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Safety at Signalized Intersections (Short Version)

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Collage of photos including different signal head types and a signal equipment box.

FHWA logo and FHWA Office of Safety Logo: Safe Roads for a Safer Future, Investment in roadway safety saves lives.

speaker notes:

This is an approximately 30-minute presentation on the topic of red-light running (RLR). Topics covered include:

Nature and magnitude of the problem
Documents available to help with countermeasure selection
Types of crashes and countermeasures associated with addressing specific types of crashes

Please note that the long version of this presentation goes into much more detail about individual countermeasures and the associated crash reduction factors.

slide 2

FHWA Safety Focus Areas

speaker notes:

Major Points to Make:

FHWA has identified these 4 primary focus areas for improving safety and reducing crashes. This presentation will look exclusively at safety issues related to SIGNALIZED INTERSECTIONS.

Fatalities attributed to the four primary focus areas:

Intersections – 21%
Roadway Departure – 58%
Pedestrians – 11%
Speeding – 32%

slide 3

Nationwide Fatalities

There were 41,059 highway fatalities in 2007. Where did they occur?

About half of all crashes and half of all injury crashes occur at intersections.

Pie chart indicates 79 percent of fatalities occurred at non-intersections and 21 percent occurred at intersections.

speaker notes:

Major Points to Make:

This slide represents the most recent published crash data in the FARS database. Includes only FARS elements of "intersection" and "intersection-related" fatalities.

slide 4

Intersection Fatalities

There were 8,657 intersection fatalities in 2007. Where did they occur?

speaker notes:

Major Points to Make:

Looking at just intersection fatalities in general, we see that well over 1/2 occur in urban areas and the majority occur on arterial facilities. 60% of intersection fatalities occur on arterial streets.

For rural fatalities, about 9% occur at signalized intersections
For urban fatalities, about 39% occur at signalized intersections

Source: FARS database

slide 5

Traffic Signals

There are at least 3 million intersections in the United States.

At least 300,000 are signalized.

Photo of a post-mounted traffic signal head with a black backplate.

speaker notes:

Major Points to Make:

These are very gross estimates. There is no nation-wide inventory of traffic signals. The point to make is that roughly 10% (but likely even less) of the intersections in the United States are signalized.

slide 6

Intersection Fatalities

Graph shows that 2,755 fatalities occurred at signalized intersections, 5,539 fatalities occurred at unsignalized intersections, and 363 occurred at other or unknown locations.

speaker notes:

Major Points to Make:

As noted in the previous slide, roughly 10% of intersections are signalized. However, fatalities at signalized intersections constitute 1/3 of the total number of fatalities.
The data are from FARS for 2007 and includes only the FARS elements of "intersection" and "intersection-related" fatalities.

Other notes:

32% of all intersection fatalities occur at signalized intersections.
The 5,539 fatalities at UNSIGNALIZED intersections include 3,082 at stop-controlled, 131 at other regulatory control (such as yield), 2,689 where the type of control is either unknown (363) or was not considered a contributor to the fatal crash.
Crashes at signalized intersections tend to be different than those at unsignalized intersections in both type of crash and severity level.

slide 7

Intersection Safety Guidance

NCHRP Report 500 Volume 12
Guide sheets
Safety Strategies brochure

Collage of images showing the front pages of the referenced documents.

speaker notes:

Major Points to Make:

FHWA has numerous resources available to help traffic and transportation engineers analyze intersections from a safety viewpoint.
Web sites will be shown at the end of the presentation.
Many are free to download from the Internet.
Another document that is nearing completion that will help identifying low cost countermeasures is: Low-Cost Countermeasures to Deploy at Stop-Controlled and Signalized Intersections Experiencing Crashes. This document is currently anticipated to be complete and posted on the FHWA Office of Safety web site in the Spring of 2009.

slide 8

Typical Signalized Intersection Crash Types

Right angle
Rear end
Left turn
Sideswipe
Pedestrian/bicycle

Two photos, both of crashes at signalized intersections with first responders on the scene.

speaker notes:

Major Points to Make:

These are the most common crash types that occur at signalized intersections. Each type will be highlighted with typical countermeasures in upcoming slides.
Right angle crashes are between vehicles on perpendicular approaches.
Left turn crashes occur between vehicles on opposite approaches where one vehicle is turning left and the opposing vehicle is going straight.

slide 9

Crash Reduction Factors

Quantitative results from research or other studies
Expected reduction in crashes from implementation of a specific countermeasure

Image of the cover of an FHWA document entitled 'Toolbox of Countermeasures and their Potential Effectiveness to Make Intersections Safer.'

speaker notes:

Major Points to Make:

Crash reduction factors (CRFs) provide a quick way for transportation agencies to estimate crash reductions associated with highway safety improvements. Many States and local jurisdictions use these factors to make program-planning decisions about implementing specific treatments and/or to quickly determine the costs and benefits of selected alternatives.
CRFs are the quantitative results from research and/or evaluation studies, indicating the percentage reductions in crashes that can be expected after implementing treatments or programs. Not all countermeasures presented have CRFs associated with them.
The long version of this presentation contains numerous CRFs for the various countermeasures. They are taken primarily from NCHRP Report 500: Volume 12 – A Guide for Reducing Collisions at Signalized Intersections and from the Toolbox Brief (graphic). All of the countermeasures discussed in the report ARE NOT included in this presentation. This is only a sample of recommended countermeasures.
Not all of the countermeasures have been subjected to studies to determine their CRFs (as evidenced by their categorization as either Proven, Tried or Experimental in the NCHRP Report 500 Volumes 5 & 12)

slide 10

Angle Crashes

42% of fatal crashes at signalized intersections
Potential countermeasures:
- Optimize change intervals
- Improve sight distance
- Restrict access
- Provide targeted enforcement
- Restrict parking
- Construct roundabouts

Collage of photos including a diagram depicting a 90 degree crash between two vehicles trying to cross an intersection simultaneously, an urban intersection, a roundabout, a signal enforcement camera, and an intersection with poor sight distances.

speaker notes:

Major Points to Make:

Point out the type of crash and that angle crashes account for 42% of fatal crashes at signalized intersections.
Angle crashes are between vehicles on perpendicular approaches (as shown in the diagram).
Left turn crashes occur between vehicles on opposite approaches where one vehicle is turning left and the opposing vehicle is going straight.
Also of note is that fatal angle crashes involving motorcycles are higher in proportion to all vehicles. Angle crashes proportion involving motorcycles is around 70%. 13% of ALL fatal crashes at signalized intersections involve motorcycles.

Potential countermeasures:

Optimize change intervals: If they are not set properly, optimizing change intervals to the time determined using the ITE formula is a very low cost countermeasure and very effective. It is critical to the success of any potential red-light camera program.
Improve sight distance: Sight distance is often overlooked at signalized intersections doe to the more positive control of side street traffic. However, it can have an effect on right-turn-on-red vehicles.
Restrict access: Restricting access to commercial properties near intersections by closing driveways on major streets, moving them to cross streets, or restricting turns into and out of driveways will help reduce conflicts between through and turning traffic.
Provide targeted enforcement: Enforcement is a potential countermeasure to unsafe and illegal motorist behavior at intersections. Studies report the reduction of traffic law violations when enforcement is used.
Restrict parking: Parking adjacent to turning and/or through lanes on intersection approaches may create a hazard.
Construct roundabouts: Many studies have found that one of the benefits of roundabout installation is the improvement in overall safety performance

slide 11

Rear End Crashes

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

Collage of images, including a diagram of a rear-end collision, a road sign warning of a signal ahead, a large intersection with a signal head for each lane, an intersection with clear lines of sight, and an oversized signal head.

speaker notes:

Major Points to Make:

Point out the type of crash and that rear-end crashes account for 8% of fatal crashes at signalized intersections.

Potential countermeasures:

Increase visibility of intersection and/or traffic signals: Lack of visibility of traffic control devices may contribute to crash experience at signalized intersections.
Increase awareness: Some crashes at signalized intersections may occur because drivers are unaware of the presence of an intersection or are unable to see the traffic control device in time to comply.
Improve signal coordination: Signal coordination has long been recognized as having beneficial effects on the quality of traffic flow along a street or arterial. Good signal coordination can also generate measurable safety benefits.
Install turn lanes: Right-turn lanes can minimize collisions between vehicles turning right and following vehicles. Left-turn lanes allow separation of left-turn and through-traffic streams, thus reducing the potential for rear-end collisions.
Control approach speeds: Slowing vehicle speeds on intersection approaches can improve safety for motorists, pedestrians, and bicyclists.
Optimize change intervals: Discussed on previous slide.

slide 12

Left Turn Crashes

21% of fatal crashes at signalized intersections
Potential countermeasures:
- Employ protected left turn phasing
- Implement turn restrictions
- Improve turning lane design
- Reconstruct approaches
- Improve sight distance
- Improve signal coordination

Collage of images, including a diagram of a left turning car impacting a vehicle traveling straight through an intersection, a sign next to a signal head indicating restricted left turn hours, an offset left turn lane, and a permissive/protected left turn signal at an intersection.

speaker notes:

Major Points to Make:

Point out the type of crash and that left turn crashes account for 21% of fatal crashes at signalized intersections.

Potential countermeasures:

Employ protected left turn phasing: Left turns are widely recognized as the highest-risk movements at signalized intersections. Protected left turn phases significantly improve the safety for left-turn maneuvers by removing conflicts with the left turn.
Implement turn restrictions: Safety at some signalized intersections can be enhanced by restricting or prohibiting turning maneuvers.
Improve turning lane design: The design of the left-turn lane is crucial to its effectiveness as either a safety or operational improvement strategy.
Reconstruct approaches: Signalized intersections may have such a significant crash problem that the only alternative is to change the nature of the intersection itself.
Improve sight distance: Discussed on previous slide (#10)
Improve signal coordination: Discussed on previous slide (#11)

slide 13

Sideswipe Crashes

13% of fatal crashes at signalized intersections
Potential countermeasures:
- Install pavement markings
- Provide protected left turn phasing

Two images, one a diagram of two vehicles on opposite approaches attempting to turn left and colliding in a sideswipe type collision. The second image is an aerial photo of an intersection where dashed lines curve out and to the left from dual left turn lanes, crossing through the intersection proper to guide left turning vehicles. Dashed lines also guide vehicles traveling straight across the intersection to the opposite side.

speaker notes:

Major Points to Make:

Point out the type of crash and that sideswipe crashes account for 13% of fatal crashes at signalized intersections.

Potential countermeasures:

Install pavement markings: Providing positive guidance for drivers, especially at complex intersections, can help reduce collisions.
Provide protected left turn phasing: Discuss on previous slide (#12).

slide 14

Pedestrian/Bicycle Crashes

25% of fatal crashes at signalized intersections
Potential countermeasures:
- Improve signal hardware
- Improve pedestrian/bicycle facilities
- Provide information and education

Collage of images, including a diagram of a left turning vehicle impacting a pedestrian, a photo of a wheelchair-bound pedestrian waiting for the walk signal at a mid-block crosswalk, a photo of a dedicated bike lane set off by dashed lines that parallels the roadway and crosses an intersection like a crosswalk, and a photo of a countdown signal head.

speaker notes:

Major Points to Make:

Point out the type of crash and that pedestrian/bicycle crashes account for 25% of fatal crashes at signalized intersections.

Potential countermeasures:

Improve signal hardware: Nearly one-third of all pedestrian-related crashes occur at or within 50 feet of an intersection.
Improve pedestrian/bicycle facilities: Because pedestrians are the most vulnerable of all transportation facility users, particular attention to pedestrian safety is needed.
Provide information and education: Providing targeted public information and education (PI&E) on safety problems at intersections is a preventive measure that can help improve driver compliance with traffic control devices and traffic laws.

slide 15