Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand...
Transcript of Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand...
-
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference - May 19, 2009Presented by:Jaesup Lee, Virginia Department of TransportationDean Munn, The Corradino Group
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
IntroductionTraffic Data used in basic analysis and model estimationData Development and DefinitionFree Flow SpeedTraffic Flow (Uninterrupted vs. Interrupted)Link Capacity Various Curve Fittings by Functional ClassFindings and Further ResearchOutline
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
IntroductionProject Goals
Use empirical data obtained from Virginia facilities to evaluate speed-flow relationships
Test various volume-delay functional forms for each facility type and determine which provides the best performance
Calibrate volume delay function parameters for each facility type
Outcome should be suitable for implementation in Virginia urban travel models
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
IntroductionFundamental Elements of Volume-Delay Estimation
Converting spot speeds to space-mean speed
Characteristics of free-flow
Identifying boundary between uninterrupted and interrupted flow
Using knowledge of this boundary to estimate the maximum sustainable flow rate (Capacity)
Use empirical observations to fit VDF curve parameters
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Traffic Monitoring System (TSM) Data5,848 locations from 17,400 detector locations availableThree locations per classification selected
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Traffic DataData records are a summary of each 15 minute period Speed bins are in 5 mph incrementsData records are organized by lane and vehicle classCUBE/Voyager script simplifies dataSpot speeds are converted to Space Mean Speeds
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Processed DataSpeed vs DensitySpeed vs FlowSpeed by Time of Day
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Estimating Free Flow SpeedHCM recommends using mean value for low volume conditionsStandard practice also includes using 85th Percentile speed71.1 mph73.7 mph
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Defining Interrupted FlowPlots of flow vs density and speed vs density show two flow states
Others have defined the transition point as the maximum flow or the density at maximum speed, but this is not representative of typical conditions
Statistical techniques can define the transition between the two statesFlow vs. DensitySpeed vs. DensityInterrupted FlowInterrupted Flow
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Defining Interrupted FlowWe define interrupted flow as: Any speed below the threshold where there is 0.0001% probability that it is the same as freeflow.
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Defining Interrupted FlowRural Freeway example, with flow states identified
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Interrupted FlowHistogram Percent with Interrupted Flow vs. Flow Density
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Estimating CapacityOur data shows a classic logistic distributionWe estimated parameters (using density as the only variable) to create a probability function that best fits the data
Capacity corresponds to flow density with a 50% probability of being interrupted PI = 1/[1 + e(b1D+ b0)], where D = Density (veh/mi)
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
99.5% Probability of Interrupted Flow0.50% Probability of Interrupted Flow50.0% Probability of Interrupted FlowCapacity EstimatesThis example gives a 39.7 pc/mi Density Threshold or a 2384 pc/hr Max Flow Rate
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsVolume-Delay Functions - Using the computed capacity, the following volume delay functions were estimated based on speeds during uninterrupted flow
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Curve Fitting - non-linear regression
Goodness of Fit R-squared Root Mean Square ErrorNon-Parametric tests e.g. Chi-Square
Other Criteria - suitability for model applicationsFitting Volume Delay Functions
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsUrban Interstate
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsRural Interstate
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsUrban Expressway
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsRural Principal Arterial
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsUrban Other Principal Arterials
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsRural Minor Arterial
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsUrban Minor Arterial
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsRural Collector
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsUrban Collector
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsRural Local
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsSummary of calibrated inputs to VDF fitting process
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Fitting Volume Delay FunctionsSummarized results from VDF fitting process
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Initial FindingsStandard VDF functions are all capable of performing adequately across road classes
For a given road class, VDF parameters fitted for one location, seem to be transferable to other locations
Goodness of fit measures do not strongly differentiate between functions
The Akcelik function, with its more rigorous theoretical underpinnings, seems to work very well
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Next StepsAdditional facility types
Check model transferability to other facilities
Compare HCM capacity, planning capacity, and empirical capacity
Continue to automate analysis process
Test functions in urban models (assignment convergence, average travel speeds)
New VDF functional forms and calibrated parameters will become part VDOT modeling standards
Investigation of Speed-Flow Relations and Estimation of Volume Delay Functions for Travel Demand Models in Virginia TRB Planning Applications Conference, May 19, 2009
Q & A
Thank you !
Contact pointsJaesup Lee: [email protected] Munn: [email protected] Raw : [email protected]
******
*