Calibrating Highway Safety Manual Equations for Application in Florida Dr. Siva Srinivasan, Phillip Haas, Nagendra Dhakar, and Ryan Hormel (UF) Doug Harwood and Darren Torbic (MRI) Funded by Florida Department of Transportation

Highway Safety Manual Published by AASHTO in 2010 Provides tools to conduct quantitative safety analyses –Methods for a roadway safety management program –Predictive methods to estimate crash frequency by severity –Crash modification factors (CMFs)

HSM Facility Types Rural two-way two-lane highways –Undivided segments –Three-leg minor stop controlled intersections –Four-leg minor stop controlled intersections –Four-leg signalized intersections Rural multilane highways –Undivided segments –Divided segments –Three-leg minor stop controlled intersections –Four-leg minor stop controlled intersections –Four-leg signalized intersections Urban and Suburban Arterials –Two-lane undivided segments –Three-lane segments with two-way left-turn lanes –Four-lane undivided segments –Four-lane divided segments –Five-lane segments with two-way left-turn lanes –Three-leg minor stop controlled intersections –Four-leg minor stop controlled intersections –Three-leg signalized intersections –Four-leg signalized intersections

CMF 1x …CMF yx = crash modification factors specific to facility type x and geometric design and traffic control features y C x = calibration factor to adjust SPF for local conditions for facility type x HSM Crash Prediction N predicted = predicted average crash frequency for an individual site for a specific year N spf = predicted average crash frequency for base conditions Segments –N = exp[ a + b×ln(AADT) + ln(Length) ] Intersections –N = exp[ a + b×ln(AADT major ) + c×ln(AADT minor ) ]

Why Calibrate? HSM models were developed in national studies –Segments based on Washington –Intersection based on California Calibrate for local factors –Weather –Driver behavior and population –Crash reporting methods & thresholds –Animal populations Distinct calibration factor for each facility type and crash severity inclusion

HSM Calibration Procedure Identify facility types Collect road characteristic data Collect crash data Apply SPF for crash prediction Apply CMFs Compute calibration factor

Segment Calibration

Roadway Data Year-end archives of FDOT RCI obtained for Roadways split into homogeneous segments Segments with incomplete or inaccurate data removed

Crash Data Crashes extracted from the Crash Analysis Reporting System (CARS) – Only includes fatal and injury crashes –CARS only includes long-form crash records –Calibration factors developed for fatal and injury crash frequency prediction Intersection crashes removed –“occurring at an intersection” –“influenced by an intersection” Crashes assigned to segments based on Roadway ID and milepost

HSM Facility Types

Statewide Segment Calibration Results

Intersection Calibration

Intersection Data Listing of all Florida intersections obtained from FDOT Safety Office Restricted to analysis of only HSM defined facility types –Rural two-lane two-way roads and multilane highways Three-leg stop controlled Four-leg stop controlled Four-leg signalized –Urban arterials Three-leg stop controlled Three-leg signalized Four-leg stop controlled Four-leg signalized Restricted to analysis of intersections of two state maintained roads –AADT and crash data not available for non-state roads

Intersection Characteristics Two primary sources –RCI Available for each year individually –Google maps Only available for date of satellite image Assumption made that these data were applicable for all years –Site removed if construction was present in image –Site removed if site characteristics in RCI changed

Approaches with LT Lanes: 4 CMF 1i = 0.66 Approaches with RT Lanes: 2 CMF 3i = 0.92 Google Data Collection

Approaches with LT Lanes: 4 CMF 1i = 0.66 Approaches with RT Lanes: 2 CMF 3i = 0.92 LT-Protected: 4 Approaches CMF 3i = Lighting Present CMF 3i = 0.91 No Red-Light Cameras RTOR Permitted

3 Bus Stops: CMF 1p = School: CMF 2p = Alcohol Establishments: CMF 3p = 1.12 Pedestrian Volume: Med-Low (240/day) Max Lanes Crossed: 9

Crash Data Crashes extracted from the Crash Analysis Reporting System (CARS) – Fatal and injury crashes only –CARS only includes long-form crash records Intersection crashes identified –“occurring at an intersection” –“influenced by an intersection” Crashes assigned based on node ID

Intersection Facility Types

Intersection Calibration Results

Intersection Calibration Spreadsheet Sample

Intersection Calibration Spreadsheet Can be used for future recalibration Specific to each facility type Requires user entry of AADT and crash data Hidden cells allow for intersection characteristics to be updated as needed –Lighting, turn lanes, etc. Calculates SPFs and CMFs to determine predicted crashes Calculates calibration factor for both KAB and KABC severity levels

HSM Calibration Summary Calibration allows for HSM implementation in Florida Calibration factors developed for intersection and segments –Fatal and injury crashes only Calibration benefits of segment calibration –Improved prediction over uncalibrated models (error, absolute error, variance) Limited data availability for intersections –Significantly restricted by requiring the intersection of two state maintained roads –Significant manual effort involved for data collection

Future Potential HSM Research Areas Expansion to include models and calibration for more facility types Development of CMFs for additional geometric design, traffic control, and area attributes Implementation of localized calibration – by region or areas with otherwise similar characteristics Exploration of alternative crash prediction methods and modeling structures Investigation of crash prediction validation and comparison metrics

Thank you!