FUTURE CMF RESEARCH AND CHALLENGES Traffic Records Forum October 27, 2014 Daniel Carter, UNC HSRC

Motivation How do site characteristics and countermeasures affect road safety?  CMF How do site characteristics and countermeasures affect a CMF?  The question at hand

Research Project NCHRP – Guidance on the Development and Application of Crash Modification Factors UNC Highway Safety Research Center Vanesse Hangin Brustlin, Inc. Persaud and Lyon, Inc. Kittleson and Associates, Inc. Structured by three main objectives

OBJECTIVE 1. TRANSFERABILITY Develop guidelines for calibration of current CMFs to assess treatment effectiveness at sites for which key site characteristics may be different.

Transferability Rural Connecticut Rural Maine Rural Kansas Rural Washington

Questions When a countermeasure is applied to a different type of site, will it be MORE effective? Or LESS? Or EQUAL? When will this be the case? What site characteristics will impact the CMF value?

Using Existing Data Information from the CMF Clearinghouse Treatments with many studies Cumulative meta-analysis CMFunctions Detailed disaggregate data analysis Information on individual locations Location-specific characteristics

Exploration of Influential Factors Treatment Influential Factors on the CMF Area and Facility Type Study Citation Installation of safety edge treatment Paved vs unpaved shoulder types Rural 2 lane roads Graham, J.L., Richard, K.R., O'Laughlin, M.K., Harwood, D.W., "Safety Evaluation of the Safety Edge Treatment" Report No. FHWA-HRT , Federal Highway Administration, Washington, DC. (2011) Signal to roundabout conversion Number of lanes (1 vs. 2), area type (urban vs. suburban), number of intersection legs (3 vs. 4) Signalized intersections in urban and suburban areas Srinivasan, R., Baek, J., Smith, S., Sundstrom, C., Carter, D., Lyon, C., Persaud, B., Gross, F., Eccles, K., Hamidi, A., and Lefler, N., "NCHRP Report 705: Evaluation of Safety Strategies at Signalized Intersections.", Washington, D.C., Transportation Research Board, National Research Council, (2011)

Guidance to Produce Guidance on overall procedure for selecting and applying a CMF Guidance on identifying influential factors for a CMF Preset list of influential factors for common safety treatments and treatment categories Guidance for identifying influential factors if CMF is not in the preset list Guidance on testing CMFs for homogeneity Guidance on adjusting CMFs for differences in site conditions Physical characteristics Volume distribution Crash type and severity

OBJECTIVE 2. MULTIPLE COUNTERMEASURES Develop guidelines for how existing and future CMFs can be combined in a single location with multiple treatments.

Multiple Countermeasures

Questions Will multiple countermeasures have an effect that’s GREATER than the individual countermeasures? Or LESS? Or EQUAL? And when will this be true?

Identified Existing Methods for Combining CMFs Multiplicative Methods Dominant Effect Method Dominant Effect by Crash Type Dominant Common Residuals Method Estimating Combined Effect for Unknown Interaction

Define Ground Truth Level Treatment Q 1 (Not Present)2 (Present) Treatment P A (Not Present)A1A2 B (Present)B1B2

Assess and Validate Methods Assess validity of identified methods (compare results of methods to ground truth) Identify most possible scenarios of interaction effects Select best method (or develop a new one) and validate against real world dataset

Guidance to Produce Guidance on combining single CMFs to estimate combined effects Step-by-step procedures and examples for selecting and applying appropriate method(s)

Example of Guidance to Produce Define Applicability of Individual CMFs (i.e., to what crash types and severities do the individual CMFs apply?) Same Crash Type and Severity Define Categories for Individual Treatments (e.g., roadway, roadside, intersection) Same General Category Large Potential Interaction Effect: Apply Method 1 Different General Category Medium Potential Interaction Effect: Apply Method 2 Different Crash Type and Severity Define Categories for Individual Treatments (e.g., roadway, roadside, intersection) Same General Category Small Potential Interaction Effect: Apply Method 3 Different General Category Negligible Potential Interaction Effect: Apply Method 4

OBJECTIVE 3. CRASH MODIFICATION FUNCTION DEVELOPMENT Develop recommended procedures for formulating and calibrating future CMFs that identify key influential site characteristics.

CMFunction Development

Questions How can CMFunctions be developed from regression model coefficients? Key is to explore interactive effects between the CMF and non- CMF related variables (e.g., interaction between centerline rumble strips and AADT). How can CMFunctions be developed from CMF point estimates? CMF point estimates from the same study with a variety of application circumstances. CMF point estimates from different studies Combination of the first two scenarios

Guidance to Produce Guidance for developing CMFunctions and assessing fit Guidance for quantifying the CMF standard error when computed as a function. Guidance on planning and designing studies (e.g., experimental) and treatments to better facilitate the development of CMFunctions

Potential Data Sources Two-way to multi-way stop control (NC) Improved curve delineation (CT, WA) Stop to signal control conversion (NC, CA) Improving pavement friction (MN, PA)

Thank You Daniel Carter UNC Highway Safety Research Center