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I am looking at ways in which a heavily polluting taxi rank near a train station could reduce its pollution footprint. My first thought was that the pollution was mostly down to idling and I am thinking of various ways to tackle idling by taxi drivers.

Another reason for the pollution, the reason for this question (and possibly a larger source of the pollution than idling) is the constant 'edging forward' caused when: as each taxi at the front of the queue leaves after collecting a passenger, all the taxis in the queue move forward by one space and then stop. Sometimes there is a queue of 30 taxis and each taxi may move forward and then stop 30 times for every single customer they collect.

This 'edging forward' behaviour encourages the taxis to keep their engines running at idle because there is less time spent stationary. It is also less efficient edging forward in this way than if all the taxis moved forward by a larger degree every time they did move.

I was wondering whether there are any specific solutions to prevent this 'edging forward' behaviour in a queue of cars that would apply to a taxi rank?

(of course any other areas, ferry terminals for example or manual toll booths may also benefit or provide a solution).

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  • 3
    Use electric cars for taxis. This is already happening, e.g. at Schiphol airport in The Netherlands.
    – user2451
    Nov 15 '19 at 19:34
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Have the taxis (*) fill two or more lanes (| |) leading to the station, with one ready to pick up the next passenger (:)) coming out.

    |*|*|
    |*|*|
    |*|*|
    |*|*|

:)   *

Once that cab leaves, an attendant at the head of the lanes signals for the next taxi to move forward, ready for the next passenger.

    |*|*|
    |*|*|
    |*|*|
    | |*|

     *

All other taxis are parked with engines off.

Once that lane is empty, it can fill up with new taxis, and those in the next lane over are called for new pickups.

For a busy airport/station, more lanes, longer lanes, and multiple spots for pickup could be arranged.

    |*|*|*|*|*|
    |*|*|*|*|*|
    |*|*|*|*|*|
    |*|*|*|*|*|
    | |*|*|*|*|
    | |*|*|*|*|



     *
     *
     *
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  • Thank you, I think this would work well (although I don't think an assistant would always be possible). Do you think maybe sensors and video cameras could help? youtu.be/jqYMghbbK3k
    – atreeon
    Nov 17 '19 at 15:41
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A variant of the system suggested by @LShaver, would be to use the numbered ticket system sometimes found in supermarket deli counters. Each arriving taxi takes a sequentially numbered ticket (which could easily be electronic using an app of some kind), and parks up in a parking area.

When a passenger arrives, they press a button, and the next number is called, and the taxi with that number then pulls up to the pick up area to collect the passenger. The button-pushing could alternatively be done automatically by a sensor noting the previous taxi leaving, so that the passengers don't have to do anything, or wait.

E.g. A taxi arrives and gets ticket 31. They see that number 25 is displayed, so they know that there are 5 taxis ahead of them, and that taxi 25 is waiting at the pick up area. A passenger arrives, and 25 takes them and goes - 26 is displayed, and the taxi with that number goes up to the pick-up area.

In a busy area, you could have the same system for passengers - they too take a ticket, with the same number on it, so the passenger with ticket 23 gets the taxi with ticket 23...

Another variant could use a camera to read the licence number of each taxi as it enters the holding area, and use that instead of issuing a ticket.

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  • Thank you Nick C, I was thinking along these lines too. You would have to have a few screens around the place but maybe an app could also help and the alert could be sent to a taxi driver's phone in case they miss the number pop up on the screen. I would have thought the idea of reading a license number wouldn't be too difficult either. Should be quite an inexpensive and easy solution (maybe more involved than mine with the gates and two sensors but then the additional benefit of there being zero edging forward). It also allows electric charging because the cars would remain stationary
    – atreeon
    Nov 19 '19 at 14:36
  • The only downside to this would be if two or three numbers were called very close to one another there could be a little race for the drivers to beat one another but...if there is a small queue towards the pickup point of a couple of cars then this might remove the urgency of getting there...and I assume all taxi drivers are well behaved too :-)
    – atreeon
    Nov 19 '19 at 14:39
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    @atreeon but then if three numbers are called, all three drivers would know they're going to get a fare, so there's no need to rush to beat each other. They have no idea which fare is going to be the most lucrative after all!
    – Nick C
    Nov 19 '19 at 15:34
  • yeah, i agree, it is a small problem, with identifying the number plates that makes things fairly simple for the drivers too. I think it would need some kind of admin, like all the systems proposed but the admin could be done remotely via cctv.
    – atreeon
    Nov 19 '19 at 18:08
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This is mainly a legal problem, with technical aspects. The difficulty in any system will be modifying driver behaviour. You really need enforceable laws against unnecessary idling, where the law, not the driver, defined what's necessary. One way to do this is to only permit taxis that can't idle (electric or hybrid cars).

Otherwise however good your system, people will just sit stationary for longer at a time, idling just as much.

In a long thin taxi rank a simple system can work: the front car always moves to the head of the queue, but subsequent cars don't move forwards until they can move at least (2 or) 3 spots forwards. This means they sit 3 times as long in one spot, and start their engines 3 times less often if they do switch off. I've sometimes seen this behaviour emerge naturally, in ferry check-in queues, and so long as no one cuts in to the gap in the queue, it has the advantage that not every driver needs to understand for there to be some benefit*. Bollards between parallel queues would help, along with lots of signs, but in the case of taxi ranks you'd need an attendant with authority. Certainly in my experience taxi drivers are among the most like drivers to complain about the price of fuel while doing nothing to reduce the amount they use.


*I'm always one of the first to adopt this approach so I look out for it: I drive very little but my only motor vehicle (a campervan; more than half its mileage is on trips where I'm sleeping in it) is rather thirsty at idle.

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  • Thank you, good suggestion. I always take that approach too. I usually try to wait for as long as possible (in the ferry queue sometimes 6 or 7 cars even but people do get impatient).
    – atreeon
    Nov 17 '19 at 15:34
  • I would like to add that idling is only one source of the problem and potentially, the edging forward behaviour could create more pollution than is created through idling.
    – atreeon
    Nov 17 '19 at 19:37
  • Yes, edging forwards is inefficient, but (assuming manual transmission here) moving the same distance in fewer moves should mean less slipping the clutch, so be more efficient.
    – Chris H
    Nov 17 '19 at 19:56
  • yup, definitely good to reduce the number of stop starts.
    – atreeon
    Nov 17 '19 at 22:12
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What you could do is have a specially marked box that has the space for say 7 cars and instructions as follows.

  1. if box is completely clear drive forwards onto it.
  2. if a space becomes available do not move forwads (unless space is completely clear or the box is filling up from empty)

1 - all 7 spaces are empty

🚕 🚕 🚕 🚕 🚕 🚕 🛑 _  _  _  _  _  _  _     🚇

2 - so the cars move forward until the box is full

🚕 🚕 🚕 🚕 🚕 🚕 🛑 🚕 🚕 🚕 🚕 🚕 🚕 🚕     🚇

3 - a car at the front leaves because a pickup place by the station becomes available. The cars behind the box stay where they are

🚕 🚕 🚕 🚕 🚕 🚕 🛑 _  🚕 🚕 🚕 🚕 🚕 🚕     🚇

4 - more cars leave the box to pick up passengers. The cars behind the box continue to stay where they are

🚕 🚕 🚕 🚕 🚕 🚕 🛑 _  _  _  🚕 🚕 🚕 🚕     🚇

5 - all spaces become empty again so we go back to step 1.

🚕 🚕 🚕 🚕 🚕 🚕 🛑 _  _  _  _  _  _  _     🚇

this would reduce the edging forward behaviour which is poor in terms of fuel economy and pollution. With reducing the eding forward behaviour it will also give the taxi drivers more of an opportunity to switch off their engines and idle less.

n.b. I did consider having a traffic light that could change every 2-3 minutes. The problem with this is that it will not respond to the amount of clients. For example if you had one passenger every 4 minutes, with a traffic light system, you would still get the edging forward behaviour and associated pollution costs. Also if a very busy train came in then it may not move forward quickly enough. Possibly this could work if you had a sensor linked to the traffic light that would identify how much space was available ahead and change colour in response.

n.b. 2 - you could automate this further by having a barrier for the stop sign, and a sensor at the beginning of the box for 7 cars. Once 7 cars are sensed to have passed through the box, we open the barrier and let another 7 fill up the space.

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A fairly inexpensive and simple automated system could be this.

when sensor2 counts 7 cars pass into the pickup area the gate opens and 7 more cars pass through before the gate closes (counted by sensor1)

                                      |  🚕|    🚂
             gate                     |  🚕|   station
____________closed____________sensor2_|  ↗ |📍  and
🚕 🚕 🚕 🚕  ⛩️  - - - - - - - -🚕 ⁞ 🚕 🚕|🚶pickup
‾‾‾‾‾‾‾‾‾‾‾‾sensor1 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾|    | 🚶 area
                                      |  🚕| 🚶 🚂

7 cars are counted to have passed through sensor2, so the gate opens

            gate                      |    |    🚂
            open                      |  🚕|   station
_____________⛩️_______________sensor2_|    |📍  and
🚕 🚕 🚕 🚕 → → → → → - - - - - -  ⁞     🚕|🚶pickup
‾‾‾‾‾‾‾‾‾‾‾‾sensor1 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾|    | 🚶 area
                                      |  🚕| 🚶 🚂

as 7 more cars pass through the gate the gate closes

                                      |  🚕|    🚂
             gate                     |  🚕|   station
____________closed____________sensor2_|    |📍  and
🚕 🚕 🚕 🚕  ⛩️  - -🚕 🚕 🚕 🚕 🚕⁞  → → | 🚶pickup
‾‾‾‾‾‾‾‾‾‾‾‾sensor1 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾|    | 🚶 area
                                      |    | 🚶 🚂
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  • the design is cool yes?!!!
    – atreeon
    Nov 19 '19 at 6:50

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