Appendix E to Part 236 - Human-Machine Interface (HMI) Design
49:4.1.1.1.30.11.125.1.68 : Appendix E
Appendix E to Part 236 - Human-Machine Interface (HMI) Design
(a) This appendix provides human factors design criteria
applicable to both subpart H and subpart I of this part. HMI design
criteria will minimize negative safety effects by causing designers
to consider human factors in the development of HMIs. The product
design should sufficiently incorporate human factors engineering
that is appropriate to the complexity of the product; the gender,
educational, mental, and physical capabilities of the intended
operators and maintainers; the degree of required human interaction
with the component; and the environment in which the product will
be used.
(b) As used in this section, “designer” means anyone who
specifies requirements for - or designs a system or subsystem, or
both, for - a product subject to subpart H or subpart I of this
part, and “operator” means any human who is intended to receive
information from, provide information to, or perform repairs or
maintenance on a safety-critical product subject to subpart H or I
of this part.
(c) Human factors issues the designers must consider with regard
to the general function of a system include:
(1) Reduced situational awareness and over-reliance. HMI
design must give an operator active functions to perform, feedback
on the results of the operator's actions, and information on the
automatic functions of the system as well as its performance. The
operator must be “in-the-loop.” Designers must consider at a
minimum the following methods of maintaining an active role for
human operators:
(i) The system must require an operator to initiate action to
operate the train and require an operator to remain “in-the-loop”
for at least 30 minutes at a time;
(ii) The system must provide timely feedback to an operator
regarding the system's automated actions, the reasons for such
actions, and the effects of the operator's manual actions on the
system;
(iii) The system must warn operators in advance when it requires
an operator to take action;
(iv) HMI design must equalize an operator's workload; and
(v) HMI design must not distract from the operator's safety
related duties.
(2) Expectation of predictability and consistency in product
behavior and communications. HMI design must accommodate an
operator's expectation of logical and consistent relationships
between actions and results. Similar objects must behave
consistently when an operator performs the same action upon
them.
(3) End user limited ability to process information. HMI
design must therefore minimize an operator's information processing
load. To minimize information processing load, the designer
must:
(i) Present integrated information that directly supports the
variety and types of decisions that an operator makes;
(ii) Provide information in a format or representation that
minimizes the time required to understand and act; and
(iii) Conduct utility tests of decision aids to establish clear
benefits such as processing time saved or improved quality of
decisions.
(4) End user limited memory. HMI design must therefore
minimize an operator's information processing load.
(i) To minimize short-term memory load, the designer shall
integrate data or information from multiple sources into a single
format or representation (“chunking”) and design so that three or
fewer “chunks” of information need to be remembered at any one
time.
(ii) To minimize long-term memory load, the designer shall
design to support recognition memory, design memory aids to
minimize the amount of information that must be recalled from
unaided memory when making critical decisions, and promote active
processing of the information.
(d) Design systems that anticipate possible user errors and
include capabilities to catch errors before they propagate through
the system;
(1) Conduct cognitive task analyses prior to designing the
system to better understand the information processing requirements
of operators when making critical decisions; and
(2) Present information that accurately represents or predicts
system states.
(e) When creating displays and controls, the designer must
consider user ergonomics and shall:
(1) Locate displays as close as possible to the controls that
affect them;
(2) Locate displays and controls based on an operator's
position;
(3) Arrange controls to minimize the need for the operator to
change position;
(4) Arrange controls according to their expected order of
use;
(5) Group similar controls together;
(6) Design for high stimulus-response compatibility (geometric
and conceptual);
(7) Design safety-critical controls to require more than one
positive action to activate (e.g., auto stick shift requires two
movements to go into reverse);
(8) Design controls to allow easy recovery from error; and
(9) Design display and controls to reflect specific gender and
physical limitations of the intended operators.
(f) The designer shall also address information management. To
that end, HMI design shall:
(1) Display information in a manner which emphasizes its
relative importance;
(2) Comply with the ANSI/HFS 100-1988 standard;
(3) Utilize a display luminance that has a difference of at
least 35cd/m2 between the foreground and background (the displays
should be capable of a minimum contrast 3:1 with 7:1 preferred, and
controls should be provided to adjust the brightness level and
contrast level);
(4) Display only the information necessary to the user;
(5) Where text is needed, use short, simple sentences or phrases
with wording that an operator will understand and appropriate to
the educational and cognitive capabilities of the intended
operator;
(6) Use complete words where possible; where abbreviations are
necessary, choose a commonly accepted abbreviation or consistent
method and select commonly used terms and words that the operator
will understand;
(7) Adopt a consistent format for all display screens by placing
each design element in a consistent and specified location;
(8) Display critical information in the center of the operator's
field of view by placing items that need to be found quickly in the
upper left hand corner and items which are not time-critical in the
lower right hand corner of the field of view;
(9) Group items that belong together;
(10) Design all visual displays to meet human performance
criteria under monochrome conditions and add color only if it will
help the user in performing a task, and use color coding as a
redundant coding technique;
(11) Limit the number of colors over a group of displays to no
more than seven;
(12) Design warnings to match the level of risk or danger with
the alerting nature of the signal; and
(13) With respect to information entry, avoid full QWERTY
keyboards for data entry.
(g) With respect to problem management, the HMI designer shall
ensure that the:
(1) HMI design must enhance an operator's situation
awareness;
(2) HMI design must support response selection and scheduling;
and
(3) HMI design must support contingency planning.
(h) Ensure that electronics equipment radio frequency emissions
are compliant with appropriate Federal Communications Commission
regulations. The FCC rules and regulations are codified in Title 47
of the Code of Federal Regulations (CFR).
(1) Electronics equipment must have appropriate FCC Equipment
Authorizations. The following documentation is applicable to
obtaining FCC Equipment Authorization:
(i) OET Bulletin Number 61 (October, 1992 Supersedes May, 1987
issue) FCC Equipment Authorization Program for Radio Frequency
Devices. This document provides an overview of the equipment
authorization program to control radio interference from radio
transmitters and certain other electronic products and an overview
of how to obtain an equipment authorization.
(ii) OET Bulletin 63: (October 1993) Understanding The FCC Part
15 Regulations for Low Power, Non-Licensed Transmitters. This
document provides a basic understanding of the FCC regulations for
low power, unlicensed transmitters, and includes answers to some
commonly-asked questions. This edition of the bulletin does not
contain information concerning personal communication services
(PCS) transmitters operating under Part 15, Subpart D of the
rules.
(iii) 47 Code of Federal Regulations Parts 0 to 19. The FCC
rules and regulations governing PCS transmitters may be found in 47
CFR, Parts 0 to 19.
(iv) OET Bulletin 62 (December 1993) Understanding The FCC
Regulations for Computers and other Digital Devices. This document
has been prepared to provide a basic understanding of the FCC
regulations for digital (computing) devices, and includes answers
to some commonly-asked questions.
(2) Designers must comply with FCC requirements for Maximum
Permissible Exposure limits for field strength and power density
for the transmitters operating at frequencies of 300 kHz to 100 GHz
and specific absorption rate (SAR) limits for devices operating
within close proximity to the body. The Commission's requirements
are detailed in parts 1 and 2 of the FCC's Rules and Regulations
(47 CFR 1.1307(b), 1.1310, 2.1091, 2.1093). The following
documentation is applicable to demonstrating whether proposed or
existing transmitting facilities, operations or devices comply with
limits for human exposure to radiofrequency RF fields adopted by
the FCC:
(i) OET Bulletin No. 65 (Edition 97-01, August 1997),
“Evaluating Compliance With FCC Guidelines For Human Exposure To
Radiofrequency Electromagnetic Fields”,
(ii) OET Bulletin No 65 Supplement A, (Edition 97-01, August
1997), OET Bulletin No 65 Supplement B (Edition 97-01, August 1997)
and
(iii) OET Bulletin No 65 Supplement C (Edition 01-01, June
2001).
(3) The bulletin and supplements offer guidelines and
suggestions for evaluating compliance. However, they are not
intended to establish mandatory procedures. Other methods and
procedures may be acceptable if based on sound engineering
practice.
[75 FR 2720, Feb. 15, 2010]