Wisconsin Department Intelligent Transportation Systems (ITS) CHAPTER 6 VARIABLE MESSAGE SIGNS

Transcription

1 CHAPTER 6 VARIABLE MESSAGE SIGNS December, 2000

2 6. Variable Message Signs (VMS) 6.1. Introduction and Usage Variable message signs (VMS) are traffic control devices used to provide motorists enroute traveler information. They are commonly installed on full-span overhead sign bridges, post-mounted on roadway shoulders, and overhead cantilever structures. The information is most often displayed in real-time and can be controlled either from a remote centralized location or locally at the site. VMS are designed to affect motorist behavior to improve traffic flow and operations. Traveler information displayed on VMS may be generated as a result of a planned or unplanned event, which is programmed or scheduled by operations personnel. Examples of traveler information include: Travel times between known destinations Congestion conditions along a freeway corridor Construction notices Special event notice and motorist instructions Maintenance operations schedule Pending sever weather announcement Incident notification The objective of providing the information is to allow the motorist time to avoid an incident, prepare for unavoidable conditions, or to give travel directions. For all information displayed the goal is to have a positive impact on the motorist s travel time VMS Types Currently in Operation There are currently four different types of VMS operating in Wisconsin. Each type has a different purpose. Freeway VMS are located on stretches of highway and are designed to inform motorist traveling at high speed. Arterial VMS are found along heavily travel roadways leading to the freeway system and are seen by motorist traveling at slower speeds. Line Matrix VMS are specially designed to integrate into existing or new Type 1 Freeway guide signs for the purpose of adding a dynamic or blank-out (on/off) message. Changeable messages signs (CMS) or portable VMS are intended to operate in a location for a short period of time and then be moved to a new location or stored until needed again. Each VMS type, except CMS, will be addressed in this Chapter. For guidance on CMS deployment, consult the State Traffic Engineer. States Types of VMS Technology There are multiple types of VMS technology currently deployed across the United Flip Disk - This technology utilizes a system of small circular, square, or rectangular disks, which individually rotate or flip to form characters on the VMS. Each disk has reflective material on one side that, when flipped, is exposed to form the message. Light Emitting Diode (LED) - LED technology utilizes clusters of solid-state diodes that form a single pixel. When voltage is applied, each diode glows. By turning December,

3 voltage on or off, each pixel cluster is manipulated into forming the characters or pattern of the displayed message. Fiber Optic - Fiber optic VMS technology utilizes bundles of fiber optic strands strung between each pixel and a lamp source. A single lamp source will power several pixels. To control which pixels are displayed, shutters are placed in front of each pixel. When a message is displayed the magnetically controlled shutters open or remain close to form a character or pattern. Hybrid - A typical hybrid VMS utilizes both flip disk and either fiber optic or LED technology. Each flip disk has a hole in its center for light to pass through. The light is generated by a fiber optic bundle or LED cluster. When the pixel is activated the disk is flipped, allowing light to pass through the hole while displaying the reflective side of the disk to traffic. When the pixel is off its reflective surface is rotated, or flipped, blocking the light source. Figure 6-1 provides a summary of advantages and disadvantages for each technology. Technology Advantages Disadvantages Flip Disk Proven technology Low power requirements Provides a sharp legible message More moving parts leads to additional maintenance Reflective disk surfaces can become sunbleached over time Not very visible during low level light conditions at long distances LED Visibility is good under most lighting conditions Fewer moving parts require less maintenance LED are rated for 100,000 hours of service Fiber Optic Good visibility under normal operating conditions Provides a sharp legible message Hybrid Can still utilize sign if light source fails Provides a sharp legible message Smaller cone of vision reduces message legibility at close distances Diodes can be sensitive to heat More moving parts leads to additional maintenance Lamps are typically rated for only 8,000 10,000 hours of service Can not adjust illumination intensity for various light conditions More moving parts leads to additional maintenance Reflective disk surfaces can become sunbleached over time Figure 6-1: VMS Technology Advantages and Disadvantages VMS Matrix Displays Messages are limited by the type of VMS used and its display space configuration or matrix. There are three typical types of matrix displays: character, line, and full. In a charter matrix a separate display space is made available for each letter of the text message. A charter matrix of 8 horizontal by 3 vertical has only 24 display spaces available. In a line matrix there is no physical separation between the charters in a single line of text. However, in a line matrix there still remains a separation between different lines of text. In a full matrix no physical December,

4 separations exist between individual characters or lines in the message. A message can be shown at any size and location as long as it is within the display space. The exhibit below demonstrates the differences between the matrix types. Character Matrix Line Matrix Full Matrix Figure 6-2: Variable Message Sign Matrix Displays Messages displayed on a VMS are done by using single or multiple-phases. A phase is defined as the limits of the display area available for text, bitmaps, or animation. Messages that require more information than can be shown on a single VMS display space may require the use of multiple phases. Multiple phases allow more than one message to be displayed at a location VMS Design Process The design process presented here demonstrates the steps needed for proper VMS deployment. It does not, however, take every possible variable into consideration. The designer must proper judgment within each step for a successful deployment. Figure 6-3 provides a graphical representation of this process. 1) Collect preliminary data required for the proposed variable message sign deployment 2) Determine VMS type 3) Determine corridor placement for VMS implementation 4) Collect site-specific data required for the proposed variable message sign location 5) Select the VMS site required for design 6) Determine cabinet placement for the VMS. 7) Perform underground infrastructure 8) Determine the communications medium used for the proposed location 9) Revisit steps 4 through 8 until final design is complete 10) Begin the process to establish electrical service for the proposed location with the local power company. This should be done early in the design process to establish an acceptable electrical service location. 11) Utilizing the table found at the back of this chapter and the information contained within Appendix A, determine the construction details needed for the proposed design, details which need to be modified, and new details which need to be created to provide a complete construction plan. 12) Utilizing the table found at the back of this chapter and the information contained within Appendix B, determine the special provisions needed for the proposed design, special provisions which need to be modified, and new special provisions which need to be created to provide a complete construction plan. In the following sections each task is broken down in more detail. In each step there are additional subtasks, which need to be preformed as part of the overall design. Care should be taken by designers to familiarize themselves with all steps before proceeding. December,

5 COLLECT PRELIMINARY DATA DETERMINE VMS TYPE DETERMINE CORRIDOR PLACEMENT FOR VMS COLLECT SITE SPECIFIC DATA DETERMINE SITE PLACEMENT OF VMS STRUCTURE DESIGN (not covered under this manual) ESTABLISH CABINET LOCATION ESTABLISH POWER SERVICE PREPARE UNDERGROUND INFRASTRUCTURE DETERMINE COMMUNICATIONS MEDIUM 1 PERFORM CABLE ROUTING MODIFY, AND CREATE CONSTRUCTION DETAILS MODIFY, AND CREATE SPECIAL PROVISIONS VMS DESIGN COMPLETE 1 Refer to Chapter 9 on Communications for further information. Figure 6-3: VMS Design Process December,

6 6.5. Data Collection Data collection required for VMS deployment is broken into two areas: preliminary data collection, and site-specific data collection. Under preliminary data collection, the following information will need to be obtained to determine the area, corridor, and type of the variable message sign. Intended purpose of the VMS Type of information to be displayed on VMS Alternate route diversion points Under site-specific data collection, the following information will need to be obtained to determine the exact location of the variable message sign. Base mapping with local roadway network linked to the segment under review for the VMS Existing roadway horizontal alignment Roadway vertical information Existing sign inventory Location of power along roadway segment 6.6. Determination of VMS Type Prior to locating VMS along a roadway segment, some engineering decisions need to be made, and VMS type selected. The type of decisions that a designer must address prior to selecting a location include: Intended purpose of the VMS Will the VMS serve the general traveling public, a special event generator, or is it needed for upcoming construction? Type of information to be displayed on VMS Will the VMS be used for only one message that is blanked on or off, a few select messages needing limited lines, or a wide range of information displayed? The type of information to be displayed will determine if a character, line, or full matrix VMS is necessary. Type of VMS technology What advantages and disadvantages to the technology being deployed will need to be considered or accounted for in the design VMS Site Selection and Placement Using data and information collected during the previous step, site selection is now possible. The following demonstrates how that information is utilized when selecting sites for possible deployment. Alternate Route Diversion Points In an urban roadway network, VMS should be located in advance of alternate route access points on the network to allow motorists to take action in response to the message on the sign. In an urban setting there are typically many other signs that compete for motorists attention, and VMS should be placed for maximum visibility and impact. The minimum distance a freeway VMS should be placed prior to an access point is one mile. On an arterial December,

7 roadway segment, the distance may vary based on issues such as speed limits, local factors, and right-of-way constraints. Existing Horizontal Alignment Data To ensure proper viewing of the VMS, message sites must be located on tangent roadway sections. The introduction of even minor curves along the roadway can impact visibility. Current VMS technology limits a pixel s cone of visibility to only a few degrees. Because of this, minor changes in the horizontal alignment may make the message unreadable. The designer should look for sites that are located on tangents and allow a motorist at least 900 to 1000 feet of clear sight distance to the sign while traveling 55 mph or faster. If the motorist is traveling between mph, the minimum distance needed should be 500 feet. Existing Vertical Alignment Data Vertical alignment along the roadway also impacts the visibility of the VMS. The cone of visibility (discussed previously) limits the visibility of the VMS in these areas. If there are a limited number of potential locations available, an upward grade is desirable. Ideal site locations along roadway segments within 1% grade or less are desirable. VMS should not be placed along grades exceeding 4%. Existing Sign and Traffic Control Inventory VMS should not compete with other existing signs or interfere with traffic control devices. The designer must take inventory of all signs and traffic control devices along a roadway segment to properly place the VMS. Based on this inventory, existing signs may need to be moved to accommodate proper VMS placement. On the freeway, the minimum distance between Type I guide signs and a VMS is 800 feet. On arterial streets the distance allowed between Type I signs and a VMS is approximately 400 feet. Since the VMS signs are typically installed in elevated positions care should be taken by the designer to also identify possibly conflict with the VMS blocking other existing traffic control devices. Location of Power Along Roadway Segment Locating existing power along a roadway segment helps a designer understand how difficult it might be to power a potential VMS site. It is desirable to locate the cabinet and electrical service as close together as possible. All power service locations require approval from the utility company prior to installation Site Design Site design is broken into several tasks, which deal with the placement of the VMS structure and its supporting infrastructure. These tasks include the following: VMS supports/location VMS height requirements Cabinet locating Underground Infrastructure Power requirements Conduit routing Safety consideration December,

8 Some of the tasks will require some level of engineering judgment by the designer. In any case, all VMS site locations must be approved by and coordinated with the District Signing Engineer. Each is explained in more detail below. VMS Supports/Location On the freeway, overhead supports are preferred side-mounted or cantilever structures. Overhead VMS are generally more legible. On the freeway, the supports are located 6 feet behind the shoulder. Support protection must be provided in this instance, since the vertical support is located inside the clear zone. Typically, guardrail is installed for protection, but concrete barrier wall may also be used if already present. Concrete barrier wall is significantly more expensive than guardrail. Additionally, impact attenuators are suitable for protecting horizontal supports. VMS deployed on local streets have been deployed using supports located just outside of the roadway shoulder. Shielding is not required on arterial supports provided that vertical face curb is present, and the speed limit assigned to the roadway is 40 mph or less. VMS Height Requirements Per the Manual on Uniform Traffic Control Devices (MUTCD), the minimum distance between the crown of the roadway and the bottom of a freeway guide sign is 18 feet. This takes into consideration future pavement overlays that might raise the roadway surface. On freeway VMS the 18-ft requirement does not apply to the sign itself, but rather to the lowest point of the structure. The 18-foot minimum is also used for arterial VMS that are mounted on cantilevers. Figure 6-4 provides graphical representation of mounting height requirements for various types of VMS deployment. Cabinet Location Locating controller cabinets at VMS sites is done differently for freeway and arterial deployments. Due to right-of-way constraints, arterial VMS controller cabinets are typically located in close proximity to the sign or mounted directly on the support structure. The freeway VMS controller cabinets, however, are located at a distance of approximately 100 feet from the front of the sign. This distance is to allow an individual to view the sign from the cabinet and provide a safe location outside the clear zone. The 100 feet is a typical deployment distance that is favorable to most VMS manufacturers. Distances longer than 100 feet may impact communications between the VMS and the controller. Figure 6-5 provides graphical representation of controller cabinet locations for various types of VMS deployment. Underground Infrastructure When the controller cabinet, electrical service and VMS have been placed, the underground conduit infrastructure can be designed. Issues to keep in mind when designing the conduit infrastructure include: Pull Box Spacing - Pull boxes should be spaced within 200 feet. Terrain - Conduit infrastructure should be designed on relatively flat (4:1 slope or flatter) terrain. For steeper sloped terrain (3:1 or greater), conduit may be run perpendicular to (i.e., up or down) the slope to locations where the terrain is more suitable for conduit installation. December,

9 Type of VMS Overhead Sign Bridge Height Requirement 18-feet from roadway crown to lowest point on the sign. Note typically the lowest point is the base of the catwalk. 18 Cantilever 18-feet from roadway crown to lowest point on the sign. 18 Shoulder Mounted 8-feet from the roadway crown to the base of the sign. 8 Figure 6-4: Mounting Heights of Variable Message Signs Freeway VMS Controller Cabinet Overhead Sign Bridge Structure Arterial VMS Controller Cabinet- Cantilever and Shoulder Mounted Top View Top View CANTILEVER Min. 100 ft Max distance per manufacturer s maximum communication distance Controller Cabinet attached to supports Controller Cabinet X - max distance while still able to view sign face; clear zone requirements per AASHTO SHOULDER MOUNT Figure 6-5: VMS Controller Cabinet Locations December,

10 Conduit Size - 3-Inch conduit is typically used for detector station raceways, since a) cost savings between 3-inch and smaller diameter conduits is minimal, and b) 3-inch conduit may provide for greater future expansion depending on the number of cables and % fill of the conduit. Conduit entering electrical service pedestals must be sized per pedestal requirements. Conduit Fill - The size and number of conduits along a run is dependent on percentage of fill as established by the National Electric Code (NEC). This is dependent upon the size and number of individual cables. Electrical service The power distribution wires running between the electrical service and the controller cabinet consist of stranded copper single conductors, cross-linked polyethylene (XLP), USE rated. Section 655 of the standard specifications may provide guidance on additional requirements. The gauge of conductors must be calculated per the requirements of the National Electric Code. Electrical Wire Routing The conduit system for VMS sites needs to be bonded together, due to the fact that power cables are running within the system. Bonding all metallic components of the system together assures that there will be no difference in voltage potential across two points in that system. In addition, grounded conductor needs to be run with current-carrying cables (such as traffic signal conductors, power distribution wires, etc.), which returns the circuit s current at zero voltage. The bonding/grounding wires in system typically uses Electrical Wire, Traffic Signals, No. 10, Item in the State s Standard Specifications. The gauge of grounded conductor must be calculated per the requirements of the National Electric Code. There is a distinct method required for the bonding system. Examples of this method can be found in Chapters 3 and 4. The pull boxes do not require grounding if the total voltage encountered in the pull box is 50 volts or less. In District 2, a policy has been made to bond and ground all conduit systems, since equipment is frequently added to various locations in the future. For assistance in bonding and grounding of underground systems, consult the State Electrical Engineer. Cable Routing Cable routing for variable message signs typically involves the connection of communication and power to the controller cabinet from the sign and from the cabinet to the power and communication resources. Communication cable from the cabinet to the VMS is typically proprietary to the VMS manufacturer. Outside of the VMS Communication cable the current standardized cables are utilized. The power distribution wires running between the controller cabinet and the electrical service should be in a separate conduit. Power and communication cables should not be mixed together. In addition, the power and communication cables for the variable message sign should also be kept in separate raceways. Safety Considerations A site must be designed to allow for safe maintain and operation of the VMS and its controller cabinet. To address safety issues the following question should be asked: December,

11 Does the site allow safe and easy access to the sign for maintenance vehicles? How exposed will maintenance vehicles and personnel be to live traffic while at the site? Can personnel access the controller cabinet without having to use the roadway shoulder? Answering these questions the designer may choose to make additional site modifications. Safety considerations should also be considered when for the site s construction Communication Requirements Communication between the VMS and control center allows information to be disseminated on a real-time basis, providing up-to date information to the motorist. The control center can communicate with the VMS via a voice-grade telephone line, either standard wire based or cellular. Dedicated communications, such as a state owned fiber optic cable, state owned copper twisted pair cable, spread spectrum radio, or a combination of the three, could also be used to provide communications between the VMS and the control center. Chapter 9 provides additional information on communication types and requirements Power Requirements District 2 A 100 Amp, 120/240 volt, single phase, three wire underground electrical service is required for electrical service installation. The electrical service will be furnished and installed by the Wisconsin Electric Power Company up to a demarcation point, which consists of a electrical service. The electrical service must conform to the requirements as found in the Electric Service and Metering Manual as issued by Wisconsin Electric. The location of the electrical service must receive approval from the utility company. The electrical service will include two 50-amp circuit breakers rated at 22,000 AIC. The requirements for power cable between the electrical service and controller cabinet can be found under the Cable Routing section of this chapter. At locations which require a remotely located electrical service, a 100 Amp outside rated breaker box with space for 6 circuits, but no main breaker, will be attached to the side of the cabinet. Also, a 50 Amp single circuit breaker rated at 22,000 AIC will be installed within the breaker box to serve as a local electrical service disconnect point VMS Hardware Requirements The components of a VMS sign installation consist of the controller, the VMS housing, the sign dimming system, the display technology, electrical service (meter) pedestal, and communications. Each of these components and their characteristics are outline below and in the Special Provisions. Display Criteria Freeway VMS are full matrix signs capable of displaying three lines of text with 18" characters per line. Arterial VMS are full matrix signs capable of displaying three lines of text with 8" December,

12 characters per line. Line matrix signs should be capable of displaying two lines of text with either 18" or 8" characters per line depending on if they are deployed in a freeway or arterial location. VMS Controllers A microprocessor-based controller located at the sign site as shown on the plans will operate each sign. The VMS controller will provide the electronics necessary to receive and interpret commands from the VMS master, to issue a response to the VMS master, and to display messages on the sign. The VMS controller will accept commands and issue responses through an RS232C data port at user-selectable rates of 1200 and 9600 bps. The controller will support communications with the VMS master using a RJ-48S jack network interface via an Ameritech 3002 multipoint circuit. The controller should have sufficient EPROM memory to store a minimum of 32 messages for immediate display upon command from the VMS master or local control. The controller should also have sufficient RAM memory to upload and download messages. The controller should be able to perform messaging operations, including but not limited to, flashing on and off, inverse character display on and off, and sequencing. The controller must be able to write any messages at an effective rate of 60 characters per second. The VMS controller should incorporate a watchdog timer to detect an out-ofprogram condition and reset the microprocessor. The controller should be designed for fail-safe prevention of improper information display in the case of malfunction. As a minimum, this should include an automatic blanking feature, which immediately clears the message displayed on the sign in the event of a communications failure, invalid transmission from the VMS master, or power failure. The VMS controller must be capable of operating in a local control mode. For local control mode the controller should have as a minimum: operator selection of dimming levels, operator selection of 32 pre-stored messages, and diagnostic routines capable of testing full sign operation. The local control will be switchactivated inside the cabinet and accomplished via thumbwheels or keypad with menu-driven LCD display. While in the local mode, the VMS master will continue to monitor the sign's status and display. The controller must be provided with an RS-232 for plugging in a laptop computer for running diagnostic testing and downloading/uploading messages. When the cabinet doors are open in the controller, circuit breakers, fuses, switches, and indicators should all be readily visible and accessible. VMS Housing The VMS housing should be constructed to present a clean, neat appearance. The equipment located within the housing must be protected from moisture, dust, dirt, and corrosion. The housing interiors should be non-corrosive metal cage support frames to mount December,

13 the display elements. The frame support should be able to withstand and minimize vibration when the sign is mounted with any number of display elements. The housing should be provided with 2 lifting eyes to be used when placing the housing on the sign structure. The lifting eyes should be located where required. The lifting eye must have sufficient structural strength to allow the sign to be lifted or moved without causing any damage or permanent deformation to any part of the sign. The sign should be fabricated from 3.2mm (0.125 inch) (minimum) thick 3003-H14 or 5052-H32 aluminum alloy and designed to withstand kilograms per square meter (80 psf) as specified in the latest AASHTO publication entitled Standard Specification for Structural Supports for Highway Signs, Luminaries, and Traffic Signals. The housing should provide sufficient ventilation on both sides and below the housing using louvered vents. All fans and other forced air devices must be thermostatically controlled and use standard-size removable filters. Screened weep holes should be provided to allow the drainage of any water that may collect in the housing. All housing should include a single sheet, UV stabilized, and UV filtering, polycarbonate front panel. The front panel should employ an anti-glare sheeting substance. The front panel should be mounted securely as to withstand a 90 mph wind load, and not obscure any of the pixels in the sign. A heating element (such as a heat strip or wire) is typically installed around the front panel to prevent ice or frost accumulation on the sign face. All housings should allow for access for all maintenance activities to all interior components of the sign through the front panel. Sign Dimming System Each sign should be provided with a system that senses the background ambient light level and provides a minimum of 7 field-adjustable intensities (dimming). The dimming system should contain three commercially available photoelectric sensors installed in watertight metal enclosures on the VMS housing. The photoelectric sensors should be capable of being continually exposed to direct sunlight without impairment of performance. The photoelectric sensors should be placed to they view the front, rear, and top of the sign. The VMS controller should determine the operating mode (local or central) and select the appropriate method of implementing dimming VMS Construction Details Construction details previously used during construction of VMS sites are found in Figure 6-6. These details, in Adobe Acrobat format, can be found in Appendix A. Electronic Microstation versions of these files can also be found on the ITS CD VMS Special Provisions Special provisions for items used in contracts containing VMS equipment are listed in Figure 6-7. These special provisions, in Adobe Acrobat format, can be found in Appendix B. Electronic files of the special provisions (Microsoft Word version 7.0) can also be found on the December,

14 File Name Description cabbase CONCRETE BASE, CONTROLLER CABINET breaker CABINET BREAKER PEDESTAL INSTALLATION meter1 FREE STANDING ELECTRICAL SERVICE AND SUPPORTING STAKE meter2 ELECTRICAL SERVICE TO CABINET 170pr2 170 PROCESSOR & CABINET DETAILS (2 OF 11) 170pr3 170 PROCESSOR & CABINET DETAILS (3 OF 11) 170pr4 170 PROCESSOR & CABINET DETAILS (4 OF 11) 170pr6 170 PROCESSOR & CABINET DETAILS (6 OF 11) cabidplq CABINET IDENTIFICATION PLAQUE vmsdim VMS SIGN STRUCTURE LAYOUT vmsfoot VMS FOUNDATION WITH INTEGRAL BARRIER vmstrans VMS FOUNDATION TRANSITION FROM DOUBLE FACED BARRIER beamgrd BEAM GUARD INSTALLATION avmscant AVMS CANTILEVER STRUCTURE, TYPE 1 avmssign AVMS SIGN LAYOUT linematx LED LINE MATRIX VMS avmsgrnd GROUND MOUNTED ARTERIAL VMS Figure 6-6: VMS Construction Details Filename Description cabbase CONCRETE BASE, CONTROLLER CABINET, ITEM fieldcab FIELD CABINET, ITEM meterped METER BREAKER PEDESTAL, ITEM breakerbox BREAKER DISCONNECT BOX, ITEM 9005 fwyvms LED VMS ASSEMBLY (FULL MATRIX), ITEM linevms LED LINE MATRIX VARIABLE MESSAGE SIGN, ITEM polemtcabinet DOUBLE DOOR POLE MOUNTED CABINET, ITEM arterialvms ARTERIAL VMS ASSEMBLY (FULL MATRIX), ITEM vmsmodules FURNISH ARTERIAL VMS ASSEMBLY SIGN MODULES, 8-INCH, ITEM surveyvms SURVEY VMS LOCATION, ITEM surveyavms SURVEY ARTERIAL VMS LOCATION, ITEM portvms SOLAR, PORTABLE, LIGHT EMITTING DIODE (LED), CHANGEABLE MESSAGE SIGN, DELIVERED, ITEM powerwires POWER DISTRIBUTION WIRE, NO 4 AWG, ITEM 90030; POWER DISTRIBUTION WIRE, NO 6 AWG, ITEM 90030; POWER DISTRIBUTION WIRE, NO 8 AWG, ITEM 90030; POWER DISTRIBUTION WIRE, NO 10 AWG, ITEM Figure 6-7: VMS Special Provisions December,