Understanding how the type and location of intersections affect crashes is important to reduce these crashes effectively. This paper discusses the development of regional safety performance functions (SPFs) based on a new context classification system developed by the Florida Department of Transportation (FDOT). This classification system (which has not previously been used) categorizes intersections into eight different categories based on land use and other parameters, allowing SPFs to be developed for up to 32 different types of intersections. The Model Inventory of Roadway Elements (MIRE) 2.0 was used as the standard inventory for the data elements collected. Using MIRE 2.0 allows for the procedures conducted in this study to be easily implemented in other states. SPFs were developed for two intersection groups. First, a linear regression model was built to predict missing minor traffic volumes. This statistically significant model ( p-value < 0.05) had an adjusted R-square of 0.7648. Data were collected for over 25 potential predictor variables (including a regional variable for FDOT districts) and used to fit a negative binomial model to each studied intersection group. Some variables (such as major traffic volume) were significant for both groups, but each SPF had unique variables (such as speed limit and road width). Different regions were significant for each group, showing how crashes vary for different intersection types in different regions. By allowing for the development of SPF models for many intersection classifications, FDOT’s context classification system can be used by other agencies to identify crash-influencing factors better for different conditions.
The emergency shoulder use (ESU) was implemented in Florida in September 2017 to facilitate mass evacuation before Hurricane Irma made landfall on the shores of Florida. ESU was implemented on the northbound I-75 for about 39 h and eastbound I-4 for about 6 h when the left shoulders were opened for use as travel lanes. This study discusses the operational and safety effects of ESU. The operational effects of ESU were studied and compared with other alternatives including one-way operation (contraflow) and both left and right shoulder use. The findings showed the left shoulder ESU could be an effective alternative to one-way operation. The one-way operation was not a preferred method as it can only be operated during the day time, requires massive resource allocation, and hampers emergency services reaching to different parts of the state. However, ESU on the left shoulder offers minimal disturbance to traffic and is easy to deploy. The safety impact analysis was performed by conducting a descriptive statistical comparison of crash types, severity, and other relevant factors during ESU operations. The crash analysis showed that the observed number of crashes on an urban I-75 segment during ESU operation is commensurate with normal operation with saturated traffic conditions, in contrast a rural segment experienced a higher observed crash rate than the predicted rate with saturated traffic conditions. The predictive analysis of ESU crashes also showed that ESU implementation helped to reduce the expected number of crashes significantly.
Safety performance functions (SPFs) are essential tools to help agencies predict crashes and understand influential factors. Florida Department of Transportation (FDOT) has implemented a context classification system which classifies intersections into eight context categories rather than the three classifications used in the Highway Safety Manual (HSM). Using this system, regional SPFs could be developed for 32 intersection types (unsignalized and signalized 3-leg and 4-leg for each category) rather than the 10 HSM intersection types. In this paper, eight individual intersection group SPFs were developed for the C3R-Suburban Residential and C4-Urban General categories and compared with full SPFs for these categories. These comparisons illustrate the unique and regional insights that agencies can gain by developing these individual SPFs. Poisson, negative binomial, zero-inflated, and boosted regression tree models were developed for each studied group as appropriate, with the best model selected for each group based on model interpretability and five performance measures. Additionally, a linear regression model was built to predict minor roadway traffic volumes for intersections which were missing these volumes. The full C3R and C4 SPFs contained four and six significant variables, respectively, while the individual intersection group SPFs in these categories contained six and nine variables. Factors such as major median, intersection angle, and FDOT District 7 regional variable were absent from the full SPFs. By developing individual intersection group SPFs with regional factors, agencies can better understand the factors and regional differences which affect crashes in their jurisdictions and identify effective treatments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.