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FHWA Home / Safety / Intersection / Safety at Signalized Intersections (Long Version)

Safety at Signalized Intersections (Long 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 1-hour presentation on the topic of red-light running (RLR). Topics covered include:


slide 2

FHWA Safety Focus Areas

Slide depicts the four FHWA safety focus areas: intersections, pedestrians, roadway departure, and speeding.

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:


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?

Graphics indicate that 39 percent of intersection fatalities occurred in rural areas, and 61 percent occurred in urban areas. Further, 5,232 fatalities occurred on arterials, 1,472 occurred on collectors, 1,739 occurred on local roads, and 214 occurred in unidentified locations.

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.

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:

Other notes:


slide 7

Intersection Safety Guidance

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

speaker notes:

Major Points to Make:


slide 8

Typical Signalized Intersection Crash Types

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

speaker notes:

Major Points to Make:


slide 9

Crash Reduction Factors

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:


slide 10

Angle Crashes

Graphic representation of two vehicles crashing into each other at a 90 degree angle, such that the vehicles are in the shape of a sideways T when they intersect.

speaker notes:

Major Points to Make:


slide 11

Optimize Change Intervals

Intervals that are too long encourage disrespect and lead to red-light running.
Intervals that are too short violate driver expectancy and lead to abrupt stops.
AASHTO Report 500 Volume 12

Countermeasure CRF
Change Intervals per ITE Total = 8%
Ped/Bike = 37%
Multi-vehicle = 9%

Photo of a signalized intersection in an urban area with a banner across it that reads 'Low Cost Countermeasure.'

speaker notes:

Major Points to Make:


slide 12

Improve Sight Distance

The driver of a vehicle approaching an intersection should have an unobstructed view of the entire intersection, including any traffic-control devices, and sufficient lengths along the intersecting highway to permit the driver to anticipate and avoid potential collisions.
AASHTO "Green Book"

Photograph of a signalized intersection where sight distance for one approach is blocked by a high hedge on one corner.

speaker notes:

Major Points to Make:


slide 13

Restrict Access

Driveways should not be located within the functional area of an intersection.
Intersection Safety Brief #13: Access Management"

A photo of a four-lane roadway separated by double yellow center lines where left turns into businesses are prevented by channelizing devices running along the center line. A superimposed diagram show sample guidance for access management used by Florida DOT.

speaker notes:

Major Points to Make:


slide 14

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.
AASHTO Report 500 Volume 12

Countermeasure CRF
Automated Enforcement Total = 12%
Right Angle = 25%
Left Turn = 45%

Two photographs, one of a post-mounted red light camera device installed at an intersection, the other of a signal head with an enforcement assistance light mounted at the bottom of the head.

speaker notes:

Major points to make:


slide 15

Restrict Parking

Parking maneuvers into or out of on-street parking stalls can affect the operation and safety of the through traffic lane adversely.
NCHRP Report 457: Evaluating Intersection Improvements: An Engineering Study Guide

Countermeasure CRF
Restrict Parking Total = 49%
Pedestrian = 30%

Photograph of an urban intersection where a No Parking sign is posted in advance of a right turn lane. A banner that reads 'Low Cost Countermeasure' runs across the image.

speaker notes:

Major Points to Make:


slide 16

Convert to Roundabout

Many studies have found that one of the benefits of roundabout installation is the improvement in overall safety performance.
Roundabouts: An Informational Guide

Countermeasure CRF
Convert signalized intersection to roundabout Total = 48-67%
Injury = 60-78%
Fatal/Incapacitating = 90%

Two photos of roundabouts.

speaker notes:

Major Points to Make:


slide 17

Rear End Crashes

* Discussed previously

Graphic image of one vehicle crashing into the one in front of it on the approach to an intersection.

speaker notes:

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slide 18

Increase Visibility of Signals

...12 inch signal indications shall be used for all signal sections in all new signal faces...
Proposed amendment to the MUTCD

Countermeasure CRF
Convert to 12-inch Lenses Total = 11-24%
Injury = 16%
Add Supplemental Heads Right angle = 35%
Rear end = 28%
Total = 28%

Two photographs, one of a large signal head with black backplate, and one of an intersection where, in addition to overhead signals, post-mounted signal heads have been set to the right and left of the approach lanes.

speaker notes:

Major Points to Make:

Methods for improving visibility of traffic signals and signs include the following:


slide 19

Increase Visibility of Signals

Countermeasure CRF
One Primary Head Per Lane Total = 28%
Rear end = 28%
Right-angle = 35%
Add Backplates Total = 13%
Right-angle = 50%

Two photos, the first of an intersection with one signal head for each lane on the approach. The second photo shows a signal in the process of having backplates installed.

speaker notes:

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slide 20

Increase Awareness of Intersection

[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.
Manual on Uniform Traffic Control Devices

Countermeasure CRF
Advance Warning Signs Total = 22%
Right Angle = 35%
Dilemma Zone Protection Fatal/injury = 39%

Two photos, one of an overhead sign with flashing beacons warning traffic to be prepared to stop when the beacons are flashing. The second is of a signal ahead sign at the side of a roadway before a curve, behind which is a signalized intersection. A banner reas 'Low Cost Countermeasure.'

speaker notes:

Major Points to Make:


slide 21

Improve Signal Coordination

Apart from its operational benefits, signal coordination is known to reduce vehicle conflicts along corridors where traffic signals are coordinated.
Signalized Intersections: Informational Guide

Countermeasure CRF
Signal Coordination Right Angle = 32%

Photo of a congested urban area.

speaker notes:

Major Points to Make:

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.

Coordinated signals produce platoons of vehicles that can proceed without stopping at multiple intersections. Reducing the number and frequency of required stops and maintaining constant speeds for all vehicles reduce rear-end conflicts. In addition, signal coordination can improve the operation of turning movements. Drivers may have difficulty making permitted turning maneuvers because of a lack of gaps in through traffic. Crashes may occur when drivers become impatient and accept a gap that is smaller than needed. Such crashes could be reduced if longer gaps were made available.


slide 22

Install Turn Lanes

Provision of an exclusive left-turn bay...generally improves the operations of all movements...
NCHRP Report 457: Evaluating Intersection 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

Two photos, one featuring a right-turn-only lane, one featuring a left-turn-only lane.

speaker notes:

Major Points to Make:


slide 23

Control Approach Speeds

Since speed contributes to crash severity, lowering speeds on approaches to intersections can help reduce the severity of crashes. Slowing vehicle speeds...can improve safety for motorists, pedestrians, and bicyclists.
AASHTO Report 500 Volume 12

Two photos, one of a long, single-lane, rural road on an approach to a signal featuring warning beacons and signal ahead signs, the other featuring speed enforcement cameras mounted on poles at the side of a rural road. A banner reads 'Low Cost Countermeasure.'

speaker notes:

Major Points to Make:


slide 24

Left Turn Crashes

* Discussed previously

Graphic image of a left turning car crashing into the side of a car that is traveling straight through an intersection.

speaker notes:

Major Points to Make:


slide 25

Employ Protected Left Turn Phasing

The phasing and sequencing of a traffic control signal have the potential to affect both the safety and efficiency of vehicle and pedestrian traffic movement at the intersection.
Toolbox on Intersection Safety and Design

Countermeasure CRF
Add Protected-Only Left Turn Phase Total = 27%
Left turn = 48%
Right angle = 54-63%
Rear end = 27-35%
Add Permissive/Protected Left Turn Phase Left turn = 17%
Right angle = 25%

Two photos, one of protected left only signal head, the other of a permissive/protected left turn signal head.

speaker notes:

Major Points to Make:


slide 26

Implement Turn Restrictions

When the right-of-way needed to provide [left-turn] storage is not available, left-turn restriction is a means of eliminating [safety and operational] problems.
NCHRP Report 457: Evaluating Intersection Improvements: An Engineering Study Guide

Countermeasure CRF
Prohibit Left Turns Total = 45%
Left turn = 90%
Rear end = 30%
Pedestrian = 10%
Prohibit RTOR Rear end = 20%
Right angle = 30%
Sideswipe = 20%

Two images, one depicting a sign next to a signal head indicating no left turn during restricted hours, the other featuring a no right turn sign that can be illuminated to restrict right turns or turned off to allow them.

speaker notes:

Major Points to Make:


slide 27

Improve Turn Lane Design

[Offset left turn lanes help] improve safety and operations of the left-turn movement by improving driver acceptance of gaps...
Signalized Intersections: Informational Guide

Two photos of offset left turn lanes.

speaker notes:

Major Points to Make:


slide 28

Reconstruct Approaches

If other less expensive methods cannot be used or are ineffective, horizontal or vertical (or both) realignment of approaches may be a solution.
AASHTO Report 500 Volume 12

Two photographs of intersections. One is an aerial photo of a roadway with a Y-split that has been treated with a newly built road segment that connects the two branches of the Y and a signalized intersection at the connector. The other is of an intersection that uses a jughandle before the crossroad and a loop roadway beyond the crossroad to provide indirect left turn treatments

speaker notes:

Major Points to Make:


slide 29

Sideswipe Crashes

* Discussed previously

Graphic image of two vehicles on opposite approaches attempting to turn left  and colliding in a sideswipe type collision.

speaker notes:

Major Points to Make:


slide 30

Install Pavement Markings

Providing positive guidance for the driver in the form of pavement markings can help eliminate driver confusion and eliminate vehicle conflict by channeling vehicles in their proper turn path.
Signalized Intersections: Informational Guide

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. Banner reads 'Low Cost Countermeasure.

speaker notes:

Major Points to Make:


slide 31

Pedestrian/Bicycle Crashes

Graphic image of a left turning vehicle colliding with a pedestrian.

speaker notes:

Major Points to Make:


slide 32

Improve Signal Hardware

...all new pedestrian signal heads shall include a pedestrian change interval countdown display... A pedestrian change interval countdown display shall be added to all existing pedestrian signal heads...
Proposed amendments to the MUTCD

Countermeasure CRF
Countdown Signal Heads Total = 20%
Pedestrian injury = 25%

Photo of a pedestrian countdown signal.

speaker notes:

Major Points to Make:

Traffic control hardware improvements that can be made to an intersection to increase pedestrian safety include the following:


slide 33

Improve Pedestrian/Bicycle Facilities

Because pedestrians are the most vulnerable of all transportation facility users, particular attention to pedestrian safety is needed.
AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities

Countermeasure CRF
Bicycle Lanes Bicycle = 36%
Provide Sidewalks (both sides) Pedestrian = 88%

Two photos, one of a disabled person waiting to cross the road at a mid-block crosswalk, the other of a dedicated bike lane that extends, like a pedestrian crosswalk, across a multi-lane intersection.

speaker notes:

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slide 34

Information and Education

Collage of images representing outreach products as well as words indicating means of disseminating information, including: web sites, in-school programs, printed materials, radio and TV, community outreach, and speed trailers.

speaker notes:

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slide 35

For More Information

NCHRP Report 500 Series Volume 12
http://safety.transportation.org/

Manual on Uniform Traffic Control Devices
http://mutcd.fhwa.dot.gov/

Signalized Intersections: Informational Guide
http://www.fhwa.dot.gov/publications/research/safety/04091/

FHWA Office of Safety
http://safety.fhwa.dot.gov/


speaker notes:

Major Points to Make:

Page last modified on September 4, 2014.
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000