1. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
HSM Practitioner’s Guider for Two-Lane Rural Highways Workshop
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Exercise II – US 52 from Sageville to Holy Cross – Prediction of Safety Performance for Curves and Comparison to Substantive Safety Performance
- Session #5
Session #5 – Exercise II – US 52 in Iowa (west of DuBuque and the Mississippi River) – Prediction of Safety Peformance for curves and Comparison to Substantive Safety Performance
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

2. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Outcomes:
Identify Curve Crashes
Predict crash frequency for base conditions using SPF Base Model
Apply CMFs for existing conditions to predict the safety performance of Curves
Compare predicted safety performance of Curves to actual safety performance
Learning Objectives for Session #5 – Exercise II – Prediction of safety performance for horizontal curves
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

3. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

4. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

5. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Geometric Information:
Length: miles
ADT: 2,500
Lane Width: 11 feet
Shoulders: Paved 0 feet
Gravel 4 feet
Hazard Rating: 5
Driveways: (none on curves)
Total Length of Curves = 4,826 ft or mi
US 52 Geometric Plan information
Traffic Volume (AADT): 2,500 vehicles per day
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

6. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Exercise II – US 52 from Sageville to Holy Cross
Geometric Information: Curves - no spirals
Curve #
Delta
Radius
Length
S.V. fo e 1
104 deg ft
1,225.5 ft
0.01
2- “A”
104 deg 33’
836.6 ft
1162 ft
0.00
3- “B”
63 deg 56’
477.5 ft
532.8 ft
4- “C”
67 deg 04’
558.9 ft
5- “D”
42 deg 15’
352 ft
6- “E”
62 deg 58’
524.8 ft
0.02
7- “F”
28 deg 10’
955 ft
469.4 ft
US 52 Geometric Plan information
Total Curve Lengths = 4,826 feet = mi
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

7. HSM Practicitioner's Guide for Two-Lane Rural Highways Workshop
Exercise II: US 52 from Sageville to Holy Cross – Segments/Grade/Curves
August 2010
LOCATION
NUMBER
On Roadway Segments 63
Within Intersection 16
Intersection Related 1
On-Grades 3
On Curves 39
Total
122
Crashes by location
Session 2 – Exercise I

8. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Exercise II – US 52 from Sageville to Holy Cross
From the US 52 corridor crash information, perform the following:
(a) Identify Curve Crashes and (b) Determine Predicted Crash Frequency for base conditions for the 7 Horizontal Curves (crashes/year)
Compute CMF3r and CMF4r for the 7 horizontal curves on US 52.
Apply appropriate CMFs to determine the Predicted Crash Frequency for existing conditions for the curved sections (crashes/year)
Compare the Actual Crash History (Substantive Performance) to the Predicted Crash Frequency (crashes/yr)
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

9. HSM Practicitioner's Guide for Two-Lane Rural Highways Workshop
Exercise II: US 52 from Sageville to Holy Cross – Segments/Grade/Curves
August 2010
LOCATION
NUMBER
On Roadway Segments 63
Within Intersection 16
Intersection Related 1
On-Grades 3
On Curves 39
Total
122
1 (a): Identify Crashes on Curves
Session 2 – Exercise I

10. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
Exercise II – US 52 from Sageville to Holy Cross
August 2010
1 (b). Compute the Predicted Crashes on Horizontal Curves for base conditions:
For the 7 Horizontal Curves:
Nspf-rs curves1-7 = (ADT) (Lcurve)(365)(10-6)e-0.312
= (2,500)(Lcurve x)(365)(10-6)e-0.312
Using the SPF Base Model calculate the predicted curve crashes for base conditions for each of the 7 curve lengths.
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

11. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Exercise II – US 52 Curves
Nspf-rs = (AADTn) (L) (365) (10-6) e
1.(b):
Curve Information: No Spirals
Curve
Radius (ft)
Lc (ft)
Lc (mi)
Spiral (S)
S.V.
Nspf-rs 1
670
1,226
0.232
0.01
0.155
2- “A”
837
1,162
0.220
0.00
0.147
3- “B”
478
533
0.101
0.067
4- “C”
559
0.106
0.071
5- “D”
352
0.045
6- “E”
525
0.099
0.02
0.066
7- “F”
955
469
0.089
0.059
US 52 Geometric Plan information
Table of geometric data (radius, lengths, presence of spirals, superelevation variance) and resulting calculation for Predicted Crash Frequency for Base Conditions (Nspf-rs).
Total:
0.914 mi
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

12. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Use Worksheet Exercise II
Compute CMF3r and CMF4r for the 7 horizontal curves on US 52.
Apply appropriate CMFs to determine the Predicted Crash Frequency for existing conditions for the curved sections (crashes/year)
a. Apply appropriate CMFs to the 7 Horizontal Curves (Use values for CMF1r CMF2r & CMF10r from Exercise I):
Determine/calculate the appropriate CMFs for existing geometric conditions for the seven horizontal curves. Assume roadway geometric conditions are the same as the tangent segments for Lane Width, Shoulder Width & Type, and Roadside Hazard Rating/Roadside Design.
CMF1r for Lane width
CMF2r for Shoulder width and type
CMF 3r for Horizontal Curves
CMF 4r for Superelevation Variance
CMF10r for Roadside Hazard Rating (Roadside Design)
Npredicted-rs curves = Nspf-rs curves (CMF1r x CMF2r x CMF3r x CMF4r x CMF10r)
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

13. HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
Exercise II – US 52 Curves
Nspf-rs = (AADTn) (L) (365) (10-6) e
Eqs: 10-14, 15, & 16
US 52 Geometric Plan information
Table of geometric data (radius, lengths, presence of spirals, superelevation variance) and resulting calculation for Predicted Crash Frequency for Base Conditions (Nspf-rs).
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

14. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
August 2010
4. Compare the Actual Crash Frequency per year to the Predicted Crash Frequency for the curves
Actual Curve crashes = 39 / 5 years
= _____ crashes per year
Npredicted-rs curves = _____ crashes per year
Comparing the predicted value (1.3 crashes per year) to the actual safety performance of the curves (7.8 crashes per year). The fact that actual crashes are 6 times greater then predicted implies that safety countermeasures are needed to reduce the potential of curve related crashes.
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

15. Exercise II – US 52 from Sageville to Holy Cross
HSM Practioner's Guide for Two-Lane Rural Highways Workshop
Exercise II – US 52 from Sageville to Holy Cross
August 2010
Outcomes:
Identified Curve Crashes
Predicted crash frequency for base conditions using SPF Base Model
Applied CMFs for existing conditions to predict the safety performance of Curves
Compared predicted safety performance of Curves to actual safety performance
Learning Objectives for Session #5 – Exercise II – Prediction of safety performance for horizontal curves
Session 5 – Predicting Highway Safety for Curves for 2-Lane Rural Highway Segments

16. Questions and Discussion:
HSM Practitioner's Guide for Two-Lane Rural Highways
August 2010
Exercise I: US 52 from Sageville to Holy Cross
Questions and Discussion: