Chapter 2 Flashcards
(40 cards)
What are some of the uses for traffic analysis?
Quantifying measures of performance (ex: real time capacity assessment and incident detection)
Establishing trends in traffic growth as a basis for future investments (ex: when will a highway reach max capacity?)
Determining when a traffic signal is necessary at an intersection
Assessing the impact of new infrastructure (ex: traffic impact of new highway bridge)
What are some of the old technologies used to collect traffic data?
Pneumatic road tubes (across one or more likes of a roadway)
Loop detector
What are the two types of loop detectors? How are they different?
Single loops and double loops
Double loops are two consecutive single loop detectors placed a short distance apart
Double loops are better at capturing vehicle speed of a traffic stream
Briefly describe how a loop detector works.
The inductance through the loop is measured over time
When a metal vehicle passes over the loop, the inductance is briefly interrupted
Look at when the inductance is interrupted for the time stamps of vehicles passing
What are the two parameters that can be measured with single loops?
Occupancy (o): % of the time loop is occupied per interval
Volume (n): vehicles per interval
How do you calculate the speed for a double loop detector?
Speed = distance between detectors / (time of detection at second loop - time of detection at first loop)
How do you calculate the vehicle length for a double loop detector?
Vehicle length = speed × average of the on-times for the loop detectors (how long they’re activated for)
What are vehicle lengths calculated from double loop detectors used for?
Classifying vehicles into different categories, such as truck and passenger cars
What are some examples of modern traffic data collection technologies?
Radar
Magnetic sensors
Video-based sensor (thermal video cameras, visual spectrum)
Lidar
What are the two types of sensors used for traffic sensing?
Point-based: look at a specific point over time (ex: radar)
Trajectory-based: look at a specific vehicle at multiple points along its trajectory (ex: video based sensors such as thermal video and 3D LiDAR)
What sort of data can be collected from point-based sensors?
Vehicle speed (per lane)
Vehicle classification
Time headway and spacing
What are some advantages and disadvantages of point-based speed data?
Advantages:
They are often non-intrusive and therefore have limited impact on traffic during installation
They are often wireless
Disadvantages:
They usually come at a high cost (both the sensors themselves and the required infrastructure to support them)
What are some examples of sensors providing point-based speed data?
Radar-based sensors
Magnetic sensors
Lidar sensors
What are some examples of sensors providing trajectory-based speed data?
Video-based sensors for tracking (using computer vision)
Video-based sensors for license plate recognition
Thermal video
Bluetooth, radio frequency identification
Describe the general flow of information through traffic management centers
Real-time traffic data (and historical data) is fed to traffic models which give real-time traffic estimation and prediction
Descriptive conditions and predictions are given to traffic management centers which then give the network guidance (variable message signs), signal controls, etc.
The network responds to these inputs and a surveillance system collects the real-time traffic data to again be inputted into the traffic models
Define intelligent transportation systems (ITS).
The application of advanced and emerging technologies (computers, sensors, etc.) in transportation to save lives, time, money, energy, and the environment
What are the three main parameters used to describe the traffic flow (give their units too)?
q: flow (veh/h)
u: speed (km/h)
k: density (veh/km)
What are uninterrupted flows? Where can they be seen?
Flows that operate free from the influence of traffic control devices such as signals and stop signs
Ex: freeways, multilane highways, two-lane highways
What are interrupted flows? Where can they be seen?
Traffic streams that operate under the influence of signals and stop signs
Ex: streets or intersections in urban areas
Note that environmental conditions (such as weather or time of day) can also affect the flow of traffic
Define traffic flow (rate).
The number of vehicles over any period of time.
q = n / t
What is the difference between volume and flow rate?
Volume is the actual number of vehicles passing a point during a given time period
Flow rate is the number of vehicles passing a point during a time interval but usually expressed as an equivalent hourly rate
What are the two types of speed? How are they different? What kind of technologies find each?
Time-mean speed: the average of actual vehicle speeds at one single observation point (usually found through radar)
u_t = sum(u_i) / n
Space-mean speed: the speed based on the time necessary for a vehicle to travel a known length of roadway; need at least two observation points (often through double loop detectors, Bluetooth sensors, cameras)
u_s = l / t_avg
t_avg = sum(t_i) / n
Also: u_s = n / sum(1 / u_i)
Define traffic density.
The number of vehicles present on a given length of roadway
k = n / l
Define time headway.
The time elapsed between the arrival of a leading vehicle and the following vehicle at a designated point
