Field Guide for Inspecting Signalized Intersections to Reduce Red-Light Running
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Copies may be obtained from the FHWA Report Center by e-mail to email@example.com by fax to 301-577-1421, or by phone to 301-577-0818, or may be downloaded from the FHWA website at: http://safety.fhwa.dot.gov/intersection/redlight/redl_reports/.
Document prepared by:
Hugh W. McGee, Ph.D., P.E.
©2005 Institute of Transportation Engineers. All rights reserved.
Printed in the United States of America
The Federal Highway Administration (FHWA) recognizes red-light running as a national safety problem, resulting in as many as 176,000 injuries and 1,000 fatalities annually, and an economic loss estimated at $14 billion per year. The solution to the problem involves education, enforcement and engineering measures. To publicize the engineering measures that can be taken, FHWA and the Institute of Transportation Engineers (ITE) prepared a report to provide information that could be used to proactively ensure that intersectionscan be engineered to discourage red-light running. The final product, Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red-Light Running (1), addresses design and operational features that may need to be upgraded or modified to discourage red-light running. The report characterizes the red-light running safety problem, identifies and provides guidance on the application of numerous engineering measures that can be taken to reduce red-light running, and provides a separate chapter describing a process for addressing the safety problem at a specific location.
To supplement this report and provide more details on how to conduct a site investigation, this field guide was prepared. The field guide suggests a procedure for conducting an investigation of a specific intersection that has been identified as a red-light running problem site. Presumably this identification has resulted from a review of red-light running violation and crash data. Having done so, the next step should be an investigation of the site to identify possible engineering deficiencies that could contribute to violations and crashes, and to form initial opinions as to the possible countermeasures. Final selection of appropriate countermeasures should be made based on further engineering analyses.
The field inspection guide is prepared in connection with the Intersection Field Inspection Form found at the end of the guide.
Field Site Review
The purpose of the field site review is to identify any engineering design or operational deficiencies that may contribute to red-light running and the resulting crashes and to form initial opinions as to possible countermeasures. From an engineering perspective, red-light running may be reduced if, in general, any one of these actions is taken:
It is paramount that the driver can see the traffic signal displays far enough in advance of the intersection so that he/she can stop safely upon viewing the yellow or red display. Then, upon viewing the yellow, and certainly the red indication, ensure that the signal operations and conditions do not entice the driver to intentionally or unintentionally enter on red. We must also ensure that a driver who tries to stop his/her vehicle can successfully do so before entering the intersection.
Recognizing that some drivers will intentionally violate the red signal at certain times and situations, those conditions that encourage this behavior must be minimized. Finally, engineers should examine whether or not the traffic signal is the most appropriate choice of control for the intersection. Consideration should be given to the possible replacement of the signal with another form of traffic control or design that eliminates the signal (e.g. a roundabout) and, therefore, the red-light running problem.
In view of this general goal, items to be considered in the review include:
Materials and Personnel Needed
The materials required for conducting the field site review include the following:
The inspection can be made by one person who has training and/or experience in traffic engineering principles. A second person is desirable to assist in the required measurements and to "get a second opinion" about deficiencies or possible countermeasures.
As with all field work, the inspectors should follow the agency's policies and procedures regarding personnel safety and traffic control.
Intersection Field Inspection Form
An Intersection Field Inspection Form has been prepared to assist in the inspection and is included at the end of the field guide. This form is also included full-size (8 1/2 x 11 inch) as a PDF at www.ite.org/library/redlight/FieldInspectionForm.pdf and at http://safety.fhwa.dot.gov/intersection/redlight/redl_reports/. It can be downloaded from these sites and multiple copies can be made. Alterations to the form may be necessary to meet the needs of your organization. How to use the form will be explained in the remainder of this guide.
The first entries are to record the name of the intersection and the specific approach. An inspection form is needed for each approach that is to be inspected. It is recommended that an inspection be conducted for all approaches even if one or more legs or approaches has not been identified as a problem-upon inspection one or more deficiencies could be detected on the "non-problem" approaches.
The entries are as follows:
Part 1. Check Signal Visibility
The first item to check is the signal visibility available to drivers as they approach the signal. Here, you need to confirm whether or not there are unobstructed sight lines to the signal heads from a sufficient distance upstream. The entries to be made are as follows:
Type of Signal Mounting: Traffic signal heads can be placed on 1) span wire, 2) mast arm, 3) a pole, or 4) a structure. For any given approach, there may be any combination of the above. Also, signal heads can be placed nearside (just at or before the physical intersection), within the intersection boundaries, or far-side (just beyond the cross road). On the field sheet, indicate the type of signal mounting. If more than one mounting is used, then indicate this. You might want to take photographs of the signal displays for each approach, both from a distance and then close to the intersection.
Sight Distance to the Signal (Section 4.D.15):
The Manual on Uniform Traffic Control Devices (MUTCD), (2) stipulates if two signal faces cannot be seen within the minimum distances shown in Table 1, then a sign shall be installed to warn approaching traffic of the traffic signal. If any approach is on a curve and/or grade that restricts visibility/sight distance, measure the distance from the nearest signal head for the through movement to the point on the approach where the signal is first in view. Compare the distance to the values in Table 1 for the appropriate speed. If the 85th percentile speed is not known, choose a speed that is at least 10 mph higher than the posted speed limit. Measuring the sight distance is not necessary if the signal is clearly visible from a considerable distance upstream.
Requires Advance Warning Sign?: If the sight distance is less than required by the values in Table 1, indicate by circling yes, otherwise circle no.
Advance Signal Warning Sign Present?: Indicate if there is an advance signal warning sign. Take a photograph of the sign if you have a camera.
Is anything blocking the view of the signals?: Even though the minimum sight distance is met, continuous view to all or a portion of the signal face may be blocked by either utility lines, tree branches, or other objects. Drive towards the signals from a sufficient distance upstream in each approach lane and take note if this situation exists. Note the nature of the blockage and take a photograph of it (consider summertime if the inspection is being made during the nonfoliage seasons). If the opportunity presents itself, drive behind any box-type trucks to see if they block the view.
Can signal faces on other approaches be seen?: Intersections with more than four approach legs and those with approaches at non-90 degree angles frequently experience a situation where the signal displays for other approaches can be seen from the approach being investigated. If not properly shielded with visors, this can cause driver confusion and some drivers may misinterpret the signal display for the appropriate approach. Indicate if this situation exists and if yes, mark whether visors, shields, or programmable lenses are being used. Check each lane on the approach.
Conflicting Signal Displays
Part 2. Check Signal Conspicuity
Could visual clutter detract from signal detection?: While the signals may be visible from the required distances, they may not be conspicuous to the driver. In terms of traffic control devices, such as a traffic signal, conspicuity means the ability for the specific device to be seen among other highway and non-highway features that compete for motorists' attention. There are many roads and streets that have dense commercial development with many signs and other forms of advertising that cause visual clutter and make it more difficult for the motorist, especially one who is unfamiliar with the road, to detect and react to traffic signals. Where this occurs it may be necessary to augment the signal display with additional signals and/or a double red signal section.
To check this possibility, it is recommended that the investigator drive through the intersection and note on each approach whether or not there is visual clutter. In doing so, the inspector should try to imagine how a driver unfamiliar with the area would view the scene. The inspection can be done during the day, and then, if there is reason to believe that nighttime would be more severe, a night inspection should be made as well. If it is believed that the visual clutter could detract from clearly seeing the signal, circle yes.
Are Signal Indications Confusing?: The next check is to determine if the signal indications may be confusing. Sometimes signal head placement can be confusing or mistakenly identified to a driver approaching the intersection. For example, signals for left-turn traffic can be confused with those for through traffic, especially if there is a NO LEFT TURN (R3-2) sign. Also, if there is another signalized intersection a short distance downstream, and depending upon the approach grades, the signal for the second intersection can be confused for being the control for the first intersection. This could be particularly troublesome if the first signal displays red while the second signal displays green. Make note if any confusing condition exists.
Are backplates present? Are backplates necessary?: Answer yes or no. Glare from the sun can make it difficult to see one or more signals as the driver approaches the intersection. Backplates enhance visibility and conspicuity of the signal indication by making it stand out. When you are in the field notice whether or not there are backplates on the signal.
Even if there are backplates, if the approach is on direct east or west bearing, then an inspection should be made during the critical period when the rising or setting of the sun will have the worst effect on signal visibility. If the inspection indicates that the sun glare is a problem and backplates are needed, circle yes to that question. Also, indicate whether or not other glare-reducing steps are needed. Re-positioning one or more of the signals may be necessary in this case.
Signal Lens Type: Note if the red signal lenses have either incandescent bulbs or LEDs. Signals with LED lenses are typically brighter than incandescent bulbs.
Signal Lens Size Adequate?: The next entries determine if the size of the red-signal lens as determined by its diameter is adequate.
These are all conditions that would indicate the need for 12-inch signal lenses.
Number of Signal Heads Adequate?: The MUTCD requires that there be at least two signal heads for the major movement (usually the thru movement, but may be for a turning movement). It is desirable to have one for each lane. To check for the adequacy of signal heads, enter the following:
Placement of Signal Heads: Note the placement of the signal heads in relation to the marked lanes. If the signal heads are not centered over the marked lanes, circle N.
Part 3. Check Signal Control Parameters
An inappropriately short or long yellow-change interval and the lack of an all-red clearance interval are two features that can contribute to red-light running and the resulting crashes. The yellow-change interval is simply the first interval following the green interval during which the yellow signal indication is displayed. The all-red clearance interval is an optional interval that follows a yellow-change interval and precedes the next conflicting green interval. It is frequently referred to as the all-red interval, because all approaches have a red signal display during this interval. The use of an all-red interval will not likely reduce red-light running violations, but it will help to avoid crashes if red-light running occurs in the first few seconds of the red indication. The two intervals are usually considered together as the change period and can be calculated using the following formula found in the most recent edition of ITE's Traffic Engineering Handbook (3):
CP = change period of yellow plus all-red
The equation above has been altered to include the assumed values of t, a and L, and a factor for converting miles per hour into feet per second.1 If your agency uses different values, then you will need to modify the equation accordingly.
The first two terms of the equation are typically used for the yellow-change interval and the last term is for the all-red interval. To evaluate these features, determine the following:
Then, enter the following for the phase that serves the through movement on this subject approach:
These two times should be available from the controller unit; if not, then it will be necessary to determine these times in the field using a stopwatch.
Next, enter the following:
Red-Change Interval Adequate?: Compare the calculated red-change interval to the actual interval and note if it is adequate.
Part 4. Check Other Factors
Horizontal Location of Signal Faces: With respect to red-light running, traffic signals not properly located at the intersection (see Part 2 "Placement of Signal Heads") may induce red-light running. Referring to Figure 1, if the signal is placed too close to the stop line, the driver already stopped at the line, may not be able to see the signal and may enter the intersection prematurely. Also, if the signal is placed further away from the stop line than prescribed in Figure 1, then the motorist may not associate the signal with the stop line and inadvertently enter the intersection on red. On the form, enter the distance from the stop line to the first far-side signal for the through movement.
Pavement Condition: If the pavement surface along the approach near the stop line appears to be slippery because of a smooth, polished condition or is severely rutted, motorists may be reluctant to decelerate to a stop when the yellow appears and may subsequently run a red-light. Observe the condition of the pavement along the approach for either of these conditions and circle the most applicable condition on the form.
Reconsider Signal Installation: It is possible that traffic signal control is no longer warranted and could be replaced with a lower order control. A more detailed study is required to determine if the traffic signal should be removed. However, if it is observed during the inspection that the traffic volume levels on both the major and minor street are light (even during the peak traffic periods), then this should be noted.
Part 5. Identify Promising Countermeasures
Having completed the inspection and observed one or more deficiencies, then potential countermeasures to address the deficiency should be considered. On the form check off if any of the deficiency types are identified and countermeasures that you feel may be appropriate. The potential countermeasures for each category of deficiency are listed below.
1) Install additional signals on the near side of the intersection
Signal Timing Operation Deficiency
Other Measures to Consider
The selection of the final countermeasure(s) should be made by the responsible engineer. The full report Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red-Light Running should be reviewed for this activity.
To download a one page form, visit:
INTERSECTION FIELD INSPECTION FORM
Intersection Identification: _______________________________________ with ________________________________
Approach Name: _________________________________ Direction Heading: ______________________________
PART 1. CHECK SIGNAL VISIBILITY
Type of Signal Mounting: Span Wire Mast Arm Pole Structure
Sight Distance to the Signal: _______feet
Requires Advance Warning Sign? Y N
Advance Signal Warning Sign Present: Y N
Is anything blocking the view of the signals? Y N
If yes, describe___________________________________________________
Can signal faces on other approaches be seen? Y N
If yes, do these signals have visors, shields, or programmable lenses? Y N
PART 2. CHECK SIGNAL CONSPICUITY
Could visual clutter detract from the signal? Y N
Are the signal indications confusing? Y N
If yes, explain:_____________________________________________________________________
Are backplates present? Y N
Are backplates necessary? Y N
Are other glare-reducing steps needed? Y N
Signal lens type: Incandescent LEDs
PART 3. CHECK SIGNAL CONTROL PARAMETERS
Grade (as decimal) g =____________(uphill is positive)
Approach speed V =_____________mph
Cross street width W =____________feet
Calculate the needed change period (CP) for this approach using agency practice or the following equation:
PART 4. CHECK OTHER FACTORS
Is horizontal location adequate? Y N
Pavement condition on approach: Adequate Polished Severely Rutted
Should signal warranting study be conducted? Y N
PART 5. IDENTIFY PROMISING COUNTERMEASURES
___Install additional signals on near side
___Add signals to achieve one per lane
Signal Timing Operation Deficiency
___Change yellow interval
___Determine if signal is warranted
Inspection By: ______________________________________________Date:________________
1. Institute of Transportation Engineers/Federal Highway Administration. Making Intersections Safer:A Toolbox of Engineering Countermeasures to Reduce Red-Light Running. Washington, DC: ITE, 2003.
2. Federal Highway Administration. Manual on Uniform Traffic Control Devices for Streets and Highways, Washington, DC: Federal Highway Administration, 2003.
3. Institute of Transportation Engineers. Traffic Engineering Handbook. Washington DC: Institute of Transportation Engineers, 1999.
1 The original formula includes the following parameters:
1099 14th Street, NW, Suite 300 West
How to drive a roundabout (WSDOT)