Dispatch (logistics)
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Dispatch is a procedure for assigning customers to taxicabs, couriers, emergency services, and other mobile units. Clients are matched to vehicles according to the order in which clients called and the proximity of vehicles to each client's pick-up location. Telephone operators take calls from clients, then either enter the client's information into a computer or write it down and give it to a dispatcher. In some cases, calls may be assigned a priority by the call-taker. Priority calls may jump the queue of pending calls. In the first scenario, a central computer then communicates with the mobile data terminal located in each vehicle (see computer assisted dispatch); in the second, the dispatcher communicates with the driver of each vehicle via two-way radio.
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[edit] Manual dispatch systems
Examples of manual systems of tracking status of vehicles or resources in a dispatched fleet include cards, punched tags, and plastic icons.
[edit] Cards
Card systems employ a set of shelves with a slot for each unit in the dispatch fleet. Each vehicle or resource has a slot in the shelving system. In it, a card, like a time card used to track an employee's work hours, is stored. A time clock, similar to the one that stamps work hours on a time card, is used to stamp event times on each card. At the beginning of a work day, the resource's identifier or other information is handwritten on the card. Each time the resource's status changes, the card is punched in the time clock and a new status entry is handwritten on the card. The card collects a series of entries through the work shift.
In a tow truck example, the card might be labeled with the tow car's radio identifier, "Downtown 6" and may be labeled with the vehicle number or data about the capabilities of the specific tow car. It might give a weight capacity, show the unit as a flat bed or cradle snatcher, or mention the unit carries a can of Diesel fuel. The name of the staff on the car might be noted. At the start of a shift, the dispatcher would note the unit "available" and time stamp the card. At the assignment to a call, the call information would be written on the card and the card might be stamped at the moment the assignment is read to the tow car crew. The string of notes and time stamps allows dispatch staff to get a clear picture of the status of a small fleet.
Some systems use shelving with red and green lights and a switch at the back of the card slot. If the resource's card is pushed all the way into the card slot, the switch is actuated and an indicator lamp turns red. This identifies the tow car whose card occupies that slot as not available or assigned to a call. Leaving the card pulled partway out leaves the indicator green, showing the dispatcher that unit is available. Is anyone available? The lights are supposed to give the dispatch staff a snapshot of their resource situation.
A major flaw of this system is that cards are inside shelves and trying to look at an entire set of cards to evaluate the overall situation requires the dispatcher to pull out every card, one at a time, and read it. If two or more resources are sent to the same call, the dispatcher has a lot of writing to do.
[edit] Punched tags
Punched tag systems employ a set of pegs with each peg holding tags for one unit in the dispatch fleet. Each vehicle working the current shift has a peg with a tag describing the unit's current status. A time clock, similar to the one that stamps work hours on a time card, is used to stamp times on each tag. At the beginning of a work day, the resource's identifier may be posted above the peg. The unit's start time is stamped and their status is written on the tag. Each time the resource's status changes, a new tag is written and the tag is time stamped in order to log the time the unit's status changed. The peg collects a stack of tags through the work shift.
In a tow truck example, the peg might be labeled with the tow car's radio identifier, "Downtown 6" and may be labeled with the vehicle number or data about the capabilities of the specific tow car. It might give a weight capacity, show the unit as a flat bed or cradle snatcher, or mention the unit carries a can of Diesel fuel. The name of the staff on the tow car might be noted. At the start of a shift, the dispatcher would note the unit "available" and time stamp a tag, then hang it on that unit's peg. At the assignment to a call, the call information would be written on another tag and the tag might be stamped at the moment the assignment is read to the tow car crew. The tag would then be hung on that unit's peg. The stack of tags allows dispatch staff to get a clear picture of the status of a small fleet.
Some systems use colored tags to show general categories of events such as "available". For example, each unit that is available might have the fact noted on an orange tag. Is anyone available? A glance at the pegboard shows anybody whose tag is "orange" is available. An repossession might use a yellow tag to identify a service call with a safety issue where the police should be called in the event the tow car crew doesn't check in by radio within five minutes. A blue tag might show a resource is taking a dinner or lunch break.
A major flaw of this system is that tags can easily be posted on the wrong peg, causing confusion. This can be countered by writing unit identifiers on every tag: a lot of work. In colored-tag systems, it's always possible to run out of certain colors of tags, messing up the system. If two or more resources are sent to the same call, the dispatcher has a lot of writing to do.
[edit] Plastic icons
In a plastic icon system, the a blank panel on the communications console or a nearby wall is fitted with a sheet of Velcro. The material has vertical stripes painted on it, making a column for each of several possible status conditions. The simplest system is two columns: available and unavailable. Magentized icons can be used in place of Velcro. The icons can be colored or shaped to identify the type of unit or some other feature of the resource.
Each vehicle working the current shift has an icon placed in the column describing the unit's current status. A log book is used to track times, event details, and other information about calls for service. In a tow truck example, the icon might be labeled with the tow car's radio identifier, "Downtown 6". During a shift, the icon would be moved by the dispatcher into whatever column describes the resource's current condition. Alternatively, there could be columns for some other condition such as the names of move-up or standby points where resources are sent to backfill for busy tow cars.
A major flaw of this system is that icons can easily be misplaced or fall off of the status board. Magnetic objects can damage cathode ray tube displays if they get too close to the display face or housing.
[edit] Airline dispatch
In airline operations, dispatchers exert great authority over flights. A dispatcher shares legal responsibility for a flight's safety with its pilot, and may delay, divert or cancel a flight at any time. This checks and balances mechanism improves the safety of the dispatch system. A dispatcher typically must be licensed by the aviation authority of a country. The examination for the licence requires the candidate to demonstrate extensive knowledge in meteorology and aviation, to a level that is comparable to that of a holder of an airline transport pilot licence.
[edit] Capacity and metrics
There is a limit to how many field units can be managed. This varies with circumstances. For example, a parcel delivery service dispatcher may encounter higher traffic around Christmas. Work is not evenly distributed across time: in any dispatch system there are traditional peaks or busy hours in requests for service. Some workplace cultures will allow longer wait times than others.
Systems may use a communications protocol to reduce talking time, allowing interaction with a larger dispatch fleet. Air traffic control and towing are two examples. The use of abbreviations or standard phrases can reduce the length of a transaction. Capacity may be reduced by relaxed communications protocol such as a delivery dispatcher giving a lengthy description of a customer complaint over the radio.
It's generally accepted that giving field units computers connected with the computer-aided dispatch, or another enterprise system used for dispatch, unloads voice two-way radio channels and increases capacity. Users research information on their terminal or laptop instead of calling in with a request that the dispatcher do it.[1] One source suggests radio traffic drops by 30% when computers are available to mobile users.[2]
[edit] Radio
Measurements of communications may reflect dispatch capacity. A partial definition of capacity comes from the number of communications channels required to support a dispatch fleet. Two metrics of channel capacity may be: 1) the number of field units or resources dispatched, and; 2)number of push-to-talk presses per day.[3] A resource may refer to a fire engine, tow truck, taxi, or refuse truck, regardless of how many walkie-talkies, mobile radios, or persons were fielded along with each resource.
One suggestion is that 100 to 150 mobiles is the maximum practical on one channel.[4] Another suggests 60-70 units as a maximum.[5] The difference in these two ranges probably reflects the wording. For example, 120 mobiles may mean radios: 60 units each containing a mobile radio and an officer with a walkie talkie.[6] For dispatch systems like take-out food delivery, where life safety is not an issue, delays may be acceptable. Delays increase capacity.
Another possible measure of capacity is system push-to-talk presses. A 187-day study of four Contra Costa County, California Sheriffs Department conventional two-way radio dispatch channels showed an average of around 2,500 push-to-talk presses per day. The count was within +/-350 a day across all four primary dispatch channels.[7]
[edit] Telephone
A method used for telephone traffic analysis may fit some circumstances. One evaluation looked at 1) peak of busy hour usage, 2) average hourly usage, 3) message length in seconds, 4) maximum delay or wait time desirable, and; 5) maximum percent of users being delayed. Traffic analysis can be applied to radio or telephone communications.[8]
Most office telephone systems have some facility for recording calling volumes, and incoming call timing. Dispatch centers use Automatic call distribution (ACD) groups which can be evaluated for metrics such as average wait time, abandoned calls, and calls per hour. These numeric data can be entered into spreadsheets for analysis of trends. [9]
In dispatching, US emergency medical services literature suggests that telephone calls to a dispatching facility should be answered in the first few rings. One document suggests emergency calls to dispatch should result in busy signals once per 100 calls during the busiest hour.[10] In business call centers, similar standards are suggested by consultants in order to provide an ideal customer experience and to outperform competing services.[11] Sufficient staffing should be in place so that 90% of emergency calls are, "...answered within 10 seconds, or with no greater than three rings, during the average busy hour," according to one source.[12] Tolerable wait times vary from one culture and region to another: some cultures expect immediate service; others will tolerate waits for some services.
[edit] Notes
- ^ Suggested reading: "Congestion and Coverage Concerns," Contra Costa County Public Safety Mobile Radio Master Plan, (Fairfax, Virginia: Federal Engineering, Inc., 2002,) pp. 18.
- ^ "4.5 Mobile Data Systems," San Rafael Police Radio Committee: Report to Mayor and City Council, (San Rafael, California: City of San Rafael, 1995,) pp. 23.
- ^ Some touch screen radio dispatch consoles can keep a tally of push-to-talk presses.
- ^ See: "Section I: General," The California Highway Patrol Communications Technology Research Project on 800 MHz, 80-C477, (Sacramento, California: Department of General Services, Communications Technology Division, 1982,) pp. I-5.
- ^ Suggested reading: "Congestion and Coverage Concerns," Contra Costa County Public Safety Mobile Radio Master Plan, (Fairfax, Virginia: Federal Engineering, Inc., 2002,) pp. 18.
- ^ It may also reflect differences in operational styles between the Contra Costa Sheriffs Department and Highway Patrol. It might be that the average Highway Patrol officer interacts less often with their dispatcher.
- ^ Data were supplied by the Sheriffs Department. Suggested reading: "Congestion and Coverage Concerns," Contra Costa County Public Safety Mobile Radio Master Plan, (Fairfax, Virginia: Federal Engineering, Inc., 2002,) pp. 18.
- ^ For one example, see: "3.2.10.1 Current System Problems," Trunked Radio System: Request For Proposals, (Oklahoma City, Oklahoma: Oklahoma City Municipal Facilities Authority, Public Safety Capital Projects Office, 2000) pp. 89-90.
- ^ See InTelegy customer service web site for a brief overview of call metrics.
- ^ "Introduction: EMS Communications," Planning Emergency Medical Communications: Volume 2, Regional-level Planning Guide, (Washington, DC: Department of Transportation, National Highway Traffic Safety Administration, 1995) pp. 11.
- ^ See InTelegy customer service web site (ibid) for more information on call metrics.
- ^ "Introduction: EMS Communications," Planning Emergency Medical Communications: Volume 2, Regional-level Planning Guide, (Washington, DC: Department of Transportation, National Highway Traffic Safety Administration, 1995) pp. 11. For a discussion of telephone traffic statistics and busy hours, see: American Telephone and Telegraph Company, Basic Traffic Analysis, ISBN 0133354075.
