The United States is taking a giant leap toward a nationwide wireless system of connected vehicles and smart infrastructure. How? By means of the world's largest real-world test.

The U.S. transportation system is at a critical juncture. In the past, as the Nation's population and economy grew, roads and highways expanded along with them. However, this is no longer the case. The current infrastructure has reached capacity, and the transportation network is bursting at its seams. A growing population has led to an increase in vehicles on the roads, resulting in users spending 4.8 billion hours sitting in traffic in 2010 and wasting 1.9 billion gallons (7.2 billion liters) of fuel. Traditional methods of solving transportation problems are no longer enough. The United States cannot simply build its way out of the congestion problem.

Moreover, the Nation must further reduce the number of traffic crashes and road fatalities and serious injuries. Standard vehicle safety features, such as supplemental restraint systems, antilock brakes, electronic stability control, and improved road design and emergency response, have contributed to significant reductions in traffic fatalities. Still, deaths from vehicle crashes hover at more than 30,000 per year. A groundbreaking change is needed. The transportation community must create and innovate, and rethink the realm of possibilities to increase safety and reduce congestion.

The solution? Envision a system in which vehicles and smart roadside infrastructure are connected virtually and are in constant communication with each other through a secure, interoperable wireless network. In this future, cars, trucks, buses, and other vehicles "talk" to each other and to traffic signals, work zones, tollbooths, school zones, and other elements of the infrastructure, sharing valuable safety and mobility information. The U.S. Department of Transportation (USDOT) has invested in the research to make this vision of connected vehicles and smart infrastructure a reality in the not-too-distant future.

"As the number of vehicles equipped with these technologies grows, the available data will increase as well," says Brian Cronin, research team leader, USDOT's Intelligent Transportation Systems (ITS) Joint Program Office. "This data-rich environment can support a wealth of applications that can improve mobility; reduce transportation's environmental impacts; provide cost savings; and, most important, improve the safety of highways and roads to substantially reduce the number of fatalities and injuries."

The Technology And the Benefits

Connected vehicle systems that support crash-avoidance safety applications will likely be based on dedicated short-range communications under the IEEE 802.11p standard. This technology, based on a special mode of operation for IEEE 802.11p developed for communications among rapidly moving vehicles, is called Wireless Access in Vehicular Environments (WAVE). Many mobility and environmental applications, and others that are not time-critical, could be based on cellular or other types of wireless technology.

Regardless of the technology used, a high-speed wireless communications platform offers an opportunity to combine data from infrastructure (such as slippery road surface conditions) with data from vehicles (such as speeds through curves) to assess the likelihood of crashes (such as run-off-road). The result is the delivery of more accurate and robust hazard warnings to drivers.

The benefits extend to the collection of data for use in improving the transportation system. Connected vehicles and infrastructure will transmit anonymous messages, ensuring the privacy of drivers and their vehicles while generating new data about how, when, and where vehicles travel. Numerous applications could use this information to provide a number of advantages. In addition to warnings to drivers in order to avoid potential crashes, benefits include delivering vehicle location and speed information to traffic signals to adjust phasing and avoid vehicle idling, road conditions to State and local agencies to help improve maintenance and service, and traffic and transit information to help travelers select optimal routes.

Some of the types of data that can be captured and managed include information on safety, weather and environmental conditions, congestion, and costs for tolls and parking. Data sources include both traditional providers, such as traffic management centers and automated vehicle location systems, and nontraditional ones, such as mobile devices and connected vehicle equipment. Data also can be collected from sources such as toll gantries, parking facilities, and transit stations. Not only could the resulting information help motorists make better travel decisions, but also transportation agencies could use public and private sector data on all modes and roads to transform highway management.

Integrating Infrastructure And Vehicle Data

Public agencies, including USDOT, have invested extensively in both infrastructure- and vehicle-based technologies and countermeasure applications that improve highway safety and mobility. Transportation agencies have implemented many of these systems to improve road safety, but the systems act independently, and most are unable to communicate or interact with each other.

Recognizing the promise of a transportation system in which vehicles and infrastructure communicate with one another, USDOT, along with its State and local counterparts, and private industry and research institutions are evaluating applications that integrate infrastructure and vehicle data to provide more robust and reliable alerts and warnings to drivers. These cooperative systems offer the advantage of enabling the collection and sharing of real-time data. They also could provide specific, dynamic warnings that are more reliable than static signs and more likely to capture drivers' attention. Also, integrated systems are likely to be more cost effective than infrastructure-only or vehicle-only solutions.

"Some problems are hard to address with systems that are based on infrastructure only or vehicle equipment only," says Ray A. Starr, assistant State traffic engineer with the Minnesota Department of Transportation (MnDOT). "A vehicle-to-infrastructure system may provide a better solution for problems such as truck rollovers on freeway exit ramps, for example, where the vehicle and load characteristics play a big part in providing an appropriate warning. MnDOT is also interested in the possibility of obtaining real-time travel time information, especially in locations where obtaining such information is currently difficult or expensive, such as on signalized roadways or through rural roadway work zones."

Advanced V2I Safety Applications

As part of its connected vehicle research, USDOT's vehicle-to-infrastructure (V2I) program is developing the following advanced V2I safety applications related to intersection safety and speed management.

Red light violation warning: Based on vehicle speeds and distances to intersections, this technology provides invehicle alerts to drivers about potential violations of upcoming red lights.

STOP sign gap assistance: This technology assists drivers at STOP-sign-controlled intersections via vehicle gap detections, alerting motorists when it is unsafe to enter intersections.

Curve speed warning: If a driver's current speed is unsafe for traveling through an upcoming road curve, this technology will alert the motorist to slow down.

Currently, none of these applications exist in a true V2I context, but instead in various forms that are either infrastructure-only or vehicle-only solutions. The V2I program's research aims to integrate these solutions and create truly connected environments of advanced roadside infrastructure and communicating vehicles to provide warnings to drivers regarding unsafe conditions at intersections and roadway curves.

Red Light Violation Warnings

At signalized intersections, this application alerts drivers that a traffic signal has turned red, or is about to turn red, prior to the point where the vehicle would be unable to stop safely. The invehicle devices would issue warnings to drivers if they are about to run a red light. A vehicle equipped with this application, when approaching a similarly equipped intersection, would receive messages about the intersection geometry, signal phase and timing, and (if necessary) adjusted speed recommendations.

The application would reduce the number of vehicles exposed to cross-traffic due to intersection violations. At the same time, the application might reduce the number of rear-end crashes caused when a traffic signal turns yellow and a driver brakes too quickly for the driver in the following vehicle to respond. Unlike current systems of external static signs that flash to warn a driver to stop, the red light violation warning application will be an invehicle warning to the driver based on real-time data, including current roadway and vehicle operating conditions.

To realize benefits, the application only requires equipped vehicles approaching equipped intersections. This single-vehicle approach maximizes the potential benefit to drivers and road operators, while simplifying deployment logistics. The benefit to society would increase as the numbers of equipped intersections and vehicles grow.

Installation at key intersections could provide the basis for national deployment of initial infrastructure safety communications, such as signal phase and timing information, as well as reliable positioning and geospatial mapping techniques. Once these technologies are available and used by vehicles, they will facilitate many other safety applications, including both V2I and vehicle-to-vehicle (V2V) applications.

With increased deployment of infrastructure-based sensing equipment and higher penetration of equipped vehicles, crashes beyond those caused by traffic signal violations could be addressed by implementing enhanced crash avoidance systems. Increased market penetration, plus deployment of vehicle-sensing equipment at intersections to detect nonequipped vehicles, will facilitate the development of cooperative systems that help avoid crashes based on erroneous gap acceptance, such as left-turn crossing-path crashes. These cooperative systems also would warn drivers of vehicles that have the right of way about potential violations by other vehicles.

Connected Vehicles-Infrastructure The Federal Highway Administration's (FHWA) Exploratory Advanced Research (EAR) Program focuses on longer term, higher risk research with a high payoff potential. The program is sponsoring research on next-generation connected vehicle-infrastructure systems. The following summarizes a few of the ongoing studies. In 2007, FHWA launched a project called Development and Evaluation of Selected Mobility Applications for Vehicle-Infrastructure Integration to study how wireless connectivity between vehicles and infrastructure might help reduce congestion and effectively increase highway capacity. Researchers at the Partners for Advanced Transit and Highways (PATH) program at the University of California, Berkeley, conducted this 4-year project in cooperation with the California Department of Transportation (Caltrans). The ability to modulate the speed and spacing of individual vehicles in relation to unseen events farther downstream has the potential to keep traffic flowing smoothly, safely, and at its optimum density. With dedicated short-range communications, long-range traffic management opportunities are now conceivable. This research project, sponsored by the EAR Program, modeled, tested, and demonstrated prototype systems to improve traffic flow by calculating and communicating speed guidance directly to individual vehicles. The program also aims to achieve closer coordination, shorter vehicle separation gaps, and higher effective lane capacities through vehicle-to-vehicle communications, vehicle-to-infrastructure communications, and cooperative adaptive cruise control. Other objectives include reducing heavy-truck fuel consumption and doubling the capacity of truck-only lanes by forming and maneuvering automated three-truck platoons. More information is available at www.fhwa.dot.gov/advancedresearch/pubs/inchwyfact.cfm. Another study, Intersection Control for Autonomous Vehicles, is pursuing a radical approach to keeping traffic moving. This project, awarded by FHWA in 2008, is being conducted at the University of Texas at Austin. The intersection control system proposed in this study promises to process traffic more efficiently than traffic lights and STOP signs without compromising safety. Its development is guided by a set of criteria that includes the use of current or near-term sensor technologies, adoption of a standardized communications protocol, and the ability to deploy incrementally, allowing expansion to additional intersections and adaptation to increasing numbers of autonomous vehicles. Absolute collision prevention, even under conditions of communications failure, and high levels of efficiency are the primary goals. More information is available at www.fhwa.dot.gov/advancedresearch/pubs/10023/index.cfm. A third study, Advanced Freeway Merge Assistance, is designed to improve the efficiency and safety of freeway merges using dedicated short-range communications. FHWA awarded this project in 2009 to the University of Virginia Center for Transportation Studies. The university researchers aim to develop and evaluate candidate freeway merge assistance systems that might significantly improve operations in a connected vehicle environment. Currently, freeway merge areas present significant bottleneck and safety concerns. The university created a traffic simulation for connected vehicle technology with funding from Caltrans, FHWA, the National Science Foundation, and the Virginia DOT. The project also will help prepare transportation agencies to make full use of connected vehicle technology as it emerges. More information is available at www.fhwa.dot.gov/advancedresearch/pubs/10076/index.cfm. Another study, Investigating Advanced Traffic Signal Control, focuses on providing comprehensive real-time information on the movement of vehicles throughout the entire road network, leading to a transformational change in how traffic is controlled and addressing the significant problem of congestion along arterial routes. The EAR Program-sponsored research is taking place in partnership with BMW, Caltrans, and the University of California at Berkeley and Riverside. More information is available at www.fhwa.dot.gov/advancedresearch/pubs/11044/index.cfm. FHWA also launched a study of vehicle-highway automation research and development activities outside the United States as an initial-stage international scan, conducted by the California PATH program and Cambridge Systematics, Inc. The purpose is to summarize the current state of cooperative vehicle-highway automation systems in Europe and Asia, and help inform decisions about future related activities in the United States. The level of activity in this area of study has increased significantly in Europe and Japan. The research is based on meetings, demonstrations, site visits, and a literature review. The review covers systems that provide drivers with a range of automation capabilities, from driver assistance to fully automated driving, with an emphasis on cooperative systems that involve active exchange of information between vehicles and the roadside and among individual vehicles. Once published, the report will be available on the EAR Web site at www.fhwa.dot.gov/advancedresearch/pubs.cfm. Connected vehicles could help to minimize crashes on busy urban streets like this one. To learn more about the EAR Program, visit www.fhwa.dot.gov/advancedresearch. The site features information on research solicitations, updates on ongoing research, links to published materials, summaries of past EAR Program events, and details on upcoming events. For more information, contact David Kuehn at 202-493-3414 or david.kuehn@dot.gov, Terry Halkyard at 202-493-3467 or terry.halkyard@dot.gov, or Zachary Ellis at 202-493-3193 or zachary.ellis@dot.gov. --Zachary Ellis, FHWA

STOP Sign Gap Assistance

This application warns drivers on secondary minor roads when it is unsafe to proceed through a STOP-sign-controlled intersection. This will help drivers maneuver through cross traffic, reducing the number of conflicts and crashes. The vision is that the initial application will be deployed at intersections with the highest number of safety problems.

Departments of transportation (DOTs) have deployed multiple installations of a similar technology, called intersection conflict warning systems, throughout the country at rural, STOP-controlled intersections. For example, MnDOT is deploying conflict warning systems at up to 100 rural, STOP-controlled intersections throughout the State. These systems typically consist of a combination of static signs, vehicle detection equipment, and dynamic elements such as flashing lights or message boards. For example, as a vehicle on the major road approaches the intersection, a dynamic warning is activated at the STOP sign on the minor road.

These systems are only infrastructure-based and do not leverage the benefits of an integrated system of connected vehicles and infrastructure. The STOP sign gap assistance application, however, uses both V2V and V2I technologies, including invehicle and roadside signage warning systems. The application detects vehicles on the major road and issues a warning to the driver on the minor road when there is an insufficient gap for safe passage through the intersection. The application works for all varieties of intersections -- divided and undivided roadways, skewed intersections, and so forth.

The STOP sign gap assistance application uses a dynamic driver-vehicle interface for invehicle warnings and driver-infrastructure interface for automated external signage. Because the automated driver-infrastructure signs are external, they provide warnings of unsafe gaps to drivers of both equipped and nonequipped vehicles. In this way, the application can provide immediate benefits to all drivers.

Curve Speed Warning Application

This application warns drivers entering curves about excessive speeds. According to the Transportation Research Board, road departure crashes result in approximately half of all fatal highway crashes. Excessive speed in curves can lead to loss of vehicle control, run-off-road, collision, and rollover crashes. Any of these events, alone or in combination, could result in death, injury, and vehicle or property damage or loss. DOTs have deployed multiple installations of curve speed warning systems throughout the country as a means of reducing crashes.

The Michigan Department of Transportation (MDOT) has installed two of these systems in the Detroit area. The systems incorporate data from radar speed detectors, roadway surface sensors, visibility sensors, and vehicle detection sensors to detect the presence of traffic congestion on the curves. The data from these detectors and sensors help to determine the appropriate message to display on dynamic message signs to warn motorists approaching the curves. Anticipated benefits from the systems include improved motorist safety, reduced crashes and traffic congestion, and measurable performance to determine system benefit-cost ratios over time.

These benefits are from an infrastructure-only system. Imagine the potential benefits from an advanced system of infrastructure and connected vehicles that will improve safety around curves through the use of V2V and V2I technologies. Unlike current curve speed warning applications that largely provide standard static warnings based on radar-detected speeds, the connected vehicle application will provide real-time warnings based on current driving conditions, unique to specific drivers and vehicles. The application will be functional for all types of curves, whether they are part of the roadway's geometry or whether they involve roads diverging into different paths, such as exit ramps.

The V2I curve speed warning application also will include the capability to calculate safe curve speeds in real time based on current road and weather conditions, along with other data on vehicle dynamics, such as whether tires slip. The application will provide warnings in sufficient time for drivers to receive the warning messages and react accordingly.

V2I Mobility Applications

The development of smart infrastructure is critical to developing connected vehicle mobility applications. These applications would use V2I connectivity to gather vehicle probe data, such as information on vehicle position, speed, acceleration, and direction. Transportation agencies could fuse these data with other sources of real-time data to maximize system productivity and enhance mobility.

Through a program called Dynamic Mobility Applications, USDOT researchers are exploring the potential benefits of mobility applications. The following five applications would leverage V2I connectivity.

The first application would use much more comprehensive data collected from all connected vehicles to accurately predict lane-specific flows of vehicles, the number of cooperating connected vehicles, and other driving characteristics in real time to transform how traffic signal systems are designed, deployed, and monitored. By using data via V2I connectivity, these new systems can improve traffic signal operations significantly to maximize traffic flows in real time.

A second application would inform visually impaired pedestrians of when to cross at intersections and how to remain aligned with crosswalks. The smartphones of registered blind users would alert traffic signal controllers and drivers to the presence of visually impaired pedestrians waiting to cross, and could help the pedestrians determine when it is safe to enter the crosswalk.

The third application would help transit agencies better manage bus service. The application would enable the agencies to grant buses priority at traffic signals based on factors such as number of passengers, schedule and headway adherence, service type, and peak direction of travel.

The fourth would provide travel information to commercial vehicle operators, including freight-specific route guidance, and facilitate coordinated load management to reduce empty-load trips.

A final application would facilitate integrated transit operations, such as passenger connection protection, transit dispatching, and new forms of operational practices intended to enhance dynamic ridesharing.

These applications could improve commutes by reducing travel times, enhance the efficiency of goods movement and transit operations, and reduce the need for expensive traffic improvement projects along corridors.

Smart Roadside Initiative

A separate, ongoing effort within USDOT's V2I program is the Smart Roadside initiative, which will enable wireless communication between commercial vehicles and infrastructure at highway speeds. The increased demand for over-the-road shipping is resulting in legally loaded commercial vehicles queuing up at inspection stations, which causes unnecessary delays in the supply chain. The queues also are straining the resources of agencies responsible for delivering effective size and weight enforcement programs and monitoring hours of service in order to ensure highway safety.

The Smart Roadside initiative aims to improve States' enforcement ability by deploying advanced roadside equipment at strategic points along commercial vehicle routes. Through technology such as dedicated short-range communications, roadside equipment would provide a wireless communications platform among vehicles, the road, and regulatory agencies, facilitating more thorough inspection of vehicles without regular stops and improving the safety, mobility, and efficiency of truck movements and operations.

Securing Connected Vehicle Communications

For the connected vehicle concept to work, communications between vehicles and infrastructure (and eventually pedestrians and other road users) must be both timely and trusted. In addition, the system must protect the privacy of drivers and other users, and ensure that data are not altered between transmission and receipt. Systems requiring trusted, secure communications often rely on encryption. However, the process of encrypting and decrypting messages would inhibit rapid communication of safety-critical messages, defeating the purpose of a very low-latency communications system. V2V safety applications are based on providing information to the driver in "crash imminent" situations.

To provide trusted, secure communications in a connected vehicle environment, USDOT is researching the use of certificates, in which each entity within the connected environment is provided a series of certificates that are valid for a specified time interval. The entity will attach the appropriate certificate to a broadcast, which is validated by the receiver. The present concept is that certificates will have short lifetimes to preserve the privacy of the sender.

Such a system will necessitate continuous generation and distribution of new certificates through a certificate management system. Advanced infrastructure will be critical to this approach. The roadside equipment might serve as an Internet portal for this process, receiving and using digital certificates to secure transmitted information. Other models and communications methods also are under evaluation to provide the required certificates.

Cost Savings from Connected Environments

The vision of V2I communications is that a minimum level of infrastructure will be deployed to provide a maximum level of benefits. The selected V2I safety applications (red light violation warning, STOP sign gap assistance, and curve speed warning) will provide new capabilities for detecting vehicles and warning motorists about potential unsafe conditions at intersections and curves.

A connected vehicle environment would enable DOTs to replace traditional infrastructure components, such as loop detectors and video monitors, with roadside equipment units that send and receive data and potentially activate warning systems. Before reaching an intersection, connected vehicles would communicate with the roadside equipment to request a traffic signal change. Applications are under development that will allow agencies to optimize signal control for mobility and to reduce environmental impact. For example, during periods of poor air quality, the system can prioritize the movement of commercial vehicles. Even under normal circumstances, reducing idling at intersections will improve engine efficiency and gas mileage and will reduce emissions.

The connected vehicle and infrastructure environment would lead to significant savings for DOTs by reducing the cost to maintain detectors, video monitors, and other infrastructure. Unlike loop and video detectors, ITS components will have service lifetimes comparable to the traffic signal controllers.

The market penetration of equipped vehicles is expected to take many years, but early adopters will still realize benefits. Safety applications require deep market penetration to fully realize benefits, but dynamic mobility applications can offer more immediate returns on the investment. Early connected vehicles could influence a transportation network that includes unequipped vehicles by slowing down following cars or relieving traffic by taking alternate routes. These actions could contribute to improved traffic flow.

In addition, participating State and local agencies would have access to a robust collection of real-time, multimodal data that could help to improve management and maintenance of roads and infrastructure. Agencies that invest in the technology and infrastructure now will help to provide the core infrastructure for the path to national deployment.

They also would have the advantage of not having to buy new smart equipment later, as the infrastructure would be forward and backward compatible. This compatibility would enable deploying agencies to continue to serve the existing unequipped vehicle fleet, while providing data and information to connected vehicles to enable motorists to make informed decisions related to driving safely.

"Hosting the connected vehicle environment in southeast Michigan provides an invaluable opportunity for the many vehicle manufacturers and parts suppliers that are based in this region," says Jim Sayer, head of the Human Factors Group at the University of Michigan Transportation Research Institute and project manager of the Safety Pilot Model Deployment. "We suspect that its proximity to 'Motor City' will facilitate use of the environment in support of furthering V2V and V2I technological developments."

Real-World Tests

On August 21, 2012, USDOT launched the world's largest test of connected vehicle technology in a real-world, multimodal operating environment. Using approximately 3,000 cars, trucks, and buses (and some infrastructure) equipped with wireless communications devices, this model deployment is creating a highly concentrated environment of vehicles talking to each other and to infrastructure, as a means to evaluate how the system works in the real world and to quantify the probable benefits of a connected vehicle environment.

The University of Michigan Transportation Research Institute is conducting the model deployment with everyday drivers carrying out their normal routines on the streets and highways of Ann Arbor, MI. For 1 year, until August 2013, their equipped vehicles are sending, receiving, and translating data and conveying warnings to nearby drivers of other equipped vehicles when specific safety hazards occur. The Michigan researchers will extend these capabilities to a limited set of V2I applications as well. And USDOT will use the data collected from the vehicles to learn how different types of motorists respond to safety messages in the real world and to determine the technology's effectiveness at reducing crashes.

Several other State and local agencies also are leading the way toward the future deployment of a connected vehicle system nationwide. For example, the Maricopa County Department of Transportation (MCDOT) in Arizona is conducting a connected vehicle prototype initiative called the MCDOT SMARTDrive Program^TM. The prototype will test new V2V and V2I technology systems, including vehicle prioritization at traffic lights, along 2.3 miles (3.7 kilometers) in Anthem, a planned community near Phoenix in Maricopa County.

The SMARTDrive field test involves six interconnected traffic lights, dedicated short-range communications devices, integrated Wi-Fi and Bluetooth^® connections, closed-circuit TV cameras, traffic detection and data collection software, fiber-optic signal interconnected systems, and communication connections to Maricopa's traffic management center. The first SMARTDrive application being tested is a vehicle prioritization system that can simultaneously provide traffic signal priority to multiple emergency vehicles converging at the same time at an intersection.

As more automobiles are equipped with onboard devices that can communicate with traffic signals, other vehicles on the roadway, and real-time traffic control centers, this system will help prevent collisions between emergency vehicles and private automobiles. MCDOT also will test applications such as transit vehicle priority, traveler information, and pedestrian crosswalk systems.

Ultimately, the data from USDOT's model deployment and State-run test sites will help the National Highway Traffic Safety Administration make a decision in 2013 on the future of connected vehicle technology. This decision could lead to a revolutionary transformation of the Nation's transportation system.

From Research to Implementation

With the advent of modern, instrumented vehicles and roadside electronics, the use of innovative techniques to assist motorists in making intelligent decisions based on real-time road conditions is now possible. Applications that use data from connected vehicles and roadside infrastructure offer the promise, not only of major improvements in highway safety and mobility, but also the reduction of the environmental impacts of highway travel.

USDOT is working to establish the necessary platforms to support the subsequent development and growth of applications and data. The intent is to start with the development of a small suite of applications that ideally will spawn a broader range of ideas in the marketplace and facilitate a more robust and dynamic connected vehicle environment.

"For more than a decade, USDOT has worked through its ITS research program to leverage advanced technology and help develop solutions that can transform the Nation's surface transportation safety, mobility, and environmental performance," says John Augustine, deputy director of the ITS Joint Program Office. "With the launch of USDOT's Safety Pilot Model Deployment in Ann Arbor this past August, we could be on the verge of just such a transformation. This first-of-its-kind road test of connected vehicle technology will provide USDOT with critical information to inform the agency's decision on whether to proceed with additional activities, including potential rulemaking. In the meantime, USDOT continues to work with its partners in public agencies, the automotive industry, and the wireless industry to pave the way toward the implementation and deployment of connected vehicle technology in the coming years."

 

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Carl Andersen is FHWA program manager of V2I Communications. He holds an M.S. in physics from the Naval Postgraduate School and a B.S. in marine science from the United States Coast Guard Academy.

For more information, contact Carl Andersen at 202-493-3045 or carl.andersen@dot.gov.