TITLE:
Calibration and Evaluation of Link Congestion Functions: Applying Intrinsic Sensitivity of Link Speed as a Practical Consideration to Heterogeneous Facility Types within Urban Network
AUTHORS:
Enock T. Mtoi, Ren Moses
KEYWORDS:
Travel Demand Modeling, Congestion Functions, ITS Data Applications
JOURNAL NAME:
Journal of Transportation Technologies,
Vol.4 No.2,
April
21,
2014
ABSTRACT:
This
paper explores the use of archived data to calibrate volume delay functions (VDFs)
and updates their input parameters (capacity and free-flow speed) for planning
applications. The sensitivity analysis of speed to change in congestion level
is performed to capture functional characteristics of VDFs in modeling specific
facility types. Different sensitivity characteristics shown by the VDFs
indicate that each function is suitable to a particular facility type. The
results of sensitivity analysis are confirmed by the root mean square percent
error (RMSPE) values calculated using the Orlando Urban Area Transportation
Study (OUATS) model results and observed data. The modified Davidson’s function
exhibits remarkable performance in nearly all facility types. The strength of
the modified Davidson’s function across a broad range of facilities can be
attributed to the flexibility of its tuning parameter, μ. Fitted Bureau of Public Road (BPR) and conical delay functions
show lower RMSPE for uninterrupted flow facilities (freeways/expressways,
managed lanes) and higher values for toll roads (which might have partial
interruptions due to toll booths) and signalized arterials. Akcelik function
underperforms on freeways/expressways and managed lanes but shows some
improvements for toll roads and superior results for the signalized arterials.
This was a desired strength of Akcelik function when modeling link travel speed
on facilities where stopped delays were encountered.