 6:55 pm ]
Post subject:  Re: Question on unmet demand surveys
bunny wrote:
Passenger departures = Cabs with passenger
Cab departures = Cabs leaving rank without passengers. Either giving up or on radio jobs


Thanks, that kind of makes the numbers make a bit more sense.

However, the reason I thought the numbers meant something else was the wording:

"The survey suggests 5,000 passenger departures occur per week from ranks in the area, involving 6,000 cab departures."

In particular, the word 'involving' suggests that the two numbers are linked somehow, but you are saying they are separate.

If it had been worded like this then it would make more sense in terms of what you're saying:

"The survey suggests 5,000 passenger departures occur per week from ranks in the area, *as well as* 6,000 cab departures."
Author:  Sussex [ Sun Oct 22, 2017 8:44 pm ]
Post subject:  Re: Question on unmet demand surveys
Looking at a few SUD surveys at some ranks passenger departure exceed cab departure and at other ranks its the reverse.

The only answer has got to be what Mr Bunny said.

I suppose it is evidence that those taxis were available at some time, and if there had been customers queuing at the rank, then they would have taken them before they got their radio job.
Author:  StuartW [ Mon Oct 23, 2017 3:04 am ]
Post subject:  Re: Question on unmet demand surveys
Sussex wrote:
Looking at a few SUD surveys at some ranks passenger departure exceed cab departure and at other ranks its the reverse.


Ah, thanks, that's answered my next question - at first I thought cab departures could include both with and without passengers, but at some ranks the passenger departures exceed cab departures :?

Quote:
The only answer has got to be what Mr Bunny said.

I suppose it is evidence that those taxis were available at some time, and if there had been customers queuing at the rank, then they would have taken them before they got their radio job


Not really sure what to make of it, but reason I asked was because the Average Cab Delay figure didn't ring true, but I was assuming it meant average cab wait for passenger, but suspect it must include the cabs which departed the rank empty, so not sure if the average cab delay figure tells us anything significant.

But going back my original post, the following statement must be misleading:

"The survey suggests 5,000 passenger departures occur per week from ranks in the area, involving 6,000 cab departures."
Author:  Sussex [ Mon Oct 23, 2017 4:00 pm ]
Post subject:  Re: Question on unmet demand surveys
StuartW wrote:
Not really sure what to make of it, but reason I asked was because the Average Cab Delay figure didn't ring true, but I was assuming it meant average cab wait for passenger, but suspect it must include the cabs which departed the rank empty, so not sure if the average cab delay figure tells us anything significant.

Think the Average Cab Delay issue is a red herring anyway as it doesn't pay any part in the final SUD figure.

If the surveyor is using the tried and tested flawed Halcrow type survey.
Author:  Sussex [ Mon Oct 23, 2017 4:03 pm ]
Post subject:  Re: Question on unmet demand surveys
StuartW wrote:
"The survey suggests 5,000 passenger departures occur per week from ranks in the area, involving 6,000 cab departures."

As it is written it makes no sense.

But other than a few people in a few areas no one reads SUD surveys, apart from the one line sentence explaining if there is SUD or not, and how many cabs are required to meet any unmet demand.
Author:  StuartW [ Mon Oct 23, 2017 8:50 pm ]
Post subject:  Re: Question on unmet demand surveys
Sussex wrote:
StuartW wrote:
Not really sure what to make of it, but reason I asked was because the Average Cab Delay figure didn't ring true, but I was assuming it meant average cab wait for passenger, but suspect it must include the cabs which departed the rank empty, so not sure if the average cab delay figure tells us anything significant.

Think the Average Cab Delay issue is a red herring anyway as it doesn't pay any part in the final SUD figure.

If the surveyor is using the tried and tested flawed Halcrow type survey.


Yes, was a Halcrow survey. Well spotted - obviously an astute observer of these things. =D>

Never really looked that closely at these things before, but even the straightforward bits seem easy to pick holes in. :-s
Author:  Sussex [ Tue Oct 24, 2017 9:00 am ]
Post subject:  Re: Question on unmet demand surveys
StuartW wrote:
Yes, was a Halcrow survey. Well spotted - obviously an astute observer of these things. =D>

Never really looked that closely at these things before, but even the straightforward bits seem easy to pick holes in. :-s

All it needs now is for someone to actually work out the flawed mathematics behind the SUD equation.
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