CE 4640: Transportation Design Prof. Tapan Datta, Ph.D., P.E. Fall 2002

Highway Safety: Facts & Figures National crash statistics for 2000* 41,821 people were killed in 6,394,000 reported motor vehicle traffic crashes 3,189,000 people were injured 4,286,000 crashes were PDO type *Source: National Highway Traffic Safety Administration (NHTSA)

Highway Safety: Facts & Figures Source: National Highway Traffic Safety Administration (NHTSA)

Highway Safety: Facts & Figures Source: National Highway Traffic Safety Administration (NHTSA)

Highway Safety: Facts & Figures Source: National Highway Traffic Safety Administration (NHTSA)

Highway Safety: Facts & Figures Michigan crash statistics for 2000* 1,382 people were killed in 424,852 reported motor vehicle traffic crashes 121,826 people were injured 336,572 crashes were PDO type *Source: Michigan Office of Highway Safety Planning (MOHSP)

Highway Safety: Facts & Figures Michigan crash facts for 2000* Every 1.2 minutes a traffic crash occurs One person is killed in a crash every 6.3 hrs One person is killed in an alcohol-related crash every 19.1 hrs One driver under age 21 is in a fatal crash every 28.2 hrs One person is injured in a crash every 4.3 minutes One pedestrian is injured every 3.6 hrs One bicyclist is injured every 4.7 hrs *Source: Michigan Office of Highway Safety Planning (MOHSP)

Goals of a Traffic Engineer Can be one or more of the following: Reduce the frequency or rate of traffic crashes Reduce the frequency or rate of injury crashes Reduce the frequency or rate of fatal crashes Reduce the frequency or rate of specific crash categories, such as, alcohol-related, speeding, older-driver crashes

Elements of Highway Safety Driver Vehicle Roadway Traffic Engineer has no control

Safety Improvement Approaches Reducing crash occurrence Installing safety measures Correcting hazardous roadway features Improving driver skills by training Reducing the severity of crashes Proper geometric design, guardrail, median barrier, breakaway sign post Improving crash survivability Vehicle safety features, like air bag, seat belts, energy-absorbing bumper

Safety Improvement Approaches Programmatic safety efforts Federal and State programs to promote safety on a policy level State vehicle inspection program National speed limit National 21-year-old drinking age Federal vehicle design standards Design aspects of safety Safer design of roadways Horizontal and vertical alignment Roadside design Median barriers Gore areas

Highway Safety Improvement Program (HSIP) PLANNING COMPONENT IMPLEMENTATION COMPONENT EVALUATION COMPONENT

Overview of the Highway Safety Improvement Program PLANS FOR THE TOTAL HIGHWAY SYSTEM PLANNING AND DESIGN CONSTRUCTION SAFETY OPERATION AND MAINTENANCE HIGHWAY SAFETY IMPROVEMENT PROGRAM (HSIP) ADMINISTRATIVE DECISIONS DESIGN STANDARDS, ETC. CONCERNING GOALS, OBJECTIVES PLANNING COMPONENT IMPLEMENTATIONCOMPONENT EVALUATION COMPONENT Overview of the Highway Safety Improvement Program

IMPLEMENTATION COMPONENT PLANNING COMPONENT PROCESS 1 COLLECT AND MAINTAIN DATA PROCESS 2 IDENTIFY HAZARDOUS LOCATIONS AND ELEMENTS PROCESS 3 CONDUCT ENGINEERING STUDIES PROCESS 4 ESTABLISH PROJECT PRIORITIES IMPLEMENTATION COMPONENT PROCESS 1 SCHEDULE AND IMPLEMENT SAFETY IMPROVEMENT PROJECTS EVALUATION COMPONENT PROCESS 2 DETERMINE THE EFFECT OF HIGHWAY SAFETY IMPROVEMENTS Highway Safety Improvement Program at the Process Level

DEFINE THE HIGHWAY LOCATION REFERENCE SYSTEM PROCESS 1. COLLECT AND MAINTAIN DATA SUBPROCESS 1 DEFINE THE HIGHWAY LOCATION REFERENCE SYSTEM SUBPROCESS 2 COLLECT AND MAINTAIN CRASH DATA. SUBPROCESS 3 COLLECT AND MAINTAIN TRAFFIC DATA. SUBPROCESS 4 COLLECT AND MAINTAIN HIGHWAY DATA. PLANNING COMPONENT PROCESS 2. IDENTIFY HAZARDOUS LOCATIONS AND ELEMENTS PROCESS 3. CONDUCT ENGINEERING STUDIES SUBPROCESS 1 COLLECT AND ANALYZE DATA. SUBPROCESS 2 DEVELOP CANDIDATE COUNTERMEASURES SUBPROCESS 3 DEVELOP PROJECTS PROCESS 4. ESTABLISH PROJECT PRIORITIES

Highway Safety Improvement Program at the Subprocess Level PROCESS 1. SCHEDULE AND IMPLEMENT SAFETY IMPROVEMENT PROJECTS IMPLEMENTATION COMPONENT SUBPROCESS 1 SCHEDULE PROJECTS SUBPROCESS 2 DESIGN AND CONSTRUCT PROJECT SUBPROCESS 3 CONDUCT OPERATIONAL REVIEW PROCESS 1. DETERMINE THE EFFECT OF HIGHWAY SAFETY IMPROVEMENTS SUBPROCESS 1 PERFORM NON-CRASH BASED PROJECT EVALUATION SUBPROCESS 2 PERFORM CRASH BASED PROJECT EVALUATION EVALUATION COMPONENT SUBPROCESS 3 PERFORM PRGRAM EVALUATION SUBPROCESS 4 PERFORM ADMINISTRATIVE EVALUATION Highway Safety Improvement Program at the Subprocess Level

Crash Data Collection Police Officer collects necessary crash information from the site Traffic Crash Report Form (UD-10) is used to gather: Date, time, location information Weather, pavement, lighting condition Driver information Injury, fatality information Type and severity of crash A hand sketch showing the positions of vehicles at the time of crash Other information

Traffic Crash Report Form (UD-10)

Crash Data Recording Data collected in UD-10 Forms are entered into the computer system to develop a statewide crash database Local government departments may develop their own data system For example, SEMCOG’s Comprehensive Analysis Safety Tool (CAST)

A Sample CAST Output

A Sample Collision Diagram

Typical Traffic Crash Location File and Crash Location Index Card

Computerized Spot Map

Process 2: Identify Hazardous Locations and Elements Purpose To identify hazardous spots, sections, and elements based on the crash, traffic and highway data obtained from Process 1

Procedures Involved in Identification Procedure 1- Frequency Method Procedure 2- crash Rate Method Procedure 3- Frequency Rate Method Procedure 4- Rate Quality Control Method Procedure 5- Crash Severity Method Procedure 6- Hazard Index Method Procedure 7- Hazardous Roadway Features Inventory Method

Hazardous highway locations may or may not be high-crash locations It is important for the highway agency to also consider the identification of locations with a potential for high-crash numbers or severity

Time Consideration Time period should be short enough to identify sudden changes in crash patterns Time period should be long enough to assure reliability in identifying hazardous locations Multiples of one year are preferred Segment Length Considerations Spot Section In both cases should have consistent characteristics of: Geometrics Traffic volumes Condition

Data Input

Procedure 1 - Frequency Method Used to identify and rank locations on the basis of number of crashes This method is the easiest to apply and does not require the use of traffic volume data Used by many agencies to select the initial group of high crash locations for further analysis A critical value must be established for location selection (such as 9 or more crashes per year)

Advantages Effective as a tool for providing continuous monitoring of the crash situation in an area Provides simple, direct method for identifying hazardous locations Disadvantages No consideration of exposure Does not account for crash severity Does not give consideration to locations with a high potential for crashes, but with no past crash experience

Procedure 2 - Crash Rate Method It combines the crash crash with the various exposure factors Vehicle Miles of Travel (VMT) Population Registered Vehicles

Crash Rate Crash Rates are calculated for a location, segment or an area based on: Vehicle Miles of Travel (VMT) Crash Rates are also calculated for an area based on: Population Registered Vehicles

Crash Rate Calculation Crash Rate at a location, Rsp= Freq. of Crashes*106 (365)(T)(V) Crashes per million vehicles where T = Period of study (years) V = Average Annual Daily Traffic (For intersection, sum of all approach volumes)

Crash Rate Calculation Crash Rate at a segment, Rse= Freq. of Crashes*106 (365)(T)(V)(L) Crashes per million vehicle miles of travel where T = Period of study (years) V = Average Annual Daily Traffic L = Length of the section (miles)

Crash Rate Calculation Crash Rate for an area = Freq. of Crashes*106 VMT Crashes per million Vehicle Miles of Travel Freq. of Crashes*1000 Population Crashes per 1,000 Pop Freq. of Crashes*1000 Registered Vehicles Crashes per 1,000 Regd. Vehicles

Advantages Combines the use of an exposure factor (traffic volume) and a frequency factor Remains a relatively simple, direct method Disadvantages May over represent hazard at locations with very low traffic volumes Requires additional data Does not account for crash severity Does not give consideration to locations with a high potential for crashes, but with no past crash experience

Example Problem

Example Problem Using Frequency Method for Total Crashes: Rank Intersection Total Crash Freq. 1 Plymouth Road & 50 Middlebelt Road 2 Crook Road & 38 Auburn Road 3 Livernois Road & 12

Example Problem Crash Rate at a location, Rsp= Freq. of Crashes*106 Using Crash Rate Method for Total Crashes: Crash Rate at a location, Rsp= Freq. of Crashes*106 (365)(T)(V) Crashes per million vehicles where T = Period of study (years) V = Average Annual Daily Traffic (For intersection, sum of all approach volumes)

Example Problem Total Crash Rate at Crook & Auburn 38*106 (365)(1)(35,700) Crashes per million vehicles = 2.92 Crashes per million vehicles Similarly, we calculate crash rates for other locations.

Example Problem Using Crash Rate Method for Total Crashes: Rank Intersection Total Crashes per Million Vehicles 1 Crook Road & 2.92 Auburn Road 2 Plymouth Road & 2.82 Middlebelt Road 3 Livernois Road & 1.29

Procedure 3 - Frequency Rate Method Normally applied by first selecting a large sample of high crash locations based on a “number of crashes” Then, crash rates are computed and the locations are priority ranked by crash rate A some what different procedure was developed to compare the dual influence of frequency and rate in a matrix pattern (as shown in the next slide)

Multidimensional Crash Data Analysis Matrix Priority 1 Crash Rate Priority 2 Crash Frequency

Frequency Rate Matrix for Total Crashes for the Example Problem Priority 1 Priority 2 Total Crashes per Million Vehicle Miles Priority 3 Crash Frequency

Advantages Alleviates the need to calculate rates at every crash location Uses both frequencies and rates to assess hazard Reduces the exaggerated effect of the crash rate on low volume roads and the exaggerated effect of high frequencies at high-volume intersections Disadvantages May require considerable funds and manpower More complex Does not account for crash severity Does not give consideration to locations with a high potential for crashes, but with no past crash experience

Procedure 4 - Rate Quality Control Method Utilizes a statistical test Determines whether the crash rate at a location is significantly higher than a predetermined average rate for locations of similar characteristics In this method, the crash rate at a location is compared to a “critical rate”

Procedure 4 - Rate Quality Control Method The equation for calculating the critical rate is as follows: Rc = Ra + K (Ra / M)1/2 + 1/(2M) where, Rc = Critical rate for spot or section Ra = Average crash rate for all spots of similar characteristics or on similar road types M = Millions of vehicles passing over a spot or millions of vehicles miles of travel on a section K = A probability factor

P (Probability) 0.005 0.0075 0.05 0.075 0.10 K-value 2.576 1.960 1.645 1.440 1 .282 The most commonly used K values are 2.576 (P = .005) and 1.645 (P = 0.05) Advantages Reduces the exaggerated effect of the crash rate on low volume roads and the exaggerated effect of high frequencies at high-volume urban intersections Flexible enough to accommodate changing crash patterns Allows for statistical reliability in identifying location

Disadvantages Relatively complex Manual application is time consuming and expensive Does not take severity of crashes into account Does not give consideration to locations with a high potential for crashes, but with no past crash experience

Procedure 5 - crash Severity Method Description Used to identify and priority-rank high-crash locations Some states consider only injury and fatality crashes in identifying Other states apply weighting factors to crash based on their severity and then compute some form of severity index

Crash severity are often classified by NSC within the following five categories Fatal Crash - one or more deaths Type-A Injury Crash - Bleeding wound, distorted member Type-B Injury Crash - Bruises, abrasion, swelling, limping Type-C Injury Crash - Involving no visible injuries but complaint of pain (probable injury) PDO Crash - Property Damage Only

Equivalent Property Damage Only (EPDO) Method The equivalency factors vary by state. The formula below is used by Kentucky: EPDO = 9.5 (F+A) + 3.5 (B+C) + PDO where, F = No. of fatal crashes A = No. of A-Type injury crashes B = No. of B- Type injury crashes C = No. of C- Type injury crashes PDO = No. of PDO crashes

Advantages Accounts for the severity of crashes Highly applicable to rural areas, where high percentages of severe crashes occur Disadvantages The severity of a crash is highly dependent on many factors which are unrelated to the highway location (i.e. age and health of passengers, type of vehicle involved, etc.) Does not consider locations with a high potential for crashes

Procedure 6 - Hazard Index Method It employs a formula to develop a rating index for each suspect site Factors used in the formula are No. of crashes per year Crash rate Crash severity Sight distance Volume/capacity ratio Traffic conflicts Erratic maneuvers Driver Expectancy Information system deficiencies

Hazard Index Method Example

Advantages Comprehensive use of numerous factors related to locational hazards Highly adaptable, factors which do not apply or are not available may be deleted from analysis Considers both crash data and variables which indicate a high potential for crashes Disadvantages Large amounts of information are necessary Deletion of too many factors from analysis reduces its effectiveness Requires considerable expertise in highway safety and human factors May require data that is not readily available

Procedure 7 - Hazardous Roadway Features Inventory It is one way of selecting sites with potential for high-crash severity or numbers Based on comparison of existing features with safety and design standards

Examples of Hazardous Features Blunt-end guardrail barrier terminals Narrow bridges Steep roadside slopes Rigid roadside objects Narrow lanes and shoulders Slippery pavements Sharp radii on horizontal curves and ramps Hazardous highway-railroad grade crossings

Advantages Considers locations that are potentially hazardous (even though large number of crashes may not have been observed Considers locations (e.g., railroad grade crossings, roadside hazards) which have a potential for high-severity crashes Disadvantages Can require large amounts of data Requires personnel with experience in highway safety Improvement expenditures must be justified on some basis other than reduction in crash experience

Left-turn Head-on Collisions: Probable Causes Restricted sight distance Too short amber phase Absence of special left-turning phase Excessive speed on approaches

Left-turn Head-on Collisions: Studies to be Performed Review existing intersection channelization Volume count for through & left-turn traffic Review signal phasing Study the need for special left-turn phase Perform spot speed study

Left-turn Head-on Collisions: Possible Countermeasures Provide adequate channelization Install traffic signal if warranted by MUTCD Increase amber phase Provide special phase for left-turning traffic Prohibit left turns Reduce speed limit on approaches Provide all-red phase

Rear End Collisions at Unsignalized Intersections: Probable Causes Improper channelization High volume of turning vehicles Slippery surface Inadequate intersection warning signs Excessive speed on approaches Inadequate roadway lighting

Rear End Collisions at Unsignalized Intersections: Studies to be Performed Review existing channelization Volume count for through & turning traffic Check skid resistance Perform spot speed study Check for adequate drainage Check roadway illumination

Rear End Collisions at Unsignalized Intersections: Possible Countermeasures Create right or left turn lanes Increase curb radii Prohibit turns Provide “Slippery When Wet” sign Increase skid resistance Improve drainage Reduce speed limit Improve roadway lighting

Angle Collisions at Signalized Intersections: Probable Causes Restricted sight distance Inadequate roadway lighting Poor visibility of signal Excessive speed on approaches

Angle Collisions at Signalized Intersections: Studies to be Performed Volume count on all approaches Field observations for sight obstructions Review signal timing Check roadway illumination Perform spot speed study

Angle Collisions at Signalized Intersections: Possible Countermeasures Remove obstructions to sight distance Increase amber phase Provide/increase all-red interval Prohibit curb parking Install backplates, larger heads for signals Improve location of signal heads Reduce speed limit at approaches

A Project Example An improvement project was undertaken by WSU for AAA, Michigan One of the study stretch was Eastern Corridor Problems were identified through studies and analyses Possible countermeasures were suggested

Sample Intersection Before Improvement Eastern Avenue & Franklin Street

Problems Identified A few of the intersections without a left-turn lane had a queue and associated delay Signals were not properly located for clear visibility Signal heads were small 8 Too short all-red intervals at a few locations

Suggested Countermeasures Exclusive left-turn lanes were added wherever needed Replaced existing span wire mounted signal configuration with box span installation Relocated signal heads to improve visibility Replaced 8” signal heads with 12” signal heads       

Suggested Countermeasures Implemented longer all-red intervals at locations where needed (Eastern Avenue 2.0 seconds; minor streets 2.0 seconds) Installed secondary post mounted signal heads to improve visibility for left turn traffic Installed back plates on signals to improve visibility

Sample Intersection After Improvement Eastern Avenue & Franklin Street (After)

Non-Accident Measures Reduce the number of conflicts at an intersection, by prohibiting turns or movements Definition of Traffic Conflict: an evasive action taken by the driver of a vehicle to avoid an impending collision