Unmanned Aerial Aircraft Systems in Traffic Surveillance, Control and Engineering

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/24th January 2018, Emmanouil N.BarmpounakisEleni I.VlahogianniJohn C.Golias/ Acquiring  and processing video streams from static cameras has been proposed as one of the most efficient tools for visualizing and gathering traffic information. With the latest advances in technology and visual media, combined with the increased needs in dealing with congestion more effectively and directly, the use of Unmanned Aerial Aircraft Systems (UAS) has emerged in the field of traffic engineering.

In this paper, we review studies and applications that incorporate UAS in transportation research and practice with the aim to set the grounds from the proper understanding and implementation of UAS related surveillance systems in transportation and traffic engineering. The studies reviewed are categorized in different transportation engineering areas. Additional significant applications from other research fields are also referenced to identify other promising applications. Finally, issues and emerging challenges in both a conceptual and methodological level are revealed and discussed.

Traffic surveillance and monitoring has been one of the main tools for Transportation Managers and Engineers for years and an integral part of traffic management and control strategies (Papageorgiou et al., 2008). Several algorithms or systems have emerged to track moving object and analyse traffic, such as (Hsieh et al., 2006; Liu et al., 2008; Shukla and Saini, 2015; Sivaraman and Trivedi, 2013). The visual perspective of the manner traffic (either vehicles or people) evolves over space and time may assist the understanding of recurrent traffic conditions, the efficient management of pedestrian and vehicle traffic, as well as the traffic and demand management under unexpected transportation network conditions (e.g. extreme congestion, adverse weather conditions, riots, terrorist attacks), that may severely deteriorate the performance of the transportation networks and affect the security and safety of users.

Collecting visual information for large networks can be a challenging procedure. Installing stationary cameras to monitor the extent of a transportation facility has been a successful practise for years. Nevertheless, several practical issues may emerge; for example, there are cases where the area to be monitor is large and cannot be covered from static cameras. Moreover, installing stationary cameras and supplementary infrastructure can sometimes be too costly, especially when an area does not need to be monitored anymore.

Even if the cost parameter from the problem of the transportation infrastructure monitoring could be alleviated, the problem of acquiring visual information and gathering data under the emergence of unexpected events is still not addressed. An extreme event may occur at any place and any time. The response to such events should be made in a timely manner to reduce their effects to the transportation system. Evidently, from an emergency response perspective, a setting of static cameras fails to provide a clear picture of the unexpected extreme event, as the setting is specific usually with limited ability to cover a transportation system

Additionally, in rural environments, where problematic areas are sparser, operators would sometimes have to deal with large time intervals between identifying the situation, assessing all necessary steps and lastly taking measures to tackle it, losing valuable time for safety and security and/or resources allocation. Therefore, some practitioners would use ground vehicles as a supplement to the input coming from cameras along the network. Sometimes though, the area of interest may not be accessed immediately, for example when a road accident causes heavy traffic jams upstream the arterial or when the emergency area is not accessible. Similar conditions may arise in an urban setting, where dense road networks sometimes add excessive delay for an emergency vehicle to reach its destination and provide first aid.

Until now, Manned Aerial Vehicles (MAV), usually helicopters operated by the police or air medical services, have been the most appropriate means of providing live picture and information to the control centers and/or provide first aid in an utmost situation. Except for the fact that – in principle - a MAV has high fixed and operation costs, there are many cases that sending a helicopter with people inside or extremely costly equipment, over the area of interest is not always feasible, due to high risk.

Recently, Unmanned Aerial Aircraft Systems (UAS) have been proposed as an alternative in order to overcome the above-mentioned limitations and shortcomings of current practices. A UAS consists of three components: (1) the aircraft, which is defined as an Unmanned Aerial Vehicle (UAV or drone); (2) communication and control; and (3) the pilot. This paper aims to review research dedicated to using UAS in transportation and the advantages of airborne video as a means for acquiring high quality naturalistic data for both practitioners and researchers. The structure of the paper is as follows. First, the advantages of the UAS are described and their technical characteristics that can make them a game changer in Intelligent Transportation Systems (ITS) infrastructure monitoring. Following, we describe some of the latest advances in their technological aspects and important applications that UAVs have already been used for. Then, an analytical review of papers for airborne video footage is conducted. Finally, some issues and challenges concerning UAVs safe and effective integration into ITS applications are discussed.

Unmanned aerial vehicles for transportation and traffic engineering

A UAV or drone is any aircraft, which is not operated by a pilot on-board. This means that the aircraft is controlled either by a pilot on the ground or by electronic systems (semi or fully autonomously). UAVs can be further categorized by the type of their wings to fixed-wing aircrafts, that use wings to generate the lift because of forward airspeed, and rotary wing aircrafts, that use (rotor) wings revolving around a single axis to generate the lift. Although UAVs were firstly introduced for military missions, their use has been recently expanded to civil applications; the last was facilitated by a burst in the UAV industry which systematically provides smaller and lower cost aircrafts (Mahadevan, 2010).

A significant part of the civil applications is focused on aerial photography (Cheng, 2015). Lately, UAVs have found applications in many areas (agriculture, search and rescue missions, infrastructure inspection), especially with the latest advances in their technology and the related sensor technologies (Budiyono, 2008). For transportation engineers, UAS have been introduced as a novel and cost-effective “eye-in-the-sky” solution mainly to collect massive trajectory data from road arterials and replace the old approach of using already pre-installed cameras.

Most UAVs can be on air in a matter of minutes and, with the latest advances in their lightweight materials and equipment, they can cover large distances in very short time intervals, while most of the UAVs use eco-friendlier energy sources (for detailed description of UAV types, technical specifications etc. see the review in Gupta et al. (2013)). In addition, since a UAV can be programmed to fly automatically to a specific area, it could reach the specific area of interest more rapidly since it takes less time to be on air than a MAV. The fact that no crew is required onboard makes it optimal for emergency evacuation situations (e.g. small or large scale evacuations) or high-risk situations (e.g. terrorist attacks), where no more lives are put in danger. Moreover, their comparatively smaller size, they can reach inaccessible places for a MAV, for example a dense urban area with tall buildings and other transportation infrastructure. The advantage of their small size is also crucial when it comes to gathering naturalistic data over a road arterial. Although this may raise some privacy issues that will be analyzed in a later paragraph, UAVs offer a more non-intrusive way of recording traffic phenomena (Barmpounakis et al., 2016).

While each type of UAV (rotary or fixed wings) have distinct advantages over the other, both of them may offer a top view of a road arterial or an intersection, and issues like hidden views, difficult viewing angles and limited length can be more easily resolved. When it comes to rotary-wing UAVs, they are most of the times more versatile, being able to land in limited spaces or maneuver to provide the ideal picture to the operating center. An important asset is that most commercial rotorcrafts are equipped with high definition cameras and combined with their hovering abilities, researchers have the potential to acquire high quality traffic data. As it can easily be understood, the aerial view of a UAS could provide useful insights to researchers, while they could be of crucial importance in emergency response situations, for example UAVs that provide a rapid first aid during an utmost incident.

Original article text may read here:
Unmanned Aerial Aircraft Systems for transportation engineering: Current practice and future challenges

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Emmanouil N.BarmpounakisEleni I.VlahogianniJohn C.Golias
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