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Safety at Unsignalized Intersections

Short Version

FHWA logo. FHWA Office of Safety logo.

Collage of three photos of unsignalized intersections: one is of a stop sign in a neighborhood, one is of a sign indicating an intersection ahead, and a third is of a stop on an approach to a rail crossing.

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slide notes:

Major Points to Make:

This is an approximately 30-minute presentation on the topic of safety at unsignalized intersections. Topics covered include:
- Nature and magnitude of the problem
- Documents available to help with countermeasure selection
- Types of crashes
- Countermeasures and associated crash reduction factors

slide 2

FHWA Safety Focus Areas

Image highlights the four FHWA Office of Safety focus areas: intersections, pedestrians, roadway departure, and speeding.

slide 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 UNSIGNALIZED INTERSECTIONS.

Fatalities attributed to the four primary focus areas:

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

slide 3

National Statistics

Stylized graph shows that 56.7 percent of fatal and injury crashes occur at intersections, and 43.3 percent occur at non-intersection locations. For the all crashes category, 53.5 percent occurred at intersections and 46.5 occurred at non-intersection locations.

slide notes:

Major Points to Make:

These data represent the total of all crash data from the years 2002-2006. It shows that a little more than half of all crashes occur at intersection locations. And a slightly higher percentage of fatal and injury crashes occur at intersections. However, the next slide shows the numbers for just fatalities...

slide 4

National Statistics

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 that 79 percent of highway fatalities in 2007 occurred in non-intersection locations and 21 percent occurred at intersections.

slide 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 5

Intersection Fatalities

There were 8,657 intersection fatalities in 2007.

Where did they occur?

Stylized bar chart shows that in 2007, 5,232 fatalities occurred on arterial roads, 1,472 fatalities occurred on collectors, 1,739 occurred on local roads, and 214 occurred at undesignated locations. Of these 8,657 fatalities, 39 percent occurred in rural areas and 61 percent occurred in urban areas.

slide notes:

Major Points to Make:

Looking at just intersection fatalities, 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, approximately 90% occur at unsignalized intersections.
For urban fatalities, approximately 60% occur at unsignalized intersections (see next slide)

Source: FARS database

slide 6

Intersection Fatalities

Stylized graph shows that of all fatalities that occurred at unsignalized intersections, 3,091 occurred at urban locations and 3,099 occurred at rural locations. Of all fatalities that occurred at signalized intersections, 1,991 occurred at urban locations and 329 occurred at rural locations. In the 'other' category, 78 fatalities occurred at urban locations and 78 were at rural locations.

slide notes:

Major Points to Make:

Fatalities at unsignalized intersections constitute about 2/3 of the total number of fatalities.
The data are from FARS and represent the estimated figures for the year 2007. The percentages are based on the AVERAGE percentages for the years 2002-2006 and includes only the FARS elements of "intersection" and "intersection-related" fatalities.
Motorcycle crashes have been on a steady increase for many years possibly due to the increase in motorcycle riders (according to the Insurance Information Institute: Motorcycle riding has become more popular in recent years, appealing to a new group of enthusiasts consisting of older and more affluent riders. Sales of all types of two-wheelers were about 1.1 million in 2008).
In 2006, there were over 800 fatalities involving motorcyclists at unsignalized urban intersections and approximately 500 fatalities involving motorcyclists at unsignalized rural intersections.

slide 7

Intersection Safety Guidance

NCHRP Report 500 Volume 5
Guide sheets
Safety Strategies brochure

Collage of covers for the documents listed on this slide.

slide 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 Intersection Crash Types

Right angle
Rear end
Left turn
Sideswipe
Pedestrian/bicycle

Image of several wrecked vehicles at an intersection crash.

slide notes:

Major Points to Make:

These are the most common crash types that occur at unsignalized 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

Cover for an FHWA/ITE flyer entitled 'Toolbox of Countermeasures and Their Potential Effectiveness to Make Intersections Safer.'

slide 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 countermeasures shown in this presentation are taken primarily from NCHRP Report 500: Volume 5 – A Guide for Addressing Unsignalized Intersection Collisions 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

Account for 53% of fatal crashes at unsignalized intersections

Collage of photographs depicting methods that can reduce angle crashes, including constructing roundabouts, applying access management, improving awareness of intersections with signs and markings, clearing sight triangles, and improving turn lane design.

slide notes:

Major Points to Make:

Point out the type of crash and that angle crashes account for 53% of fatal crashes at unsignalized intersections. Not all of the countermeasures covered in Report 500 are illustrated in this presentation.
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.
Improve turn lane design: Right turn lanes can be offset by moving them laterally so that vehicles in the right-turn lanes no longer obstruct the view of the minor road driver.
Apply access management techniques: Restricting turns from driveways can greatly improve safety but coordination with businesses is critical to success.
Clear sight triangles: Adequate sight distance for drivers at stop- or yield-controlled approaches to intersections has long been recognized as among the most important factors contributing to overall safety at unsignalized intersections.
Construct roundabouts: Recent research has estimated the effectiveness of installing a modern roundabout at previously unsignalized locations at a 38% reduction in total crashes, a 76% reduction in injury crashes, and a 90% reduction in fatal and incapacitating-injury crashes.
Improve awareness of intersection: The visibility of intersections and the ability of approaching drivers to perceive them can be enhanced by installing larger regulatory and warning signs at intersections and/or installing double signs. Other techniques not shown: use splitter islands, overhead beacons, rumble strips, lighting.

slide 11

Angle crashes

Two photos, one depicting a vehicle rolling through a stop sign, the other of a vehicle turning left into an acceleration lane prior to merging with fast-moving freeway traffic.

slide notes:

Major Points to Make:

Reduce/eliminate skew: When roadways intersect at skewed angles, the intersections may experience numerous safety problems.
Targeted enforcement: Enforcement options are a potential countermeasure to unsafe and illegal motorist behavior at intersections.
Construct acceleration lanes: When acceleration by entering traffic takes place directly on the traveled way, it may disrupt the flow of through-traffic. To minimize this operational problem due to left-turning traffic at divided highway intersections, median acceleration lanes may be used.
Close/relocate intersections: For some unsignalized intersections with crash histories, the best method of improving safety may be to close or relocate the intersection.
Post appropriate speed limits: Speed is often cited as one of the major contributing factors to crashes. It is not necessarily the rate of speed that a vehicle is traveling that causes a crash, but the speed variance between vehicles.

slide 12

Rear End Crashes

Account for 6% of fatal crashes at unsignalized intersections

Collage of images depicting methods to prevent rear end crashes, including providing a shoulder bypass lane on two-lane roads, erecting supplemental overhead signing to warn of stops ahead, and installing turn lanes.

slide notes:

Major Points to Make:

Rear-end crashes account for 6% of fatal crashes at unsignalized intersections.
Some of the countermeasures that may be helpful at reducing rear-end crashes include:
- Install turn lanes: Left and right turn lanes remove vehicles waiting to turn from the through-traffic stream, thus reducing the potential for rear-end crashes.
- Provide shoulder bypass lanes: At three-legged intersections on two-lane highways, shoulder bypass lanes can provide an effective substitute for a left-turn lane on the major road where provision of a left-turn lane is economically infeasible.
- Supplemental overhead signing: The visibility of stop signs and, thus, the ability of approaching drivers to perceive them, can be enhanced by providing supplementary stop signs suspended over the roadway.

slide 13

Rear End Crashes

Two photos, one of a right turn acceleration lane after a right turn only entrance to a highway, the other of STOP AHEAD pavement markings and signage warning motorists of a stop beyond a curve in the roadway.

slide notes:

Major Points to Make:

Provide right-turn acceleration lanes: An acceleration lane is an auxiliary or speed-change lane that allows vehicles to accelerate to highway speeds before entering the through-traffic lanes of a highway.
Provide pavement markings: Providing pavement markings with supplementary messages (such as "STOP AHEAD") can help alert drivers and thus enhance the ability of approaching drivers to be more aware of the presence of the intersection.

The countermeasures listed under the "Also" heading are also applicable to this type of crash, but were discussed earlier.

slide 14

Left Turn Crashes

Account for 8% of fatal crashes at unsignalized intersections

Also:

Provide lighting
Clear sight triangles
Provide left turn acceleration lanes
Construct roundabouts
Close/relocate high-risk intersections

Collage of photos depicting methods of decreasing left turn crashes, including improving turn lane designs, using indirect left turn treatments such as jughandles, and implementing turn restrictions.

slide notes:

Major Points to Make:

Left turn crashes account for 8% of fatal crashes at unsignalized intersections.
Some of the countermeasures that may be helpful at reducing left turn crashes include:
Improve turn lane design: left-turn lanes can be offset by moving them laterally so that vehicles in opposing lanes no longer obstruct the opposing driver.
Use indirect left turn treatments: Indirect left-turn treatments include the use of jug-handle roadways before the crossroad, loop roadways beyond the crossroad, and directional median crossovers beyond the crossroad.
Implement turn restrictions: Safety at some unsignalized intersections can be enhanced by restricting turning maneuvers, particularly left turns, during certain periods of the day (such as peak traffic periods) or by prohibiting particular turning movements altogether.

The countermeasures listed under the "Also" heading are also applicable to this type of crash, but were discussed earlier.

slide 15

Sideswipe Crashes

Account for 2% of fatal crashes at unsignalized intersections

Also:

Provide right-turn acceleration lanes

slide notes:

Major Points to Make:

Sideswipe crashes account for 2% of fatal crashes at unsignalized intersections.
Some of the countermeasures that may be helpful at reducing sidesipe crashes include:
- Install pavement markings: This strategy is designed to minimize the occurrence of side-by-side queuing and angle stopping.
- Provide lane assignment signing or marking: Providing lane assignment signs (or markings) to guide motorists through complex intersections can alleviate confusion and lead to safer driving conditions. Pavement markings are often used to supplement lane assignment signs.

Providing right turn acceleration lanes is also applicable to this type of crash, but was discussed earlier.

slide 16

Pedestrian/Bicycle Crashes

Account for 14% of fatal crashes at unsignalized intersections

Collage of images depicting methods to reduce pedestrian and bicycle crashes, including providing traffic calming through devices such as pedestrian bulbouts, improving facilities by providing adequate pavement markings and signage to alert drivers to crosswalks, and providing information and outreach about crash reduction.

slide notes:

Major Points to Make:

Pedestrian/bicycle crashes account for 14% of fatal crashes at unsignalized intersections.
Some of the countermeasures that may be helpful at reducing left turn crashes include:
- Improve pedestrian and bicycle facilities: Improvements to pedestrian facilities (short of grade separation) that may reduce conflicts between motorists and nonmotorists include:
  - continuous sidewalks;
  - signed and marked crosswalks;
  - pedestrian signs, signals, and markings;
  - sidewalk set-backs; and
  - lighting.
- Provide traffic calming: The goals of traffic calming are typically to reduce vehicle speeds, traffic volume, or both. Volume control measures limit traffic by restricting vehicle access. They include full street closures, half closures, diagonal diverters, median barriers, and forced-turn islands.
- Provide information and education: Information and education can be geared towards reducing crashes of ALL TYPES. However, it is presented here because of the fairly easy way to target pedestrians and bicyclists in schools and other civic organizations.