Evaluation of Methods for Computing Free-Flow Speed and Its ‎Significance in the HCM 2010; Case Study: A Ramp-Weaving Segment

Document Type: Research Paper

Authors

1 Assistant Professor, Department of Transportation Engineering, Isfahan University of Technology, Isfahan, Iran

2 MSc. Grad., Civil Engineering, Transportation Research Institute, Isfahan University of Technology, Isfahan, Iran

Abstract

The core methodology of the Highway Capacity Manual (HCM) 2010 for freeway analyses is based on Free-Flow Speed (FFS). Moreover, weaving segments are major elements of freeway facilities that form where two one-way traffic streams intersect by merging and diverging maneuvers. Hence, this study used three different methods to compute FFS of a ramp-weaving segment, and then employed the proposed HCM 2010 model to analyze the weaving. Comparison of the model results and the field data indicated that the HCM 2010 method for field measurement of FFS outperformed the other two methods. Nonetheless, the considerably poor performance of the HCM 2010 model in predicting the speed of non-weaving vehicles adversely affected the ultimate outcome of the model and caused under-predicted results. Thus, by app.lying slight modifications to the field measurement method of FFS for non-weaving flow, this study proposed a novel method which produces significantly more favorable results compared to other methods. Considering these results alongside the context in which manuals like the HCM are calibrated in, elegantly demonstrates the merit of this study because the HCM traffic models depend on several contextual factors including vehicle technical characteristics and traffic behavior. This implies that most recent editions of manuals may not always be the most accurate ones for the traffic conditions throughout the highways of Iranian cities.

Keywords


- AASHTO (American Association of State Highway and Transportation Officials) (2010) “Highway safety manual”, 1st ed., Washington, DC., Part A, Chapter 2, pp. 12-15.

- Chen, D. and Ahn, S. (2018) “Capacity-drop at extended bottlenecks: merge, diverge, and weave”, Transportation Research Part B: Methodological, Vol. 108, pp. 1-20.

- Fazio, J., Wiesner, B.N. and Deardoff, M.D. (2014) “Estimation of free-flow speed”, KSCE Journal of Civil Engineering, Vol. 18, No. 2, pp. 646-650.

- Federal Highway Administration (2009) “Manual on uniform traffic control devices”, 2009 edition with revisions No. 1 and 2 incorporated, Dated May 2012, Washington, DC., Part 2, Chapter 2, pp. 27-110.

- Findley, D. J., Schroeder, B. J., Cunningham, C. M. and Brown, T. H. (2016) “Highway engineering planning, design, and operations”, USA: Elsevier, Part 5, pp. 293-357.

- Ghavidel Abraghan, R. and Afandizadeh Zargari, S. (2016) “Developing a model for estimating weaving and non-weaving speed within highways weaving segments (Tehran)”, International Journal of Transportation Engineering, Vol. 4, No. 2, pp. 75-86.

- Hill, C., Elefteriadou, L. and Kondyli, A. (2015) “Exploratory analysis of lane changing on freeways based on driver behavior”, Journal of Transportation Engineering, Vol. 141, No. 4, pp. 1-11.

- Kiattikomol, V., Chatterjee, A., Hummer, J. E. and Younger, M. S. (2008) “Planning level regression models for prediction of crashes on interchange and noninterchange segments of urban freeways”, Journal of Transportation Engineering, Vol. 134, No. 3, pp. 111-117.

- Liu, X. C., Wang, Y., Schroeder, B. J. and Rouphail, N. M. (2012) “Quantifying cross- weave impact on capacity reduction for freeway facilities with managed lanes”, Transportation Research Record: Journal of the Transportation Research Board, Vol. 2278, No. 1, pp. 171-179.

- Mamdoohi, A. R., Saffarzadeh, M. and Shojaat, S. (2015) “Capacity drop estimation based on stochastic app.roach app.lied to Tehran-Karaj freeway”, International Journal of Transportation Engineering, Vol. 2, No. 4, pp. 279-288.

- Pande, A. and Wolshon, B. (2016) “Traffic engineering handbook”, 7th ed., USA: John Wiley & Sons, Chapter 9, pp. 485-525.

- Roess, R. P. and Prassas, E. S. (2014) “The highway capacity manual: a conceptual and research history”, Vol.1, Switzerland: Springer International Publishing, Chapter 8, pp. 249-338.

- Roess, R. P., and Ulerio, J. M. (2009) “Capacity of freeway weaving segments”, Transportation Research Record: Journal of the Transportation Research Board, Vol. 2130, pp. 34-41.

- Scott-Parker, B. (2017) “Emotions, behaviour, and the adolescent driver: A literature review”, Transportation Research Part F: Traffic Psychology and Behaviour, Vol. 50, pp. 1-37.

- Skabardonis, A. and Kim, A. (2010) “Weaving analysis, evaluation and refinement”, California PATH Research Report, Institute of Transportation Studies, University of California, Berkeley, Report No: CA10-0982, Chapter 2, pp. 3-14.

- Skabardonis, A. and Mauch, M. (2015) “Evaluation of methodologies for analyzing freeway ramp weaving”, Transportation Research Record: Journal of the Transportation Research Board, Vol. 2483, No. 1, pp. 130-139.

- TRB (Transportation Research Board) (2012) “NCHRP Report 600: human factors guidelines for road system”, 2nd ed. National Academy of Sciences, Washington, DC., Part I, Chapter 1, pp. 1-2.

- TRB (Transportation Research Board) (2010) “Highway capacity manual”, 5th ed., National Academy of Sciences, Washington, DC., Volume 2, Chapter 12, pp. 1-55.

- TRB (Transportation Research Board) (2000) “Highway capacity manual”, 4th ed., National Academy of Sciences, Washington, DC., Part III, Chapter 24, pp. 1-40

- TRB (Transportation Research Board) (1985) “Highway capacity manual”, 3rd ed., National Academy of Sciences, Washington, DC., Part II, Chapter 4, pp. 1-19.

- TRI (Transportation Research Institute) and Kittelson (Kittelson & Associates) (2008) “Analysis of freeway weaving sections”, NCHRP Project 3-75 Final Report, Transportation Research Institute, Polytechnic University Brooklyn, N.Y., and Kittelson & Associates, Portland, Oregon, Chapter 1, pp. 1-23.

- Wan, X., Jin, J. P., Gu, H., Chen, X. and Ran, B. (2017) “Modeling freeway merging in a weaving section as a sequential decision-making process”, Journal of Transportation Engineering, Part A: Systems, Vol. 143, No. 5, pp. 1-13.

- Wang, X., Hadiuzzaman, Md., Fang, J., Qiu, Z. T. and Yan, X. (2014) “Optimal ramp metering control for weaving segments considering dynamic weaving capacity estimation”, Journal of Transportation Engineering, Vol. 140, No. 11, pp. 1-10 .

- Yi, L., Lu, J. and Ma, Y. (2011) “Analysis of freeway weaving section: a review and assessment of methods”, Paper presented at the 3rd International Conference on Transportation Engineering, Chengdu, July 23-25.

- Zhang, Y. (2005) “Capacity modeling of freeway weaving section”, PhD diss., Virginia Polytechnic Institute and State University, Chapter 2, pp. 5-25.