ASUDD: What hangs over the road?
On the streets of our cities and on the highways, electronic scoreboards, variable information signs, various sensors and video cameras began to appear. Traffic lights are rapidly getting wiser, and every self-respecting city seeks to organize a "traffic control center". Demand creates supply, and some companies are starting to explore a new direction for them - traffic automation.
Projects in this area from the category of “hanging equipment on poles and drank the budget” are smoothly shifting towards “solving transportation problems of the city before elections”, which implies a more reasonable approach to design and the achievement of quite practical and socially useful goals. And if earlier these projects were exclusively in the hands of builders, now they have begun to attract system integrators and software developers. It is for this reason that this publication appeared. Who knows what you, colleagues, will have to automate next time?
Today we look at the road "hardware", installed on highways.
As with any automated control system, the ASTM receives information “from the fields” or from the operator, processes it and generates control actions. Accordingly, it is possible to divide everything that is “in the fields” into two groups. The first group collects information, and the second has an impact on traffic flows.
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The task of the transport stream detectors is to collect the following stream information:
Transport flow detectors are equipped with two or three sensors of different types (“dual” and “triple” technologies). Thus, in the "triple" detectors, the microwave radar measures speed, the ultrasonic detector provides an assessment of the dimensions and classification of machines into classes, and the multi-channel infrared detector provides counting machines, determining the intensity and occupancy.
As a rule, a detector can monitor only one lane. Therefore, they are placed on a support by several pieces at once, according to the number of lanes. Accordingly, the intensities are summed up, and the rates and occupancy are averaged.
According to the three indicators listed above, it is possible to determine the state of the flow at the “cross section”, that is, at the site under the detectors. When the flow of cars increases, for example, during rush hours, the intensity and speed first increase. Then the speed drops a little, and then comes what we call "traffic jam". Cars go slowly and with stops, the intensity drops sharply, the speed too. And employment, on the contrary, increases dramatically.
The following graph shows a picture of real detectors on a four-lane highway per day.
The naked eye can see how a traffic jam appears in the evening rush hour. In general, a simple science. If we add here the analysis of statistics for previous periods, we get a full-fledged system for collecting and preprocessing information about traffic flows.
On highways, sometimes you can see high masts, on which a kind of “pepelats” barrel is installed (a metal box option), from which all sorts of curious things stick out - weathercocks, antennas and lenses. This is an automatic weather station. It collects information about weather conditions and road surface conditions. For example, information about the presence on the pavement of "black ice", which on the highway may lead to very bad consequences. The list of measured parameters can reach three dozen positions and it looks very tedious to bring it here.
Weather stations periodically transmit weather information as a text or XML file to interested parties. For example, in ASUDD. Weather information can affect the introduction of certain speed limits, as well as the launch of specific control scenarios in the zone of "cataclysm"
Video surveillance itself on the road is of little interest to us as software developers. As a rule, video surveillance is a separate subsystem and does not apply to control software ASUDD. But the fact that an analytical module can be connected to the video stream is very interesting to us. Because it makes it possible to automatically record all sorts of incidents in the field of visibility that the operator can overlook. For example, now there are systems that can determine the accident, unforeseen stopping of vehicles, dropped cargo, fire and traffic against the flow. It makes no sense to cover all the way with these systems, since it is quite expensive. But here in the tunnels or on mountain serpentines, the use of these systems is justified.
Automatic incident detection systems consist of video cameras fixed above the road and correctly “targeted” and analytical software, which in the bottom line tells the operator or system the place and type of incident recorded.
Traffic management for motorists is expressed in their usual form - in the form of road signs, traffic lights and all sorts of information on electronic scoreboards. Sometimes automatic barriers are used (in parking lots, in tunnels and on toll roads). In the west, it is also customary to restrict entry to highways (On-ramp metering).
Variable information signs and displays are arrays of LEDs with a rather complex filling. Since they are designed to work in outdoor conditions, they provide heating, cooling, condensation and icing protection. They know how to control their condition (like all other road equipment) and are made of fairly durable material. Near the electronic road sign looks frightening - it is a kind of closet with a man's visot, the LEDs are hidden inside the recesses in a solid grid. The sign should be clearly visible at a distance and at the same time should not glare in the sun.
Signs can display a fixed number of pictures, depending on the models. Electronic scoreboards also differ in various restrictions on fonts, the number of lines and the number of "pixels" horizontally. Some are able to display letters only in separate boxes, and some provide complete freedom within their “permission”. Traffic controllers help to manage all this.
Here is a photo of a typical road controller. Usually these poor fellows are installed in outdoor conditions in special iron cabinets.
Road controllers are ordinary industrial computers. As a rule, they have “obkotsany” Linux inside them. In functionality, they are significantly different from each other. The copy in the photo can collect telemetry information from traffic flow detectors and light signs and scoreboards on the same support. As can be seen in the photo, he has a contact LCD screen, which allows the installer to perform device configuration in the field. Often, controllers are provided with interfaces for fast backup and recovery, which allows configuration in a warm office, and on a cold wind on a support, only quickly fill information into the controller if this cannot be done over the network (for example, in the case of using GPRS networks). Some controllers may contain additional control programs that allow them to act independently when the connection to the center is broken.
Interfaces and network protocols of controllers are rigidly standardized, all documentation is open. While the internal corporate software and control algorithms are protected "better than Fort Knox."
Historically, the division of equipment on the "trunk" and "city". We reviewed the first group. But on the urban equipment we will allocate a separate post, as there are their controllers, their traditions and their own terminology.
Next time we will look at how adaptive traffic control schemes work, how traffic lights interact with each other over a network and what architectural solutions are used in the market to manage intersections in cities.
Projects in this area from the category of “hanging equipment on poles and drank the budget” are smoothly shifting towards “solving transportation problems of the city before elections”, which implies a more reasonable approach to design and the achievement of quite practical and socially useful goals. And if earlier these projects were exclusively in the hands of builders, now they have begun to attract system integrators and software developers. It is for this reason that this publication appeared. Who knows what you, colleagues, will have to automate next time?
Today we look at the road "hardware", installed on highways.
As with any automated control system, the ASTM receives information “from the fields” or from the operator, processes it and generates control actions. Accordingly, it is possible to divide everything that is “in the fields” into two groups. The first group collects information, and the second has an impact on traffic flows.
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Traffic flow detectors
The task of the transport stream detectors is to collect the following stream information:
- intensity (number of cars per unit of time)
- average rate per interval
- fullness of the lane or road (percentage of the occupied road space)
Transport flow detectors are equipped with two or three sensors of different types (“dual” and “triple” technologies). Thus, in the "triple" detectors, the microwave radar measures speed, the ultrasonic detector provides an assessment of the dimensions and classification of machines into classes, and the multi-channel infrared detector provides counting machines, determining the intensity and occupancy.
As a rule, a detector can monitor only one lane. Therefore, they are placed on a support by several pieces at once, according to the number of lanes. Accordingly, the intensities are summed up, and the rates and occupancy are averaged.
According to the three indicators listed above, it is possible to determine the state of the flow at the “cross section”, that is, at the site under the detectors. When the flow of cars increases, for example, during rush hours, the intensity and speed first increase. Then the speed drops a little, and then comes what we call "traffic jam". Cars go slowly and with stops, the intensity drops sharply, the speed too. And employment, on the contrary, increases dramatically.
The following graph shows a picture of real detectors on a four-lane highway per day.
The naked eye can see how a traffic jam appears in the evening rush hour. In general, a simple science. If we add here the analysis of statistics for previous periods, we get a full-fledged system for collecting and preprocessing information about traffic flows.
Automatic road weather stations (ADMS)
On highways, sometimes you can see high masts, on which a kind of “pepelats” barrel is installed (a metal box option), from which all sorts of curious things stick out - weathercocks, antennas and lenses. This is an automatic weather station. It collects information about weather conditions and road surface conditions. For example, information about the presence on the pavement of "black ice", which on the highway may lead to very bad consequences. The list of measured parameters can reach three dozen positions and it looks very tedious to bring it here.
Weather stations periodically transmit weather information as a text or XML file to interested parties. For example, in ASUDD. Weather information can affect the introduction of certain speed limits, as well as the launch of specific control scenarios in the zone of "cataclysm"
Video surveillance and automatic video analysis
Video surveillance itself on the road is of little interest to us as software developers. As a rule, video surveillance is a separate subsystem and does not apply to control software ASUDD. But the fact that an analytical module can be connected to the video stream is very interesting to us. Because it makes it possible to automatically record all sorts of incidents in the field of visibility that the operator can overlook. For example, now there are systems that can determine the accident, unforeseen stopping of vehicles, dropped cargo, fire and traffic against the flow. It makes no sense to cover all the way with these systems, since it is quite expensive. But here in the tunnels or on mountain serpentines, the use of these systems is justified.
Automatic incident detection systems consist of video cameras fixed above the road and correctly “targeted” and analytical software, which in the bottom line tells the operator or system the place and type of incident recorded.
Signs and scoreboards
Traffic management for motorists is expressed in their usual form - in the form of road signs, traffic lights and all sorts of information on electronic scoreboards. Sometimes automatic barriers are used (in parking lots, in tunnels and on toll roads). In the west, it is also customary to restrict entry to highways (On-ramp metering).
Variable information signs and displays are arrays of LEDs with a rather complex filling. Since they are designed to work in outdoor conditions, they provide heating, cooling, condensation and icing protection. They know how to control their condition (like all other road equipment) and are made of fairly durable material. Near the electronic road sign looks frightening - it is a kind of closet with a man's visot, the LEDs are hidden inside the recesses in a solid grid. The sign should be clearly visible at a distance and at the same time should not glare in the sun.
Signs can display a fixed number of pictures, depending on the models. Electronic scoreboards also differ in various restrictions on fonts, the number of lines and the number of "pixels" horizontally. Some are able to display letters only in separate boxes, and some provide complete freedom within their “permission”. Traffic controllers help to manage all this.
Traffic controllers
Here is a photo of a typical road controller. Usually these poor fellows are installed in outdoor conditions in special iron cabinets.
Road controllers are ordinary industrial computers. As a rule, they have “obkotsany” Linux inside them. In functionality, they are significantly different from each other. The copy in the photo can collect telemetry information from traffic flow detectors and light signs and scoreboards on the same support. As can be seen in the photo, he has a contact LCD screen, which allows the installer to perform device configuration in the field. Often, controllers are provided with interfaces for fast backup and recovery, which allows configuration in a warm office, and on a cold wind on a support, only quickly fill information into the controller if this cannot be done over the network (for example, in the case of using GPRS networks). Some controllers may contain additional control programs that allow them to act independently when the connection to the center is broken.
Interfaces and network protocols of controllers are rigidly standardized, all documentation is open. While the internal corporate software and control algorithms are protected "better than Fort Knox."
But what about the traffic lights?
Historically, the division of equipment on the "trunk" and "city". We reviewed the first group. But on the urban equipment we will allocate a separate post, as there are their controllers, their traditions and their own terminology.
Next time we will look at how adaptive traffic control schemes work, how traffic lights interact with each other over a network and what architectural solutions are used in the market to manage intersections in cities.
Source: https://habr.com/ru/post/124249/
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