1 30 12 Automated Traffic Enforcement Work Session_Engineering PresentationBattery Backups installed as a standard ITS
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Factors Affecting
Intersection Safety
• Count Down Peds
• Signal Head Location and Position
(Backplates)
• Vision Triangles - Visibility of Signal
Heads
Factors Affecting
Intersection Safety
t
Count Down Ped
Signals
• Work well at pre -timed intersection
such as downtown signals
• If used every cycle along Hwy 20 or
NW Arterial they would loose there
.
.
ash 1y o•esyncronize•
to traffic approaching the
traffic control signal..."
Factors Affecting
Intersection Safety
•Signal Head Location and
Position (back plates)
• MUTCD - "The two primary
faces required as a minimum
should be continuously visible
MUTCD - Vision Triangle
Center of approa h
110 ft
180 ft"'
40 1 ft'
120 ft"
Minimum distance of signal faces from
stop line
Maximum distance from stop line for 8 -inch
signal face
Maximum distance from stop line for 12 -inch
signal faces, unless a near -side supplemental
signal face is used
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Factors Affecting
Intersection Safety
• Yellow Duration
• Red Duration
• Average Green Duration
• Average Cycle Length
• Consistent Traffic Control
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YELLOW �It RED __0,
DURATION DURATION
Engineering Safety Solutions
Intersections
• Design
• Example Projects
• Infrastructure /
Equipment
Yellow and Red Times
• a cu a ions
B
•
•
Yellow Light Timings
Yellow light timings need to be
consistent (Uniform) in how they are
calculated.
Institute of Transportation Engineers
ITE has formulas for calculatin •
yellow and red times.
Yellow Time = S eed Limit = 10.
•
Yellow Light Timings
• Yellow durations have minimum of 3
seconds and a maximum of 6
seconds
• "Rule of Thumb"
Yellow Light Timings
ITE - Institute of Transportation Engineers
Y = t -I
V
2a ± 64.4 g
Y = yellow interval in seconds
t = reaction time in seconds (1.0 s)
v = 85Th percentile approach speed
. -• -
- - ,
feet /sec /sec
g = grade of approach over the
breakin • distance
Every intersection currently has an all
. _
ilk
•
Red Light Timings
The MUTCD red clearance interval
determined by engineering practices.
red durations are optional but not to
exceed 6 seconds .
Red Light Timings
ITE - Institute of Transportation Engineers
R
w +l
V
R = red interval in seconds
w = Width of intersection, in feet
I = length of vehicle, set at 20 feet
v = speed of vehicle, in feet /second
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TRAFFIC SIGNAL EQUIPMENT RECORD AND CONDITION DIAGRAM
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Adding 7 Second To
Yellow Light Times
• Yellow durations have minimum of 3
seconds and a maximum of 6
seconds
• Need to be consistent with how
yellow timings are calculated
Intersection Design
Parameters
• Geometric Designs
• Roundabouts
• Turn Lanes
• Number of Lanes
• Approach Speed
• Traffic Volume
• ra is ""arrants
• Detection - Replaced Loops
.
of or ran is ow
Traffic Management
• Traffic Counts
• NW Arterial
• Located between major
intersections
• Cameras
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How Engineering Improves
Intersection Safety
NW Arterial
- Added and lengthened turning lanes.
- Installed count down peds
- Installed new vehicle detection
- Coordinate traffic flow through the
corridor.
- • - - - . - - .
- Added right turn overlaps (right turn
arrows)
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