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Publication Number: FHWA-RD-03-066

Portable Changeable Message Sign Handbook - Pcms

FHWA Contact: Ken Opiela, HRDS-05, (202) 493-3371

TABLE OF CONTENTS

Introduction
What is a PCMS?
When Should a PCMS be Used?
PCMS Screen Characteristics
     Matrix Types
PCMS Message Design Process
     Message Selection
     Message Display
     Default Message
     Changing a PCMS Message
     Standard Abbreviations
     Display Time
     Maximum Number of Phases
Placement of a PCMS
     Laterally
     Longitudinally
     PCMS Height
     Sight Distance
When to Discontinue PCMS or Alter Message
Other Operational Issues
     Brightness
     Maintenance
Appendices
     Setup Checklist
     Definitions
     Metric Conversions

 

Portable Changeable Message Sign Handbook Cover

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INTRODUCTION

The purpose of this handbook is to present basic guidelines for the use of portable changeable message signs (PCMS). This handbook presents information on the PCMS and is intended to illustrate the principles of proper PCMS use.

This handbook is not intended to be a standard.

Standards that apply to the PCMS are found in the Manual on Uniform Traffic Control Devices (MUTCD) at http://mutcd.fhwa.dot.gov/.

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WHAT IS A PCMS?

A PCMS is a traffic control device that is capable of displaying a variety of messages to inform motorists of unusual driving conditions. This capability is achieved through elements on the face of the sign that can be activated to form letters or symbols. The message is limited by the size of the sign (usually three lines with eight characters per line). A PCMS is housed on a trailer or on a truck bed and can be deployed quickly for meeting the temporary requirements frequently found in work zones or accident areas.

A PCMS:

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WHEN SHOULD A PCMS BE USED?

A PCMS can be used to alert and inform motorists during one of the following scenarios:

A PCMS can provide a unique message that alerts the motorist and supports standard signing for:

A PCMS also can provide informational messages, such as:

A PCMS can be an effective temporary traffic control device when used appropriately. By its very nature, it draws the attention of the motorist; however, this effect can be diminished if this device is overused. The PCMS should not replace any of the signing detailed in the MUTCD and should not be used if standard traffic control devices adequately provide the information the motorist needs to travel safely.

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PCMS SCREEN CHARACTERISTICS

Matrix Types

The type of message screen can affect the message that is chosen and the distance at which it can be read. Three screen types (or matrix types) are described below:

Modular Matrix, comprised of character blocks
Modular- The simplest matrix-type signs are those that are comprised of character blocks. A sign would have, for example, three lines with eight character blocks per line.
Continuous Line Matrix, continuous matrix for each line of text
Continuous Line Matrix- A somewhat more flexible type of PCMS uses a continuous matrix for each line of text. These signs offer the ability to use proportionally spaced fonts, as opposed to the monospaced text displayed by discrete character blocks. The benefits include a more natural-looking sign and, therefore, an easier-to-read message.
Full Matrix, comprised of elements that can be activated
Full Matrix- The full-matrix PCMS is the most flexible type. The entire sign face is comprised of elements or pixels that can be activated to display a message. These signs offer the ability to vary the height of characters, display simple graphics, and use proportionally spaced fonts.

Depending on the matrix type, the height of a character can vary from 457 to 1372 millimeters (mm) (18 to 54 inches). Most PCMS units allow only eight characters on a line, no matter what the character height. Each character shall, as a minimum, be five pixels wide by seven pixels high.

Character Height, inches Legibility Distance, feet
18 720
24 960
54 2160
1 inch = 25.39 mm
1 ft = .306 m

The legibility distance of the character depends on its height. The legibility distances to the left are based on the standard that 25.4 mm (1 inch) characters can be read at 12.2 meters (m) (40 feet (ft)).

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PCMS MESSAGE DESIGN PROCESS

Message Selection

PCMS use on construction and maintenance projects should be treated as an integral part of the traffic control plan (TCP). Desired messages, locations, and general time periods of display should be listed for all known or anticipated PCMS use during the project. Of course, additional opportunities to use the PCMS may come up during the life of the project, and the TCP should allow for these unanticipated messages. However, the governing agency should retain control over selection and display of the unanti-cipated messages.

Message Display

A PCMS message can use one, two, or, when absolutely necessary, three phases in which to relay its message. Below are message guidelines for the number of phases required to convey the message.

One-Phase PCMS:
Line 1—Describe problem.
Line 2—Identify location or distance ahead.
Line 3—Provide motorist instruction.

Two-Phase PCMS:
Phase 1—Describe problem.
Phase 2—Provide motorist instruction.

Three-Phase PCMS:
Phase 1—Describe problem.
Phase 2—Identify location or distance ahead.
Phase 3—Provide motorist instruction.

Care must be given to ensure a short message length and to avoid repeating messages covered by static signing.

Default Message

A default message should be programmed into the PCMS in case the unit becomes disabled. Since the default message will act as a warning to field personnel that the PCMS has malfunctioned, a message should be chosen that will not alarm motorists and will not be used for any other purpose. Alternatively, to indicate that the PCMS is malfunctioning, a pattern such as solid bars may be used.

Changing a PCMS Message

It is desirable to have the PCMS display the most correct and appropriate information to the motorist as possible. However, there are times when the PCMS will not have the desired message as one of the standard messages in the database. In this case, the required message must be added to the database.

The control system needs to include a display screen upon which messages can be reviewed before being displayed on the PCMS.

It is recommended that an instruction manual be stored with the PCMS for in-field programming of the message.

Standard Abbreviations

Abbreviations may be used when creating or editing PCMS messages. Do not make up abbreviations; use the following list of standard abbreviations to ensure that the motorist does not misinterpret the message.

Acceptable Abbreviations

Word
Abbr.
Word
Abbr.
Alternate
ALT
Minor
MNR
Avenue
AVE
Normal
NORM
Boulevard
BLVD
North
N
Cannot
CANT
Northbound
NB
Center
CNTR
Parking
PKING
Do Not
DONT
Right
RHT
East
E
Road
RD
Eastbound
EB
Service
SERV
Emergency
EMER
Shoulder
SHLDR
Entrance
ENT
Slippery
SLIP
Enter
ENT
South
S
Expressway
EXPWY
Southbound
SB
Freeway
FRWY
Speed
SPD
Hazardous Material
HAZMAT
Street
ST
High-Occupancy Vehicle
HOV
Temporary
TEMP
Highway
HWY
Traffic
TRAF
Hour(s)
HR
Travelers
TRVLRS
Information
INFO
Vehicle
VEH
It Is
ITS
Warning
WARN
Junction
JCT
West
W
Lane
LN
Westbound
WB
Left
LFT
Will Not
WONT
Maintenance
MAINT
 
 
Major
MAJ
 
 
Miles
MI
 
 

Acceptable Abbreviations with Prompt Word

Word
Abbr.
Prompt
Access
ACCS
Road
Ahead
AHD
Fog*
Blocked
BLKD
Lane*
Bridge
BRDG
(name)*
Condition
COND
Traffic*
Congestion
CONG
Traffic*
Construction
CONST
Ahead
Downtown
DWNTN
Traffic*
Exit
EX, EXT
Next*
Express
EXP
Lane
Hazardous
HAZ
Driving
Interstate
I
(followed by route number)
Local
LOC
Traffic
Lower
LWR
Level
Major
MAJ
Crash
Minor
MNR
Crash
Oversized
OVRSZ
Load
Prepare
PREP
To Stop
Pavement
PVMT
Wet*
Roadwork
RD WK
Ahead
Route
RT
Best*
Turnpike
TRNPK
(name)*
Township
TWNSHP
Limits
Upper
UPR
Level
*Prompt word goes before abbreviation.

Abbreviations That Are Not Acceptable

Abbr.
Intended Word
Common Misinterpretation
ACC
Accident
Access (Road)
B4
Before
None
CLRS
Clears
Colors
DLY
Delay
Daily
FDR
Feeder
Federal
L
Left
Lane (Merge)
LT
Light (Traffic)
Left
PARK
Parking
Park
POLL
Pollution (Index)
Poll
RED
Reduce
Red
STAD
Stadium
Standard
WRNG
Warning
Wrong

 

REMEMBER:

  • Signs are the primary channel of communication to the motorist.
  • PCMS credibility is crucial.
  • The PCMS should communicate what action motorists need to take and when this action should occur.
  • Unnecessary information should be avoided.
  • PCMS should be left blank if there is nothing to report and moved if no longer needed.

Display Time

Each phase of a PCMS should be displayed long enough to allow reading by the motorist; however, unnecessarily long display times should be avoided. The following display times are suggested:

Maximum Number of Phases

The PCMS should have adjustable display rates so that the entire message can be read at least twice at either the posted speed, the off-peak 85th percentile prior-to-work-starting speed, or the anticipated operating speed. Given the need to display each phase for 1.5 to 3 seconds, there is a practical limit on how many phases can be displayed to the motorist for any one message. Concise design should be used to limit the message to two phases.

The conditions in the following table could allow motorists sufficient distance and time to read three phases twice.

Character Height, inches Speed, mph
18 40
24 50
54 Any
1 inch = 25.39 mm
1 mile (mi) = 1.61 kilometers (km)

These conditions are based on a presumed PCMS minimum character legibility of 40-to-1 of character height. It should be noted that different technologies will affect the character legibility.

REMEMBER:

  • One-phase messages are ideal.
  • Two-phase messages are acceptable if necessary.
  • Three phases should be used only when necessary and should contain a simple message.
  • The message can be split into two PCMS units if desired.
  • Do not flash a message to attract the motorist's attention. This practice has been found to be a distraction to motorists, especially at night.
  • Do not allow the message to scroll or travel horizontally or vertically across the face of the sign.

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PLACEMENT OF A PCMS

Laterally

If possible, the PCMS should be placed closest to the lane for which the message applies. The PCMS normally is placed on or just outside the shoulder. A PCMS can become a roadside hazard if not protected from an errant vehicle. If it cannot be protected by a guardrail or barrier, then it is recommended that orange cones or drums be used to increase the likelihood that motorists will notice the PCMS.

Care should be taken not to place the PCMS so far off the roadway that the PCMS is not in the motorist's cone of vision long enough to read the message. Factors that change the motorist's cone of vision are:

In addition, the PCMS should be placed on level ground and turned 3 degrees toward the roadway from the perpendicular edge of the roadway to reduce glare.

Longitudinally

The placement of a PCMS depends on how far upstream it needs to be placed and whether the upstream location has a sufficient sight distance for the PCMS to be viewed before motorist action is required.

Ilustration of placement of a verticle PCMS sign

The upstream location from the decision point depends on what type of action is required of the motorist. An example of a minor action is a lane change by the motorist. A major action would be the motorist having to make a detour from the current road.

For a minor action, the PCMS should be placed from 152.5 m to 305 m (500 ft to 1,000 ft) upstream of the decision point, regardless of speed.

For a major action, if the speed is less than or equal to 64 kilometers per hour (kph) (40 miles per hour (mph)), the PCMS should be placed at least 305 m (1,000 ft) upstream of the decision point. If the speed is greater than or equal to 72 kph (45 mph), then the PCMS should be placed at least 1.61 km (1 mi) upstream of the decision point.

There should be a minimum spacing of at least 305 m (1,000 ft) between PCMS units or a PCMS and an arrow panel. Multiple PCMS units should be placed on the same side of the roadway.

PCMS Height

When in operating mode, the bottom of the PMCS message panel shall be at least 2 m (7 ft) above the roadway.

Sight Distance

For highway travel, it is desirable to have a visibility distance of 0.8 km (0.5 mi) for a PCMS, while for slower travel, shorter distances are acceptable. Keep in mind that because curves or hills may hide a PCMS, the PCMS may have to be located farther away from the decision point so that there will be enough time for the motorist to read the message.

In placing a PCMS, it is important to keep in mind that:

After the PCMS has been located in the field, verify that the sight distance is greater than the required visibility and legibility distances.

Finally, because local motorists become familiar with the new conditions so quickly, the PCMS should be moved periodically (e.g., every few weeks) so that it continues to command the attention of motorists.

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WHEN TO DISCONTINUE PCMS OR ALTER MESSAGE

One of the most significant problems perceived with a PCMS is credibility. A failure to display the correct information on a PCMS creates a negative image in motorists' minds.

REMEMBER:

  • Update PCMS information when possible.
  • When not in use, the PCMS should be turned perpendicular to the flow of traffic so that motorists do not see its screen (if possible).

 

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OTHER OPERATIONAL ISSUES

Brightness

Current PCMS boards operate by means of one of two technologies (neither of which allow for an adjustment of field brightness):

Maintenance

As with all mechanical equipment, routine maintenance is recommended to preserve the life of the PCMS and to ensure that it is running safely and properly.

Suggested maintenance steps include:

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APPENDICES

Setup Checklist

check mark Does the PCMS tell the motorist to do something?
check mark Are static signs not readily available?
check mark Does the PCMS tell drivers something new?
check mark Has approximately 1.5 to 3.0 seconds of cycle time been provided for each phase of the PCMS so that each phase can be read twice?
check mark Have standard abbreviations been used?
check mark Can the PCMS be seen from the recommended visibility and legibility distances?
check mark Is the PCMS safely placed on or just off the shoulder?

 

REMEMBER:

  • Move the PCMS periodically so that it continues to command the attention of the motorists.
  • Black out or edit the PCMS message when it no longer applies.
  • Ensure that the brightness of the PCMS changes automatically as required by lighting conditions.
  • Maintain and clean the PCMS on a regular basis

Definitions

Character—Letter, numeral, or symbol formed by a group of pixels, usually an array of five-wide by seven-high pixels.

Cycle Time— Time that the entire message is displayed.

Graphic—Array or configuration of pixels that forms an image or symbol for the purpose of conveying information.

Legibility Distance—Distance at which a motorist with normal vision can read a message.

Message—Group of characters, numerals, and symbols or a graphic image used to convey a warning or instruction. A message may be presented to the motorist during one, two, or three phases.

Phase—Letters, words, and/or symbols displayed at one time.

Metric Conversions

From English Multiply By To Metric
inch
25.4
millimeters (mm)
foot
0.30
meters (m)
yard
0.91
meters (m)
mile
1.61
kilometers (km)
mph
1.61
kilometers per hr (kph)


The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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