Complex reaction time - The time to respond to more than one stimulus with one or more possible responses or while performing an additional task. Therefore, every response by a driver is a complex reaction time.
Contrast – The ratio of the difference of contrast reflectivity of the stimulus against its background relative to the contrast reflectivity of the background. (c_{s – Cb) / cb}

0.5 Audible stimuli

_{1. Illuminated object (includes
reflective objects)}

_{2. High Contrast (>25%)}

_{3.
Moderate contrast (10-25%)}

_{4.
Low contrast (<10%)}

_{According to Weber's Law the difference threshold for lighting is 8%.}

_{Detection – The act
of discovering or determining the true character of, or presence of, an object.
To be able to state that a particular stimulus is sensed but cannot be (or has
not yet been) identified.

Detection Task – In
research, sensing a stimulus without identification.

Detection time - The
time from the point that a stimulus is first visible to the moment that the
stimulus is perceived by the observer.

Difference threshold
– The least difference at which a stimulus can be discriminated (detected)
from other stimuli 50 percent of the time (just noticeable difference or
absolute threshold). [Weber’s Law]

Discern - the quality of being able to grasp and comprehend what is (was) obscure.

Driver Response Equation (DRE) -
A calculation of driver response time based upon a Multiple Stepwise Linear
Regression that was developed through a meta-analysis of over 140 driver
response studies (Muttart, 2003a, 2003b).

Driver Response Time
– A generic term used to describe research that measured a driver’s
response, regardless of the transition components included.

Driving task (1. Yes
or 2. No)

Eccentricity – The
degrees to which the stimulus was presented to the subject relative to the
direction the subject was looking. Typically refers to the direction away from
straight ahead that the driver was looking. For the purposes of the research by
Muttart (2003) it is used interchangeably with peripheral angle from the
vehicle-fixed x-axis (straight ahead). Measured in degrees. Common
eccentricities are listed below:
0 Straight ahead; 3-4 At the lane edge, 4-7 At the road
edge if in passing lane;
16 Speedometer/_{gauges; 27 Rear
view mirror; 35-45 Side mirrors;}
_{50 Radio or center console; If eccentricity is greater
than 50 degrees, enter 50.}_{Calculated in the following
manner:}E = ATAN (S_lat./ S_long.)
where S is distance and E is eccentricity
_{Experiment location

1. Laboratory 2. Simulator 3. Closed course 4. Road

Gender (1-male,
2-female)

Hazard
– (or potential hazard) Any object in or near a road, or obstacle to
negotiate through or around.

Headway – The
distance that a vehicle is flowing behind another vehicle in seconds. Example.
The measured time between the moments the lead car passes a landmark and the
following car passes that same landmark. Measured in seconds.

Identify - to
recognize something as something that has been seen before (to be able to say
who or what it is). Claiming that two or more things are essentially the same.

Immediate
Hazard – A hazard that requires an avoidance response.

Inattentional blindness –
the inability of an alert observer to detect a relatively conspicuous stimulus
when engaged in a mental task involving a primary stimulus.

IN CAR CREED - Acronym for the prerequisite analysis
before applying a driver response time. Stands for Immediate, Neutralized,
Contrast, Anticipation, Recall, Context, Relative velocity, Eccentricity,
Expectancy, Driving task.

Lanes – Is a term
used only when estimating the response of a driver who is responding to a
vehicle changing lanes. Lanes refers to the number of lanes away that the
intruding vehicle originally emerged from.

From next lane
From one lane over (2 lanes away)

Lighting – Natural ambient
(1. Day; 1.5 Dawn or Dusk; or 2. Night)

Methodological variable
– a variable that is related to the methodology of the research. These include
anticipation, driving task, transition time and experiment type (laboratory,
simulator, road or closed course).

Movement – Refers
to movement of the target and whether the target was moving laterally relative
to the observer of longitudinally.

1. Yes, moving 2. Yes, collinearly
3. Stationary

Movement time – The
time involved in implementation of the chosen response. This is the time from
first movement to response implementation (accelerator to brake or first
movement of the steering wheel to full desired rotation of the steering wheel).
Also referred to as motor response.

Mechanical latency – The
time necessary for the vehicle to implement the desired response. This is the
time that expires from the moment the brake is applied until the moment
effective braking occurs or from the moment steering is turned until the moment
the vehicle begins to move laterally.

NASA TLX Score –
A perceived stress scale used by researchers to attempt to evaluate the workload
experienced by the subject.

Perception – To
attain awareness or recognize an object. Perception is primarily cognitive
rather than emotional or impulsive, although all three aspects are manifested.
Simply stated, perception is vision plus a cognitive component (assessment or
categorization).

Perception-reaction – The
time that expires from the moment a stimulus is first perceived until the moment
the observer first moves in response to that stimulus.

Perception-response time –
Is the time that expires from the moment the stimulus is perceived until the
moment that the vehicle begins to respond. The perception-response time is the
perception-reaction time plus the transition time. Or perception-response time
is the perception-reaction time plus the movement time plus the mechanical
latency.
Periphery – The outward bounds of the visual field as
distinguished from the Central vision.

Reaction time (or simple reaction time)
– The shortest time between a single stimulus onset and a known single first
response.

Recognize – To acknowledge or take notice in a definite way as
something previously known.

Relative velocity: Detection threshold of –
Based upon the research by Hoffman & Mortimer (1996) and others, drivers are
not capable of detecting relative speed in a vehicle following situation until
the subtended arc angle of the lead vehicle expands at a rate of 0.003 radians
per second. _Calculated
_{as D = Sqrt(width x Closing Speed/0.003)}
_{Response complexity
– A nominal attribute allotted to a response based upon the number of
responses available to the driver and the number of maneuvers implemented during
the response.
1. Press button or verbal

2. Brake only – it was only
option OR Steer only, only option was to steer
3. Brake only or steer only-option
to brake and/or steer
4. Brake and swerve-Option was to
Brake and/or Steer

Road type

1. Rural 2. Urban 3. Highway 4.
Arterial

Saccadic movement – Eye
movements from one fixation point to another during visual search. During eye
movement there is little or no seeing. Typically used when referring to scanning
behavior of drivers who are looking in differing directions for gaps to traffic
in an attempt to drive onto a main road from a side road.

Saccadic time – The
sum of time of the intervals during which the eye is in motion as opposed to
fixating. According to research by Robinson et al. (1972), a last look in the
opposite direction is associated with a latency of approximately 1 second.

Sensation – A mental
process due to immediate bodily stimulation whether consciously processed or not
(Before the detection threshold is met the stimulus may not be consciously
processed).

Sight Distance - According
to AASHTO 4^{th ed., 2001, p. 127 – Eye height
- 1080 mm [3.5’] based upon studies of vehicle size and human anthropometry.
Trucks 2330 mm [7.6’]. Height of object – 600 mm [2’] above road surface
(Headlights & Taillights ~600 mm above road). (Fambro, Fitzpatrick &
Koppa, 1997). P. 660 - Sight triangle – Assumed location of driver’s eye 4.4
m (14.4’) behind the edge of traveled way. (For stop control on minor road).
Field observations: drivers stop with vehicle front < 2 m [6.5’] from edge
of major road. Front of vehicle to driver’s eyes < 2.4 m [8’] (Harwood,
Mason, Brydia, Pietrucha, & Gittings, 1996). With the distance listed above,
measure the sight distance from the location and height of the driver's eyes on
the side road to an object 2' (0.6 m) above ground level.}

Speed of vehicle
(km/h)

Strength of stimulus
Strength of stimulus will involve the number, size, intensity, or movement of
the stimuli that the observer must respond to.

Stimuli, Number of

1 stimulus

2 or more stimuli that is spatially
separate (exception would be non-spatially separate with one interfering
with identification of other) and are being (or are required to be) mentally
processed.

Stressor - Any
stimulus regardless of intensity. In the context of this research a stressor can
possess positive or negative consequences and it need not be mentally processed.

Substantive variable
– A variable that has been cited in previous research as being an influence
upon the response time of their subjects.

Subtended arc angle – The
angle (or cone) that an object (target) comprises. Measured by taking the Arc
tangent of the height of the object
divided ^{_{by the distance between the object and
observer. ATAN (ht/d).}}
^{_{Time-to-contact – is
the time between the moment that a stimulus is first presented to the observer
and the moment that the observer reaches that stimulus (the impact location
typically).

Topography –
Is whether there were topographical elements at the scene or not. Therefore,
this is an issue of No or yes. Topographical elements such as intersections,
vertical and horizontal curves have been shown to add context to a driver’s
perception in vehicle following and path intrusion responses.

1. Straight 2. Intersections,
Horizontal curves or vertical curves

Transition time – is
the time between the first movements of the responder until the vehicle begins
to respond. In essence it is the movement time plus the mechanical latency. See
breakdown of transition time research below.

Transition Time (Clock stop)

First movement (Foot Off
Accelerator, 1st hand movement)
First response (Brake pedal 1st
applied or Steering accomplished)
First vehicle response (Start of
deceleration or lateral movement)

Light Measurement Terms
candela: the
base unit of luminous intensity in the International System of Units that is
equal to the luminous intensity in a given direction of a source which emits
monochromatic radiation of frequency 540 x 1012 hertz and has a radiant
intensity in that direction of 1/683 watt per unit solid angle.   Also
called candle; abbreviation cd.

candlepower:
luminous intensity expressed in candelas. Abbreviation cp.

foot-candle: a
unit of illumination on a surface that is everywhere one foot from a uniform
point source of light of 1 candle and equal to one lumen per square foot.
Approximately 10.7639 lux. Abbreviation ftc or fc.

foot-lambert: a
unit of luminance (photometric brightness) equal to 1/ candela per square foot,
or to the luminance of a perfectly diffusing surface that emits or reflects one
lumen per square foot. Approximately 3.42625 nit. Abbreviation
ft-L. Called also equivalent foot-candle.

illuminance: the
luminous flux per unit area on an intercepting surface at any given point.
Also called illumination; luminous flux density.

lambert: A unit
of luminance (photometric brightness) that is equal to 1/ candela per square
centimeter, or to the luminance of a perfectly diffusing surface that emits or
reflects one lumen per square centimeter.   Abbreviation L.

lumen: a unit of
luminous flux equal to the light emitted in a unit solid angle (1 steradian) by
a uniform point source of one candela intensity. Abbreviation lm.

lumen-hour: a
unit quantity of light (luminous energy), equal to the quantity of light
radiated or received for a period of 1 hour by a flux of 1 lumen.
Abbreviation lm-hr

lumen per watt:
the unit of luminosity factor and luminous efficacy. Abbreviation lm/w.

lumen-second: a
unit quantity of light (luminous energy), equal to the quantity of light
radiated or received for a period of 1 second by a flux of 1 lumen.
Abbreviation lm-sec

luminance: the
luminous intensity of a surface in a given direction per unit of projected
area. Also called brightness.

luminance factor:
The ratio of the luminance of a body when illuminated and observed under certain
conditions to that of a perfect diffuser under the same conditions.

luminosity factor:
The ratio of the luminous flux in lumens emitted by a source at a
particular wavelength to the corresponding radian flux, in watts, at the same
wavelength this is a measure of the visual sensitivity of the eye.
Also called luminosity.

luminosity function:
A standard measure of the response of an eye to monochromatic light at various
wavelengths the function is normalized to unity at is maximum value. Also
called luminosity curve; spectral luminous efficiency; visibility function.

luminous coefficient:
A measure of the fraction of the radian power of a light source which
contributes to its luminous properties, equal to the average of the luminosity
function at various wavelengths, weighted according to the spectral intensity of
the source. Also called luminous efficiency.

luminous efficacy:
1. The ratio of the total luminous flux in lumens emitted by a source of
light over all wavelengths to the total radiation flux in watts. 2.
The ratio of the total luminous flux emitted by a light source to the power
input of the source; expressed in lumens per watt.

luminous emittance:
The emittance of visible radiation weighted to take into account the different
response of the human eye to different wavelengths of light; in photometry,
luminous emittance is always used as a property of a self-luminous source, and
therefore should be distinguished from luminance.   Also called
luminous excitance.

luminous energy:
The total radiant energy emitted by a source, evaluated according to its
capacity to produce visual sensation.   Measured in lumen-hours or
lumen-seconds.

luminous flux:
The time rate of flow of radiant energy, evaluated according to its capacity to
produce visual sensations; measured in lumens.

luminous intensity:
The luminous flux incident on a small surface which lies in a specified
direction from a light source and is normal to this direction, divided by the
solid angle (in steradian) which the surface subtends at the source of
light. Called also light intensity.

lux: a unit of
illumination equal to the direct illumination on a surface that is everywhere
one meter from a uniform point source of one candela intensity or equal to one
lumen per square meter. Abbreviation lx.   Also called
meter-candle.

nit: a unit of
luminance, equal to 1 candela per square meter. Abbreviation nt.

phot: A unit of
illuminance equal to the illumination of a surface, 1 square centimeter in area,
on which there is a luminous flux of 1 lumen, or the illumination on a surface
all points of which are at a distance of 1 centimeter from a uniform point
source of 1 candela. Also called centimeter-candela.}}

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