Comparing Operation and Safety between a New Nano Interchange andConventional System Interchange

Interchange safety modeling;Interchange operation;GEE;Generalized log-linear model;Left-hand ramp;Nano interchange

Moon, Jae Pil ; Billy M. Williams, Committee Member,John R. Stone, Committee Member,Joseph E. Hummer, Committee Chair,Nagui M. Rouphail, Committee Member,Moon, Jae Pil ; Billy M. Williams ; Committee Member ; John R. Stone ; Committee Member ; Joseph E. Hummer ; Committee Chair ; Nagui M. Rouphail ; Committee Member

University:North Carolina State University

关键词: Interchange safety modeling;    Interchange operation;    GEE;    Generalized log-linear model;    Left-hand ramp;    Nano interchange;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/5526/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

The primary purpose of this research is to estimate the capability and applicability of new nano interchange designs as they compare to conventional four-level interchanges. Nano interchanges were conceived to provide drivers with high speed and short travel distances while requiring less right of way in dense urban areas where real estate is expensive. This research consists of two tasks: (1) operational evaluation and (2) safety evaluation.The operational evaluation compares measures of effectiveness (MOEs) between nano interchanges and conventional interchanges for thirty volume scenarios comprised of varied data for through volumes, ramp volumes, and percentages of heavy vehicles. The estimations were conducted for an entire interchange and for key freeway segments. The MOEs for an entire interchange are travel time, speed, delay time, and ramp travel time; and the MOEs for key freeway segments are density, speed, and level of service.The safety estimations were made by building safety prediction models for collisions that may occur in the influence areas of ramps. These safety models are based on negative binomial distribution and quantified safety effects of traffic, geometric, and environmental factors using three statistical methods: (1) a generalized linear model with only main effect variables, (2) a generalized linear model with main effects and interaction terms, and (3) the new Hauer method model. Specifically, this study addresses the safety effectiveness of left-hand ramps, which are needed in the nano interchange designs, because the safety effects have not been well quantified in previous studies. Considering goodness-of-fit statistics such as the likelihood-ratio test, Akaike?s information criterion (AIC), ordinary R-squared values,the Miaou method, and CURE plots, the best safety models were chosen for four collision categories: (1) Total collisions of all types, (2) Severe collisions, (3) Related Total collisions,and (4) Related Severe collisions.The operational evaluation for an entire interchange shows that conventional interchanges perform better than nano interchanges for the volume scenarios tested. The analyses of key freeway segments show that most of operational difficulties for the nano interchanges are in diverging influence areas located on upgrade segments. The analyses also indicate that several merging influence areas that are connected to ramps with steeper and longer upgrades also have lower performance levels.The safety prediction model developed unique linear or non-linear relationships among traffic, geometric, and environmental factors. Left-hand ramps appear to have higher collision frequencies than right-hand ramps, and on-ramps have higher collision frequencies than off-ramps. In addition to estimating the safety effects, this study compares three modeling procedures. This research shows that the Hauer procedure sufficiently represents linear and non-linear relationships in terms of diverse functional forms by each explanatory variable, whereas a generalized log-linear model does not adequately develop linear relationships for some explanatory variables in terms of linear functional forms. However, the generalized log-linear model with interaction terms among independent variables fits to data as well as the Hauer procedure.Finally, based on these estimations, the operational and safety problems of nano interchanges are addressed in this study, and the following recommendations are made to improve the operation and safety effectiveness of the interchange: (1) deceleration or acceleration lanes could be extended; (2) a two-lane off-ramp or on-ramp for the nano interchange could be considered; and (3) left-hand ramps could be replaced by right-hand ramps.