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

Executive Summary

Travel time to a destination is a key piece of information that motorists want and need. It is vital for travelers to make good decisions about which route to take and whether to divert from their planned path. Technology now makes it feasible to provide drivers with real-time information about how long it will take to reach a given destination. While travel time information has traditionally been provided by transportation agencies only on major urban freeways, travel time messages are now being communicated on arterial roadways.

The collection of travel time data and proper dissemination is a challenging problem that deserves a systematic review. The purpose of this project 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:

• Identifying, reviewing, and synthesizing available and emerging technology (both nationally and internationally) for obtaining data necessary for calculating travel times on arterials
• Collecting and summarizing agencies' experiences with using such technology
• Providing guidance to agencies for making the best use of available and emerging technologies to meet future needs
• Determining the feasibility of deploying such technologies.

It should be noted that the current report focuses on arterial travel time (ATT) data technology considerations. It 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. A more recent set of guidelines has been developed based on the experiences of the I-95 Corridor Coalition Vehicle Probe Project (University of Maryland Center for Advanced Transportation Technology, 2011).

The Transportation Management Center (TMC) Pooled Fund Study recognized the need to collect travel time data on arterial roads, knowing that it must first be determined if technologies are being developed to obtain data necessary for calculating travel times that address specific challenges. Due to the challenges inherent in this environment and a limited history of implementations, there was a need to provide transportation agencies with information that will help them to implement such systems in a practical and cost-effective way. There are many challenges and benefits in collecting and distributing travel times on arterial highways.

For example:

• Travel times are not collected in isolation and often their uses are determined by the local goals and communication needs—and these can be quite different for and between arterials.
• Arterial roadways can vary greatly in their location and use.
• Arterials present unique issues such as signal timing disruptions and dropping out of the route at various points such as parking lots, side streets, alternate routes, etc.
• Urban arterials may be part of a dense and complex roadway network that creates challenges in distinguishing between "signal" and "noise" (i.e., detected motorists/vehicles that should be used to calculate travel times versus those that should not).

Table 1. Candidate ATT technologies

Technology	Spot Speed	Segment Travel Time	Real-Time Tracking	Sensor Location	Coverage Per Sensor	% Vehicles Detected/ Matched†	Implementation Cost	Non-traffic-info Functions‡	Traffic Volumes	Vehicle Class
Bluetooth detection		X		Roadside/above road	All lanes	Low	Low	Low
Toll tag reader		X		Roadside/above road	One or more lanes**	Low	Med	Med
In-pavement magnetic detectors		X		In pavement	One lane	High	Med	Low	X	X
Automatic license plate reader (ALPR)		X		Roadside/above road	One or more lanes**	Med	Med	Med	X	X
Machine vision	X	X*		Roadside/above road	One or more lanes**	High	Med	High	X	X
Connected vehicle	X	X*		Roadside/above road & in vehicle	All lanes	???	Low	High
Radar, microwave, LIDAR	X			Roadside/above road	One or more lanes**	High	Med	Med	X
Inductive loops	X	X*		In pavement	One lane	High	Low	Low	X	X*
Crowdsourcing			X	None	All lanes	???	Low	Low
Cell phone signal monitoring		X		None	All lanes	???	Low	Low
* Possible depending upon capabilities of technology. ** Multiple lanes possible depending upon capabilities of technology and sensor placement. † Can vary substantially depending on a variety of factors; estimates are approximate based on user experience. ‡ Other functions can include tolling, traffic law enforcement, unregistered vehicle detection, cooperative safety, etc. ??? Unknown/no basis for assessment.

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

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

The core of the report discusses available and emerging ATT data sources as well as implementation considerations, advantages, and limitations on each. The key highlights of each follow:

Bluetooth Detector

Wireless technology that allows electronic devices to communicate directly with one another; recently emerged as viable ARTT collection tech; open standard, allows for off-the-shelf equipment; detection range limited to about 328 feet (100 meters); less expensive than many other options; flexible; some potential privacy concerns; detection technology relies on drivers' use of Bluetooth-enabled devices.

Toll Tag Reader

Detect radio frequency ID of automated toll tags, mature technology, inconspicuous, detection accuracy can decrease with distance, limited to areas with adequate toll tag fleet penetration, some potential privacy concerns, electronic tolling becoming increasingly common.

In-pavement Magnetic Detectors

Arrays of magnetometers installed in pavement, can identify and match vehicles based on each vehicle's unique magnetic signature, quick installation and self-calibrating, wireless sensors require access points and possibly repeaters, high vehicle detection rate, device life span of about 10 years, no privacy concerns.

Automatic License Plate Readers

Optical cameras capture images of license plates and software "reads" the information; mature technology (over 30 years); installed above the roadway and requires direct line-of-sight; particularly sensitive to factors that reduce visibility, privacy issues are a concern.

Machine Vision

Use of video cameras to monitor flow; installed above the roadway or on poles on the roadside; data bandwidth is a consideration; highly customizable set of features; privacy can be a concern for high-resolution systems; potential uses are likely to expand with advances in technology, processing power, and data transmission capabilities.

Connected Vehicle

Short range radio communications between vehicles and vehicles to infrastructure, technology is in very early stages of development, radio transceiver installed in host device within a vehicle,; privacy protocols are being established, very inexpensive cost on a per unit basis, usefulness for travel time calculations uncertain, depends on implementation factors, potential for widespread use if initiative continues to develops.

Radar, Microwave, and LIDAR

A sensor emits radio waves (radar), microwaves, or a laser beam (LIDAR), which reflects off of vehicles; mature and widely used technology; many products available with a variety of different implementation approaches; complete privacy to drivers.

Inductive Loops

Magnetic loops in pavement detect vehicle presence, and multiple loops can be used to calculate travel times; mature and widely used technology, though use for ATT data collection is rare; high detection rate; very inexpensive, but invasive installation and maintenance can increase costs; complete privacy to drivers.

Crowdsourcing

Drivers' vehicles or mobile devices provide information to a public or private entity, and that information is used to generate traffic/travel time; early stage technology; critical mass of users are necessary for success; vehicle/motorist must have device capable of transmitting information; no roadway infrastructure needed; privacy issues are minimal or non-existent when data transmitted to agencies who purchase data; use likely to increase.

Cell Phone Signal Monitoring

Cell phone location information is automatically and anonymously downloaded from cellular network switching centers in real time; relatively mature technology and cell phone use is almost ubiquitous; data provided by vendors, and data are anonymous when provided to agencies; shows adequately precise measurements of travel time.

Several implementations of ATT data collection are also discussed: a) I-95 Corridor Coalition; b) Utah County, UT, I-15; c) multiple routes in Houston, TX;, d) Flagstaff, AZ, US 180; e) Atlanta area, GA; f) Essex County, United Kingdom.

In addition, two case studies are reviewed in detail and lessons learned from the implementations are summarized:

Chandler, AZ

• There are advantages to using open-source software
• Conduct preliminary tests
• Weigh options across multiple vendors
• Bluetooth detection-based travel time is an inexpensive way to add valuable information to existing dynamic message signs (DMS)
• Limit exposure to system failures
• Consider additional data uses
• Eliminate barriers to data sharing St. Louis, MO
• Deploy system slowly
• Verify travel time data using other methods
• Keep accurate implementation and asset management records
• Seamless integration between agencies is beneficial
• Involve public in issues relevant to them

St. Louis, MO

• Deploy system slowly
• Verify travel time data using other methods
• Keep accurate implementation and asset management records
• Seamless integration between agencies is beneficial
• Involve public in issues relevant to them

The report synthesizes the prior information and brings together the state-of-the-art in ATT data collection technologies and the state-of-the-practice in ATT implementations to develop a set of best practices that are based on systematic evaluation (where possible) and real-world experiences. The best practices related to the data collection technology only; a complete set of best practices for ATT programs is beyond the scope of this effort. These were developed with the understanding that every implementation of ATT involves a unique set of objectives, challenges, constraints, and environments. Therefore, rather than providing prescriptive guidance, this chapter emphasizes the key considerations at each step of the planning, implementation, and management process.

One of the most important lessons learned by ATT program implementers is the importance of asking the right questions during the planning and implementation stages. Therefore, each key consideration is phrased as a question and is followed by discussion of related issues.

These questions are focused on the following general areas:

Needs Assessment, Planning, and Specifications Development

• What are the ultimate outcomes desired?
• What are the funding and scheduling constraints?
• What is the desired ATT coverage area?
• What are the needs for scalability and mobility?
• Are real-time data required?
• What secondary benefits can be achieved?
• What are the requirements for data accuracy and timeliness?
• What partnerships are beneficial and necessary?
• What are the infrastructure requirements?
• Are data needed during low volume times?

Selecting and Acquiring Data Collection Technology

• What software, hardware, and other architectural requirements exist?
• What are the initial and ongoing costs of each technology?
• Should the technology be purchased or rented?
• How long is the data path?
• What system features can be automated?
• How will data security and privacy be protected?
• How can preliminary data collection technology testing be conducted?
• How should a vendor be solicited?
• How much ongoing support is offered by the vendor?
• What is the division of responsibilities and rights?
• Who owns the data?

Implementation, Management, and Evaluation

• How can sensor locations be selected?
• What technology documentation is available?
• How should the program operate when missing data?
• How should field equipment be monitored and maintained?
• How can data quality be verified?
• How should public and media relations be handled?
• How can the effectiveness of the program be evaluated?

Although ATT data collection is a relatively new and rapidly evolving area, ATT can be successfully implemented when a project is properly planned and executed. The importance of proper planning cannot be overstated. Successful implementers have carefully considered project objectives and have provided detailed implementation plans. Regardless of the latest specific data collection technology released, asking the right questions is paramount, beginning with planning, continuing to the selection stage, and culminating with execution and evaluation. Practitioners who focus on asking the right questions and heed the lessons learned by colleagues will greatly increase the chances of a successful implementation.