Safety at Signalized Intersections Safety at Signalized Intersections Gary B. Thomas Gary B. Thomas Texas Transportation Institute Texas Transportation Institute Traffic Gurus Annual Meeting Traffic Gurus Annual Meeting May 14, 2008 May 14, 2008
FHWA Safety Focus Areas FHWA Safety Focus Areas Signalized Intersections 2
Nationwide Fatalities Nationwide Fatalities There were 41,059 highway There were 41,059 highway fatalities in 2007. fatalities in 2007. Non-Intersections Where did they occur? Where did they occur? 79% Intersections About half of all all crashes and half of crashes and half of About half of 21% all injury crashes occur at all injury crashes occur at intersections. intersections. Signalized Intersections 3
Intersection Fatalities Intersection Fatalities There were 8,657 intersection fatalities in 2007. There were 8,657 intersection fatalities in 2007. Where did they occur? Where did they occur? 6,000 5,232 5,000 39% in 39% in rural areas rural areas 4,000 Fatalities 3,000 2,000 1,739 61% in 61% in 1,472 urban areas urban areas 1,000 214 0 Arterial Collector Local Unknown Signalized Intersections 4
Traffic Signals Traffic Signals Signalized Intersections 5
Intersection Fatalities Intersection Fatalities 2,755 5,539 363 Signalized Intersections 6
Intersection Safety Guidance Intersection Safety Guidance • NCHRP Report 500 Volume 12 • Guide sheets • Safety Strategies brochure Signalized Intersections 7
Typical Signalized Intersection Crash Types Typical Signalized Intersection Crash Types • Right angle • Rear end • Left turn • Sideswipe • Pedestrian/bicycle Signalized Intersections 8
Crash Reduction Factors Crash Reduction Factors • Quantitative results from research or other studies • Expected reduction in crashes from implementation of a specific countermeasure Signalized Intersections 9
Angle Crashes Angle Crashes • Account for 42% of fatal crashes at signalized intersections • Potential countermeasures: – Optimize change intervals – Improve sight distance – Restrict access – Provide targeted enforcement – Restrict parking – Construct roundabouts Signalized Intersections 10
Optimize Change Intervals Optimize Change Intervals Intervals that are too long encourage Intervals that are too long encourage disrespect and lead to red-light running. disrespect and lead to red-light running. Intervals that are too short violate driver Intervals that are too short violate driver expectancy and lead to abrupt stops. expectancy and lead to abrupt stops. AASHTO Report 500 Volume 12 AASHTO Report 500 Volume 12 E R U S A E M R E T N U O C T S O C W O L Countermeasure CRF Change Intervals per ITE Total = 8% Ped/Bike = 37% Multi-vehicle = 9% Signalized Intersections 11
Improve Sight Distance Improve Sight Distance The driver of a vehicle The driver of a vehicle approaching an intersection approaching an intersection should have an unobstructed should have an unobstructed view of the entire intersection, view of the entire intersection, including any traffic-control including any traffic-control devices, and sufficient lengths devices, and sufficient lengths along the intersecting highway along the intersecting highway to permit the driver to anticipate to permit the driver to anticipate and avoid potential collisions. and avoid potential collisions. AASHTO “Green Book” AASHTO “Green Book” E R U S A E M R E T N U O C T S O C W O L Signalized Intersections 12
Restrict Access Restrict Access Driveways should not be located within Driveways should not be located within the functional area of an intersection. the functional area of an intersection. Intersection Safety Brief # 13: Access Management Intersection Safety Brief # 13: Access Management Signalized Intersections 13
Provide Targeted Enforcement Provide Targeted Enforcement Enforcement is a potential Enforcement is a potential countermeasure to unsafe countermeasure to unsafe and illegal motorist behavior and illegal motorist behavior at intersections. Studies at intersections. Studies report the reduction of traffic report the reduction of traffic law violations when law violations when enforcement is used. enforcement is used. AASHTO Report 500 Volume 12 AASHTO Report 500 Volume 12 Countermeasure CRF Automated Enforcement Total = 12% Right Angle = 25% Left Turn = 45% Signalized Intersections 14
Restrict Parking Restrict Parking Parking maneuvers into or out of Parking maneuvers into or out of on-street parking stalls can affect on-street parking stalls can affect the operation and safety of the the operation and safety of the through traffic lane adversely. through traffic lane adversely. NCHRP Report 457: NCHRP Report 457: Evaluating Intersection Improvements: Evaluating Intersection Improvements: An Engineering Study Guide An Engineering Study Guide Countermeasure CRF LOW COST COUNTERMEASURE Restrict Parking Total = 49% Pedestrian = 30% Signalized Intersections 15
Convert to Roundabout Convert to Roundabout Many studies have found that one Many studies have found that one of the benefits of roundabout of the benefits of roundabout installation is the improvement in installation is the improvement in overall safety performance overall safety performance Roundabouts: An Informational Guide Roundabouts: An Informational Guide Countermeasure CRF Convert signalized Total = 48-67% intersection to Injury = 60-78% roundabout Fatal/Incapacitating = 90% Signalized Intersections 16
Rear End Crashes Rear End Crashes • Account for 8% of fatal crashes at signalized intersections • Potential countermeasures: – Increase visibility of intersection and/or traffic signals – Increase awareness – Improve signal coordination – Install turn lanes – Control approach speeds – Optimize change intervals* * Discussed previously Signalized Intersections 17
Increase Visibility of Signals Increase Visibility of Signals …12 inch signal indications shall be …12 inch signal indications shall be used for all signal sections in all new used for all signal sections in all new signal faces… signal faces… Proposed amendment to the MUTCD Proposed amendment to the MUTCD E R U S A E M R E T N U O C T S O C W O L Countermeasure CRF Convert to 12-inch Lenses Total = 11-24% Injury = 16% Add Supplemental Heads Right angle = 35% Rear end = 28% Total = 28% Signalized Intersections 18
Increase Visibility of Signals Increase Visibility of Signals Countermeasure CRF One Primary Head Per Total = 28% Lane Rear end = 28% Right-angle = 35% Add Backplates Total = 13% Right-angle = 50% Signalized Intersections 19
Increase Awareness of Intersection Increase Awareness of Intersection [A signal ahead sign] shall be installed on an approach to a [signal] that is not [A signal ahead sign] shall be installed on an approach to a [signal] that is not visible for a sufficient distance to permit the road user to respond to the device. visible for a sufficient distance to permit the road user to respond to the device. Manual on Uniform Traffic Control Devices Manual on Uniform Traffic Control Devices LOW COST COUNTERMEASURE Countermeasure CRF Advance Warning Signs Total = 22% Right Angle = 35% Dilemma Zone Protection Fatal/injury = 39% Signalized Intersections 20
Improve Signal Coordination Improve Signal Coordination Countermeasure CRF Signal Coordination Right Angle = 32% Apart from its operational benefits, signal coordination is known to reduce Apart from its operational benefits, signal coordination is known to reduce vehicle conflicts along corridors where traffic signals are coordinated. vehicle conflicts along corridors where traffic signals are coordinated. Signalized Intersections: Informational Guide Signalized Intersections: Informational Guide Signalized Intersections 21
Install Turn Lanes Install Turn Lanes Provision of an exclusive left-turn Provision of an exclusive left-turn bay…generally improves the bay…generally improves the operations of all movements… operations of all movements… NCHRP Report 457: Evaluating Intersection NCHRP Report 457: Evaluating Intersection Improvements: An Engineering Study Guide Improvements: An Engineering Study Guide Countermeasure CRF Add Left Turn Lane Total Urban = 7-19% Injury Urban = 9-17% Total Rural = 15-18% Add Right Turn Lane Total = 4% per approach Signalized Intersections 22
Control Approach Speeds Control Approach Speeds LOW COST COUNTERMEASURE Since speed contributes to Since speed contributes to crash severity, lowering speeds crash severity, lowering speeds on approaches to intersections on approaches to intersections can help reduce the severity of can help reduce the severity of crashes. Slowing vehicle crashes. Slowing vehicle speeds…can improve safety for speeds…can improve safety for motorists, pedestrians, and motorists, pedestrians, and bicyclists. bicyclists. AASHTO Report 500 Volume 12 AASHTO Report 500 Volume 12 Signalized Intersections 23
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