Multi-functions wireless surveillance systems can be developed by adding other sensing modalities to the traffic surveillance systems. An important one is the modality for sensing road conditions which is presented in section 7.2.1. The wireless communication capability of the sensor networks also allows it to talk to other ITS systems. Since the sensor nodes are located on the pavement, the networks can be a very useful tool in the
Vehicle-Infrastructure Integration (VII) framework. It can be used to exchange information between different systems and extend the vehicle-infrastructure communication range. Its
applications in VII are presented in section 7.2.2.
7.2.1 Road Conditions Sensing Modality
There were over 1.4 million road conditions-related crashes in 2001, causing over 615,000 injured, over 6,900 dead and over 1 billion hours delay [7.25, 7.26]. The monitoring of adverse weather and road conditions in real-time is essential for safety enhancement and roadway maintenance [7.22].
The detection of water, ice, snow, fog and lighting conditions can be used to determine whether the visibility, weather and road conditions are safe for driving. Warnings of potential hazard (e.g. icing on bridges) can be given to drivers via VMS, in-vehicle navigation system or other media. This safety enhancement is especially useful when the conditions are not obvious to the drivers (e.g. poor lighting conditions, black ice). Traffic signal controls [section 7.1.1] can be adjusted according to the change in road conditions.
This information is also used in roadway maintenance to determine the type and extent of surface treatments needed for keeping the roadway drivable.
According to the experience from Minnesota [7.23], such systems improve traffic safety, enlarge roads capacity and allow an effective planning of future investment. National surface transportation weather observing and forecasting system (Clarus) [7.25] has been initialized by the Federal Highway Administration (FHWA) to implement road conditions monitoring system nationwide.
State-of-the-art sensor technologies [3.4] are ready for these applications. For example, a micro-sensors board designed for weather monitoring is developed under the TinyOS project [section 3.2], known as the MICA weather board MTS400 [7.23]. It includes sensors for measuring temperature (ice and snow), humidity (rain and fog), light intensity (lighting condition) and air pressure. In addition, acoustic sensors can be used to estimate wind speed and accelerometers can be used to estimate weight of vehicles. All of these sensors are integrated into a board with the size of a name card. A picture of MTS400 is shown in Fig. 7.2.1.1 [7.24]. This sensor board is designed to be used with MICA sensor nodes family [section 3.2.2], and it can be integrated into Sensys’ sensor nodes [section
Fig. 7.2.1.1 Picture of MICA weather board MTS400 manufactured by Crossbow [7.24]
The power consumption of this additional sensing modality is relative small as the sampling frequency can be as low as once every 15 minutes. Its effect on the system lifetime can be further minimized by using a number of sensor nodes at the same site to take care of the tasks alternatively, or by using an extra node to concentrate on monitoring the road conditions. This plug-and-play feature allows additional sensing modalities to be added to the wireless sensor networks surveillance system without modifying the system framework. Therefore, deployments of different sensing capabilities can be customized according to specific applications and locations.
7.2.2 Vehicle-Infrastructure Integration (VII)
Half of the 43,000 deaths that occur each year in U.S. result from vehicles entering or leaving the freeway, and traveling unsafely through intersections [7.27]. Aimed at
minimizing these accidents, and the associated traffic delay and cost, the U.S. Department of Transportation (USDOT) has proposed the VII initiative. It studies the development of a nationwide wireless communication infrastructure that allows vehicle and vehicle-infrastructure communications. With the push from the government, it is foreseen that every car manufactured in US will be equipped with a standardized wireless
communication device and a GPS unit for integrating with the VII infrastructures within 10 years. The Dedicated Short Range Communications (DSRC) protocol is adopted as the standard. Radio spectrum at 5.9 GHz is specifically allocated for the use of DSRC [7.28].
Vehicles with communication capability can serve as anonymous probe vehicles for collecting traffic information and road conditions [section 2.1.1.3]. The data can be fused with the existing surveillance database and enhances the real-time traffic control [section 7.1]. Traffic accidents are prevented by warning the drivers when their vehicles are entering an intersection unsafely or when they are running dangerously close to other vehicles. A good example of such applications is Intersection Decision Support [7.29], which activates left-turn warning signs if other vehicles are approaching the intersection from the opposite direction, so that Left Turn Across Path/Opposite Direction (LTAP/OD) and Left Turn Across Path/Lateral Direction (LTAP/LD) crashes can be avoided [7.29]. A typical system configuration of IDS is shown in Fig. 7.2.2.1 [7.29].
Fig. 7.2.2.1 Typical system configuration of Intersection Decision Support (IDS) [7.29]
The proposed wireless sensor networks can be used with VII in two ways:
i, Once VII is deployed in a nationwide sense, the road will be filled with a mixture of vehicles and infrastructures with and without communication capability. The sensor networks can provide surveillance support to the system for vehicles and infrastructures that do not have the communication capability. This allows the associated ITS applications to be used independent of the VII penetration rate.
ii, The sensor networks can also adopt the standardized DSRC protocol so that they can be used to extend the range of vehicle-vehicle and vehicle-infrastructure communications, by acting as repeater nodes. This mixed system lowers down the deployment cost by
minimizing the need for building new infrastructure along the side of road. This makes the systems cost efficient enough to be deployed in large scale, especially for applications that need advance detection [section 7.1.1].
Ch. 8 Conclusion
Between 1980 and 1998, vehicle miles traveled increased 72% while the number of lane miles increased only 1% [7.20]. The current pace of improvement in transportation system is not sufficient to keep up with even a slow growth in the traffic demands in most major urban areas. There is a great need for advanced surveillance capabilities to complement the rapid deployment of ITS strategies. Because of the highly intrusive characteristic of
inductive loop detectors, the quest for researching a reliable and cost-effective alternative system, which can provide traffic data at the same accuracy level as inductive loop systems, has been underway for some time.
This report describes the design and development of a novel wireless sensor networks based traffic surveillance system, which has a detection accuracy comparable to that of well-maintained inductive loop detectors [section 4.4]. It offers a very attractive alternative to inductive loops for traffic surveillance. The sensor networks have a much higher
configuration flexibility, which allows the system to be scalable and deployable everywhere in the traffic networks. The availability of these data opens up new
opportunities for intelligent traffic operations and control [Ch. 7]. Having a lower system life-cycle cost than inductive loop, video and radar detector systems [section 2.1.2], the sensor networks are cost-effective enough for large scale deployment.
Total coverage of surveillance does not need to stay in the simulation stage anymore. The proposed wireless sensor networks have the potential to revolutionize the whole traffic surveillance and control industry [Ch. 7]. A summary of contributions from this research project is presented in section 8.1. And several potential future developments of this system are provided in section 8.2.