In the case of fast-food drive-through systems, we believe that a touch- screen system can accurately reflect a menu's hierarchical structure, and can be an efficient, easy to use interface for customers.
From our user analysis and questionnaire, we know that for drive-through systems, we can assume that most users will not be experts, but will instead be casual users. Thus, in this design, we focus on novice users, while still allowing experts some freedom to make shortcuts. To help novices, we use metaphor, a spatial graphical model, and a great deal of "knowledge in the world", or recognition.
Central to this design is a specially designed touch-screen, with a graphical menu on it. The menu is broken up in an organized, hierarchical fashion so that knowing the names of the items is not a requirement for any user. The areas on the screen which are "touchable" at any time are represented by graphical buttons. These buttons are designed to resemble real buttons such as those in an elevator or on a keyboard, so that they provide an affordance for pushing by the user. There are several areas on the screen, each with a different purpose.
The main menu area is a row of permanent (always visible) "buttons", or touchable items, which break down the menu items into large, general categories, such as sandwiches, drinks, side items, and desserts.
The second-level menu area changes according to which main menu button is selected. For example, if the user presses the button labeled "sandwiches", the second-level area might change to reveal a group of buttons corresponding to all sandwiches served at the restaurant. Each button should be labeled with the name, as well as a picture of the item in iconic form.
Some second-level buttons lead to the display of fine-grain selections in another area on the screen. For example, pressing the hamburger button in the second-level area might lead to a list of toppings in the fine- grain area that the user might select from. Each fine-grain selection area has a default setting (e.g. all toppings on the hamburger) that is assumed if the user makes no change in this area.
The function key area is a row of permanent buttons which allow the user to perform the most basic of tasks for the system, such as cancellation of an item, accepting a current selection, or sending the order to the kitchen. Another set of function keys (either the numbers 0-9, or simply up and down arrow buttons) set the quantity of the item being ordered. These buttons would give immediate feedback by displaying the quantity continuously. The default quantity would be one.
Finally, there is an area which lists the current order of the customer, along with price information. As in the voice-recognition system, this is used as feedback to the user that what he/she is doing is correct, and so that mistakes can be caught at the earliest possible stage of the process.
In order to correlate the buttons in different areas of the screen, two methods are used. First, each main menu button has a different color, and the second-level menu items have the same color as their parent button in the main menu. Also, items in the fine-grain selection area are linked by a line to their parent in the second-level area.
We use various aural and visual cues to guide the user in the right direction, and to provide feedback to the user. One task that shows this principle is the pressing of a button. When a button is touched, it beeps and lights up so that the user is alerted in two ways that the action was successful.
Also, we use imagery as "knowledge in the world", since all of the second-level buttons have pictures of the menu items they represent. The user need not remember the name of an item or what it looks like.
We propose an audio help system as well. When the user makes a mistake, or when a certain mode is entered, the system can give some brief spoken and/or text instructions to guide the user along the correct path.
The cancellation mechanism can work in one of two ways. First, for novice users, simply pressing the cancel button (which is always visible) will clear the screen of all buttons, replacing them with a larger version of the list of selected items. Voice and text instructions tell the user to touch the item to be cancelled. When this is performed, the system returns to its previous state.
Alternately, the expert user may touch an item in the list of ordered items from anywhere in the menu hierarchy. When an item in the list is selected, the cancel button will light up and/or flash. To cancel the item, the user simply presses the button, or presses anywhere else on the screen to return to ordering. This functions more like a lightweight mode, since there is no major change in the screen's state.
The send order button is used when the user is completely satisfied with the order, and wishes to submit it to the kitchen. At this point, a receipt is printed and the system instructs the user to drive to the next window.
We have described the features of the touch-screen system that are distinct from the voice-recognition system of section 2.1. Of course, this interface should also include many of the aspects described there, such as a credit-card payment option, an intelligent system that anticipates the user's needs and asks questions to lead them in the right direction, on-screen nutritional information, and integration with the computer screens in the kitchen. These features can remain largely unchanged from the design presented in that section.
Finally, we must address an issue related to public health. Some respondents to our questionnaire expressed concern that a touch-screen system would not be healthy if hundreds of people used it every day and touched the screen with their fingers. This is a real concern, and so we offer one possible solution. It would be possible to construct a machine similar to those used on toilets in airports, where a thin layer of plastic is placed over the seat (or screen in our case) for each new user. This is a simple motor-driven device, and could be synchronized with the main system to unroll a new sheet of plastic each time a user arrived. It would not hinder the viewing of the information on the screen or the touching of the buttons by the user. If it is determined that a touch-screen system poses a health risk, this could be a solution.
2.2.2 Design Rationale
For this design, we have attempted to use many of the most common principles
in user interface design. Unlike the voice-recognition system, its conceptual
model is quite different from that of the current system, so we must work
harder to make this a natural and intuitive interface for the user.
As we noted above, we make use of a great deal of metaphor and spatial reasoning to guide the user. An example metaphor is that of a simple button. By causing a space on the screen to look like a physical button, we provide an affordance to push in that space, and implicitly constrain the user from pressing the screen in other places. The consistent spatial design of the menu quickly teaches the user where to look for the desired information.
Also, we saw that aural and visual cues and feedback are important in the system, so that users feel confident in their actions and immediately realize when an error has been made. The pictures and text allow for easy recognition by the user, and use both left and right brain processing in parallel. The colors and lines attached to buttons help the user keep track of the current state of the system, reducing mode errors.
Finally, the use of predefined areas of the screen for various levels of buttons and information is a slightly novel idea. Many hierarchical menu systems completely erase the old menu when an item is chosen, so that the new menu can take up the entire screen. By making the function keys and main menu buttons always visible, however, we've allowed for quick transitions between states of the system, and access to the accept, cancel, quantity selection, and send order functions from any state.
2.2.3 User Scenario
This system would handle the user scenario described in the introduction
in the following way:
It may well take longer to order with this system than with the current interface, but with the use of multiple ordering stations, the average wait time should be about the same or less. Besides, the benefits gained from avoiding mistakes and providing more user control (over payment options, for example) more than make up for any deficiency.