1. Report No.

FHWA-JPO-09-066

2. Government Accession No.

EDL No.- 14498

3. Recipient’s Catalog No.

4. Title and Subtitle

Microscopic Analysis of Traffic Flow in Inclement Weather

5. Report Date

November 2009

6. Performing Organization Code

7. Author(s)

Hesham Rakha, Daniel Krechmer, Gustave Cordahi, Ismail Zohdy, Shereef Sadek, and Mazen Arafeh

8. Performing Organization Report No.

9. Performing Organization Name and Address

Virginia Tech Transportation Institute
3500 Transportation Research Plaza (0536)
Blacksburg, VA 24061

Cambridge Systematics, Inc.
4800 Hampden Lane, Suite 800
Bethesda, MD 20814

10. Work Unit No.

11. Contract or Grant No.

DTFH61-06-D-00004

12. Sponsoring Agency Name and Address

Research and Innovative Technology Administration
U. S. Department of Transportation
1200 New Jersey Avenue, SE
Washington, DC  20590

13. Type of Report and Period Covered

Guidelines

14. Sponsoring Agency Code

HOP

15. Supplementary Notes

COTM’s for FHWA are Roemer Alfelor and C. Y. David Yang.

16. Abstract

Weather causes a variety of impacts on the transportation system.  An Oak Ridge National Laboratory study estimated the delay experienced by American drivers due to snow, ice, and fog in 1999 at 46 million hours.  While severe winter storms, hurricanes, or floodings can result in major stoppages or evacuations of transportation systems and cost millions of dollars, the day-to-day weather events such as rain, fog, snow, and freezing rain can have a serious impact on the mobility and safety of the transportation system users.  Despite the documented impacts of adverse weather on transportation, the linkages between inclement weather conditions and traffic flow in existing analysis tools remain tenuous.  This is primarily a result of limitations on the data used in research activities.

The scope of this research included use of empirical data, where available, to estimate weather impacts on three categories of submodels related to driver behavior, longitudinal vehicle motion models (acceleration, deceleration and car-following models), lane-changing models and gap acceptance models.  Empirical data were used to estimate impacts of adverse weather on longitudinal and gap acceptance models but no suitable datasets were identified for lane-changing models.  Existing commercial microsimulation software packages were then reviewed to identify whether and how weather-related factors could be utilized in these models.  The various submodels used in these packages to estimate longitudinal motion, lane-changing and gap acceptance models were evaluated.  The research found that for the most part, weather-related factors could be incorporated into these models, although the techniques vary by package and by type of model.  Additional empirical research is needed to provide confidence in weather-related adjustment factors, particularly as relates to ice and snow.  This report concludes with some recommendations of future research related to weather and traffic flow.  Additional work is proposed related to human factors and microscopic traffic modeling.

17. Key Words

Weather, traffic flow, statistical models, human factors, microsimulation

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No of Pages

119

22. Price

N/A