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62 Cards in this Set
- Front
- Back
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what is ITS |
intelligent transportation systems combine transportation systems with information technology to improve safety, mobility, environmental impact |
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In what areas is ITS used? |
traffic management construction management traveller information public transit management emergency management Electronic tolling advanced sensing autonomous vehicles |
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what are early examples of ITS |
traffic cop gas light |
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describe moore's law |
transistor count in a given area doubling every two years |
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What is a model? |
A device that idealizes and simplifies real-world systems so that they may be better understood and manipulated/optimized |
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What parameters are needed in traffic modelling? |
speed density flow |
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What ways can speed be measured |
time mean speed space mean speed |
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what is the difference between the ways of measuring speed? |
Time Mean Speed: Avg. of instantaneous speeds observed at one location Space Mean Speed: Avg. of travel times over a given distance interval |
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What are the advantages of time mean speed? disadvantages? |
Time Mean Speed: easier to measure -- only one fixed measurement location tends to overestimate speed |
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What are the advantages of space mean speed?disadvantages? |
Space Mean Speed: better representation of true speed more difficult to measure |
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What are the types of headway? |
Space headway = 1/density Time headway = 1/flow |
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What type of speed can loop detectors measure? |
Space mean speed |
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what are the variants of traffic signal control? |
fixed pre-timed semi-actuated fully actuated coordinated adaptive |
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Describe fixed/pre-timed TSC |
cycle and phase durations fixed regardless |
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where should fixed/pre-timed TSC be used? |
intersections with high equivalent demand |
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Describe Semi-actuated TSC |
minor approaches have sensors which signal demand for signal change |
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Where would semi-actuated TSC be employed? |
Intersections with unequal demand |
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Describe Fully-actuated TSC |
All approaches have sensors which signal demand for signal change |
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Where would fully-actuated TSC be used? |
intersections with low, equivalent demand |
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Describe coordinated TSC |
multiple intersections have fixed cycles that are offset to create progression between greens promotes pontooning |
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where would coordinated TSC be used? |
areas where traffic flows in one direction between many intersections |
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Describe Adaptive TSC |
Intersection equipped with sensors to observe current traffic state signals adapt according to current traffic conditions |
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Where is Adaptive TSC best used? |
areas of high traffic variability |
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What are the two TSC Standards? |
NEMA CCG |
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What are the differences between the two TSC standards? |
NEMA considers each movement as a phase CCG considers a grouping of movements as a phase |
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What are the TSC Movement types? |
protected permissive protected-permissive |
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what are the TSC Phase Types? |
Advance Leading/Lagging Overlapping Exclusive |
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What is an example of a leading/lagging phase |
one direction has a left turn before the through |
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what is an example of an overlapping phase type? |
non-conflicting movement from perpendicular approaches WBR and NBL |
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What is an example of exclusive TSC Phase? |
one phase without any others ex. ped. scramble |
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what legislation governs traffic, transit, pedestrian, bicycle elements? |
highway traffic act |
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what considerations might interfere with optimized TSC times? |
municipal duration requirements |
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what are the stages in the 4 stage model? |
trip generation trip distribution mode choice route planning |
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Describe trip generation |
considers traffic flow between Traffic Analysis Zones (TAZ) |
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Why is the gravity model better than the doubly constrained growth factor model? |
incorporates notions of travel cost do not need trips for individual OD pairs, only for sums |
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what is mode choice utility? |
potential user's preference or satisfaction with a particular mode of transportation |
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who came up with the principles of trip assignment? |
wardrop |
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what are the two principles of trip assignment? |
User equilibrium: Individuals act non-cooperatively to minimize personal travel cost System optimal: users cooperate to minimize avg. travel cost |
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what are the levels of traffic simulation hierarchy? |
macroscopic: high level mesoscopic: mid-level microscopic: low level |
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describe macroscopic traffic simulation |
high level models link/road dynamics large traffic networks Useful for planning large infrastructure projects rely on theoretical models computationally inexpensive but abstract |
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describe mesoscopic traffic simulation |
mid-level models vehicles as platoons versatile scale used to model medium sized networks ex. entire city |
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describe microscopic traffic simulation |
low level models individual vehicle dynamics includes network geometry, vehicle generation, vehicle dynamics |
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Describe microscopic network geometry |
roads (links) intersections (nodes) number of lanes turning movements speed limit |
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what methods may be used for microscopic vehicle generation? |
poisson process |
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What sub-models may be used for microscopic vehicle dynamics? |
car-following model lane-changing model routing model |
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Describe the car-following model |
a vehicle's speed and acceleration are a function of a leading vehicle |
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Describe the microscopic routing/lane changing model |
routing controls how vehicles navigate from origin to destination i.e. actual route route is composed of successive links; links only accessible from certain lanes lane changing controls when vehicles actually change lanes |
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list some steps in the evolution of transit through history |
boat omnibus electric streetcar internal combustion engine |
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what are some issues with modern urban transit? |
not profitable construction is disruptive under-utilized disruptive technologies such as uber mess with projected volumes |
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What is TSP |
Transit Signal Priority -modulates phases to truncate or lengthen green times in order to favour public transit |
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What are the types of TSP? |
Passive: based on transit schedule Active: upon detection, system decides whether or not to give priority by extending green or shortening opposing green Adaptive: Balances transit priority with signal plan |
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What are the variations of TSP goals? |
Schedule-based: priority to maintain transit schedule Headway-based: priority to maintain headways between transit Unconditional: priority given regardless |
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what does schedule-based tsp favour? |
minimizes user waiting time for low frequency transit |
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what does headway-based tsp favour? |
prevents bunching between high-frequency transit |
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what does unconditional tsp favour? |
favours transit passengers, minimizes person delay regardless |
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what is the most common traffic sensor |
loop detector |
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what are some advantages of loop detectors? disadvantages? |
advantages: cheap, common disadvantages: limited data collection, difficult repair |
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List some varieties of sensors |
loop detectors video camera radar/infrared bluetooth connected vehicle |
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what are some advantages of video cameras as sensors? disadvantages? |
advantage: highest data collection potential can be used automatically or manually disadvantages: expensive automatic use requires algorithms weather dependant |
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what are some advantages of radar/infrared? disadvantages? |
advantages: weather independant; high quality data collection disadvantages: expensive |
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what are some advantages of bluetooth? disadvantages? |
advantages: cheap disadvantages: passive sensing potentially incomplete data
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what are some advantages of connected vehicles? disadvantages? |
advantages: high quality data; no external sensors required disadvantages: requires government action; infrastructure; big data |
