Safety Effects of Roadway Alignment Combinations Karin M. Bauer October 2012

Transcription

1 Safety Effects of Roadway Alignment Combinations Karin M. Bauer October 2012

2 Task Objectives Quantify the safety effects of horizontal curve and grade combinations Present the results in a format suitable for incorporation in the AASHTO Highway Safety Manual 10/29/ Traffic Records Forum 2

3 Available Models Safety effects of horizontal alignment on rural two-lane highways Model by Zegeer et al. developed in early 1990s CMF then developed by Harwood et al. (2000) and included in 1 st edition of the HSM 10/29/ Traffic Records Forum 3

4 Available Models (cont d) Safety effects of vertical alignment on rural two-lane highways CMFs included in 1 st edition of the HSM based on research by Miaou (1998) These CMFs apply only to straight grades 10/29/ Traffic Records Forum 4

5 CMFs Missing for: Horizontal curvature on rural multilane undivided highways, rural multilane divided highways, urban and suburban arterials Crest or sag vertical curves on rural-two lane highways Vertical alignment for facilities other than rural two-lane highways Combinations of horizontal and vertical alignments 10/29/ Traffic Records Forum 5

6 Models and CMFs were developed for the following curve and grade combinations: Curves and tangents on straight grades Curves and tangents on crest vertical curves Crest type 1 Crest type 2 Curves and tangents on sag vertical curves Sag type 1 Sag type 2 Separately for F&I and PDO crashes 10/29/ Traffic Records Forum 6

7 Types of Vertical Curves (AASHTO Green Book) Crest type 1 Crest type 2 Sag type 1 Sag type 2 10/29/ Traffic Records Forum 7

8 Data Requirements for Modeling Records must include data on curve and grade geometry Data need to be linked to systemwide roadway geometrics, traffic volume data, and crash data Only HSIS data for state highways in Washington met requirements 10/29/ Traffic Records Forum 8

9 Facility Types Initially Considered Rural two-lane highways Rural multilane undivided highways Rural multilane divided highways Urban and suburban arterials Limited data for facility types other than rural two-lane highways 10/29/ Traffic Records Forum 9

10 Washington HSIS Data Miles of Roadways 87% of total miles in database Roadway type R2U R4U R4D Urban and Suburban Arterials U2U U3T U4D U4U U5T Tangents 2, Curves Straight grades 2, Crest type Crest type Sag type Sag type /29/ Traffic Records Forum 10

11 Washington HSIS Database 3,968 mi of horizontal (including tangents) and vertical curve combinations on four roadway types 6 years of crash data: 2003 through ,243 F&I crashes 42,284 PDO crashes 69,527 Total crashes 10/29/ Traffic Records Forum 11

12 Challenges in Data Preparation Most challenging step was to define homogeneous segments for modeling We built segments to contain a specific combination of horizontal and vertical alignment features 10/29/ Traffic Records Forum 12

13 Data Cleanup Excluded segments with transitions between grades identified as angle points with atypical features (e.g., passing and climbing lanes) with obvious data problems 10/29/ Traffic Records Forum 13

14 Some Segments Were Excluded if: Segment length < 0.01 mi Both initial and final grades < 1% for Type 1 crests and sags (~ level segment) Abs(G 1 -G 2 ) < 1% for Type 2 crests and sags (~ straight grades) K [=L VC / Abs(G 1 -G 2 )] > 1,000 (~ straight grades/level segments) Curve radius > 11,460 ft (~ tangents) If horizontal curve radius < 100 ft, then record was kept but R was set at 100 ft (same as HSM Chapter 10) 10/29/ Traffic Records Forum 14

15 Alignment Combinations Used in the Analysis of Horizontal Curves and Tangents on Straight Grades Straight grades Vertical curves Level Abs(Grade) < 1% Non level Abs(Grade) 1% Type 1 Crest Type 1 Sag Type 2 Crest Type 2 Sag Tangents Base condition Horizontal curves 10/29/ Traffic Records Forum 15

16 Alignment Combinations Used in the Analysis of Horizontal Curves and Tangents at Type 1 Crest Vertical Curves Straight grades Vertical curves Level Abs(Grade) <1% Non level Abs(Grade) 1% Type 1 Crest Type 1 Sag Type 2 Crest Type 2 Sag Tangents Base condition Horizontal curves 10/29/ Traffic Records Forum 16

17 FI Crash Model for Horizontal Curves and Tangents on Straight Grades NN FFFF = eeeeee llll(aaaaaaaa) GG llll RR II HHHH RR 11 II LL HHHH CC where: N FI = fatal-and-injury crashes/mi/yr AADT = veh/day G = absolute value of percent grade; 0 percent for level tangents; 1 percent otherwise R = curve radius (ft); missing for tangents I HC = horizontal curve indicator: 1 for horizontal curves; 0 otherwise L C = horizontal curve length (mi); not applicable for tangents ln = natural logarithm function 10/29/ Traffic Records Forum 17

18 CMFs for Horizontal Curves and Tangents on Straight Grades eeeeee GG llll RR RR 11 ffffff hhhhhhhhhhhhhhhhhhhh cccccccccccc LL CCCCCC SSSS,FFFF = CC eeeeee[ GG] ffffff tttttttttttttttt oooo nnnnnnnnnnnnnnnn gggggggggggg ffffff llllllllll tttttttttttttttt (bbbbbbbb cccccccccccccccccc) eexxxx GG llll RR RR 11 ffffff hhhhhhhhhhhhhhhhhhhh cccccccccccc LL CCCCCC SSSS,PPPPPP = CC eeeeee[ GG] ffffff tttttttttttttttt oooo nnnnnnnneeeeeeee gggggggggggg ffffff llllllllll tttttttttttttttt (bbbbbbbb cccccccccccccccccc) 10/29/ Traffic Records Forum 18

19 Example CMFs for FI Crashes on Horizontal Curves and Tangents on Straight Grades Rural two-lane roadways with AADTs from 200 to 26,000 veh/day Grade (%) Tangent on nonlevel grade Radius = 1,433 ft Radius = 5,730 ft Horizontal curve length (mi) Horizontal curve length (mi) Level (< 1%) /29/ Traffic Records Forum 19

20 FI Crash Model for Horizontal Curves and Tangents at Type 1 Crest Vertical Curves NN FFFF = eeeeee llll(aaaaaaaa) RR AA II VVVV HHHH N FI = fatal-and-injury crashes/mi/yr AADT = veh/day R = curve radius (ft); missing for tangents A = abs(g 1 G 2 ) (percent); not applicable for level tangents G 1 = initial grade (percent) (positive for upgrade; negative for downgrade) G 2 = final grade (percent) (positive for upgrade; negative for downgrade) I VC HC = combined vertical and horizontal curve indicator: 1 for combined vertical and horizontal curves; 0 otherwise ln = natural logarithm function 10/29/ Traffic Records Forum 20

21 CMFs for Horizontal Curves and Tangents at Type 1 Crest Vertical Curves 10/29/ Traffic Records Forum 21

22 Example CMFs for FI and PDO Crashes on Horizontal Curves and Tangents at Type 1 Crest Vertical Curves Rural two-lane roadways with AADTs from 200 to 26,000 veh/day Vertical curve length = 500 ft K Tangent at crest Fatal-and-injury CMFs PDO CMFs Radius = 1,433 ft Radius = 5,730 ft Radius = 1,433 ft Radius = 5,730 ft /29/ Traffic Records Forum 22

23 CMF Calculation Tool--Demo 10/29/ Traffic Records Forum 23

24 Work funded by Subcontracts for HSIS-V Under Contract No. DTFH61-06-C and HSIS-VI Under Contract No. DTFH61-11-C-00050, Task 5 Safety Effects of Horizontal Curve and Grade Combinations UNC Program Manager: David L. Harkey FHWA HSIS Program Manager: Carol Tan, Ph.D. 10/29/ Traffic Records Forum 24

25 Documentation and Tools 1. FHWA Web Report: Safety Effects of Horizontal Curve and Grade Combinations, Report No. FHWA-XX-XX-XXX, Federal Highway Administration, U.S. Department of Transportation, Washington, DC, web publication 2. HSIS Summary Report: Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways 3. HSIS Website Link for CMF Calculation Tool (in Excel) 10/29/ Traffic Records Forum 25

26 MRIGlobal Project Team Karin Bauer, Principal Statistician Doug Harwood, Transportation Research Center Director Melanie Knoshaug, Associate Analyst Courtney Bokenkroger, Senior Statistician Chris Fees, Staff Traffic Engineer 10/29/ Traffic Records Forum 26