910.3 dynamic message signs (dms)
|Changeable Message Signs (CMS)|
Support. Dynamic Message Signs (DMSs) are stationary traffic control devices capable of displaying one or more alternative messages that provide travelers with real-time, traffic-related variable messages. DMSs are used to warn, regulate, route and manage traffic.
MoDOT operates DMSs through its transportation management centers (TMCs) in Kansas City (KC Scout), St. Louis (Gateway Guide) and Springfield (Ozarks Traffic). Each of these TMCs operates DMSs within its metropolitan coverage area. The KC Scout and Gateway Guide TMCs also operate DMSs on the statewide rural I-29, I-35, I-44, I-55, I-57, I-70 and US 60.
- 1 910.3.1 National DMS Policy
- 2 910.3.2 MoDOT DMS Policy
- 2.1 910.3.2.1 Basic Requirements (MUTCD 2L.01)
- 2.2 910.3.2.2 Responsibility for Operation of DMS
- 2.3 910.3.2.3 Message Priorities
- 2.4 910.3.2.4 Incident Verification
- 2.5 910.3.2.5 Legibility and Visibility of DMS (MUTCD 2L.03)
- 2.6 910.3.2.6 Installation of a DMS (MUTCD 2L.06)
- 2.7 910.3.2.7 Message Creation and Termination
- 2.8 910.3.2.8 DMS Capabilities and Message Formats
- 2.9 910.3.2.9 Acceptable Message Words and Terms
- 2.10 910.3.2.10 Acceptable Abbreviations
- 2.11 910.3.2.11 Incident Clearance Messages
- 2.12 910.3.2.12 Congestion Messages
- 2.13 910.3.2.13 Weather Messages on Dynamic Message Signs
- 2.14 910.3.2.14 Use of One-Phase and Two-Phase Messages
- 2.15 910.3.2.15 Child Abduction, Blue Alert and Ozone Alert Messages
- 2.16 910.3.2.16 Driver Safety Campaigns (MUTCD 2L.02)
- 2.17 910.3.2.17 On-Site Control of Changeable Message Signs
910.3.1 National DMS Policy
Policies, standards, and guidelines at the national level are embodied in the Manual on Uniform Traffic Control Devices (MUTCD). The primary sections in the MUTCD that address DMSs are Section 1A.15 "Abbreviations Used on Traffic Control Devices" and Section 2L "Changeable Message Signs".
910.3.2 MoDOT DMS Policy
910.3.2.1 Basic Requirements (MUTCD 2L.01)
Standard. DMSs shall display only traffic operational, regulatory, warning, and guidance information except that they may also be used to display safety messages, transportation-related messages, emergency homeland security messages, America’s Missing: Broadcast Emergency Response (AMBER) Alert messages, and Blue Alert messages. Advertising messages shall not be displayed on DMSs or their supports or other equipment.
Guidance. DMSs should not promote commercial events or entities and should not repeat guide sign, regulatory sign or warning sign messages.
Messages displayed shall convey pertinent information to assist motorists in their driving decisions. Messages shall be conveyed in a standard, non-confusing manner that allows drivers to both perceive and react to the information in a timely fashion. DMSs will be effective if five basic requirements are met.
- 1) Fulfill a need: Messages must only be posted to signs when there is a real need, and when the purpose is clear to the driver. If messages on DMSs are perceived to be unnecessary, drivers will begin to disregard all DMS messages.
- 2) Command attention: The mere size of the signs themselves help to command driver attention, but the wording of messages can also contribute. Colors and graphics may also be used in a manner consistent with MoDOT policy.
- 3) Convey a clear, simple meaning: At typical speeds, drivers have only a few seconds to notice, read and interpret posted messages. Proper composition and formatting is critical to conveying the most vital information in a manner that the driver will be able to assimilate. Consistency is an important aspect of this type of communication. Consistently composed and formatted messages become familiar to drivers and easier for them to comprehend quickly. Statewide messaging standards will improve the effectiveness of all DMS usage. Graphics can also reduce the time necessary for drivers to interpret messages.
- 4) Command respect from travelers: Fulfilling a need and conveying a clear, simple meaning are important components of commanding respect. They must also display information that is accurate and timely. Drivers will ignore all DMSs if they find information to be unreliable, either because it is frequently in error or often out-of-date.
- 5) Give adequate time for proper response: This requirement may be most pertinent to the placement of portable signs, but also speaks to the composition of messages. The desired response, in many cases, is simply for the driver to comprehend the information and become aware of possible congestion ahead. Messages that are poorly composed or contain too much information may be difficult for drivers to read in the few seconds they have while traveling at highway speed.
Guidance. Blank-out signs that display only single-phase, predetermined electronic-display legends that are limited by their composition and arrangement of pixels or other illuminated forms in a fixed arrangement (such as a blank-out sign indicating a part-time turn prohibition, a blank-out or changeable lane-use signs, or a changeable OPEN/CLOSED sign for a weigh station) should comply with the provisions of the applicable EPG article for the specific type of sign, provided that the letter forms, symbols and other legend elements are duplicates of the static messages as detailed in the EPG. Because such a sign is effectively an illuminated version of a static sign, the size of its legend elements, the overall size of the sign, and placement of the sign should comply with the applicable provisions for the static version of the sign.
910.3.2.2 Responsibility for Operation of DMS
The district engineer shall authorize the use of all DMSs, both state and contractor-furnished, and may designate a person or persons to be responsible for the authorization of use, messages to be displayed, and the care, maintenance, and security of the DMSs. Access to the DMS shall only be given to responsible individuals. The district engineer shall ensure that efforts are coordinated so that motorists are informed of the most critical information based on priority of messages listed below. In the Kansas City, St. Louis and Springfield metropolitan areas, Scout, Gateway Guide and Ozarks Traffic TMC operations staffs have been delegated the responsibility to operate the DMSs under their control.
The DMSs located on I-29, I-35 and I-70 are operated by the KC Scout TMC on a 24/7 basis with the exception of DMSs on I-70 in the St. Louis District. The Northwest, Northeast and Central Districts have the capability to operate the DMSs within their boundaries, but coordination with the KC Scout TMC is required.
The DMSs located on I-44, I-55, I-57 and US 60 are operated by the Gateway Guide TMC on a 24/7 basis. The Ozarks Traffic TMC in Springfield will have the capability to operate the I-44 DMSs located in the Southwest District. The Central, Southwest and Southeast Districts will have the capability to operate the DMSs within their boundaries; coordination of operations with the Gateway Guide TMC is required.
Districts without a TMC may also serve in a back-up role for their respective corridor in the event that the KC Scout, Gateway Guide or Ozarks Traffic TMCs have other activities in their local metropolitan areas that prevent them from managing operations on the I-29, I-35, I-44, I-55, I-57, I-70 and US 60 corridors.
910.3.2.3 Message Priorities
The following message hierarchy determines what type of message has priority should more than one request be made to post a message to the same sign. The DMS messages shall be prioritized in the following order unless overridden by a supervisor:
- 1) Emergencies, such as evacuations or closures, required by MoDOT, the State Emergency Management Agency (SEMA), local law enforcement or the military.
- 2) Hazardous and/or uncommon road conditions that require motorists to alter their driving, such as severe weather conditions, accidents, work zone activities or other incidents. Traffic operators should contact their floor supervisor when multiple incidents are taking place along the same route.
- 3) Traveler information and suggested alternative routes for delays and/or congestion caused by planned or unplanned events. Alternative routes are suggested with caution; sufficient trailblazing must be provided.
- 4) AMBER or Blue Alerts originating in the local area
- 5) Travel times
- 6) AMBER or Blue Alerts originating outside the local area
- 7) Ozone alerts
- 8) Advance date or time notice for scheduled incidents such as lane closures, road closures, moving operations or special events.
- 9) Approved standard public service messages associated with special campaigns (i.e. work zone awareness week, share the ride) or other public information that improves highway safety and reduces congestion.
- 10) When circumstances exist so that no message regarding safety or traveler information as defined by the previous listed priorities is warranted, Messages and Special Messages as outlined in EPG 910.3.2.16 Driver Safety Campaigns shall be displayed on all DMSs in Missouri. Messages shall be rotated regularly so that a variety of information is displayed to the traveling public. No message shall be excluded from the rotation unless otherwise approved by Traffic and Community Relations staffs.
Sometimes operators are faced with competing message needs when two or more incidents are simultaneously occurring on the freeway system downstream of a DMS. In such situations, operators must decide which of the incidents should be signed for, because it is not normally advisable to sign for both, unless a two-phase message is used. Procedures for posting two-phase messaging and situations that justify it are provided in EPG 910.3.2.14 Use of One-Phase and Two-Phase Messages. The following priority principles should be used in determining which competing incident should be signed for when a single phase is used:
- Messages about the closer of two or more downstream incidents on the primary freeway should receive priority over the incidents that are further downstream, except as modified by Table 910.3.2.3 Suggested Message Priority for Downstream Major Accidents, below.
- Messages about a downstream incident on the primary freeway should receive priority over incidents on downstream intersecting freeways or highways.
Suggested message priorities when a major accident occurs downstream of the closest incident on the primary highway are as shown in Table 910.3.2.3 below. District staff should be consulted prior to determining message priorities for incidents occurring on the I-29, I-35, I-44, I-55, I-57, I-70 and US 60 corridors.
Table 910.3.2.3 Suggested Message Priority for Downstream Major Accidents
|Major Accident Occurs Downstream of:||Give Message Priority to:|
|Major accident||Upstream major accident|
|Minor accident||Upstream minor accident|
|Roadwork with lane closure||Downstream major accident|
|Roadwork with freeway closure||Upstream roadwork|
|Incident (stalled vehicle, load spill, debris in roadway) requiring lane closure||Downstream major accident|
|Incident requiring total freeway closure||Upstream incident|
910.3.2.4 Incident Verification
It is very important that operators verify an incident before posting an incident message on a DMS. The best source of verification is by viewing it with a CCTV camera, but if a CCTV camera view is not available, it must be verified by a reliable source. Examples of reliable sources are Emergency Response Patrols, law enforcement agencies (i.e., MSHP, local sheriff and police departments) and MoDOT district staff or Construction/ Maintenance field staff. Media sources or the general public are not considered to be reliable sources for incident verification purposes. However, this unreliable information should be useful to operators in identifying information that needs to be explored further. Lines of communication need to be established between the above noted reliable sources and the TMCs.
It is also important that operators continue to monitor and modify, as necessary, the incident message as the incident progresses. Where CCTV camera views are not available, operators need to maintain communication with the reliable sources at the incident scene to ensure that the current message is accurate and timely. Generally when CCTV cameras are not available, operators should attempt to get updated incident information from reliable sources every 15 minutes for incidents within the metropolitan areas controlled by the KC Scout and Gateway Guide TMCs and every 30 minutes for incidents along the I-29, I-35, I-44, I-55, I-57, I-70 and US 60 corridors.
MoDOT DMS Contact List for Issue Reporting
|Northwest District||(816) 262-0367|
|Northeast District||(573) 248-5961|
|Kansas City District||(816) 607-2000|
|Central District||(800) 892-7332|
|St. Louis District||(314) 275-1500|
|Southwest District||(417) 864-1160|
|Southeast District||(573) 380-9631|
910.3.2.5 Legibility and Visibility of DMS (MUTCD 2L.03)
Support. The maximum distance at which a driver can first correctly identify letters and words on a sign is called the legibility distance of the sign. Legibility distance is affected by the characteristics of the sign design and the visual capabilities of drivers. Visual capabilities, and thus legibility distances, vary among drivers.
For the more common types of DMS, the longest measured legibility distances on sunny days occur during mid-day when the sun is overhead. Legibility distances are much shorter when the sun is behind the sign face, when the sun is on the horizon and shining on the sign face, or at night.
Visibility is the characteristic that enables a DMS to be seen. Visibility is associated with the point where the DMS is first detected, whereas legibility is the point where the message on the DMS can be read. Environmental conditions such as rain, fog and snow impact the visibility of DMS and can reduce the available legibility distances. During these conditions, there might not be enough viewing time for drivers to read the message.
Guidance. DMS used on roadways with speed limits of 55 mph or higher should be visible from ½ mile under both day and night conditions. The message should be designed to be legible from a minimum of 600 ft. for nighttime conditions and 800 ft. for normal daylight conditions. When environmental conditions that reduce visibility and legibility are present, or when the legibility distances stated in the previous sentences in this paragraph cannot be practically achieved, messages composed of fewer units of information should be used and consideration should be given to limiting the message to a single phase.
910.3.2.6 Installation of a DMS (MUTCD 2L.06)
Guidance. A DMS that is used in place of a static sign (such as a blank-out or variable legend regulatory sign) should be located in accordance with the provisions of Chapter 2A of the MUTCD. The following factors should be considered when installing other permanent DMS:
- A. The DMS should be located sufficiently upstream of known bottlenecks and high crash locations to enable road users to select an alternate route or take other appropriate action in response to a recurring condition.
- B. The DMS should be located sufficiently upstream of major diversion decision points, such as interchanges, to provide adequate distance over which travelers users can change lanes to reach one destination or the other.
- C. The DMS should not be located within an interchange except for toll plazas or managed lanes.
- D. The DMS should not be positioned at locations where the information load on drivers is already high because of guide signs and other types of information.
- E. The DMS should not be located in areas where drivers frequently perform lane-changing maneuvers in response to static guide sign information, or because of merging or weaving conditions.
910.3.2.7 Message Creation and Termination
Although it is desirable to post an incident message based on complete and perfect information, situations often occur when the operator has received only limited information on the incident from reliable sources, particularly in the early stages of the incident. In these situations, operators should determine if there is at least general information about the incident location and type. If so, the operator should post a message with the information available and be prepared to modify the message as soon as more detailed information is received.
Incident messages should be terminated when all lanes are open and all emergency responders have left the scene. In addition, incident clearance messages should be posted for a short time after the incident clears if congestion remains at the scene. Procedures for posting incident clearance messages are provided in EPG 910.3.2.11 Incident Clearance Messages.
Congestion often exists at the incident scene after the incident has cleared and the incident clearance message is terminated. In those cases, it is necessary to post congestion messages that include either travel time or congestion location information. Procedures for posting congestion messages are available.
910.3.2.8 DMS Capabilities and Message Formats
910.3.2.8.1 Design Characteristics of DMSs (MUTCD 2L.04)
Standard. Dynamic Message Signs shall be capable of displaying several messages in a sequence. Such messages shall be changed manually, by remote control or by automatic controls. DMSs shall display pertinent traffic operational and guidance information only. DMSs shall not include advertising, animation, rapid flashing, dissolving, exploding, scrolling or other dynamic elements.
Guidance. DMSs should be used as a supplement to and not as a substitute for conventional signs and markings.
DMSs should be limited to no more than three lines, with no more than 20 characters per line. The spacing between characters in a word should be between 25 to 40 percent of the letter height. The spacing between words in a message should be between 75 and 100 percent of the letter height. Spacing between the message lines should be between 50 and 75 percent of the letter height.
The first letter of every word in the message should be upper case. The minimum letter height should be 18 inches for DMSs on roadways with speed limits of 45 mph or higher. The minimum letter height should be 12 inches for DMSs on roadways with speed limits of less than 45 mph. The width-to-height ratio of the sign characters should be between 0.7 and 1.0. The stroke width-to-height ratio should be 0.2.
Standard. DMS shall automatically adjust their brightness under varying light conditions to maintain legibility.
Guidance. The luminance of DMSs should meet industry criteria for daytime and nighttime conditions. Luminance contrast should be between 8 and 12 for all conditions. Contrast orientation of DMSs should be positive, that is, with luminous characters on a dark or less luminous background. When displaying color messages avoid using full background color in nighttime conditions. Full background color at night can cause a washout effect of the text or other image being displayed.
Standard. The colors used for the legends and backgrounds on DMSs shall be as provided in Table 903.2.12.1 Common Uses of Sign Legend Colors and Table 903.2.12.2 Common Uses of Sign Background Colors.
910.3.2.8.2 Message Format
910.3.2.8.2.1 Message Length and Units of Information (MUTCD 2L.05)
Guidance. The maximum length of a message should be dictated by the number of units of information contained in the message, in addition to the size of the DMS. A unit of information, which is a single answer to a single question that a driver can use to make a decision, should not be more than four words.
Support. The maximum allowable number of units of information in a DMS message is based on the principles described in this section, the current highway operating speed, the legibility characteristics of the DMS and the lighting conditions.
Standard. Each message shall consist of no more than two phases. A phase shall consist of no more than three lines of text. Each phase shall be understood by itself regardless of the sequence in which it is read. Messages shall be centered within each line of legend. If more than one DMS is visible to travelers, then only one such sign shall display a sequential message at any given time.
Standard. Techniques of message display such as fading, rapid flashing, exploding, dissolving or moving messages shall not be used. The text of the message shall not scroll or travel horizontally or vertically across the face of the sign.
When designing and displaying messages on DMS, the following principles relative to the message should be used:
- A. The minimum time that an individual phase is displayed should be based on 1 second per word or 2 seconds per unit of information, whichever produces a lesser value. The display time for a phase should never be less than 2 seconds.
- B. The maximum cycle time of a two-phase message should be 8 seconds.
- C. The duration between the displays of the two phases should not exceed 0.3 seconds.
- D. No more than three units of information should be displayed on a phase of a message.
- E. No more than four units of information should be in a message when the traffic operating speeds are 35 mph or more.
- F. No more than five units of information should be in a message when the traffic operating speeds are less than 35 mph.
- G. Only one unit of information should appear on each line of the DMS.
- H. Compatible units of information should be displayed on the same message phase.
Guidance. Some DMS on the MoDOT system are capable of displaying multiple colors and graphics. There are limitations on what is acceptable to be displayed and limits on the size of the image (in terms of bytes).
The limit on the byte size the graphic cannot exceed is set by the National Transportation Communications of Intelligent Transportation System Protocol (NTCIP). The limit set by NTCIP is 64449 bytes for a single graphic.
To conform to these regulations and to remain consistent throughout the state there is a library of available graphics contained in the Advanced Transportation Management System (ATMS) software which may be used for certain messages. These graphics have been decided on by the Central Office Message Group and the TMCs. Any special requests may be directed to the State Highway Safety and Traffic Engineer.
When using graphics or color for a message, there are best practices that should be followed:
- Do no use graphics that have lettering smaller than 18”. Any lettering smaller than that cannot be read at fee flow speeds and will then be clutter on the sign.
- Avoid graphics that cover the entire sign. These large images take longer to push to a DMS and as previously mentioned there is a size limitation on the number of bytes allowed to be displayed according to NTCIP.
- Avoid using full background color in the nighttime conditions. Full background color at night can cause a washout effect of the text or other image being displayed. In addition, the sign will be appear too bright to the driver in dark conditions.
- Avoid text as part of the graphic. This allows a graphic to be more easily reused and the changes can be made in the text field.
- The use of color should be limited. Although the addition of color to a message can be very beneficial, if there is too much color used it can become distracting and unhelpful.
Option. A unit of information consisting of more than one word may be displayed on more than one line. An additional DMS at a downstream location may be used for the purpose of allowing the entire message to be read twice.
Guidance. If more than two phases would be needed to display the necessary information, additional DMS should be used to display this information as a series of two distinct, independent messages with a maximum of two phases at each location, in accordance with the provisions above. No more than two displays should be used within any message cycle, and each display should convey a single thought. The entire message cycle should be readable at least twice by drivers traveling at the posted speed, the off peak 85th percentile speed, or the operating speed.
When the message on a DMS includes an abbreviation, follow the provisions of Table 910.3.2.10.
910.3.2.8.2.2 General Principles
Guidance. DMS messages should present necessary information in the expected sequence that allows motorists to easily read, comprehend and rationally respond. Consistent formatting of the information enhances motorists’ expectations and reduces the time required to read and comprehend messages.
Messages should be provided to motorists that answer (MUTCD Table 2L-1):
- What happened?
- What is the effect on traffic?
- Who is the advisory for?
- What is advised?
The basic message format to answer these questions can be reduced to the following elements:
- Incident Descriptor informs the motorist of the problem (e.g., ACCIDENT, ROADWORK).
- Closure Descriptor is used in place of the Incident Descriptor when all lanes of the facility or exit ramp are closed (e.g., I-70 CLOSED, EXIT 225 CLOSED).
- Lanes Closed gives specific information about which lanes are closed (e.g., LEFT LANE CLOSED, 2 RIGHT LANES CLOSED).
- Target Audience is used when the Action Message applies to a specific group of motorists rather than all motorists passing the sign (e.g., TRUCKS, STADIUM TRAFFIC).
- Incident Location informs the motorist about the location of the problem (e.g., AT MAIN, PAST EXIT 15).
- Closure Location specifically states the location of the freeway closure and is used in place of the Incident Location (e.g., AT MAIN, AT EXIT 15).
- Effect on Travel informs the motorist of the severity of the problem in terms of delay or travel time and assists the motorist in making a decision whether to divert from the freeway or not (e.g., EXPECT DELAY, 30 MIN DELAY).
- Action message informs the motorist what to do (e.g., USE OTHER ROUTES, FOLLOW DETOUR).
Although all of these elements provide critical information for the motorist, it is usually not possible to provide them all on the same sign due to limited space. Therefore, consider tradeoffs to determine which elements are to be included and omitted for different situations.
The general DMS message format to be used statewide is as follows:
|Line 1||Incident Descriptor, Closure Descriptor, Lanes Closed or Target Audience|
|Line 2||Incident Location, Closure Location|
|Line 3||Lanes Closed (if not used in Line 1), Effect on Travel, Action|
Line 1 provides the information, intended to capture motorists’ attention, that they will soon be encountering a problem. Normally that information will be an Incident Descriptor or a Closure Descriptor and occasionally a Lanes Closed or Target Audience.
The Closure Descriptor should always be used on Line 1, in lieu of an Incident Descriptor, for road and exit closure incidents.
The Target Audience element should be on the first line if the message applies to a specific group of motorists passing the sign.
The Incident Descriptor should be omitted and replaced with the Lane Closed information on Line 1 if the Incident Descriptor cannot be identified (such as in the initial stages of the incident), if there are more important elements that need to be posted on the sign, or if messages need to be shortened to accommodate two-phase messages.
Line 2 provides location information for the incident or road closure. This location is provided in terms of the route and direction of the highway that the incident is on (if different than the road that the motorist is currently traveling on), the cross-street or highway closest to the incident (street/ highway name or exit number) and a preposition to describe the relative location of the incident to the cross-street/highway (BEFORE, AT or PAST). On the interstate corridors, mile markers are normally used for location descriptions rather than cross-streets or highways.
In determining whether to use street/highway names or exit numbers to describe incident or closure locations, street /highway names are normally more useful for motorists familiar with the area, and exit numbers are normally more useful for motorists, such as tourists, who are unfamiliar with the area. When signing for unfamiliar motorists in the Kansas City, St. Louis and Springfield metropolitan areas, the exit number of the closest cross-street/highway should be used to define the location rather than the mile marker of the incident.
When referring to interstates in the incident and closure locations, the prefix “I-” (e.g., I-70) should be used only if there is available space on the sign. Otherwise it should be omitted.
Line 3 provides specific information to the motorist about which lanes are closed (Lanes Closed) when this information has not already been placed on the first line, the severity of the incident in terms of delay or travel time (Effect on Travel), or what action the motorist is expected to take (Action Message).
The ONE LANE CLOSED message should only be used on DMSs where the lane closure is more than a mile downstream of the DMS. Using this general message rather than a specific lane closure message prevents motorists from making unnecessary early lane changes.
910.3.2.9 Acceptable Message Words and Terms
In determining the appropriate messages to post on DMSs, operators often have to choose words and terms for certain situations. To eliminate any confusion in the appropriate words and terms for these situations, the following list provides the acceptable words or terms to be used on DMSs on MoDOT-managed freeways and highways:
ACCIDENT vs. CRASH
The term CRASH is currently the preferred term used by representatives of the safety community, although it is not a common term used by the general public. No human factors studies have been conducted that have determined motorists’ understanding and response times to messages containing the term CRASH in comparison to messages containing the term ACCIDENT. Accordingly, it has been concluded that ACCIDENT is the term more generally recognized by motorists and should be used.
PAST vs. AFTER
Both terms are easily recognizable by motorists. The term PAST should be used because it is shorter and therefore takes less space.
EXIT vs. RAMP
The term EXIT should be used because it is generally better understood by motorists. RAMP is generally understood by motorists, but tends to have different shades of meaning for some motorists.
CLOSED vs. BLOCKED
BLOCKED indicates that an incident is affecting a lane or lanes and response personnel have not yet arrived while CLOSED indicates that response personnel have arrived and are directing traffic out of the affected lane or lanes. MoDOT primarily uses CLOSED, and it is considered to be the acceptable term.
Days of Week vs. Calendar Dates
When notifying motorists of future roadwork or events, Days of the Week (e.g., MONDAY, THURSDAY) should be used while Calendar Dates should never be used. Accordingly, notifications of such events should only be placed for up to a week in advance of the event.
910.3.2.10 Acceptable Abbreviations
Because DMSs have limited available space, it is often necessary for operators to abbreviate words to place the appropriate message. KC Scout and Gateway Guide staff should develop standard abbreviations for street and highway names used in the areas controlled by these TMCs. In the development of these abbreviations, expected recognition by travelers in the area should be the primary consideration.
Acceptable abbreviations for common words used on DMSs are summarized in Table 910.3.2.10.
Table 910.3.2.10 Acceptable DMS Abbreviations (MUTCD Table 1A-1 and Table 1A-2)
|Afternoon / Evening||PM||Monday||MON|
|Crossing (Other than rail-hwy)||Pounds||LBS|
|High Occupancy Vehicle||HOV||Telephone||PHONE|
|Left||LT||US Numbered Route||US|
|Miles per hour||MPH||West||W|
910.3.2.11 Incident Clearance Messages
An incident clearance message is posted on the DMS when the incident has been cleared, all lanes have been opened to traffic and some residual congestion remains upstream of the incident scene. The message is only posted for about five minutes, after which the message is terminated or a congestion message is placed. The purpose of the incident clearance message is to inform approaching motorists that all lanes are open at the incident scene, but some congestion upstream of the incident scene may still exist. The incident clearance message is not necessary if there is no residual upstream congestion when the incident clears.
910.3.2.12 Congestion Messages
Congestion is categorized as either recurring or non-recurring. Recurring congestion occurs at the same time and same location on a regular basis, usually because the traffic demand exceeds the roadway capacity at that location. Non-recurring congestion is congestion resulting from incidents, including special events, short-term roadwork or severe weather.
A congestion message is used to inform motorists that residual congestion still exists upstream of an incident after the incident clearance message has been terminated. Congestion messages can also be placed for recurring congestion when the congestion is more severe than normal, extends beyond the normal boundaries, or persists past the typical end of the peak period. Congestion messages should describe the limits of the congestion (e.g., METCALF to HOLMES) if the DMS is upstream of the congestion or the end of the congestion when the DMS is within the limits of congestion.
When congestion messages are posted on the rural corridor DMSs, it is critical that MoDOT field personnel provide KC Scout/ Gateway Guide operators timely updates on the congestion extent and limits. Updates should be provided at five- to ten-minute intervals.
When travel times are used and incorporated into the TMC software, as in the KC Scout and Gateway Guide TMCs, these travel time messages should be used in lieu of the congestion messages described above. These travel time messages provide valuable congestion information during incidents requiring two-phase messages and during other congested periods in both peak and non-peak periods. They also provide assurances to motorists when there is no congestion and the normal traffic conditions exist.
910.3.2.13 Weather Messages on Dynamic Message Signs
In addition to winter weather, travel conditions may also be impacted by other weather events such as thunderstorms, significant periods of rain, fog, or excessive wind. Severe weather is not usually considered to be an incident, but weather-related messages should be displayed for the conditions below. Other weather messages may be posted with the approval of the TMC supervisor.
- Roads are impassable due to flooding, snow, etc.
- Ice or black ice on a specific roadway segment
- Tornado sighted in area near roadway
- Low visibility due to fog in localized area
- Snow squall warnings from the National Weather Service
- High wind warnings from the National Weather Service
910.3.2.14 Use of One-Phase and Two-Phase Messages
Although operators should attempt to limit messages to a single phase, it is often necessary to use two phases to convey important information to motorists. When a two- phase message is warranted, it is critical to minimize the information on each phase to ensure that motorists will be able to read, comprehend and respond to both messages while driving at freeway speeds. The following situations will normally warrant the use of two-phase messages:
- Travel time messages are placed as the second phase to an incident message.
- Two downstream incidents are of equal priority as described in EPG 910.3.2.3 Message Priorities.
If two-phases are used, the following principles should be followed:
- Under no circumstances should more than two phases be used.
- Each phase should be understood by itself.
- Compatible units of information should be displayed on the same phase.
- Whenever possible, each phase should be limited to two lines. One way to reduce an incident message to two lines is to omit the Incident Descriptor on Line 1 and replace it with the Lanes Closed information.
- Each phase should be displayed for a minimum of three, and preferably four, seconds.
- Words or messages should never be flashed.
910.3.2.15 Child Abduction, Blue Alert and Ozone Alert Messages
If a child abduction occurs and it meets the local AMBER Plan Program’s criteria for triggering an alert, a child abduction alert (AMBER Alert) message should be displayed on all stationary DMS in the area of the abduction, but should not create adverse traffic impacts such as queues, unexpected slowing of traffic, etc. If a higher priority message is needed on a DMS, then a child abduction alert messages should be alternated with that message until the child abduction alert is cancelled.
The TMCs will be responsible for coordinating with local and state police, as well as media to determine the need for the AMBER Alert message.
- 1) The AMBER Alert Message is to remain on the DMS until:
- a) The AMBER Alert has been cancelled by the local agency or state police
- b) The TMC receives consensus from the local agency or state police to remove the message
- c) The child is recovered.
- 2) TMCs will evaluate the need for the message on the DMS every 6 hours based on information received from law enforcement and/or media.
Both KC Scout and Gateway Guide have agreements with local law enforcement officials to post child abduction alerts for abductions that meet minimum criteria. The model used by both TMCs is the national AMBER (America’s Missing Broadcast Emergency Response) Program. The AMBER Program in the St. Louis metropolitan area is referred to as the SARAA (St. Louis Area Regional Abduction Alerts) Program.
Based on their agreements with the local law enforcement agencies, KC Scout and Gateway Guide TMCs use different messages for their child abduction alerts. KC Scout posts specific information on the abduction on its DMSs, while Gateway Guide posts only general information and provides information on where to go to get specific information.
Child abduction alerts are posted on the rural corridor DMSs when the information from the KC Scout or Gateway Guide TMCs indicates that the abductor may be using one of the corridors or if local enforcement agencies on the corridors issue alerts for their local areas. If local alerts are issued, the messages to be posted should be coordinated with the local enforcement agency.
If a sworn law enforcement officer in the state of Missouri has been assaulted and suffered serious or fatal injuries and the Missouri State Highway Patrol’s (MSHP) criteria for a Blue Alert is met, MSHP may request a Blue Alert be displayed on DMS in the area of the incident. The TMCs will be responsible for coordinating with state police to determine the need for the Blue Alert message.
- 1) The Blue Alert Message is to remain on the DMS until:
- a) The Blue Alert has been cancelled by the state police
- b) The TMC receives consensus from the state police to remove the message
- 2) TMCs will evaluate the need for the message on the DMS every 6 hours based on information received from law enforcement.
Both metropolitan areas also have agreements with local agencies to place ozone alert messages when thresholds for the pollutant are exceeded. KC Scout has an agreement with the Mid-America Regional Council (MARC) and Gateway Guide has a similar agreement with Missouri Chapter of the American Lung Association.
In order to maintain the existing local agreements, these messages should continue to be used in the respective Kansas City and St. Louis metropolitan areas, and standard messages for these Alerts will not be developed.
910.3.2.16 Driver Safety Campaigns (MUTCD 2L.02)
MoDOT has developed an Electronic Message Boards Communications Plan to provide safety and public service information on all MoDOT DMSs. Details of the plan are provided to the TMCs on a monthly basis.
Guidance. When a DMS is used to display a safety or transportation-related message, the message should be simple, brief, legible and clear. A DMS should not be used to display a safety or transportation-related message if doing so would adversely affect the respect for the sign. “CONGESTION AHEAD” or other overly simplistic or vague messages should not be displayed alone. These messages should be supplemented with a message on the location or distance to the congestion or incident, how much delay is expected, alternative route or other similar messages.
Standard. When a DMS is used to display a safety, transportation-related, emergency homeland security, or Blue or AMBER alert messages, the display format shall not be of a type that could be considered similar to advertising displays.
Develop informative messages that can be used on a regular basis to provide pertinent information and reminders to travelers.
The safety messages will provide variety and guard against message boredom. Higher priority messages, as provided in EPG 910.3.2.3 Message Priorities, will always override the general messages. Special messages will be placed on the DMSs as needed. Traffic staff will regularly monitor the DMS usage.
910.3.2.17 On-Site Control of Changeable Message Signs
Portable Changeable Message Signs (CMSs) are normally used by MoDOT personnel or contractors to post information regarding construction or maintenance projects. To the maximum extent practicable, CMS messages should follow the provisions of EPG 616.6.60 Changeable Message Signs (CMSs).
Particularly in the Kansas City and St. Louis metropolitan areas, CMSs can be used to supplement the messages posted on the KC Scout and Gateway Guide DMSs. If these CMSs are to be useful in supplementing messages on DMSs, close coordination is needed between the TMC operators and those responsible for operating the CMSs to ensure that the DMSs and CMSs are not located too closely together and that that the messages don’t conflict.