Travel Time on Arterials and Rural Highways: State-of-the-Practice Synthesis on Rural Data Collection Technology
1.1 Background and Objectives
Travel time to a destination is a key piece of information that motorists want and need. It is vital in travelers making good decisions about which route to take and whether to divert from their planned path. If motorists were to be provided travel time information on rural highways, they may plan their trips accordingly with this new information, decreasing delays and the potential for congestion downstream. They may also be warned in advance of an incident, allowing sufficient time to choose an alternate route around congestion and delays.
Technology now makes it feasible to provide drivers with real time information about how long it will take to reach a given destination. Many jurisdictions within the United States collect information on freeways and that information is generally provided to travelers via DMS along freeways. In contrast, cases where the information is collected and displayed on non-freeway roads such as rural highways are relatively rare. Figure 1 shows examples of typical practice.
Travel time is also a key piece of information for transportation agencies. Real-time travel time information can allow agencies to monitor roadway performance, identify problems, develop forecasts, plan future projects, and evaluate the effects of new projects. Travel time data can also help to meet goals for integrated corridor management or meet Federal information provision mandates such as the Real-Time System Management Information Program, which was included in Section 1201 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU).
Current use of travel times for rural highways is still limited. However, interest is high and examples of successful implementations are becoming increasingly common. Researchers are investigating a variety of data collection methods that can be applied to rural highway settings, such as the use of Bluetooth detection technology (e.g., Hardigree, 2011; Puckett & Vickich, 2010), toll tag readers (e.g., Wright and Dahlgren, 2001), automatic license plate readers (e.g., Eberline, 2008), in-pavement magnetic detection (e.g., Klein, Mills, & Gibson, 2006), machine vision, radar/microwave/LIDAR (e.g., Jeng, 2010), crowdsourcing (e.g., INRIX, 2012), CV, cell phone signal monitoring (e.g., Avni, 2007), and inductive loop detectors (e.g., Blokpoel, 2009). As this list demonstrates, there is a litany of data collection technologies which have been used for rural highway travel times, but each has its own advantages and disadvantages. At this point there is no comprehensive guidance on data collection technologies and procedures.
Figure 1. RTT Signs in Washington State and Minnesota
There are numerous reviews and syntheses of travel time data collection in general. But, travel time data collection and dissemination for rural highways has unique challenges for the practitioner.
To further hone the opportunity of providing useful and accurate travel time information in rural highway locations, it is important to ask the following questions:
The purpose of this project and the resulting report was to identify, review, and synthesize information on current and potential future efforts in real-time travel time on rural highways. There were four main objectives: a) identifying, reviewing, and synthesizing available and emerging technology (both nationally and internationally) for obtaining data necessary for calculating travel times on rural highways; b) collecting and summarizing agencies' experiences with using such technology; c) providing guidance to agencies for making the best use of available and emerging technologies to meet future needs; and d) determining the feasibility of deploying such technologies.
The first objective (reviewing) is dealt with while being mindful of the ever-changing nature of recent technological advances. Unlike synthesis reports in non-technological domains that focus on research publications, many of the sources for this report were from vendors, State agencies, and practitioners who are the most up-to-date on the rapidly changing technological developments and implementation approaches.
The second objective (experiences) is addressed by incorporating lessons learned and advice (including from unsuccessful projects) from agencies' experiences using a given technological approach.
These lessons give extremely helpful insights that can be provided to the practitioner and allow the current synthesis to go beyond a simple summary of documents.
The third objective (guidance) is based on a synthesis of the first two, taking information gained from reviewing technologies and merging it with real-world experiences of practitioners. This led to the development of lists of considerations in the form of questions (and high level guidance in response) that a practitioner should use when going through the phases of assessing, planning, selecting, acquiring, implementing, managing, and evaluating a rural highway travel time system.
The final objective (feasibility assessment) was not a formal financial feasibility analysis. Instead, feasibility is taken in a broader context and refers to environmental constraints that a practitioner should take into consideration when weighing what type of system to implement. Financial information is given where available, but only in the context of background information to use when evaluating the entire practicality of an implementation approach.
The primary audience for this report is transportation agencies who are either interested in implementing a rural highway travel time data collection system, or considering making changes to an existing system. It is important to obtain, synthesize, and distribute information now so that objectively based recommendations can be provided to practitioners as they design and implement such systems.
It should be noted that the current report focuses on rural highway travel time data technology considerations and is not a primer for general travel time best practices. A good source of general travel time guidelines can be found in Turner, Eisele, Benz, & Douglas (1998). This report also focuses on travel time data collection methods that use vehicle speeds or link travel times as data sources. Efforts to estimate travel times using other data sources (e.g., traffic volumes) such as the Minnesota Arterial Travel Time Project (Athey Creek Consultants, 2009) are not addressed. In addition, there is a separate report from this project that focuses on travel time data collection technology used for arterial highways (Singer, Robinson, Krueger, Atkinson, & Myers, 2013).
The information search for this project involved two main components: the review of data collection technology and the review of practice. The search effort began with an organized set of keyword searches. Five search categories were created to encompass the key project dimensions. Using these categories, a list of search terms was compiled within each category (see Table 2). As an example, the search terms "Bluetooth" and "GPS" were both placed in the Specific Technologies category. The table below shows the initial set of search terms used within each category. Additional search terms were added for follow-up searches. Note that an asterisk represents a "wildcard" character.
The keyword search effort revealed relatively little information on RTT implementations and evaluations. The search effort then expanded to include targeted searches to explore the state of the art technologies and practices used for RTT. This search revealed a rapidly expanding world of data collection technologies and practices.
Finally, contacts with experts and implementers were made to gain a clearer understanding of current and emerging practice and to acquire additional details and direct experience reports. Two general approaches were used: 1) contacts with heads of committees and professional organizations, and 2) contacts made directly with travel time system implementers to learn about relevant implementation details. Individuals and organizations were selected for contact based on knowledge gaps that they were expected to be able to fill and their involvement in travel time programs of interest. Contacts with implementers provided a basis for implementation summaries and case studies with emphasis on explaining project logistics, decision making processes, and lessons learned. Organizational contacts provided little new information about current practice; many implementations of RTT have not been widely publicized and do not appear to be widely known among transportation engineers.
1.3 Organization of Synthesis Report
The following chapters of this report are organized around three main topics of interest to practitioners:
United States Department of Transportation - Federal Highway Administration