8-1 low cost safety improvements the tools – traffic signals – session #8
TRANSCRIPT
8-1
LOW COST SAFETY IMPROVEMENTS
The Tools –
Traffic Signals – Session #8
8-2
Traffic Signals
Learning Outcomes:
1. Identify countermeasures for operation and design deficiencies of traffic signals
8-3
Traffic Signals
• New Tools:
NCHRP 440 – Accident Mitigation Guide for Congested Rural Two-Lane Highways
NCHRP 500 – Volume 5: A Guide for Addressing Unsignalized Intersection Collisions
8-4
• New & Proven Technologies
Traffic Signals
8-5
Traffic Signals
How can Traffic Signals Reduce crashes?
Which Signal Configurations, Equipment, and Operations Reduce Crashes?
What is the Safety Effect of each?
Discussion
8-6
Safety Benefits of Traffic Signals
Install new Traffic Signal
Upgrade Traffic Signal
(Fatalities)
(Injuries)
CRF=7%
38%22%
Install new Traffic Signal – All Crashes (CTRE 00-61, 2001) CRF=27%
Proven
Tried
3 Approaches
4 ApproachesTried
Increase Crashes 2%
8-7
Safety Benefits of Traffic Signals
Change type of Traffic Control (3 and 4 approach Unsignalized to Signal Control)
Tried
ALL Right-angle Rear-end Intersection type AMF AMF AMF
Three-leg 0.93 0.80 1.75
Four-leg 1.02 0.40 1.74
CRF = 60%
Table 13.3: AMFs for Urban-Intersection Signalization (Injury-related crashes ONLY) (Persaud et al., 2002)
8-8
Is this traffic signal as safe as it could be?
Discussion
What are some Traffic Signal Features/Equipment that affect Safety?
Let’s list them
8-9
Traffic Signals Countermeasures
1. Update yellow Clearance timing
2. Add All-Red Clearance phase
3. Improve visibility (12” sections, suppl. heads, etc)
4. Add Back Plates
5. Change Permissive Lefts to Protected Only
8-10
Traffic Signals Countermeasures
6. Add Advance Warning signs with active flashers
7. Add Supplemental Signal Heads
8. Use Overhead Red “T” Heads
9. Change Late Night Yellow/Red Flash to Full Time Signal
10. Coordination of Signals
11. Controller/Actuation Upgrades
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Frequency of Red Light Running:
*TTI, Bonneson, 2003
8-12
Engineering Countermeasures to Red-Light Running:
*TTI, Bonneson, 2003
Tried
8-13
Update Clearance Intervals
All-Red TimeYellow Time
ITE Traffic Engineering Handbook
*NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals
Proven
8-14
Update Clearance Intervals
Red TimeYellow Time
ITE Traffic Engineering Handbook
CP = t + V/2a + V/20*64.4*g + (W+L)/V
For 85th percentile approach speed of 45 mph, curb radius (Stop bar to curb line of intersecting street of 50’, And Intersection width of 36 feet
= t + V/2a + V/20*64.4*g = 1.0 + 45*88/60/2*10 + 45*88/60/20*64.4*0% = 1.0 +66/20 = 1.0 + 3.3 = 4.3 seconds
Yellow Time
8-15
Update Clearance Intervals
*TTI, Bonneson, 2003
8-16
Update Clearance Intervals
*TTI, Bonneson, 2003
-reduces RLR frequency by 50-70%- reduces RLR crashes by 25%
-reduces RLR frequency by 50-70%CRF = 4 to 31% Total CrashesCRF = 1 to 30% Right Angle Crashes
8-17
Update Clearance Intervals
* From ITE Traffic Signal Handbook
Proven
*NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals
8-18
Add All-Red Clearance Interval
ITE Traffic Engineering Handbook – All-Red Clearance Interval
T = ( W + L) / V
Example: 85th Speed=45mph, W=36, curb radius=50’, L=20’Red Time = (W+L)/V = (50 + 36 + 20)/45*88/60 = 106/66 = 1.61seconds
CRF=25% for Add 1.0 Sec All-Red *Bhesania, 1991
Tried
8-19
Improve Visibility (12” Indications, Suppl heads)
Mast Arm Signals* Iowa
8” to 12” Indications, *Winston-Salem, NC
* Bonneson
CRF = 32% Related Crashes
CRF = 24% All Crashes
33-47% Right Angle Crashes
Tried
8-20
Improve Visibility (Mast Arms)
Tried
Treatment Finding
Replace pedestals with mast arms (166)
49% estimated reduction in all crashes.44% estimated reduction in fatal/injury 51% estimated reduction in property damage only (PDO) collisions.74% estimated reduction in right angle collisions.41% estimated reduction in rear end 12% estimated reduction in left-turn
8-21
Improve Visibility – Signal Head per Lane)
Tried
CRF = 10 - 22%, Total Crashes, *ICBC, Winston-Salem, NC
CRF = 47%, Right Angle Crashes
1 head for 1 Lt lane
4 heads for 4 lanes
1 head for 1 Rt lane
8-22
Improve Visibility (Add a Signal Head)
Tried
Treatment Finding
Add a signal head(135)
15% estimated increase in all collisions.47% estimated reduction in right angle collisions.
Add a primary signal head (168)
10% to 25% estimated reduction in fatal/injury 30% to 35% estimated reduction in property-damage-only collisions.15% to 45% estimated reduction in right-angle 0% to 45% estimated reduction in rear-end
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Improve Visibility (Supplemental Signal Head)
Supplemental Signal Head
CRF = 15%, Total Crashes, *ICBC, Winston-Salem, NC
Tried
CRF = 47-48%, Right Angle Crashes
8-24
Add Back Plates
No Back Plates Back Plates
Tried
CRF= 32% Right angle crashes,
CRF= 2% to 24% All Crashes
8-25
Add Back Plates
-50% reduction in RLR
* Bonneson
Tried
CRF= 2% - 24%
8-26
Retroreflectorize Back Plates
Canadian retro- reflectorized backplate
CRF=32% reduction in RLR Crashes
Tried
CRF = 12% increase in all crashes
8-27
Retroreflectorize Back Plates
Canadian retro- reflectorized backplate
32% Reduction in RLR Related Crashes
Tried
8-28
Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY
“T” Intersection 3 Thru Lanes
Westbound with ADT of 34,000; Side Street ADT is 1,400
NY 44 Westbound
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Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY
What low cost safety countermeaures would you consider?
What is the safety effect (CRF) for each?
Discussion
8-30
Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY
Relevant Countermeasures:
• Change 8” to 12” Indications
• Add Backplates• Add All-Red Phase• Revise Change
Interval• Remove Sight
Obstruction of Parked Vehicles on Southeast Quadrant
NY 44 Westbound
8-31
Left Turn Lanes + Left Turn Phases
Add a Left Turn Phase to Existing Signal
Tried
*NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation
CRF = 23% to 48% Total Crashes
CRF = 63% to 70% Left Turn Crashes
8-32
Left Turn Lanes + Left Turn Phases
Add a Protected/Permissive Left Turn Phase to Existing Signal
Tried
*NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation
CRF = 4% to 10% Total Crashes
CRF = 40% to 64% Left Turn Crashes
8-33
Left Turn Lanes + Left Turn Phases
Add a Left Turn Phase + Left Turn Lane to Existing Signal
Tried
*NCHRP 500, Objective 17.2 A1 – Employ Left Turn Signal Phase
CRF = 35% Total Crashes
CRF = 58% (Iowa), Left Turn Crashes
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Left Turn Lanes + Left Turn Phases
Signalize and Add a Left Turn Lane without Left Turn Phase
Tried
*NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation
CRF = 15%
Total Crashes
CRF = 21% to 25% Total Crashes
CRF = 46% to 54% Left Turn Crashes
8-35
Left Turn Lanes + Left Turn Phases
Signalize and Add a Left Turn Lane + Left Turn Phase
Tried58% Reduction in
Crashes, *Iowa
*NCHRP 500, Objective 17.2 A1 – Provide Left Turn Signal Phase
CRF=25% to 36% Total Crashes
CRF=43% to 45%, Left Turn Crashes
8-36
Change Permissive Left to Protected Left Only
CRF = 97% to 98% Left Turning Crashes
* Winston-Salem, NC
Proven
*NCHRP 500, Objective 17.2 A1 – Provide Protected Left Turn Signal Phase
8-37
Add Signal Ahead Advance Warning Sign
Tried
CRF= 35-40%
Winston-Salem, NC
McGee
MN DOT
8-38
Add Signal Ahead Advance Warning Sign
Tried
Treatment Finding
Post SIGNAL AHEAD warning signs—urban(98)
16%-35% estimated decrease in all collisions.
Post SIGNAL AHEAD warning signs—rural(98)
16%-40% estimated decrease in all collisions.
Post SIGNAL AHEAD signs(135)
44% estimated decrease in right-angle collisions.
Advance-warning flasher
(172)
44% decrease in all fatal/injury 53% decrease in pd crashes73% decrease in all fat/inj-angle crashes.82% increase in all rear-end fatal-injury
8-39
Add Advance Warning Sign with Active Flashers tied to Signal Operation
CRF=35% to 67% Reduction in RLR Related Crashes, *Bonneson
Tried
8-40
Add Advance Warning Signs & Flashers
Tried
Treatment Finding
Post SIGNAL AHEAD warning signs—urban(98)
16%-35% estimated decrease in all collisions.
Post SIGNAL AHEAD warning signs—rural(98)
16%-40% estimated decrease in all collisions.
Post SIGNAL AHEAD signs(135)
44% estimated decrease in right-angle collisions.
Advance-warning flasher
(172)
44% decrease in all fatal/injury collisions.53% decrease in property-damage-only73% decrease in all fatal/injury-angle 67% decrease in all fatal/injury left-turn 82% estimated increase in all rear-end
8-41
Add Supplemental Signal Head(s)
Supplemental Far Left Signal Head
8-42
Add Supplemental Signal Head(s)
Crest Vertical Curve + Right Hand CurveSight Distance is Limited By Noise Walls
8-43
Overhead Red “T” Signal Heads
Tried
CRF = 12% total crashesCRF = 33% Reduction in Rt angle crashes, *Winston-Salem, NC
8-44
Flashing Operation
Issue Benefit Detriment
Yellow on mainline/Red on side street - if volume ratio is three or more
Yellow on mainline/Red on side street – if volume ratio is less than three or if adequate sight distance is not available
8-45
Flashing Operation
Change late night flash of Yellow on mainline/Red on side street to normal operating traffic signal mode
Tried
CRF = 29% Total Crashes
CRF = 80% Right Angle Crashes
*Winston-Salem, NC
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Signal Coordination
Proven
*NCHRP 500, Objective 17.2 A4 – Employ Signal Coordination
CRF = 15% to 17% total crashes – 5 studies
CRF = 25% to 38% Right Angle Crashes
8-47
Traffic Signals
Available thru ITE
ITE website: www.ite.org
Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red Light Running
*NCHRP 500, Objective 17.2 E-3 – Implement Automated Enforcement of Red-Light Running
Proven
8-48
Traffic Signals
Review Question: What is the Recommended Practice re Calculation of Change Intervals?
CP = t + V/2a + V/20*64.4*g + (W+L)/VITE Traffic Engineering Handbook
-reduces RLR frequency by 50-70%CRF = 4 to 31% Total CrashesCRF = 1 to 30% Right Angle Crashes
8-49
Traffic Signals
Learning Outcomes:
1. Identify countermeasures for operation and design deficiencies of traffic signals
8-50
Questions?
Traffic Signals