Type B Weaving Capacity Model - Ver6-Weaving Sections：B型织造能力模型ver6交织区

Analytical Procedures for Estimating Capacity of Type B
Weaving Sections
Hesham Rakha
1
and Yihua Zhang
2


Word count: 5,126
Tables and figures: 2,250
Total word count: 7,376
TRB Paper: 05-2483
ABSTRACT
The paper identifies thirteen common configurations of Type B weaving sections. These
configurations are modeled using the INTEGRATION software for a wide range of weaving section
lengths and travel demands. Subsequently, the simulation results are utilized to develop analytical
procedures for estimating the capacity of Type B weaving sections and compared to the
HCM2000 procedures. The results demonstrate that the HCM2000 procedures suffer from four
significant drawbacks. First, the procedures can only consider relatively long weaving sections
(longer than or equal to 150 m). Second, the HCM procedures fail to capture the impact of the
distribution of weaving flows between freeway and on-ramp demand on the capacity of weaving
sections, which is demonstrated to be an important factor in the analysis weaving section
capacities. Third, the procedures do not ensure that the capacity of a weaving section reverts to
the basic freeway capacity when the volume ratio is zero (no weaving flows) regardless of the
weaving section length. Finally, the HCM procedures do not ensure consistency between the
weaving and merge/diverge procedures at the boundary conditions. The paper demonstrates that
the proposed analytical model overcomes the four identified shortcomings of the HCM2000
procedures and estimates the capacity of weaving sections to within 14 percent of the simulated
results compared to the HCM error of 151 percent.
Key words: Freeway weaving sections, capacity of freeway weaving sections, freeway capacity
modeling, HCM 2000, and INTEGRATION software.
INTRODUCTION
The freeway weaving analysis procedures in the 2000 Highway Capacity Manual (1) are based on
research conducted in the early 1970s through the early 1980s (2). Subsequent research efforts
have shown that the methods’ ability to predict the operation of a weaving section is limited (3, 4,
5), which is most probably due to the outdated and limited database that was utilized to develop
these models. As to capacity estimation of freeway weaving sections, some other methods such
as gap-acceptance and simulation methods have been used as alternatives (3, 4, 6, 7).
In this paper the INTEGRATION software is utilized to estimate the capacity of weaving sections.
The validity of the INTEGRATION software for modeling weaving sections and estimating the

1
Charles Via Jr. Depar tment of Civil and Environmental Engineering, Virginia Tech, 3500
Transportation Research Plaza (0536), Blacksburg, VA 24061. E-mail: hrakha@vt.edu.
2
Charles Via Jr. Department of Civil and Environmental Engineering, Virginia Tech, E-mail:
yizhang@vt.edu.