Project Summary Report 4940-SProject 0-4940: Photometric Requirements for Arrow Panels and

Portable Changeable Message SignsAuthors: Mark D. Wooldridge, P.E., Melisa D. Finley, John Denholm, and Douglas Mace

Project Summary Report 4940-S – 1 –Project Summary Report 4940-S – 4 –

Arrow panels are often usedin work zones to inform driversof the need for a lane change or,under certain conditions, cautionon the part of the driver.Portable changeable messagesigns are used to advisemotorists of unexpected trafficand routing situations. Althoughthese devices have been used in

traffic control applications formany years, there are no estab-lished photometric standards thatcan be used as the basis for a pro-curement specification.

This report summarizes theTexas Transportation Institute’s(TTI) recommendations for testmethods for measuring the photo-

metric properties of Type Carrow panels (Figure 1) andportable changeable messagesigns (Figure 2). The intent ofthe test method is to provideTxDOT with measurable criteriafor qualifying arrow panels andchangeable message signs forpurchase by TxDOT.

Arrow Panel and Portable Changeable Message Sign Requirements

The research is documented in the following reports:

4940-1 Photometric Requirements for Arrow Panels

4940-2 Photometric Requirements for Portable Changeable Message Signs

Research Supervisor: Mark D. Wooldridge, TTI, m-wooldridge@tamu.edu, (979) 845-9902

Researchers: Melisa D. Finley, John Denholm, Douglas Mace, and Benedict Patrick

TxDOT Project Director: Glenn Hagler, GHAGLER@dot.state.tx.us, (512) 416-2082

To obtain copies of the reports, contact Dolores Hott, Texas Transportation Institute, Information &Technology Exchange Center, (979) 845-4853, or e-mail d-hott@tamu.edu. See our on-line catalog athttp://tti.tamu.edu.

For More Details . . .

DisclaimerThe contents of this report reflect the views of the authors, who are responsible for the opinions, findings, and

conclusions presented herein. The contents do not reflect the official views or policies of the Texas Department of

Transportation (TxDOT) or the Federal Highway Administration (FHWA). This report is not intended to constitute

a standard, specification, or regulation, nor is it intended for construction, bidding, or permit purposes. The engi-

neer in charge of the project was Mark D. Wooldridge (TX-65791).

TxDOT Implementation StatusFebruary 2002

The products required for this project were test methods for measuring the photometric properties of portablechangeable message signs and Type C arrow panels.

Minimum photometric characteristics for these devices have been incorporated in TxDOT purchase specifica-tions. TxDOT test methods are being developed for the devices. Testing of arrow panels should begin inMarch. Testing of portable changeable message signs will begin in the near future.

For more information, please contact RTI RMC4 Research Engineer at (512) 465-7403.

YOUR INVOLVEMENT IS WELCOME!

ITEC.PSR0201.0502.755

Figure 1. Type C arrow panel

Project Summary Report 4940-S – 2 –

What We Did . . .Researchers investigated a num-

ber of issues related to arrow panelsand changeable message signs,focusing on the photometric charac-teristics of the devices.

What We Found . . .Arrow Panels

As shown in Figure 3, increasedviewing angle can sharply reducethe effective output of an arrowpanel as seen by the driver.Researchers reviewed potentialangularity effects due to lane posi-tioning and roadway curvature byexamining lateral clearance betweenvehicles and arrow panels in vari-ous positions. By combiningvehicular operating speeds, typicalroadway alignments, and viewing

– 3 –

times for sign displays, researchersestablished minimum angularityrequirements for viewing arrowpanels.

The daytime conspicuity of vary-ing luminous intensity levels wastested in a study that manipulatedarrow panel luminous intensity totest its influence on motorist behav-ior. Observations of the number ofvehicles in the closed lane indicatedthat luminous intensity levels wererelated to the lane-changing behav-ior of the motorists. Comparisonsbetween driver responses showedthat even in low-complexity visualenvironments there is a minimumlevel that is necessary to facilitatetimely lane changing.

Portable Changeable MessageSigns

Examining portable changeablemessage signs, researchers used aluminance meter to make a series ofbackground luminance measure-ments (sign “off”) under sun over-head, backlit, and washout condi-tions. Additional luminance meas-urements of the sign’s immediatesurroundings were taken and usedto evaluate external contrast. Bycombining well-established recom-mendations from the literature withthe background measurementsmade in the field, recommendationsfor character luminance were devel-oped so that the desired contrastlevels could be achieved under

backlit, sun overhead, and somewashout conditions.

The ResearchersRecommend . . .

Researchers developed recom-mendations for the photometricproperties of both Type C arrowpanels (diesel and solar) andportable changeable message signs,recommending changes to theirrespective specifications byTxDOT.

Arrow PanelsBased on the field studies con-

ducted and findings reported in theliterature, researchers developed atable of recommended luminousintensities for arrow panels, shownin Table 1. The values provide alevel of performance that will helpensure that most drivers in most sit-uations can see the informationthey need in a timely manner.Recommendations regarding mini-mum angularity performance werealso developed to help ensureacceptable performance in com-monly encountered situations.

Portable Changeable MessageSigns

Researchers recommend a mini-mum daytime character luminanceof 4000 cd/m2 and a contrast ratioof 5. However, both backlit andwashout conditions present tremen-

dous problems for portable change-able message sign visibility, partic-ularly with older motorists. Becauseof this, no minimum luminancelevel can ensure that the sign beread by all observers under all con-ditions. Protective screens shouldbe well maintained to maximize thecontrast that this luminance willprovide, particularly in washoutconditions.

Based on previous research,researchers recommend a minimumnighttime character luminance of30 cd/m2. Little research has beenconducted with respect to a night-time maximum character luminanceneeded to prevent unacceptable lev-els of glare; thus, a maximum valuewas not recommended.

Testing ProceduresRecommended testing procedures

were developed to ensure that spec-ified performance levels are met.The procedures center on the use ofa tripod-mounted luminance meter.By measuring the performance ofthe arrow panels or portablechangeable message signs with aluminance meter, TxDOT can reli-ably compare the performance ofpurchased equipment in the fieldwith the panel specification values.Additionally, a laboratory test on asample of the individual lamps usedin arrow panels is recommended toensure that arrow panels purchasedcan meet all specifications, includ-ing hot spot and angularity require-ments.

Project Summary Report 4940-S

Figure 3. The effect of angularity on arrow panel visibility (the arrow sign on the right is at a slight angle)

Table 1. Recommended luminous intensity requirements

>>

Figure 2. Portable changeable message sign

Project Summary Report 4940-S – 2 –

What We Did . . .Researchers investigated a num-

ber of issues related to arrow panelsand changeable message signs,focusing on the photometric charac-teristics of the devices.

What We Found . . .Arrow Panels

As shown in Figure 3, increasedviewing angle can sharply reducethe effective output of an arrowpanel as seen by the driver.Researchers reviewed potentialangularity effects due to lane posi-tioning and roadway curvature byexamining lateral clearance betweenvehicles and arrow panels in vari-ous positions. By combiningvehicular operating speeds, typicalroadway alignments, and viewing

– 3 –

times for sign displays, researchersestablished minimum angularityrequirements for viewing arrowpanels.

The daytime conspicuity of vary-ing luminous intensity levels wastested in a study that manipulatedarrow panel luminous intensity totest its influence on motorist behav-ior. Observations of the number ofvehicles in the closed lane indicatedthat luminous intensity levels wererelated to the lane-changing behav-ior of the motorists. Comparisonsbetween driver responses showedthat even in low-complexity visualenvironments there is a minimumlevel that is necessary to facilitatetimely lane changing.

Portable Changeable MessageSigns

Examining portable changeablemessage signs, researchers used aluminance meter to make a series ofbackground luminance measure-ments (sign “off”) under sun over-head, backlit, and washout condi-tions. Additional luminance meas-urements of the sign’s immediatesurroundings were taken and usedto evaluate external contrast. Bycombining well-established recom-mendations from the literature withthe background measurementsmade in the field, recommendationsfor character luminance were devel-oped so that the desired contrastlevels could be achieved under

backlit, sun overhead, and somewashout conditions.

The ResearchersRecommend . . .

Researchers developed recom-mendations for the photometricproperties of both Type C arrowpanels (diesel and solar) andportable changeable message signs,recommending changes to theirrespective specifications byTxDOT.

Arrow PanelsBased on the field studies con-

ducted and findings reported in theliterature, researchers developed atable of recommended luminousintensities for arrow panels, shownin Table 1. The values provide alevel of performance that will helpensure that most drivers in most sit-uations can see the informationthey need in a timely manner.Recommendations regarding mini-mum angularity performance werealso developed to help ensureacceptable performance in com-monly encountered situations.

Portable Changeable MessageSigns

Researchers recommend a mini-mum daytime character luminanceof 4000 cd/m2 and a contrast ratioof 5. However, both backlit andwashout conditions present tremen-

dous problems for portable change-able message sign visibility, partic-ularly with older motorists. Becauseof this, no minimum luminancelevel can ensure that the sign beread by all observers under all con-ditions. Protective screens shouldbe well maintained to maximize thecontrast that this luminance willprovide, particularly in washoutconditions.

Based on previous research,researchers recommend a minimumnighttime character luminance of30 cd/m2. Little research has beenconducted with respect to a night-time maximum character luminanceneeded to prevent unacceptable lev-els of glare; thus, a maximum valuewas not recommended.

Testing ProceduresRecommended testing procedures

were developed to ensure that spec-ified performance levels are met.The procedures center on the use ofa tripod-mounted luminance meter.By measuring the performance ofthe arrow panels or portablechangeable message signs with aluminance meter, TxDOT can reli-ably compare the performance ofpurchased equipment in the fieldwith the panel specification values.Additionally, a laboratory test on asample of the individual lamps usedin arrow panels is recommended toensure that arrow panels purchasedcan meet all specifications, includ-ing hot spot and angularity require-ments.

Project Summary Report 4940-S

Figure 3. The effect of angularity on arrow panel visibility (the arrow sign on the right is at a slight angle)

Table 1. Recommended luminous intensity requirements

>>

Figure 2. Portable changeable message sign

Project Summary Report 4940-SProject 0-4940: Photometric Requirements for Arrow Panels and

Portable Changeable Message SignsAuthors: Mark D. Wooldridge, P.E., Melisa D. Finley, John Denholm, and Douglas Mace

Project Summary Report 4940-S – 1 –Project Summary Report 4940-S – 4 –

Arrow panels are often usedin work zones to inform driversof the need for a lane change or,under certain conditions, cautionon the part of the driver.Portable changeable messagesigns are used to advisemotorists of unexpected trafficand routing situations. Althoughthese devices have been used in

traffic control applications formany years, there are no estab-lished photometric standards thatcan be used as the basis for a pro-curement specification.

This report summarizes theTexas Transportation Institute’s(TTI) recommendations for testmethods for measuring the photo-

metric properties of Type Carrow panels (Figure 1) andportable changeable messagesigns (Figure 2). The intent ofthe test method is to provideTxDOT with measurable criteriafor qualifying arrow panels andchangeable message signs forpurchase by TxDOT.

Arrow Panel and Portable Changeable Message Sign Requirements

The research is documented in the following reports:

4940-1 Photometric Requirements for Arrow Panels

4940-2 Photometric Requirements for Portable Changeable Message Signs

Research Supervisor: Mark D. Wooldridge, TTI, m-wooldridge@tamu.edu, (979) 845-9902

Researchers: Melisa D. Finley, John Denholm, Douglas Mace, and Benedict Patrick

TxDOT Project Director: Glenn Hagler, GHAGLER@dot.state.tx.us, (512) 416-2082

To obtain copies of the reports, contact Dolores Hott, Texas Transportation Institute, Information &Technology Exchange Center, (979) 845-4853, or e-mail d-hott@tamu.edu. See our on-line catalog athttp://tti.tamu.edu.

For More Details . . .

DisclaimerThe contents of this report reflect the views of the authors, who are responsible for the opinions, findings, and

conclusions presented herein. The contents do not reflect the official views or policies of the Texas Department of

Transportation (TxDOT) or the Federal Highway Administration (FHWA). This report is not intended to constitute

a standard, specification, or regulation, nor is it intended for construction, bidding, or permit purposes. The engi-

neer in charge of the project was Mark D. Wooldridge (TX-65791).

TxDOT Implementation StatusFebruary 2002

The products required for this project were test methods for measuring the photometric properties of portablechangeable message signs and Type C arrow panels.

Minimum photometric characteristics for these devices have been incorporated in TxDOT purchase specifica-tions. TxDOT test methods are being developed for the devices. Testing of arrow panels should begin inMarch. Testing of portable changeable message signs will begin in the near future.

For more information, please contact RTI RMC4 Research Engineer at (512) 465-7403.

YOUR INVOLVEMENT IS WELCOME!

ITEC.PSR0201.0502.755

Figure 1. Type C arrow panel