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Center for Transportation Studies

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Summer 2011

Cars and roads share info, alert drivers

A TechFest attendee maneuvers a Scout reconnaissance robot. photo: Matt Miranda

Today’s drivers tune into traffic updates on their car radios. But tomorrow’s drivers are likely to rely on a very different kind of radio system to help them avoid congestion. Under the U.S. Department of Transportation’s IntelliDrive research initiative, researchers are developing a range of applications that transmit data between moving vehicles, and between vehicles and the transportation infrastructure.

Professor M. Imran Hayee of the University of Minnesota Duluth’s Department of Electrical and Computer Engineering, along with his team of students, is developing a system that transmits congestion data to motorists near work zones, where traffic jams are common and collisions with maintenance workers are a safety hazard. The research is supported by the Northland Advanced Transportation Systems Research Laboratories (NATSRL), part of the ITS Institute.

The new system is one of many applications now being developed based on the Dedicated Short-Range Communications (DSRC) standard, which was allocated specifically for ITS applications by the USDOT in 1999. Like the familiar 802.11 wireless networking standards that enable laptop computers and other electronic devices to connect to data networks, DSRC is designed for short-range use—typically less than 1,000 meters. It offers high data transmission rates with low latency and is largely unaffected by weather disturbances, both of which are critical characteristics for ITS applications with rapidly moving vehicles.

DSRC is intended to support both vehicle-to-vehicle applications, such as cooperative forward-collision warning, and vehicle-to-infrastructure applications, such as electronic toll collection. In both cases, vehicles and infrastructure components become nodes on a wireless network. Each vehicle’s onboard DSRC system constantly updates the topology of its local network as vehicles and infrastructure nodes enter and leave the system’s coverage area.

Hayee designed a system consisting of a portable roadside unit (RSU) that can be installed easily in work zones and onboard units (OBUs) to be installed in vehicles. Both types of unit are commercially available. The RSU gathers data on the location and speed of nearby vehicles by engaging their OBUs. With these data, the RSU determines average travel time in the vicinity of the work zone and locates the start of congestion (SoC)—the point where traffic changes from a free-flowing state to a congested state. This information is then broadcast back to the OBUs. Each OBU calculates the distance to the start of congestion and displays the information to the driver via a separate user interface, enabling the driver to decide whether to take an alternate route and warning him or her of a sudden speed reduction.

The process of determining travel time and locating the start of congestion involves processing data from GPS receivers in the vehicles’ OBUs. Each OBU responds to queries from the roadside unit as it comes into range before encountering congestion. Although these GPS location data may entail significant errors, a preliminary errorcorrection operation is first carried out within the OBU to ensure that the vehicle is traveling toward the RSU and is within the area where data on vehicle movement will be useful for calculating travel time and locating the start of congestion.

A vehicle that passes the OBU’s preliminary location check is then subject to a fine location check by the RSU. This second, more precise check rules out the possibility that the approaching vehicle is traveling on a nearby parallel road within the error margin of the preliminary check. Only after passing the fine position check is a vehicle recognized as a source of speed and congestion data for the RSU. At this point, the OBU begins to transmit messages containing time, speed, and location data to the RSU at one-second intervals until it reaches the point where congestion ends. As soon as an OBU passes beyond the end of congestion (EoC) point, the RSU processes the data it has received, updates the start of congestion and travel time locations, and prepares to contact the next OBU to arrive in its coverage area.

Because data from private vehicles are transmitted automatically in an uncontrolled environment, protecting the privacy of users is a key concern. The DSRC communication protocols underlying Hayee’s prototype system include built-in security measures that protect DSRC applications from eavesdropping, falsification of data, and other attacks. The researchers also designed their system with privacy in mind; the RSU lacks access to any potentially identifying information from the vehicle OBUs, and data on travel time and congestion are discarded once circulated.

A TechFest attendee maneuvers a Scout reconnaissance robot. photo: Matt Miranda

Graduate student Buddhika Maitipe puts the DSRC unit in a car for the system’s field demonstration.

According to a recently published report on the research, the system can be adapted to any road by changing the input parameters of the RSU; the OBU does not require any data about the road being monitored. The RSU requires only input parameters for key GPS waypoints on the road and settings for communication with OBUs. In operation, the RSU sends specific parameters related to the road segment to the OBU, which uses these parameters in its communications with the RSU.

The use of a consumer smartphone as the driver interface is one of the innovative aspects of the prototype system, and one that allows significant cost savings, especially for those vehicles that lack a built-in dedicated interface. Rather than a dedicated driver interface, which is expected in future vehicles, each OBU is equipped with a communication interface device that can connect to a smartphone via the Bluetooth wireless networking protocol. An application installed on the smartphone connects to the OBU automatically and presents information to the driver in the form of text messages. The researchers note that the system architecture supports the use of different user interfaces as needed to avoid driver distraction.

Hayee tested the prototype extensively in a variety of congestion scenarios in both urban and rural areas. The field tests showed that the system can accurately determine travel time and the location of the start of congestion in real time under changing traffic conditions.

One limitation of the current system is that optimal performance requires a clear line of sight between the RSU and OBUs. However, the researchers already plan to address this issue in their future development of the system by enabling vehicle-to-vehicle data networking; moving data along a network of vehiclebased units rather than between only the infrastructure base station and individual vehicles will eliminate the need for a direct line of sight.