This chapter gives an overview of various terminologies in Automated Planning used by different chapters in this thesis. It explains the concept of Automated Planning as a branch of artificial intelligence and how it applies to real world problems. This chapter ends with an overview of some applications of automated planning in different field of knowledge. The next chapter introduces the basic concept of Urban Traffic Control.
Chapter 3
Introduction to Urban Traffic Control
The evolution of Urban Traffic Control (UTC) throughout the past century has been a continued effort to maintain and stabilise the increase in vehicle demand without vio- lating the ever more complex policy objectives of transport systems. UTC has evolved since the creation of mobile entities for commuting people and goods with the use of traffic officers for signalisation, monitoring and control. The first generation of auto- mated traditional controller uses fixed timing signals to control traffic at junctions. The second generation of traffic control used historic data to pre-configure traffic timing and control. The third generations use real traffic data for re-adjusting and choosing traf- fic signals with the use of detectors for the collections of real traffic data. The fourth generations were able to compute and manipulate data for forecasting traffic conditions for the creations of traffic control programs and strategies for optimal control of traf- fic situation. These trends continue, until the introduction of intelligent traffic control, which propose the use of artificial intelligent techniques combined with all other ex- isting traffic approaches for real-time detection; traffic forecasting; traffic signalization incident detection based on the principle of integrated embedded and control system engineering [69]. The field of intelligent transport systems (ITS) is now honed in the twenty-first century with advances in efficiency, quality and manufacturability of sens- ing and communication systems for traffic control. Efficient UTC system has helped
3. Introduction to Urban Traffic Control
to reduce congestion, increased economic efficiency and improved road safety and air quality [69]. Thus, urban Traffic management involves planning, monitoring and con- trol of traffic flows with the aim of maximizing the effectiveness of the use of traffic infrastructure; ensuring reliable and safe operation of transport system while address- ing environmental goals and policy objectives [55;144].
3.1
Basic Component of Urban Traffic Control System
There are basic components that are fundamental to the implementation of urban traf- fic control system. These includes Road Traffic Network and Disturbances; Traffic Control Strategies and Rules; Traffic Operator(human and non-human) and Traffic De- vices(controllers and sensors). This section gives a brief overview of these components.
3.1.1
Road Traffic Network and Disturbances
A real traffic network contains information about the state of a road traffic environment at any specific point in time. Changes to the state of a traffic network are under the influence of various disturbances. Disturbances are factors that affect the normal func- tioning of a road network. Disturbances could be planned or unplanned. An example of planned disturbance is a set of road works. This disrupts the normal flow of traffic for the entire duration of its construction. During such road works, the adjoining route and intersection signal need to be optimised in other to minimise the effect of road or lane blockage during the period of the maintenance or upgrade. Unplanned disturbances, on the other hand, are factors that are not envisaged before there interruption of the traf- fic network. These factors include but is not limited to road incident and unexpected change in traffic demand and severe weather conditions.
3. Introduction to Urban Traffic Control
Figure 3.1: Basic Component of Urban Traffic Control System
3.1.2
Traffic Control Strategies and Rules
Traffic Control Strategies and rules are extracted from the Traffic Management Policy and Guidance which is one of a series of policy documents that outline how a County Council manages, maintains and is developing transport infrastructure. Traffic Control Strategies and rules varies from county to county and changes over a period of time. A change in this rules could alter the metric and goals of any traffic control system. Traf- fic Management measures can include on-street parking controls, speed limits, HGV restrictions, direction signing, traffic calming, movement restrictions and pedestrian crossing facilities.
3.1.3
Traffic Operator
Controlling road traffic involves directing vehicular and pedestrian traffic within a net- work of connected roads; around a construction zone; accident or other road disruption. Thus, the major role of traffic operators is to manage the road network so as to ensure,
3. Introduction to Urban Traffic Control
as far as possible, the safe and convenient movement of traffic. They also ensure the safety of emergency response teams, construction workers and the general public. This could be done manually or through the use of sensing and controlling devices within the network of roads. The traffic operator is empowered to influence the control of the entire system whenever there is genuine reason to alter the goal or metric of the system as a result of policy change. Human-machine interface is the communication interface between the traffic environment and a human operator. Traffic system allows the flexibility of being altered by a human operator. Human rules and desires are sub- ject to changes, thus, the operator is able to influence the operating policy of the system by changing the goals and metric of the system when the need for changes arises, this might require re-installation of part or entire traffic component due to such changes.
3.1.4
Traffic Devices
Surveillance and sensing devises are embedded into some road network. Road traffic monitoring agencies make use of surveillance and sensing devices for retrieving the sta- tus of road networks. These devices upload the real time data in a format that can be retrieved and understood by a system or a traffic officer. For example in an urban area, existing traffic detection technologies includes but not limited to: Video Camera, Induc- tive Loops, Microwave and Infrared Sensor technology, Magnetic technology, Acous- tic technology, Radio Frequency technology, Radar technology and Global Positioning System (GPS).
Control devices are called actuators in classical control terminology. They are em- bedded into systems to change their performance to a desirable state. Control devices play vital role in UTC environment ranging from the simple traffic light to the complex controller box for signal heads. They all help to control and maintain smooth traffic operation in road network. The control devices change the state of the road network to desires state and example is the traffic signal heads.
3. Introduction to Urban Traffic Control