HSM Applications to TwoLane Rural Highways Predicting Crash

HSM Applications to Two-Lane Rural Highways Predicting Crash Frequency and Applying CMF’s for Two-Lane Rural Highway Intersections - Session #6 6 -1

Predicting Crash Frequency for Two-Lane Rural Highway Intersections Outcomes: ► Describe the SPF Base Models for prediction of Intersection Crash Frequency ► Calculate Predicted Crash Frequency for Rural Two-lane Highway Intersections ► Describe CMF’s for Rural 2 Lane Intersections ► Apply CMF’s to Predicted Crash Frequency 6 -2

Why Intersection Safety? ► A small part of overall highway system, but ► In 2008 – 7, 772 fatalities related to intersections ► (21% of Total Highway Fatalities) (KY 14% in 2018) ► Each year more than 3. 17 million intersection crashes occur (over 55% of all reported crashes) 6 -3

2008 US Total Crash Characteristics Crash Type Non Intersection Stop/No control Intersection Total Crashes Fatal/Injury Crashes Number % 2, 638, 000 45% 722, 680 43% 984, 000 17% 321, 520 19% 37% Number 42% % Signalized Intersection 1, 182, 000 20% 380, 511 23% Unclassified 1, 005, 000 17% 240, 306 14% Total 5, 801, 228 100% 1, 637, 476 100% Source: USDOT Traffic Safety Facts 2008 Early Edition, A Compilation of motor vehicle crash data from FARS and GES, Table 29, Page 52 6 -4

Physical vs Functional Area of an Intersection 6 -5

Functional Area of an Intersection ► Decision Distance ► Maneuver Distance ► Queue-Storage Distance 6 -6

Process for Prediction of Crash Frequency and Application of Crash Modification Factors Three Steps: 1. Predict Crash Frequency - Safety Performance Functions (SPF) Equations 2. Apply Appropriate Crash Modification Factors (CMFs) - Adjust predicted safety performance from base conditions to existing/proposed conditions - Are greater or less than 1: q < 1. 0 -- lower crash frequency q > 1. 0 -- increased crash frequency 3. Calibration, Cr or Ci - Accounts for local conditions/data 6 -7

Models to Predict Crash Frequency for Rural Two-Lane Highway Intersections ►Three-Approach Stop Control (Stop of Stem of Tee) ► Four-Approach Stop Control (2 -way Stop) ► Four-Approach Signal Control 6 -8

SPF Models for RURAL Two-Lane Intersections with Stop Control on Minor -Road Three-Leg Stop Controlled Intersection (3 ST): Nspf-3 ST=exp[-9. 86 + 0. 79 ln(AADTmaj) + 0. 49 ln(AADTmin)] Four-Leg 2 -Way Stop Controlled Intersection (4 ST): Nspf-4 ST=exp[-8. 56 + 0. 60 ln(AADTmaj) + 0. 61 ln(AADTmin)] AADTmaj = Avg Annual Daily Volume on Major Road (veh/day) AADTmin = Avg Annual Daily Volume on Minor Road (veh/day) 6 -9

SPF Models for RURAL Signalized Intersections Four-Leg Signalized Intersection (4 SG): Nspf-4 SG = exp[-5. 13 + 0. 60 ln(AADTmaj) + 0. 20 ln(AADTmin)] Nspf-4 SG = estimate of intersection-related predicted average crash frequency for base conditions; AADTmaj = Avg Annual Daily Volume on Major Road (veh/day) AADTmin = Avg Annual Daily Volume on Minor Road (veh/day) 6 -10

Base Conditions for Rural Two-Lane Intersections: ►Intersection Skew Angle: ► Presence of Left-Turn Lanes: ► Presence of Right-Turn Lanes: ► Lighting: 0 odegrees none 6 -11

SPF Model for RURAL Stop Controlled Intersection– Example: 1 -Way STOP on Minor Approach to a “T” Intersection (3 -leg): Discussion ►For a 1 -Way STOP with an AADT of 5000 across the top of the “T” on the main Road and 500 AADT on the minor road of the “T”, ► What is the predicted # of Crashes? 6 -12

SPF Model for RURAL Stop Controlled Intersection– Example: Three-Leg Stop Controlled Intersection (3 ST): Nspf-3 ST = exp[-9. 86 + 0. 79 ln(AADTmaj) + 0. 49 ln(AADTmin)] For AADTmaj = 5, 000 and AADTmin = 500: Nspf-3 ST = exp[-9. 86 + 0. 79 ln(5, 000) + 0. 49 ln(500)] = exp[-9. 86 + 6. 729 + 3. 045] = exp[-0. 086] = 0. 917 crashes per year or 4. 59 crashes in a 5 year period 6 -13

Safety Performance Function (SPF) Highway Safety Manual Approach: e “on ” e t ra Average Crash Rate 6 -14

“Is this a Higher Crash Frequency Site? ” Highway Safety Manual Approach: “Substantive Crash Frequency” 6 crashes/yr “Difference” “Predicted Crash Frequency” 1. 2 crashes/yr 0. 5 crashes/yr 6 -15

SPF Base Model for RURAL Signalized Intersection - Exercise 4 -Approach Signalized Intersection: Discussion ►For a 4 -Approach signalized intersection with AADT = 9, 000 on the major road and AADT = 4, 500 on the minor road, ► What is the predicted # of Crashes? 6 -16

SPF Base Model for RURAL Signalized Intersection – Example: 4 -Approach Signalized Intersection: Nspf-4 SG = exp[-5. 13 + 0. 60 ln(AADTmaj) + 0. 20 ln(AADTmin)] For range of AADTmaj from zero to 25, 200 and AADTmin from zero to 12, 500 For AADTmaj = 9, 000 and AADTmin = 4, 500: Nspf-4 SG = exp[-5. 13 + 0. 60 ln(9, 000) + 0. 20 ln(4, 500)] = 7. 5 crashes per year 6 -17

Severity Index for all highways and streets Severity index (SI) is the ratio of crashes involving an injury or fatality to total crashes * From NCHRP 486 ►. . however, Chapter 10 of the HSM provides “better” injury and fatal crash distribution by type of rural intersection control in Tables 10 -5 and 10 -6 3 -18

Crash Severity for Rural 2 -Lane Intersections Table 10 -5 6 -19

Table 10 -6: Default Distribution for Collision Types and Manner of Collisions Default Distribution of Crash Types for Rural 2 Lane Intersections 6 -20

Applying Severity Index to Rural Two-Lane Highway Intersections Example: Two-way stop controlled 4 -approach intersection with 9, 000 AADT on Major and 4, 500 AADT on minor; Fatal and Injury crashes are 5 of 9 total crashes a. Compute the actual Severity Index (SI) SI 4 st = Fatal + Injury Crashes = 5/9 = 0. 55 Total Crashes 3 -21

Applying Severity Index to Rural Two-Lane Highway Intersections b. Compute the Predicted Severity Index (SI) SI 4 st = Fatal + Injury Crashes = 43. 1/100= 0. 43 Total Crashes 3 -22

Applying Severity Index to Rural Two-Lane Highway Intersections Example: Two-way stop controlled 4 -approach intersection with 9, 000 AADT on Major and 4, 500 AADT on minor; Fatal and Injury crashes are 5 of 9 total crashes a. Actual Severity Index (SI) = 0. 55 ? b. Predicted Severity Index (SI) = 0. 43 ? - Is the Actual Severity Index higher or lower than the Predicted Severity Index? Higher ? 3 -23

Process for Prediction of Crash Frequency and Application of Crash Modification Factors Three Steps: 1. Predict Crash Frequency - Safety Performance Functions (SPF) Equations - Predict Crash Frequency for base conditions 2. Apply Appropriate Crash Modification Factors (CMFs) - Adjust predicted safety performance from base conditions to existing/proposed conditions - Are greater or less than 1: q < 1. 0 -- lower crash frequency q > 1. 0 -- increased crash frequency 3. Calibration, Cr or Ci - Accounts for local conditions/data 6 -24

HSM Crash Modification Factors for Rural Two-Lane Highway Intersections ► Configuration - Number of Legs ► Intersection Designs - Roundabouts ► Angle of Intersection (Skew) ► Left Turn Lanes ► Right Turn Lanes ► Lighting 6 -25

Comparison of 4 -leg/3 -leg Intersections Cross intersection has 32 conflict points, Offset T has 22 points Potential Conflict Points 6 -26

Number of Intersection Legs ►Crash Frequency for intersections with only 3 approaches is lower ►Crash Frequency for intersections with 4 approaches are greater than for those intersections with only 3 approaches ►Collision rates for intersections with more than 4 approaches are 2 to 8 times greater than for 4 approach Intersections 6 -27

CMF for Rural Intersection Skew Angle @ 90 degrees Skew Angle Intersection Angle = 350 • Some studies (Mc. Coy, for example) show adverse effect of skew • Skews increase exposure time to crashes; increase difficulty of driver view at stopped approach Skew = 900 – 350 = 550 SKEW = Intersection Skew Angle (degrees) as the absolute value of the difference between 90 degrees and the actual intersection angle 6 -28

CMF for Intersection Skew Angle (CMF 1 i) For 3 - legged Stop Controlled Intersections: CMF 1 i = exp (0. 0040 SKEW) For 4 - legged Stop Controlled Intersections: CMF 1 i = exp (0. 0054 SKEW) SKEW = Intersection Skew Angle (degrees) as the absolute value of the difference between 90 degrees and the actual intersection angle *NCHRP 500, Strategy 17. 1 B 16 – Realign Intersection Approaches 6 -29

CMF for Intersection Skew Angle (CMF 1 i) Intersection Skew from 90 degree side road for 4 leg Approaches Skew= CMF = 0 1. 00 15 1. 08 30 1. 18 45 1. 28 *Max skew of 15 degrees - Older Driver Handbook and ITE Max skew of 30 degrees – 2004 Green Book *NCHRP 500, Strategy 17. 1 B 16 – Realign Intersection Approaches 6 -30

CMF for Intersection Skew Angle (CMF 1 i) Example: #1 – 90 deg #2 – 45 deg #3 – 80 deg Skew = 15 CMF 1 i = e 0. 0040(15) =1. 062 #4 – 75 deg Skew = 0 CMF 1 i = 1. 000 Skew = 45 CMF 1 i = e 0. 0054(45) =1. 275 Skew = 10 CMF 1 i = e 0. 0040(10) =1. 041 For each of the four (4) intersections, calculate the safety effect of skew angle 6 -31

Solutions to Skewed Intersections New Alignment Old Alignment *NCHRP 500, Strategy 17. 1 B 16 – Realign Intersection Approaches 6 -32

6 -33

6 -34

Solutions to Skewed Intersections q. Locate Intersection at Mid-Point of Curve *NCHRP 500, Strategy 17. 1 B 16 – Realign Intersection Approaches 6 -35

Left Turn Lanes in the Rural Highway Environment Left turn lanes remove stopped traffic from through lanes • mitigate rear-end conflict • enable selection of safe gap warrants for turn lanes in the rural environment see NCHRP 457 q“Capacity” is generally not the issue *NCHRP 500, Strategy 17. 1 B 1 – Provide Left-Turn Lanes 6 -36

CMF for Left Turn Lanes (CMF 2 i) ____ NCHRP 500, Strategy 17. 1 B 1 – Provide Left-Turn Lanes 6 -37

Rural Left Turn By-Pass Lanes ► Less cost than conventional left turn lane ► At low volume intersections, may be just as effective ►Minnesota study unable to conclude bypass lanes just as safe as left turn lanes *NCHRP 500, Strategy 17. 1 B 4 – Provide By-Pass Lanes 6 -38

CMF for Right Turn Lanes (CMF 3 i) ►Right turn lanes remove slowing traffic from through lanes which are not stop controlled q“Capacity” is generally not the issue *NCHRP 500, Strategy 17. 1 B 6 – Provide Right-Turn Lanes 6 -39

CMF for Right Turn Lanes (CMF 3 i) ____ NCHRP 500, Strategy 17. 1 B 6 – Provide Right Turn Lanes 6 -40

CMF for Lighting of Rural 2 -Lane Intersections (CMF 4 i) CMF 4 i = 1 -0. 38 pni 6 -41

CMF for Lighting of Rural 2 -Lane Intersections (CMF 4 i) – Example: For 4 approach Two-Way Stop Controlled rural intersection: CMF 4 i = 1 -0. 38 pni = 1 -0. 38(0. 244) = 0. 907 NCHRP 500, Strategy 17. 1 E 2 -Improve Visibility of Intersection by Providing Lighting (P) 6 -42

Additional CMF’s from Part D and Research Beyond the SPF’s and CMF’s detailed in Part C Chapter 10: ► CMF’s for Roundabouts from Chapter 14 ► CMF for 4 -Way Stop ► CMF for STOP AHEAD Pavement marking ► CMF for STOP Beacons ► CMF for driveways within 250 feet from TTI Research 6 -43

Roundabouts are Alternatives to conventional intersections ►Number of conflicts is reduced ►Severe conflicts (angle) are eliminated ►Speed differentials are reduced or eliminated *NCHRP 500, Strategy 17. 2 B 5 – Construct Special Solutions – Roundabout Design 6 -44

CMF’s for Conversion of 2 -Way Stop Intersection to Roundabout 6 -45

Roundabouts in the rural environment *NCHRP 500, Strategy 17. 1 F 3 – Provide Roundabouts Before Converting Stop-Control to Roundabout After CMF (single lane) = 0. 29 CMF (multi-lane) = 0. 56 6 -46

Roundabouts in the rural environment Single Lane Rural Roundabout: ►Approach speed limits 45 mph, ► 60 foot right of way Before Crash Info – 2 yrs: - 12 crashes with 4 F/Inj Summit County Ohio After Crash Info – 2 yrs: - 4 crashes with 0 F/Inj 6 -47

CMF’s for Conversion of 2 -Way Stop to All. Way Stop Control 6 -48

CMF’s for STOP AHEAD Supplementary Pavement Marking 6 -49

CMF’s for Beacons Table 14 -42 Four approach, STOP control, Two lane roads 6 -50

Driveway near Rural Intersections ►Access points within 250 feet upstream and downstream of an intersection are undesirable ► Unsignalized - 20% more crashes for 3 driveways within 250 feet ► Signalized - 13% more crashes for 3 driveways within 250 feet ► Consolidate multiple access points ► Relocate access to the adjacent side road if possible 6 -51

CMF for Access Control for Rural Intersections Unsignalized Intersections: CMFnd = e 0. 056 * (dn-3) *From TTI Roadway Safety Design Synthesis, 2005) Signalized Intersections: CMFnd = e 0. 046 * (dn- 3) Where: dn = Number of driveways on both the major and minor road approaches within 250 feet of the intersection 6 -52

CMF for Access Control for Rural Intersections: Example Calculation Unsignalized Intersections: For 4 driveways on US route and 3 driveways on County Route *From TTI Roadway Safety Design Synthesis, 2005) CMFnd = e 0. 056 (dn - 3) = e 0. 056 (7 - 3) = e 0. 056 (4) = 1. 25 6 -53

Additional Low Cost Safety Measures beyond the published 2010 HSM ►Beyond the Highway Safety Manual are many proven low cost safety measures htpp: //www. cmfclearinghouse. org 6 -54

2009 MUTCD Figure 2 A-4 Intersection Typical Signing Regulatory Right-of-Way Guide Warning ►Applying the two guiding principles of: - Clarify and Simplify 6 -55

Applying Simplify and Clarify Warning Guide Regulatory Right-of-Way ►Applying the two guiding principles of: Clarify and Simplify 6 -56

Low Cost Intersection Safety Measures – Signing Countermeasures 1. Warning CMF = 0. 60 Rural CMF = 0. 70 Urban q. All-Way Stop of 2 rural State Highways 6 -57

Low Cost Intersection Safety Measures – Signing Countermeasures 2. Enhanced Warning “Double-Up” CMF = 0. 69 q. All-Way Stop of 2 rural State Highways 6 -58

Low Cost Intersection Safety Measures – Signing Countermeasures 3. Enhanced Warning Beacons CMF = 0. 75 q. All-Way Stop of 2 rural State Highways 6 -59

Low Cost Intersection Safety Measures – Signing Countermeasures 4. Advance Guide Signs q. All-Way Stop of 2 rural State Highways 6 -60

Low Cost Intersection Safety Measures – Signing Countermeasures q. Stop Sign on outside of large right turn radius is too far out of center attention window of driver 5. Regulatory Right-of-Way q. All-Way Stop of 2 rural State Highways 6 -61

Low Cost Intersection Safety Measures – Signing Countermeasures q Add Stop Sign on Island to Enhance Visibility CRF = 11% + Right Hand Supplemen tary Stop Sign 5. Regulatory Right-of-Way q. All-Way Stop of 2 rural State Highways 6 -62

Low Cost Intersection Safety Measures – Signing Countermeasures q “Double Up” Stop Signs CMF = 0. 89 6. Regulatory Right-of-Way CRF = 11% total crashes CRF = 55% Rt Angle Crashes 6 -63

Low Cost Intersection Safety Measures – Signing Countermeasures q Add Stop Beacon CMF = 0. 42 angle crashes 7. STOP Beacon q. All-Way Stop of 2 rural State Highways 6 -64

Low Cost Intersection Safety Measures – Signing Countermeasures q Install Splitter Islands on the Minor Road Approach to an Intersection 9. Splitter Island q “Call Attention” to the presence of the Intersection *NCHRP 500, Strategy 17. 1 E 3 – Install Splitter Islands on Minor Road Approaches CRF = 45% 3 -Approach CRF = 40% 4 -Approach 6 -65

Low Cost Intersection Safety Measures – Rumble Treatment Concept 1 – Narrow travel lanes by striping on Main highway 6 -66

Low Cost Intersection Safety Measures – Rumble Treatment Concept 1 – Narrow travel lanes by striping on Main highway 6 -67

Low Cost Intersection Safety Measures – Rumble Treatment Concept 1 – Narrow travel lanes by striping on Main highway 6 -68

► after 2 years, total crash reduction = 32% ► Injury/Fatal crash reduction = 34% 6 -69

Low Cost Intersection Safety Measures – Rumble Treatment Concept 2 – Add splitter Island on side road approaches 6 -70

Low Cost Intersection Safety Measures – Add Splitter Island with Stop on Centerline Concept 2 – Add splitter Island on side road approaches 6 -71

Low Cost Intersection Safety Measures – Add Splitter Island with Stop on Centerline Concept 2 – Add splitter Island on side road approaches 6 -72

Low Cost Intersection Safety Measures – Add Splitter Island with Stop on Centerline Concept 2 – Add splitter Island on side road approaches 6 -73

Predicting Crash Frequency for Two-Lane Rural Highway Intersections Outcomes: ► Described the SPF Base Models for prediction of Intersection Crash Frequency ► Calculated Predicted Crash Frequency for Rural Two-lane Highway Intersections ► Described CMF’s for Rural 2 Lane Intersections ► Applied CMF’s to Predicted Crash Frequency 6 -74

Predicting Crash Frequency for Two-Lane Rural Highway Intersections Questions and Discussion 6 -75