Download - Demand Forecasting 2008
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Transportation Engineering
Transportation Planning Process
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Transportation Planning
What are some examples of goals and objectives for a
transportation system?
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Transportation Planning
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Transportation Planning
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Forecasting Travel
How do we know what travel behavior will be like in 20
years?
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Defining Study AreaDelineate boundaries and subdivide into zonesZones Should Have Following Characteristics
Homogeneous Socioeconomic Characteristics Intrazonal Trips Should Be MinimizedUse Physical, Political, and Historical Boundaries if
PossibleZones Should Not Be Created Within Other ZonesThe Zone System Should Generate and Attract
Approximately Equal Trips, Households, Population,or Area
Use Census Tract Boundaries Where Possible.
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Example for TAZs
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Forecasting TravelPopulation and Economic Data
Transportation Inventories
Travel Surveys
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Forecasting TravelCalibration
Establishing a mathematical relationship to estimate future travel demand
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Trip Estimation ExampleA multiple regression analysis shows the
following relationship for the number of trips per household:
T = 0.82 + 1.3P + 2.1AT = Trips per household per dayP = persons per householdA = Autos per household
Zone contains 250 households with an average of 4 persons and 2 autos for each household, determine the average number of trips per day in that zone .
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Transportation PlanningEnvironmental Impact Statements
Purpose and NeedAlternativesEnvironmental Effects
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Highway EngineeringForecasting Travel Demand
Growth Rate Methods (Rural)Urban and Intercity Travel Forecasting
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Forecasting Travel DemandFactors Influencing Travel DemandLocation and intensity of land useSocioeconomic Characteristics of the population
Extent, Cost, and Quality of the available transportation
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Forecasting Travel Demand
What are some factors that affect how much you
travel?
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Forecasting Travel Demand
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Forecasting Travel DemandTrip generation
Process for determining the number of trips that will begin and end in each traffic zone.
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Trip GenerationTrip EndTrip ProductionTrip Attraction
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Trip GenerationClassification of Trips
Home-Based Work (HBW)Home-Based Other (HBO)Non Home Based (NHB)
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Trip GenerationTwo functions of trip generation
Develop a relationship between trip end production or attraction and land use
Use the relationship developed to estimate the number of trips generated at some future date under a new set of land-use conditions
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Trip GenerationCross classification method of trip generationDevelop relationship between socioeconomic measures and trip generation
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Trip Generation ExampleDevelop a set of curves showing the
number of trips per household versus income and auto ownership.
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Trip Generation ExampleHousehold #Household # Trips ProducedTrips Produced Income ($1000)Income ($1000) AutosAutos
11 22 1616 0022 44 2424 0033 1010 6868 2244 55 4444 0055 55 1818 1166 1515 6868 3377 77 3838 1188 44 3636 0099 66 2828 11
1010 1313 7676 331111 88 7272 111212 66 3232 111313 99 2828 221414 1111 4444 221515 1010 4444 221616 1111 5252 221717 1212 6060 221818 88 4444 111919 88 5252 112020 66 2828 11
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Trip Generation Example
Income Income ($1000)($1000)
Autos OwnedAutos OwnedTotal Total
00 11 2+2+
2424 2 (67)2 (67) 1 1 (33)(33) 0 (0)0 (0) 3 (100)3 (100)
24 – 3624 – 36 1 (20)1 (20) 3 3 (60)(60)
1 1 (20)(20) 5 (100)5 (100)
36 – 4836 – 48 1 (20)1 (20) 2 2 (40)(40)
2 2 (40)(40) 5 (100)5 (100)
48 – 6048 – 60 0 (0)0 (0) 1 1 (33)(33)
2 2 (67)(67) 3 (100)3 (100)
> 60> 60 0 (0)0 (0) 1 1 (25)(25)
3 3 (75)(75) 4 (100)4 (100)
TotalTotal 44 88 88 2020
Number & Percent of Household in Each Income Category Versus Car Ownership
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Trip Generation Example
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Trip Generation Example
Income Income ($1000($1000
))
Autos OwnedAutos Owned
00 11 2 +2 +
<24<24 33 55 ----24 – 3624 – 36 44 66 9936 – 4836 – 48 55 7.57.5 10.510.548 – 6048 – 60 ---- 8.58.5 11.511.5
>60>60 -- -- 8.58.5 12.712.7
Average Trips per Household Versus Income and Car
Ownership
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Trip Generation Example
Trips per Household per Day by Auto Ownership and Income
Category
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Trip Generation Example
Trips by Purpose and Income Category
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Trip Generation ExampleDetermine the number of trips per day
generated for each trip purpose. Number of dwelling units: 60Average income per dwelling unit: $44,000
Income ($)Income ($) HouseholHouseholdsds
Low (under 32,000)Low (under 32,000) 99
Medium (32,000 – Medium (32,000 – 48,000)48,000)
4040
High (over 48,000)High (over 48,000) 5151
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Trip Generation Example
IncomeIncomeCars / Cars /
HouseholdHousehold
00 11 2 +2 +
LowLow 5454 4242 44
MediumMedium 44 5858 3838
HighHigh 22 3030 6868
Percentage of Households in Each Income Category Versus Auto
Ownership
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Trip Generation Example
IncomeIncomeAutos / Autos /
HouseholdHousehold
00 11 2 +2 +
LowLow 11 66 77
MediumMedium 22 88 1313
HighHigh 33 1111 1515
Number of Trips per Household per Day
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Trip Generation Example
Pgh = number of trips per day generated by householders with income level g and auto ownership h
HH = number of householdsIg = Percentage of households with income level gAgh = Percentage of household in income level g
with h autos per household(PH)gh = Number of trips per day produced in
household at income level g and auto ownership h
Pgh=HH X Ig X Agh X (PH)gh
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Trip Generation Example
Income, # of AutosIncome, # of Autos TripsTrips Total by Total by GroupGroup
L, 0L, 0 33
1919L, 1L, 1 1414
L, 2+L, 2+ 22
M, 0M, 0 22
232232M, 1M, 1 111111
M, 2+M, 2+ 119119
H, 0H, 0 22
415415H, 1H, 1 101101
H, 2+H, 2+ 312312
Number of Trips per Day Generated
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Trip GenerationRates Based on Activity (Attraction Rates)
AttractioAttractions per ns per
HouseholHouseholdd
AttractioAttractions perns per
Non-Non-Retail Retail
EmployeEmployeee
Attractions Attractions per per
Downtown Downtown Retail Retail
EmployeeEmployee
AttractioAttractions per ns per Other Other Retail Retail
EmployeEmployeee
HBHBWW
---- 1.71.7 1.71.7 1.71.7
HBOHBO 1.01.0 2.02.0 5.05.0 10.010.0
NHBNHB 1.01.0 1.01.0 3.03.0 5.05.0
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Trip Attraction ExampleEmployed at a downtown commercial
center are 220 retail and 650 non-retail workers. Determine the number of trips per day attracted to this zone.
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Process by which trips generated in one zone are allocated to other zones
Trip Distribution
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Basic MethodsGravity Models
Growth Factor
Trip Distribution
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Trip Distribution
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A study area consist of three zones. Assume Kij is the same for all zones.
Trip Distribution Example
Trip Productions and Trip Productions and AttractionsAttractions
ZoneZone 11 22 33 TotaTotall
ProductioProductionsns
140140 330330 280280 750750
AttractionAttractionss
300300 270270 180180 750750Travel Time Between Travel Time Between
ZonesZones
ZonZonee
11 22 33
11 55 22 33
22 22 66 66
33 33 66 55
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Trip Distribution Example
Time (min)Time (min) FF11 828222 525233 505044 414155 393966 262677 202088 1313
Travel Time Versus Friction FactorTravel Time Versus Friction Factor
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Trip Distribution Example
ZoneZone 11 22 33 PP
11 4747 5757 3636 140140
22 188188 8585 5757 330330
33 144144 6868 6868 280280
Computed Computed AA
379379 210210 161161 750750
Given AGiven A 300300 270270 180180 750750
Zone to Zone Trips: First Iteration
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Trip Distribution Example
Ajk = Adjusted attraction factor for zone j, iteration k
Cjk = Actual attraction total for zone j, iteration k
Aj = Desired attraction total for attraction zone j
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Trip Distribution Example
ZoneZone 11 22 33 PP
11 3434 6868 3838 140140
22 153153 112112 6565 330330
33 116116 8888 7676 280280
Computed Computed AA
303303 268268 179179 750750
Given AGiven A 300300 270270 180180 750750
Zone to Zone Trips: Second Iteration
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Trip DistributionGrowth Factor Model
Tij = number of trips estimated from zone i to zone jti = present trip generation in zone iGx = growth factor of zone xTi = tiGi = future trip generation in zone itix = number of trips between zone i and other
zones xtij = present trips between zone i and zones jGj = growth factor of zone j
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A study area consists of four zones. The number of trips between each zone and growth factor for 5 years is shown. Determine the number of trips between each zone for future conditions.
Trip Distribution Example
ZonZonee
Present Trip Present Trip Generation Generation (trips/day)(trips/day)
Growth Growth FactorFactor
Trip Generation Trip Generation in 5 yearsin 5 years
AA 600600 1.21.2 720720
BB 700700 1.11.1 770770
CC 700700 1.41.4 980980
DD 400400 1.31.3 520520
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Trip Distribution Example
ZonZonee
AA BB CC DD
AA ---- 400400 100100 100100
BB 400400 ---- 300300 ----
CC 100100 300300 ---- 300300
DD 100100 ---- 300300 ----
TotaTotall
600600 700700 700700 400400
Present Trips Between Zones
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Trip Distribution Example
ZoneZone AA BB CC DD Estimated Estimated Total Trip Total Trip
GenerationGeneration
Actual Actual Trip Trip
GeneratiGenerationon
AA ---- 428428 141141 124124 693693 720720
BB 424288
---- 372372 ---- 800800 770770
CC 141411
372372 ---- 430430 943943 980980
DD 121244
---- 430430 ---- 554554 520520
TotalsTotals 696933
800800 943943 554554
First Estimate of Trips Between Zones
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Process to determine the number (or percentage) of trips between zones that are made by various modes (auto, carpool, transit, bike/walk)
Mode Choice
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Mode Choice
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Determine the number of transit trips per day in a zone which has 5000 people living on 50 acres. The auto ownership is 40% with zero autos per household and 60% with one auto per household.
Mode Choice Example
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Process to determine the actual routes that travelers will use
Traffic Assignment
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Basic MethodsDiversion CurvesMinimum Time PathMinimum Time Path with Capacity Restraint
Traffic Assignment
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Traffic Assignment
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Dr. Lina Shbeeb 53
linktheonCapacityC
timetravelflowfreeT
VflowtrafficassignedforlinktheontimetravelT
where
C
VTT
0
1
4
01 15.01