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21st Century Operations Using 21st Century Technologies

Travel Time on Arterials and Rural Highways: State-of-the-Practice Synthesis on Arterial Data Collection Technology

1. Introduction

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 arterial 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 arterials are relatively rare. Figure 1 shows examples of typical arterial practice.

Figure 1. ATT Signs in Chandler, Arizona

A busy arterial road with a travel time information sign mounted on an overhead gantry above the roadway indicating travel time to a significant point on the route.
Source: City of Chandler & Oz Engineering, 2011
A roadway sign indicating the travel time for the location printed on the sign.
Source: Video capture from Wimmer, 2010 on ksl.com

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 arterials 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 arterial 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 ATT, but each has its own advantages and disadvantages. At this point there is no comprehensive guidance on data collection technologies and procedures.

There are numerous reviews and syntheses of travel time data collection in general. But, travel time data collection and dissemination for arterial highways has unique challenges for the practitioner.

For example:

  • Travel times are not collected in isolation, and often the uses are determined by the goals and communication needs at a location—and these can be quite different for and between arterials.
  • Arterial roadways can vary greatly in their location and use: urban arterials often parallel major freeways in more densely populated areas while rural arterials often act as major alternates through less densely populated areas.
  • Although the access to technologies may be similar to freeways, arterials present unique issues such as signal timing disruptions, dropping out of the route at various points such as parking lots, side streets, etc.

The TMC Pooled Fund Study has recognized the need to determine if technologies are being developed to obtain data necessary for calculating travel times that address specific challenges. State and local agencies face the challenge of providing real-time travel time to motorists—which entails obtaining information on arterials—in a manner that allows drivers to take full advantage of it.

To further hone the opportunity of providing useful and accurate travel time information in arterial locations, it is important to ask the following questions:

  1. What insights and experiences have agencies developed with these technologies, and what are the best uses of these technologies?
  2. Given challenges faced in calculating and providing travel time information on arterial highways, how feasible is deploying such technology?

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 arterials. 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 arterials; 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 an ATT 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 an ATT 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 ATT 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 rural highways.

1.2 Methodology

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).

Table 2. Table of Search Terms and Categories
Travel time Data/data collection Arterial RFID Network

Travel time

Journey time

Traveler information

Monitor*

Real-time

Calculat*

Estimat*

Technology

Infrastructure

Communicat*

Instrument(ation)

Hardware

Intelligent Transportation System (ITS)

Software

Install

Collect

Wireless

Off-freeway

En-route

Freeway approach

On-ramp

Surface street

Remote

Stand-alone

Connected vehicle

Video/camera

Satellite

License plate reader

Bluetooth

GPS

Cellular/cell phone

In-pavement/loop detect*

Radar

LIDAR

Anonymous Wireless Address Matching/AWAM

Guidelines

Best practices

Operations

Implement(ation)

Traffic

Accuracy

Cost

* Indicates wildcard character

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 a substantial body of literature on data collection technologies and numerous evaluations of ATT systems, often comparing novel ATT data collection approaches against other data collection approaches or ground truth data.

The search effort then expanded to include targeted searches to explore the state of the art technologies and practices used for ATT. 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 ATT 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:

Chapter 2 discusses available and emerging RTT data sources as well as implementation considerations, advantages, and limitations of each.

Chapter 3 provides two detailed case studies and additional brief summaries of select practices in RTT data collection. These summaries reflect a broad range of implementation objectives, strategies, technologies, and constraints.

Chapter 4 brings together what we know about data sources, technologies, and current implementations to develop a set of best practices that are based on systematic evaluation, where possible, and real-world experiences. Rather than prescriptive guidance, this chapter emphasizes identifying options and practices that can be adapted to the needs of a particular situation. It is framed around questions that a practitioner can ask as he or she goes through the stages of developing and implementing an RTT data collection system.

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