Freeway Management and Operations Handbook
Chapter 13 – Information
|Ramp Management and Control (Chapter 7)
Lane Management and Control (Chapter 8)
|For both ramp and lane management control, including construction and maintenance activities, it is important to convey the ramp or lane control conditions to the motorists. Devices typically attributed to traveler information, namely the changeable message sign (e.g., overhead lane control sign for lane management, portable CMS for construction), are used.
|Traffic Incident Management (Chapter 10)
Planned Special Event Management and Control (Chapter 11)
Emergency & Evacuation Management (Chapter 12)
|Critical to the success of these management strategies in conveying real-time conditions to the pre-trip and en-route travelers. In the case of Planned Special Event Management, conveying future conditions, both known and predicted, such as a lane or road closures, is vital.
|Traffic Management Centers (Chapter 14)
|Most Traffic Management Centers house the central systems that process information, and control and manage the dissemination.
|Surveillance and Detection (Chapter 15)
|The surveillance subsystem provides much of the information that is disseminated to travelers.
|Regional Integration (Chapter 16)
|Information is shared across jurisdictional boundaries and information conveyed to the traveler can be "regional" in nature, (i.e., the effected area may not be in the local control area of the system, but may still effect local travelers.)
The key to successful driving task performance is efficient information gathering and processing (2). Likewise, properly communicating with motorists is critical to successful freeway traffic management and operations. Motorists rely on a wide variety of information to properly accomplish the control, guidance, and navigational aspects of the driving task. The roadway alignment and general terrain itself provides a great deal of this information through visual "cues;" sources such as pavement markings and regulatory, warning, and guide signs also contribute greatly to the overall information system. However, in an effective freeway management system, dynamic methods of conveying information to motorists or travelers are often needed to better operate and control the system.
Information dissemination is also managed in order to improve travel conditions in the corridor by influencing traveler behavior (by recommending diversion routes around an incident, for example). This information can be disseminated from a variety of sources (State departments of transportation, transit agencies, private-sector information service providers, etc.) using a variety of methods (changeable message signs, commercial radio traffic reports, traffic information kiosks, internet, etc.).
Traveler information can be categorized as either pre-trip or en-route.
Traveler information, pre-trip and en-route, can be categorized as either static or dynamic in nature. Static information can be defined as known or planned events, while real-time information can be defined as the most current available information at a given point in time. Real-time information differs from static information in that it continually changes based upon a wide variety of events.
Regardless of how it is provided, to be effective traveler information must be timely, complete, accurate, credible, available on demand, and perceived by the individual traveler as being relevant to their needs and providing a value when followed; otherwise, the information will be ignored. In general, for each inaccurate piece of information promulgated by the traveler interface elements, it will take numerous occurrences of accurate information to recapture the traveler's faith in the system.
The dissemination of traveler information allows travelers to effectively plan their trip prior to departure; and when en-route, to avoid congestion and problems. Motorists and transit riders want to know their choices and know what to expect – such knowledge being a key attribute of "mobility". Having accurate and real time information about the performance of the surface transportation network significantly improves the perception of a trip because this information allows travelers to make decisions that give them the sense of having more control over their life. Such knowledge not only gives the traveler better options; it removes a significant stress point, the unknown.
An ATIS case study and survey in Washington D.C. (3) indicates that that the vast majority of current ATIS users are satisfied consumers who feel they save time by utilizing these services on a regular basis. The research suggests that ATIS users do realize significant benefits in terms of time management – better on-time reliability, reduced early and late schedule delay, as well as more predictable travel. They do this, however, without significantly reducing the amount of in-vehicle travel time accumulated over a month or year of regular trip making. Overall, ATIS use proved advantageous in efficiently managing the traveler's time. Specific quantitative examples selected from the Washington DC case study include:
The dissemination of traveler information for a freeway management system (or a regional Integrated Traffic Management System (ITMS) that incorporates the freeway network) is an integral part of operating and managing the freeway. As such, it must be a key consideration in every aspect of developing the freeway management program, including the activities noted below (referring to Figure 3-1 from Chapter 3).
The information needs of travelers extend well beyond an agency's freeway infrastructure, and include other jurisdictions' freeways, the arterial network, transit facilities, airports, etc. The traveler information stakeholders must include all of these concerns. Moreover, as discussed in Section 13.3 herein, the private sector will also be an active partner in the traveler information process, and must be included as a stakeholder.
Because information dissemination must be coordinated among the various partners, a portion of the plan should be devoted to a discussion of the management structure and the agreements that will be utilized to achieve this coordination. Items to be included in this portion of the plan include:
Additional details may need to be included in the letter of agreement if some of the partners will jointly operate some of the information dissemination technologies to be implemented. For example, a transportation agency may wish to allow law enforcement personnel to access and utilize their changeable message signs or highway advisory radio equipment for managing major incidents during late-night hours when the transportation agency does not have someone on duty.
In order to assess the extent to which information dissemination efforts within a freeway management system are meeting goals and objectives, a set of performance criteria and measures-of-effectiveness pertaining to these efforts must be identified. With respect to information dissemination, performance criteria have several different, yet interrelated, dimensions that are of interest, including:
It is important to recognize that because of the complex travel patterns of travelers at any point in the roadway, it may not be possible to adequately measure the overall effects of many types of information or dissemination modes upon traffic volumes, speeds, or delays. The day-to-day variances in travel patterns themselves may mask the effects of any information disseminated during a specific event such as an incident, particularly if the information is intended for a very specific audience (such as vehicles within a freeway traffic stream destined for a specific downstream exit).
Care should be taken not to overestimate the benefits achieved by the implementation of information dissemination components in a freeway management program. Specifically, it is important to recognize that travel patterns in a freeway corridor are quite dynamic, and that some drivers will divert naturally when they encounter freeway congestion regardless of whether or not they receive information beforehand about that congestion.
It is also important to utilize the appropriate evaluation methodology. As noted in the aforementioned Washington D.C ATIS study (3), "if ATIS deployments are evaluated purely on time-savings, the benefits of ATIS will likely be grossly underestimated. ATIS users value improved travel reliability. The value of improved on-time reliability is not easily nor directly translated to purely monetary terms, but it is clear that many types of travelers can benefit from ATIS. Trucks delivering auto parts in a just-in-time manufacturing process may highly value any improvement in on-time reliability or reduction in early schedule delay. Commuters face an on-time requirement not only on the home-to-work leg of their daily trip making, but increasingly on the work-to-home return trip in order to meet daycare pickup requirements and other commitments. Improved reliability and predictability of travel are also likely good surrogates for reduced commuter stress. From this common sense perspective, it is clear that the benefit of improved travel reliability and predictability from ATIS will outweigh whatever small return is generated from the monetary equivalents of aggregate travel time reductions".
As indicated in Chapter 3, the National ITS Architecture provides a common structure or framework to promote compatibility and interoperability among systems, products, and services. The architecture defines the functions that must be performed to implement a given service, the physical entities or subsystems where these functions reside (e.g., the roadside or the vehicle), the interfaces / information flows among the physical subsystems, and the communication requirements for the information flows.
The National ITS Architecture can serve as the basic building block of the functional requirements definition process for detection and surveillance. The functions described in the National Architecture must then be detailed to match the needs and desires of the local agencies. The National ITS Architecture defines various ITS elements and strategies in terms of market packages. This concept recognizes that various ITS components must work together to achieve system goals. They are "tailored to fit separately or in combination-real world transportation problems." The National ITS Architecture defines a number of Market Packages associated with traveler information. Those most relevant to freeway operations and management include:
Other traveler information market packages include "Interactive Traveler Information", "Autonomous Route Guidance", "Dynamic Route Guidance", and ISP-Based Route Guidance, as defined in Reference 19. It is also noted that the draft Version 5 of the National ITS Architecture includes new market packages relevant to traveler information during emergencies – Wide Area Alert (which includes "Amber Alerts") and Disaster Traveler Information.
Information dissemination components of a freeway management system can range from a single device owned and operated by one agency, to an integrated collection of devices and mechanisms under the control of several agencies and several private sector entities. In this Handbook, a basic distinction is made between kinds of information dissemination technologies depending on which of three main locations it comes from:
Specific technologies are discussed below.
One of the most fundamental technologies available for disseminating traffic-related information from the roadside is that of changeable message signs (CMS). CMSs are sometimes (and interchangeably) referred to as dynamic message signs (DMS) or variable message signs (VMS). The term "DMS" is generally used within the context of the National ITS Architecture (19) and the associated standards. "CMS" is the term used in the MUTCD (Reference 21); and is also the terminology most widely used in this Handbook.
CMSs are programmable traffic control devices that can usually display any combination of characters to present messages to motorists. These signs are either permanently installed above or on the side of the roadway, or portable devices attached to a trailer or mounted directly on a truck and driven to a desired location. Portable CMSs are much smaller than permanent CMSs and are oftentimes used in highway work zones, when major crashes or natural disasters occur, or for special events (e.g., sport events) and emergency situations.
When installed, CMSs become a part of the total motorist information system. Thus the information presented on CMSs and the placement of the signs must be consistent and compatible with static signs used on the freeway. Highway signs – both static and changeable – must project a message so that the driver can:
And if necessary:
Section 2A.07 of the Manual on Uniform Traffic Control Devices (MUTCD – Reference 21) defines CMS as "traffic control devices", and requires that a CMS shall conform to the principles established in the MUTCD related to the use of signs within the right-of-way of all classes of public highways, and to the extent practical, the design and applications prescribed in Sections 6F.02 and 6F.52. Section 2E.21 of the MUTCD specifies that "Changeable message signs shall display pertinent traffic operational and guidance information only, not advertising." (Note: At the time of preparing this Handbook, a new part / chapter on changeable message signs is being developed for the MUTCD, and will be included in the next update.)
CMSs perform a critical role on freeways. Such signs can furnish motorists with real-time information that advises them of a problem and in some cases, a suggested course of action. CMSs are also used to improve motorist safety and reduce traffic congestion and delay. CMSs can be used to manage traffic by displaying the following types of messages: (5)
Table 13-2 lists the applications for which CMSs can be used. (6)
|Traffic management and diversion
|Warning of adverse conditions
|Control at crossings
|Control during construction and maintenance operations
|Special-use lane and roadway control
For the purpose of this Handbook, Changeable message signs have been classified into two categories, namely: those that have a fixed number of messages available for display; and those that essentially have an unlimited message capability (References 4, 5, 6).
Signs with a fixed number of messages (Figure 13-2) include the following:
The stacked design has reported drawbacks, in that emitted light will be diffused as it passes through the overlayed neon tubing, reducing its legibility. Conversely, the separate message design will require a fairly large sign face in order to display even a moderate number of messages.
These CMSs display characters and symbols in a matrix format, which are generally designed in the following three patterns (7):
It should be noted that although line matrix and full matrix CMSs provide flexibility in displaying different characters and symbols varying in sizes, it has been shown that in many cases, fewer characters can be displayed on a line of continuous matrix or full matrix CMS than can be displayed on a line with character matrix because of the width required for proportional characters.
Matrix technologies include the following:
The most critical locations for installing permanent CMSs are in advance of interchanges or highways where drivers have the opportunity to take some action in response to messages displayed on CMSs. A CMS should not compete with existing roadway signs. At times, relocation of some static signs may be required in order to install a CMS at a critical location. In general, a CMS should be permanently installed at the following locations: (4, 7)
The ease with which a sign can be detected in the environment (conspicuity) and the ease with which the message can be read (legibility) will enhance the effectiveness of motorists' visibility of the CMS and its message. In addition, the manner in which the message is displayed must be considered (e.g., if the message is too luminous, it can be easily detected but difficult to read because of glare.) Factors that affect the legibility of light-emitting CMSs include the character height; font style; character width (spacing and size of pixels); spacing of characters, words and lines; size of sign borders; and contrast ratio. (7)
The CMS designer and operator need to know about the actual site characteristics in the vicinity of the CMS. These characteristics dictate the amount of information that can be displayed. Among the items of interest are the following: (5)
Other design considerations include: sign size (which affects message length as well as support structure requirements), maintenance access (e.g., walk-in housings, front access), technology, viewing angle and distance, character size, and sign position relative to sun during various times of day and days of the year.
As discussed later, the maximum length of a message that should be displayed is primarily dictated by the amount of information drivers can read and comprehend during the period when they are within the legibility distance of the CMS. The maximum length of a CMS message is also controlled by the characteristics of the sign. These include the type of sign (LED, fiberoptic, etc.), the number of lines available, and the number of characters on each line. Each of these characteristics can have an effect on how far away the CMS can be read and, consequently, how much information can be presented to motorists. It should be the responsibility of the TMC manager/supervisor to assess the CMS characteristics and determine the maximum length of message to display.
Too often agencies will purchase CMSs before signing objectives and messages are determined. Often, this causes disappointment in the CMSs when these agencies cannot display the desired messages, or when the signs provide lower than expected target value and legibility for the environmental conditions present at the site. (4) Conversely, agencies may end up purchasing a more expensive CMS with capabilities that exceed their actual needs. (Additional information on developing CMS messages is provided in Section 13.3)
The use of trailer-mounted CMS provides an agency with a great deal of flexibility. The signs, which are typically much smaller than permanent, over-the-road CMSs, are used most commonly for temporary applications, such maintenance and construction activities. They are usually diesel- or solar-powered and use wireless (cellular) communications to a central management point, making them a very attractive and flexible tool.
Portable changeable message signs are usually located at the side of the road, and do not sit as high as an overhead sign, which can impair drivers visibility. Most are 3-line, 8 or 9-character signs, and although most have the capability of displaying multiple phases, they tend to be used with simple short messages to allow drivers to read and comprehend the message. The MUTCD states that no more than two phases shall be used to display a message. These signs use all of the aforementioned technologies. Figure 13-4 shows a portable CMS in a work zone.
The U.S. DOT strongly encourages state and local agencies to use DMS standards (Note: As previously noted, when describing standards and other attributes of the National ITS Architecture, the term "DMS" is typically used.). DMS standards are mature, they have undergone significant testing, and they offer immediate benefits for agencies by 1) providing interoperability between DMS and other NTCIP-compatible field devices running on common communications channels, and 2) enabling simplified administration of DMS subsystems, leading to easier overall administration. (8)
As of the time of writing this Handbook, the DMS NTCIP working group is drafting Version 2 of NTCIP 1203, Object Definitions for Changeable Message Signs. Version 2 represents a major upgrade in the functionality of the DMS standard. NTCIP 1203 allows integration of DMS devices and products from multiple manufacturers into a single system using standard communications and data. Version 2 adds features such as graphics and device status reports. This version also restructures the standard to make it easier for end users to specify product attributes and/or capabilities. A major benefit of Version 2 for end users concerns customization. Version 2 adds features and functions, such as color, that could be obtained previously only by deviating from the standard through customization.
The "Specification Guide for Procurement of NTCIP-compliant Dynamic Message Signs" (Reference 9) is a tool by which practitioners may develop a meaningful NTCIP procurement specification to purchase interoperable and interchangeable DMS. As a rule, the document does not require specific features; rather it defines how the user may include such requirements within a specification. For example, the sample wording in reference indicates how one would specify how many messages the sign should store, but does not specify a quantity as that is a project-specific decision. It is emphasized that reference is "not intended to be an educational tool explaining the concept of operation for DMS"; rather it assumes the reader / specification writer has an understanding of DMS functions and technologies.