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

EMERGENCY TELEPHONE NUMBERS

County Office __________________
District Traffic Unit __________________
Supervisor __________________
Office __________________
Shop __________________
Police __________________
Fire __________________
Medical __________________
Other __________________

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/.

Back to Top

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:

• Captures motorists' attention.
• Relays information that is difficult to accomplish with static signing.
• Is used to supplement other required signing.

Back to Top

WHEN SHOULD A PCMS BE USED?

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

• Construction or maintenance (e.g., work zone).
• Incident management.
• Special event.
• Notification of future construction or event.

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

• Speed reduction.
• Advance notice of lane closures and shifts.
• Diversion to a different route.
• Advance notice of ramp closures.

A PCMS also can provide informational messages, such as:

• Expected reopening of existing closed lane.
• Roadway status for special events.
• Crash or other incidents.
• Changes in alignment or surface conditions.

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.

Back to Top

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- 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- 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- 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.

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)).

Back to Top

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

Acceptable Abbreviations with Prompt Word

Abbreviations That Are Not Acceptable

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:

• Phases with one or two lines: 1.5 seconds.
• Phases with three lines: 3 seconds.

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.

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.

Back to Top

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:

• Distance the PCMS is placed from the side of the road.
• Number of lanes.
• Roadway curvature.

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.

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:

• The PCMS should be visible from 0.8 km (0.5 mi).
• Curves or hills may require an increase in spacing.

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.

Back to Top

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.

Back to Top

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):

• Light-emitting diode (LED) boards are internally set at the factory to monitor ambient light levels and automatically adjust the brightness of the PCMS. These boards do not allow manual overriding of light intensity.

  If an LED board is too dim under sunny conditions, or is excessively bright at night, that board should be replaced or it should be adjusted by the manufacturer.

• Flip-disk boards have no light source to be adjusted, as these are usually reflective disks.

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:

• Have an extra battery available (if the PCMS is battery-powered).
• Clean and inspect the following components:
  • Screen (monthly).
  • Sign door panel(s) (monthly).
  • Solar panel(s) (monthly).
  • Batteries (three or four times per year).
• Verify that an extra set of programming instructions are stored in the PCMS for emergency use or for "in-the-field" programming.

Back to Top

APPENDICES

Setup Checklist

	Does the PCMS tell the motorist to do something?
	Are static signs not readily available?
	Does the PCMS tell drivers something new?
	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?
	Have standard abbreviations been used?
	Can the PCMS be seen from the recommended visibility and legibility distances?
	Is the PCMS safely placed on or just off the shoulder?

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