Dynamic message signs (DMS) are integral to traffic management systems. These real-time traveler information signs display messages that advise drivers of traffic warnings, regulations, routing, and management.
DMS messages should be legible from a distance of 1/2 mile in the daytime and nighttime conditions. They should not contain fading, rapid flashing, dissolving, or moving elements.
Messages
Messages on dynamic message signs (DMS) can inform drivers of road conditions, incidents, closures, or traffic events. They can also display travel times, alternate routes, and work zone information. These signs can be either permanent or portable and use a variety of technologies, such as flip panels and multiple lights to display messages. The message content on DMSs is designed to command attention, whether the messages are warnings about congestion, construction, or speed restrictions. The DOT’s Dynamic Message Sign Message Design and Display Manual provides guidance for developing effective messages for DMSs.
DMS messages should be brief, legible, and clear. The messages should provide an overview of the incident or event that is occurring, such as how much delay to expect and what actions motorists can take. It is important to avoid overly simplistic or vague messages that may not command the attention of travelers. For example, a message such as “CONGESTION AHEAD” is an overly simplistic and unclear message. It should be supplemented with a message that includes the location or distance of the congestion or incident, how much delay is expected, and an alternative route to follow.
The brightness of DMSs should be consistent with the luminance requirements of the system for daytime and nighttime conditions. A contrast ratio 8:1 is recommended for text and backgrounds, with luminous characters on a dark background. It is important to limit the use of color messages on DMSs because too much color can be distracting. It is also important to note that a DMS should not flash messages.
Dynamic message signs can help reduce the number of crashes and congestion by alerting motorists to unique driving conditions that require special caution. The messaging is based on data from a sensor network that gathers real-time traffic and roadway conditions. The messages are displayed on digital signs and mobile units that transmit the message to a traffic management center.
DOTs often decide to install DMSs for safety reasons or to improve traffic flow, even though the initial cost of these signs is higher than that of conventional static signs. However, it is important for DOTs to consider the total operating costs of DMSs, including maintenance and operation fees and energy usage.
Controls
Dynamic message signs (DMS) and lane change signs (LCS) are part of the Intelligent Transportation Systems that help drivers stay informed of traffic conditions. These dynamic signs can be permanent or portable and can be operated by traffic management centers (TMCs). They can display a variety of messages relating to road construction, incidents, congestion, and other useful travel information. However, few studies have been conducted on the impact of these dynamic messages on driver behavior.
Depending on the traffic condition and visibility, adjusting the display settings on the DMS may be necessary. For example, when driving in fog or rain, the messages displayed on the sign should be clearer than when the road is dry and bright. These conditions require the use of a higher letter size, a longer message duration, and a shorter text-to-letter ratio.
These changes are designed to allow motorists to read the message and make quick decisions on what to do. The message should not be so long that it requires a significant reduction in speed, which can cause traffic flow problems. A lower letter height can also reduce the number of characters displayed, making it easier for motorists to read the message and avoid a slowdown or sudden drop in speed.
In addition, the message should not include any distracting elements that will detract from the effectiveness of the warning. For instance, the message should not include any animated elements such as fading, rapid flashing, or dissolving text. These techniques may annoy and confuse the motorist and should be avoided.
The optimum number of units that a DMS should display is not known, and it depends on the type of traffic condition or traffic condition warning needed. Rama and Kulmala [14] conducted a field experiment in Finland to determine the effects of two different types of DMS on driver behavior by performing before-and-after experiments in slippery road conditions at three sites. They found that the most effective DMSs were those that indicated a reduced maximum driving speed or a minimum headway between vehicles.
Another study analyzed the impact of DMSs on driver speeding behaviors using a medium-fidelity driving simulator. It compared six scenarios featuring DMSs displaying interchangeable 2-7 units of information on a 155-mi2 virtual road network. A total of 296 simulation sessions were conducted, involving 65 participants from diverse socio-demographic backgrounds.
Power
Dynamic message signs (DMS) display pertinent roadside information and warnings to en-route motorists, improving overall freeway traffic flow and commuter safety. These signs can provide valuable real-time information about the status of roadways and incidents in work zones. They can also help drivers make informed decisions that could lead to safer or shorter travel times. DMSs are commonly seen on state highways, though local transportation agencies use them as well.
DMSs are powered by electricity and are able to display text, graphics, or video. The type of display depends on the message and system requirements. Some signs can be driven by a central computer or control panel, while others are stand-alone devices that display information and respond to signals from the roadside. Some DMSs can even interact with other devices on the roadway, such as sensors and cameras.
The major requirement of DMSs is good legibility throughout the required viewing range. This is defined by the main optical parameters – contrast ratio and luminance. The LEDs should be bright enough without consuming too much power for maximum legibility. This reduces energy consumption and dissipates less heat, increasing the sign’s lifespan.
Another important consideration when choosing a DMS is the light pollution it causes. For optimal performance, the light-emitting diodes (LEDs) of a DMS should be designed to comply with both the NEMA and EN12966 standards. These standards ensure that the color coordinates of the primary colors are matched and do not produce unwanted colors due to chromatic aberration. Additionally, the light output should be consistent and not flicker.
When deciding on a DMS, comparing its initial cost to the total cost of ownership and operation fees is crucial. It is also important to consider the amount of data the sign can display. A full matrix DMS is usually more expensive than a blank-out sign.
Another important consideration is the maintenance costs of a DMS versus a BOS. A DMS requires more frequent servicing than a BOS, which has fewer moving parts. In addition, a DMS uses more electricity than a BOS, which can result in higher utility bills.
Maintenance
As with any traffic device, a dynamic message sign’s legibility is crucial for motorists’ safety. In harsh roadside conditions, sunlight, precipitation, and other elements can destroy a sign’s display, making the message difficult for drivers to read. Skyline has invested years in design research and engineering to produce the industry’s most legible message signs – built using extreme standards to withstand harsh roadside environments.
DMSs (both permanent and portable) post information on incidents, traffic congestion, lane closures, road construction, or other factors affecting travel conditions. In addition, they can also be used to supplement messages posted on changeable message signs (CMSs). Ideally, the CMSs should not be located too close to the DMSs so that the two don’t conflict with each other.
The visibility of messages on a dynamic message sign depends on their contrast ratio and luminance. Contrast ratio is the ability of a sign to distinguish one color from another under varying lighting conditions, while luminance is the amount of light required to illuminate a sign to a standard level of legibility. Skyline’s DMSs are designed to meet strict European EN12966 and NEMA TS-4 luminance requirements and are tested under a variety of weather conditions.
In addition to ensuring that messages are clearly legible under all conditions, the durability of a DMS is an important factor in its longevity and cost of ownership. Skyline’s DMSs are engineered to withstand harsh roadside environments and are built with military-grade specifications and materials for the ultimate in ruggedness and reliability.
DOTs are increasingly looking for ways to improve their lane management programs. Typically, these involve closing or opening lanes at different times of day to reduce traffic congestion and commuter travel time. Traditionally, DOTs have used large, expensive dynamic message signs to display these types of messages. However, newer research shows that smaller NTCIP-compliant Dynamic Message signs can provide the same information at a much more economical price.
The benefits of this approach are substantial. By replacing electromechanical ‘flip-disc’ messaging signs with modern electronic LED-based units, states can save on maintenance and energy costs while increasing the efficiency of their traffic operations. In fact, several US states have already achieved more than $1.75 million in savings by adopting this approach.
