I suspect I'm going to get in trouble for incorrect usage of the word
'differential', but nevermind...

I'm hoping that someone in the know (probably Paul C, given that he
was involved in the development of Oyster) might be able to provide
some background to this query.

As we all know bus fares in London are flat rate - Oyster PAYG users
pay 90p, cash fares are £2 - and the flat fare for London buses has
been around since 2004 (I think). There were peak (pre-0930) and off-
peak Oyster PAYG fares on buses for a period - but there have never
been different fares according to distance travelled.

The fact that there is a flat fare makes implementing Oyster PAYG on
buses very easy - everyone who touches-in (i.e. validates their Oyster
by scanning it) pays the same standard fare (though yes, daily price
capping may mean that they don't!).

However I was just wondering if the system had been designed so that
it could be used in a non-flat fare environment - i.e. fares based on
distance or zones. I cannot envisage a scenario where passengers had
to touch-out when they exited the bus as being remotely workable
whatsoever, so that's not really what I'm asking about.

Instead the situation I have in mind is one where the passenger has to
specifically request a destination (or zone) to the driver, who then
has to enter in into their ticket machine before the passenger then
touches-in their Oyster on the ticket machine's Oyster pad - and are
possibly also issued with a paper ticket.

Please note that I'm not advocating anything like this whatsoever - I
think it would be a total and unmitigated disaster as it would
completely negate the advantage that passengers could board the bus
quickly. However I'm interested to know whether the Oyster system is
at all capable of such a thing, or whether the presumption that bus
fares would go flat rate was built into Oyster from the start.

I ask prompted by thoughts of how, if and when stored value ITSO
smartcard ticketing finally arrives on buses elsewhere in the UK, how
the situation with regards to fares

On Fri, 25 Jan 2008 10:25:20 -0800 (PST), Mizter T
wrote:

I suspect I'm going to get in trouble for incorrect usage of the word
'differential', but nevermind...

I'm hoping that someone in the know (probably Paul C, given that he
was involved in the development of Oyster) might be able to provide
some background to this query.

As we all know bus fares in London are flat rate - Oyster PAYG users
pay 90p, cash fares are £2 - and the flat fare for London buses has
been around since 2004 (I think). There were peak (pre-0930) and off-
peak Oyster PAYG fares on buses for a period - but there have never
been different fares according to distance travelled.

The fact that there is a flat fare makes implementing Oyster PAYG on
buses very easy - everyone who touches-in (i.e. validates their Oyster
by scanning it) pays the same standard fare (though yes, daily price
capping may mean that they don't!).

However I was just wondering if the system had been designed so that
it could be used in a non-flat fare environment - i.e. fares based on
distance or zones. I cannot envisage a scenario where passengers had
to touch-out when they exited the bus as being remotely workable
whatsoever, so that's not really what I'm asking about.

Instead the situation I have in mind is one where the passenger has to
specifically request a destination (or zone) to the driver, who then
has to enter in into their ticket machine before the passenger then
touches-in their Oyster on the ticket machine's Oyster pad - and are
possibly also issued with a paper ticket.

In the very early days of Prestige (later Oyster) there was no policy
decision that TfL would implement flat fares on the bus network. The
fare scale at the time had several zonal fare values for adults plus
IIRC a flat child rate.

There was a huge discussion about the practicality of exit validation
but done without active validation by passengers. In other words you
effectively walked through a door wide scanner when you alighted and
that would read the card and deduct the fare (or add back if a max fare
on entry system was used).

The problem was that the exit technology was nowhere near mature enough,
no one had ever tested such an application and there were big questions
about what happened if there was a misread, people had two cards on
their person etc etc.

The early promotional videos from Transys showed a Dart minibus in
deepest Merstham with a ETM plus a validator whereby passengers could
select their fare and then tap their card. The driver could also set the
fare for deduction via the ETM. You don't need to be a genius to spot
some potential loopholes with such a system. I believe the system can
deal with more than one fare as that was certainly in the spec when I
was around and it would be nonsensical for TfL to have taken such a
function out of the system. Paper tickets were also considered as being
necessary to give people confidence that the electronic system had
deducted the correct fare - thankfully that aspect was never
implemented!

My guess is that the reality of making zonal fares work on buses forced
TfL into considering flat fares (although simplification had been
working its way through LT Buses for several years). This consideration
then meshed nicely with the aspirations of the Mayor to drive up bus
usage. The rest, they say, is history.

To counter the arguments that exit validation can't work and that fare
self selection can't work either I would point to Singapore and the EZ
Card (and magnetics beforehand). Prior to the EZ Card the bus system
had magnetic stored value ticket acceptance but without exit validation.
There were huge (for a bus) machines with multiple buttons for the
appropriate fare stages. You dropped your magnetic ticket in the
machine, pressed for your fare and the money was taken off your ticket
and the ticket returned to you. I suspect if you are a regular user then
this becomes second nature. As a visitor I found it awful and a real
impediment to using buses. There was no issue on the MRT as it was gated
and it was like using a magnetic ticket anywhere in the world.

With EZ card the self selection has gone and been replaced by smartcard
validation on entry and exit. There are two readers at each entrance /
exit door so two stream boarding and alighting is possible. You tap
your card on entry but nothing is deducted from the card but the entry
point is obviously written to the card. All bus stops have a display
that shows the number of stages from that stop to all other stops on
routes serving that stop. There is also the fare scale based on the
number of stages. EZ Card fares are cheaper than cash.

When the bus closes it doors and moves off the exit validators are
automatically switched off to stop people all tapping their cards and
then overriding. I believe the system is linked to GPS or similar as the
validators are only reactivated when you are within about 100m of a
stop. This is useful if you are already at the exit as you can tap just
before the stop and then alight. Others following simply tap on exit.
Interestingly the second stream validator at the front door can also act
as an exit validator for about 50 seconds once the doors are open or
longer at a terminal point where lots of people may be alighting. I
have to say I have found the whole system very easy to use and not
encountered any problems. I have witnessed others having the odd
difficulty at exit rejection but the driver calls them back and will
either take a cash fare or else do some reset transaction to allow
another go at exiting. I don't understand the technicalities of exactly
what happens but it's obviously something Transit link have specified.

The Singapore system will not allow you to board if you have negative
value on the card - they operate a deposit system which allows cards to
go negative but you must then top up off bus or pay cash. Checking the
Transit link Guide there is a wide range of fares with some flat fares
on feeder routes to MRT stations, distance based, premium fares for
expresses as well as differential charges for air conditioned and non
air conditioned vehicles (this applies to cash as well - the same
concept is used in Hong Kong too). Everyone pays for their travel but
there are concessionary cards for OAPS, children and servicemen. This
apply concessionary charges for journeys undertaken by bus / MRT. You
also get transfer rebates for interchange trips. You can get a rebate
for up to two transfers after your first trip provided you board the
next vehicle within 45 mins of exit. This applies MRT to bus and vice
versa as well as bus to bus. Interchange between MRT lines is free as
many metro networks. The rebates aren't huge but it works seamlessly -
the display tells you if you've received a rebate. Last transfer has to
be within 2 hours of the first boarding - the card reader must look back
through journey history to check the timings.

In Hong Kong you don't have exit validation but the fares structure
employs a tapering effect (and has done for decades AFAIK). The bus
system has a hierarchy in HK with feeder routes, local routes, expresses
/ cross harbour services, routes with sectional fares and premium routes
like Airbus. Typically your fare is deducted on entry. However it is
perfectly possible to pay completely different fares to get between A
and B. A feeder or local service may be flat fare throughout - that's
easy the fare value never changes. On other longer routes as well as
Cross Harbour routes the assumption is that most people will travel a
long distance or across the harbour and the fare is set for that market.
You'd therefore be crazy to board such a bus to travel 3 stops down the
road as you'd be charged the rate to go 25 stops. However as the bus
gets closer and closer to its terminal the fares drop as it can act as a
local bus without risking turning away people for a premium fare. For
example a bus starts on HK Island and crosses the Harbour and will
terminate at a housing development in Kowloon. If you board on the
Island you may pay say $8.50, even at the other side of the tunnel it
may be the same fare but perhaps within 12 stages of the eventual
terminus the fare may drop to $5 to attract some local custom but it's
likely that fare will be more expensive that a local bus in Kowloon
serving the same stretch of road to the housing development. In the
reverse direction the fare of $8.50 would apply all the way to HK Island
to deter all local traffic as the major flow is to the Island not
intermediately! Confused? A couple of service have sectional fares -
this is more like our traditional UK fare stage approach. These run to
Stanley from Central on HK Island. These services carry heavy flows to
Stanley but provide the only service to intermediate areas. On boarding
everyone is charged the Stanley fare but if you get off where a
sectional fare applies you tap again on exit and value is added back to
your card balance. Bus to Bus interchange discounts are widely offered
by the bus operators but Bus - MTR - KCR discounts are not. Prior to
the MTR takeover of the KCRC the rail networks were completely separate
and there were no through fare discounts. I understand through fares
are now being offered and intermediate gatelines are being removed -
it's fare to say that the stations were all designed for gated
interchange so they avoided the problems we have in London in having to
have validators.

I take your point about the efficacy of such a system in a somewhat less
compliant society like London. Obviously part of the success in
Singapore is the "controlled" nature of society and a social sanction if
people were to cheat. I've not seen an obvious fraud taking place but
that doesn't mean it doesn't happen. I think it might be an interesting
experiment for TfL to try exit validation on buses to see what the
issues might be in a London environment. The final point to make is that
you get interchange discounts in Singapore if you change from

Hope that's long enough for you!

--
Paul C


Admits to working for London Underground!

On Jan 25, 7:38 pm, Paul Corfield wrote:
On Fri, 25 Jan 2008 10:25:20 -0800 (PST), Mizter T
wrote:

What I cannot comprehend is how a bendibus driver can simply get on
with the job of driving EXCEPT when he has to deal with those crappy
Bus Sava tickets. The wild, ****ty, hexagonal ones.
Why do they still exist?

The Netherlands is working on a touch in and touch out zonal fare
system, and it's not working well at all.

"sweek" wrote in message
...
The Netherlands is working on a touch in and touch out zonal fare
system, and it's not working well at all.

Where I'm currently living will implement "oyster" this year and has a zonal
system. There's no way they will have a flat fare (the longest route is
about 100km) and I'm wondering how they will do it. I suspect that you will
still have to "ask the driver" and all that will happen is the "ticket" is
put on the card, rather than supplied as a piece of paper.

They have an "oyster" system in Helsinki and there, if you want to go more
than one zone (IIRC you can do 1-3), you press a numbered button on the
validator as you "touch".

tim

On Fri, 25 Jan 2008 10:25:20 -0800 (PST), Mizter T
wrote:

I suspect I'm going to get in trouble for incorrect usage of the word
'differential', but nevermind...

I'm hoping that someone in the know (probably Paul C, given that he
was involved in the development of Oyster) might be able to provide
some background to this query.

As we all know bus fares in London are flat rate - Oyster PAYG users
pay 90p, cash fares are £2 - and the flat fare for London buses has
been around since 2004 (I think). There were peak (pre-0930) and off-
peak Oyster PAYG fares on buses for a period - but there have never
been different fares according to distance travelled.

The fact that there is a flat fare makes implementing Oyster PAYG on
buses very easy - everyone who touches-in (i.e. validates their Oyster
by scanning it) pays the same standard fare (though yes, daily price
capping may mean that they don't!).

However I was just wondering if the system had been designed so that
it could be used in a non-flat fare environment - i.e. fares based on
distance or zones. I cannot envisage a scenario where passengers had
to touch-out when they exited the bus as being remotely workable
whatsoever, so that's not really what I'm asking about.

Instead the situation I have in mind is one where the passenger has to
specifically request a destination (or zone) to the driver, who then
has to enter in into their ticket machine before the passenger then
touches-in their Oyster on the ticket machine's Oyster pad - and are
possibly also issued with a paper ticket.


This would be useful on the two LLSA bus routes where Oyster PAYG is
only valid on part of the route. (Metroline 84 to Potters Bar & Unobus
614 to Barnet)

Paul Corfield wrote:

(snip)

In the very early days of Prestige (later Oyster) there was no policy
decision that TfL would implement flat fares on the bus network. The
fare scale at the time had several zonal fare values for adults plus
IIRC a flat child rate.

There was a huge discussion about the practicality of exit validation
but done without active validation by passengers. In other words you
effectively walked through a door wide scanner when you alighted and
that would read the card and deduct the fare (or add back if a max fare
on entry system was used).

The problem was that the exit technology was nowhere near mature enough,
no one had ever tested such an application and there were big questions
about what happened if there was a misread, people had two cards on
their person etc etc.

The early promotional videos from Transys showed a Dart minibus in
deepest Merstham with a ETM plus a validator whereby passengers could
select their fare and then tap their card. The driver could also set the
fare for deduction via the ETM. You don't need to be a genius to spot
some potential loopholes with such a system. I believe the system can
deal with more than one fare as that was certainly in the spec when I
was around and it would be nonsensical for TfL to have taken such a
function out of the system. Paper tickets were also considered as being
necessary to give people confidence that the electronic system had
deducted the correct fare - thankfully that aspect was never
implemented!

My guess is that the reality of making zonal fares work on buses forced
TfL into considering flat fares (although simplification had been
working its way through LT Buses for several years). This consideration
then meshed nicely with the aspirations of the Mayor to drive up bus
usage. The rest, they say, is history.

To counter the arguments that exit validation can't work and that fare
self selection can't work either I would point to Singapore and the EZ
Card (and magnetics beforehand). Prior to the EZ Card the bus system
had magnetic stored value ticket acceptance but without exit validation.
There were huge (for a bus) machines with multiple buttons for the
appropriate fare stages. You dropped your magnetic ticket in the
machine, pressed for your fare and the money was taken off your ticket
and the ticket returned to you. I suspect if you are a regular user then
this becomes second nature. As a visitor I found it awful and a real
impediment to using buses. There was no issue on the MRT as it was gated
and it was like using a magnetic ticket anywhere in the world.

With EZ card the self selection has gone and been replaced by smartcard
validation on entry and exit. There are two readers at each entrance /
exit door so two stream boarding and alighting is possible. You tap
your card on entry but nothing is deducted from the card but the entry
point is obviously written to the card. All bus stops have a display
that shows the number of stages from that stop to all other stops on
routes serving that stop. There is also the fare scale based on the
number of stages. EZ Card fares are cheaper than cash.

When the bus closes it doors and moves off the exit validators are
automatically switched off to stop people all tapping their cards and
then overriding. I believe the system is linked to GPS or similar as the
validators are only reactivated when you are within about 100m of a
stop. This is useful if you are already at the exit as you can tap just
before the stop and then alight. Others following simply tap on exit.
Interestingly the second stream validator at the front door can also act
as an exit validator for about 50 seconds once the doors are open or
longer at a terminal point where lots of people may be alighting. I
have to say I have found the whole system very easy to use and not
encountered any problems. I have witnessed others having the odd
difficulty at exit rejection but the driver calls them back and will
either take a cash fare or else do some reset transaction to allow
another go at exiting. I don't understand the technicalities of exactly
what happens but it's obviously something Transit link have specified.

The Singapore system will not allow you to board if you have negative
value on the card - they operate a deposit system which allows cards to
go negative but you must then top up off bus or pay cash. Checking the
Transit link Guide there is a wide range of fares with some flat fares
on feeder routes to MRT stations, distance based, premium fares for
expresses as well as differential charges for air conditioned and non
air conditioned vehicles (this applies to cash as well - the same
concept is used in Hong Kong too). Everyone pays for their travel but
there are concessionary cards for OAPS, children and servicemen. This
apply concessionary charges for journeys undertaken by bus / MRT. You
also get transfer rebates for interchange trips. You can get a rebate
for up to two transfers after your first trip provided you board the
next vehicle within 45 mins of exit. This applies MRT to bus and vice
versa as well as bus to bus. Interchange between MRT lines is free as
many metro networks. The rebates aren't huge but it works seamlessly -
the display tells you if you've received a rebate. Last transfer has to
be within 2 hours of the first boarding - the card reader must look back
through journey history to check the timings.

In Hong Kong you don't have exit validation but the fares structure
employs a tapering effect (and has done for decades AFAIK). The bus
system has a hierarchy in HK with feeder routes, local routes, expresses
/ cross harbour services, routes with sectional fares and premium routes
like Airbus. Typically your fare is deducted on entry. However it is
perfectly possible to pay completely different fares to get between A
and B. A feeder or local service may be flat fare throughout - that's
easy the fare value never changes. On other longer routes as well as
Cross Harbour routes the assumption is that most people will travel a
long distance or across the harbour and the fare is set for that market.
You'd therefore be crazy to board such a bus to travel 3 stops down the
road as you'd be charged the rate to go 25 stops. However as the bus
gets closer and closer to its terminal the fares drop as it can act as a
local bus without risking turning away people for a premium fare. For
example a bus starts on HK Island and crosses the Harbour and will
terminate at a housing development in Kowloon. If you board on the
Island you may pay say $8.50, even at the other side of the tunnel it
may be the same fare but perhaps within 12 stages of the eventual
terminus the fare may drop to $5 to attract some local custom but it's
likely that fare will be more expensive that a local bus in Kowloon
serving the same stretch of road to the housing development. In the
reverse direction the fare of $8.50 would apply all the way to HK Island
to deter all local traffic as the major flow is to the Island not
intermediately! Confused? A couple of service have sectional fares -
this is more like our traditional UK fare stage approach. These run to
Stanley from Central on HK Island. These services carry heavy flows to
Stanley but provide the only service to intermediate areas. On boarding
everyone is charged the Stanley fare but if you get off where a
sectional fare applies you tap again on exit and value is added back to
your card balance. Bus to Bus interchange discounts are widely offered
by the bus operators but Bus - MTR - KCR discounts are not. Prior to
the MTR takeover of the KCRC the rail networks were completely separate
and there were no through fare discounts. I understand through fares
are now being offered and intermediate gatelines are being removed -
it's fare to say that the stations were all designed for gated
interchange so they avoided the problems we have in London in having to
have validators.

I take your point about the efficacy of such a system in a somewhat less
compliant society like London. Obviously part of the success in
Singapore is the "controlled" nature of society and a social sanction if
people were to cheat. I've not seen an obvious fraud taking place but
that doesn't mean it doesn't happen. I think it might be an interesting
experiment for TfL to try exit validation on buses to see what the
issues might be in a London environment. The final point to make is that
you get interchange discounts in Singapore if you change from

Hope that's long enough for you!

--
Paul C

You tapered off at the end somewhat... but never mind that, thanks
very much for your very comprehensive and most informative post. The
pictures you paint of how things are done in Singapore and HK are
great, and rebuff my notion that a system that requires passengers to
touch-out would be unworkable.

The early Presige idea of a door wide scanner isn't something I had
really considered at all - it sounds very sci-fi! As you say it would
have presented problems for people carrying two cards, something I
have certainly done on numerous occasions.

I note that in Singapore, you say there is no fare deducted at all on
entry - it all happens on exit. I'm afraid to say (in what is perhaps
an illustration of the criminal mindset here in contrast with
Singapore!) one thing that instantly sprang to mind was what happens
is a passenger doesn't tap out on exit - would they have managed to
wangle a "free" journey, or would this discrepancy be flagged up the
next time they tried to use their EZ card?

The idea of a rebate if one transfers to another bus is an interesting
one - there are occasionally discussions here about whether free bus
transfers in London would be a good idea , perhaps instead a half-
price second bus fare might be an idea. The idea of free bus travel
before or after using the Underground also gets raised from time to
time - for a bus to Tube transfer this would take the form of a
rebate, applied on exit from the Tube.

I note in HK that there are only a couple of routes - the Stanley from
Central examples you gave - where passengers are required to touch-
out. I'm afraid again one of my early thoughts is that passengers will
be tempted to tap out early then override - and HK doesn't quite have
the same societal notions of obedience that Singapore does, so I'm
left wondering if that is an issue. I guess the threat of inspectors
boarding at any time might be enough to dissuade many from doing that.

I note what you say about the hierarchy of bus services in HK, where -
apart from the couple of examples as discussed above - flat fares are
charged on entry. How good is the fare information given at bus stops
- after all, you don't want to end up paying $8.50 simply because
you've got on a longer distance bus. Or does the type of bus and/or
the colour and branding mean the distinction between longer distance
and local buses is pretty obvious?

This has got me wondering about the notion of a similar hierarchy of
bus services in London, with more expensive 'premium' routes - perhaps
express routes. That said, there are only two express London buses
routes these days - the X68 and the X26 - and it's only really the X68
that is aimed at commuters. I remember reading a past comment on here
of how, courtesy of traffic congestion, the X68 wasn't really that
expressey, as it were! (I'll try it out some day.) I'm pretty sure
that a premium priced air conditioned bus would attract a good bit of
custom in the middle of a blistering summer heatwave!

I'm not sure whether TfL could really do a proper experiment with exit
validation - if there was no incentive to touch-out on exit, then most
people wouldn't bother. If however there was some kind of max fare
charged, then TfL would be inundated with complaints from people who
had been charged the max fare and didn't realise or understand why
that one bus route operated differently to every other! If however
there was some incentive such as a half-price fare for shorter
journeys, then I think you'd find the statistics reporting that an
implausibly large number of passengers had apparently only hopped on
the bus for a couple of stops! This could only really be countered by
extensively deploying inspectors along the route. However confusion
would still reign!

It is for the very reason that passengers would be tempted to override
- which is really just euphemism for saying 'go where they wanted to
all along but don't pay for it' - that I find it difficult to imagine
such a system working in London, or indeed elsewhere in the country.
Still, if it ever was implemented it would provide a fresh bit of
material for the perennially grumpy Evening Standard to gripe about.

Mizter T wrote

The fact that there is a flat fare makes implementing Oyster PAYG on
buses very easy - everyone who touches-in (i.e. validates their Oyster
by scanning it) pays the same standard fare (though yes, daily price
capping may mean that they don't!).

However I was just wondering if the system had been designed so that
it could be used in a non-flat fare environment - i.e. fares based on
distance or zones. I cannot envisage a scenario where passengers had
to touch-out when they exited the bus as being remotely workable
whatsoever, so that's not really what I'm asking about.

Posters here have in fact noted that many European cities DO require
bus users to touch-out on exit.

Instead the situation I have in mind is one where the passenger has
to
specifically request a destination (or zone) to the driver, who then
[...]

Most cities and PTE areas in the UK are smaller than the GLC so flat
rate in a central zone seems likely. I am sure the NG experts will
comment.

However when the charging scheme also has to work for supertram and
express services (greenline or Oxford tube in London terms) something
more is needed.

If these are limited stop and since the cost of "pay before you board"
machines is apparently tolerable a U'ground type scheme seems possible
with validators at stops.

Assuming standard buses are flat £1 fare, the card would have say £5
deducted when the user boards and touches-in and if the journey
finished at a express stop or tram stop within the city touching-out at
a stop validator would return value so the journey would cost from £1
upwards, perhaps with a minimum fare of £2 for express buses. If the
journey finished outside the city where there were no validators then
the maximum would apply. For added complication a discount for a
subsequent return journey could be allowed, even on the following day.

--
Mike D

Mizter T wrote:
This has got me wondering about the notion of a similar hierarchy of
bus services in London, with more expensive 'premium' routes - perhaps
express routes. That said, there are only two express London buses
routes these days - the X68 and the X26 - and it's only really the X68
that is aimed at commuters.

607 (express 207/427)

When I first moved to Ealing I was rather surprised that you didn't
have to pay extra to go on this, having been brought up with Greenline
coaches. Both rely mainly on fewer stops rather than faster driving to
save time.

Colin McKenzie

--
No-one has ever proved that cycle helmets make cycling any safer at
the population level, and anyway cycling is about as safe per mile as
walking.
Make an informed choice - visit www.cyclehelmets.org.

On Jan 25, 9:31*pm, Mizter T wrote:

two long, comprehensive posts cut

The idea of a rebate if one transfers to another bus is an interesting
one - there are occasionally discussions here about whether free bus
transfers in London would be a good idea , perhaps instead a half-
price second bus fare might be an idea. The idea of free bus travel
before or after using the Underground also gets raised from time to
time - for a bus to Tube transfer this would take the form of a
rebate, applied on exit from the Tube.

On this particular point, I am not quite sure what the situation
currently is anyway.

If, for example, you touch on route 555 and it breaks down or stops
short so that you get the next bus on route 555 where you get
inspected ...

Does each bus have its own ID so that the inspector can tell that you
touched on that particular bus, or does the reader just show that you
touched on route 555 within the allowed time?

In general, unlimited travel for a period of time is easier to enforce
than a (possibly unjust) charge per vehicle regardless of distance.
(I remember a combination of metro and bus being allowed in Lille in
the 1980s within an hour of clunking the ticket.)

Whatever the answer about bus IDs, it must be impossible to enforce on
the DLR and, in fact, why should you be charged double on your journey
from Shadwell to Greenwich just because you want to do some shopping
at Canary Wharf Tescos on the way (within the time)? If you drove,
you wouldn't use double the petrol.