Transcript HSM Application to Pedestrian Safety

Predicting Crash Frequency for
Two-Lane Rural Highway
Segments
2-1
Predicting Crash Frequency for Two-Lane
Rural Highway Segments
Learning Outcomes:
► Describe the Safety Performance
Functions (SPFs) for predicting Crash
Frequency for Base Conditions
► Describe the Quantitative Safety Effects of
Crash Modification Factors (CMFs)
► Apply CMFs to the SPF Base Equation
2-2
Predicting Crash Frequency for Two-Lane
Rural Highway Segments
Cross Sectional Elements
2-3
Two-Lane Rural Highway Segments
What should you expect would be the safety and
operational influence of cross sectional elements?
Crashes
Operations
Head-on
Capacity
Lane Width
Wider is “better”
Wider means “faster”
Shoulder Width
Sideslope
Clear Zone
Run-off-Road
Wider is “better”
Run-off-road
(severity)
Flatter is better
Run-off-road
(frequency and
severity)
Capacity
Functionality (peds,
bikes, emergency stops,
capacity, maintenance)
Maintenance
Flatter is better
Horizontal sight distance
2-4
Two-Lane Rural Highway Segments
Functions of shoulders in a rural environment
Clear zone
(recovery)
Highway Capacity
Clear zone
(horizontal sight
distance)
Store vehicles in
emergency
Pedestrians,
bicyclists
Protection for turns
off the roadway
Provide pavement
support
Store snow
Provide space for
maintenance activities
Enforcement
activities
2-5
Two-Lane Rural Highway Segments
Key Findings of FHWA Cross Section
Study on Two-Lane Hwys (Zegeer)
► Traffic volume influences crash rate
► Both lane and shoulder width have influence
► Roadside Hazard next biggest influence on
crashes
► Alignment affects cross section crashes
(terrain is surrogate for alignment)
2-6
Two-Lane Rural Highway Segments
Crash Severity for Two-Lane Rural Highways
Rural 2 Lane
Highway
Segment
Severity Ratio
= 32.1% for
Injury + Fatal
Crashes
2-7
HSM Crash Prediction:
18 Steps for Two-Lane
Rural Roadways
Rural Area Definition:
• Places outside urban
boundaries
• Populations of 5,000
persons, or less
Applicable to:
• Existing Roadways
• Design Alternatives for
existing or new roadways
2-8
Predicting Crash Frequency
Performance - Analysis Sections
Organizing information for Safety Analysis:
► Separate project lengths (and crashes) into
homogeneous units:
• Average daily traffic (AADT) volume (vehicles/day)
• Lane width (ft)
• Shoulder width (ft)
• Shoulder Type
• Driveway Density (driveways per mile)
• Roadside Hazard Rating
• Beginning/End of Horizontal Curves
• Beginning/End of Segments on Grade (>3%)
2-9
Subdividing Roadway Segments
Homogeneous Roadway Segments:
Lane Width
2-10
Subdividing Roadway Segments
Homogeneous Roadway Segments:
Shoulder Width
2-11
HSM Crash Prediction Method
Three Basic Elements:
1. Safety Performance Functions (SPF) Equations
►Predict safety performance for set base conditions
2. Crash Modification Factors (CMFs)
►Adjust predicted safety performance from base
conditions to existing/proposed conditions
►Are greater or less than 1:
 < 1.0 -- lower crash frequency
 > 1.0 -- increased crash frequency
3. Calibration, Cr or Ci
►Accounts for local conditions/data
2-12
HSM Crash Prediction Method
Total estimated crashes within the limits of
the roadway being analyzed:
Ntotal = ∑Npredicted-rs + ∑ Npredicted-int
Ntotal = Total expected number of crashes within
the limits of the roadway facility
∑Npredicted-rs = Expected crash frequency for all
roadway segments (sum of individual segments)
∑ Npredicted-int = Expected crash frequency for all
intersections (sum of individual intersections)
2-13
Roadway Segment Prediction Model
Npredicted-rs = Nspf-rs x (CMF1r … CMFxr) Cr
Where:
Npredicted-rs = predicted average crash frequency
for an individual roadway for a specific year
(crashes per year)
Nspf-rs = predicted average crash frequency for
base conditions for an individual roadway
segment (crashes per year)
CMF1r ... CMFxr = Crash Modification Factors for
individual design elements
Cr = calibration factor
2-14
Safety Performance Function (SPF)
SPF for Two-Lane Rural Highway Segment
Crashes for Base Conditions:
Nspf-rs = (AADTn) (L) (365) (10-6) e-0.312
Where:
Nspf-rs = predicted total crash frequency for a
roadway segment for base conditions, crashes
per year
AADTn = average annual daily two-way traffic
volume for specified year n (veh/day)
L = length of roadway segment (miles)
2-15
Base Conditions for Rural Two-Lane Roadway
Segments (CMF = 1.0)
► Lane Width:
12 feet
► Shoulder Width:
6 feet
► Shoulder Type:
Paved
► Roadside Hazard Rating:
3
► Driveway Density:
<5 driveways/mi
► Grade:
<3%(absolute value)
► Horizontal Curvature:
None
► Vertical Curvature:
None
► Centerline rumble strips:
None
► TWLTL, climbing, or passing lanes: None
► Lighting:
None
► Automated Enforcement:
None
2-16
Safety Performance Function (SPF)
Applying SPF for Base Conditions –
Example:
Nspf-rs = (AADTn) (L) (365) (10-6) e-0.312
2-lane state highway connecting a US marked
route to a primary State marked route in a
rural county;
Where:
AADT = 3,500 vpd
Length = 26,485 feet = 5.02 miles
2-17
Safety Performance Function (SPF)
Applying SPF for Base Conditions –
Example:
Where:
AADT = 3,500 vpd
Length = 26,485 feet = 5.02 miles
Nspf-rs = (AADTn) (L) (365) (10-6) e-0.312
Nspf-rs = (3,500) (5.02) (365) (10-6) e-0.312
= (3,500) (5.02) (365) (10-6) (0.7320)
= 4.69 crashes per year
2-18
Applying CMF’s for Conditions other than
“Base”
Next Step is:
Npredicted-rs = Nspf-rs x (CMF1r … CMFxr) Cr
Where:
► Npredicted-rs = predicted average crash
frequency for an individual roadway for a
specific year (crashes per year)
► Nspf-rs = predicted average crash frequency
for base conditions for an individual roadway
segment (crashes per year)
► CMF1r ... CMFxr = Crash Modification Factors
for individual design elements
► Cr = calibration factor
2-19
Crash Modification Factors (CMFs)
► CMFs quantify the expected change in
crashes at a site caused by implementing a
particular treatment, countermeasure,
intervention, action, or alternative.
► CMFs are used to adjust the SPF
estimated predicted average crash
frequency for the effect of individual
geometric design and traffic control
features.
2-20
Crash Modification Factors (CMFs)
Applying CMFs for Lane Width, Shoulder Width
& Type, Driveway Density, TWTLs, and
Roadside Design
Nspf-rs = (AADTn) (L) (365) (10-6) e-0.312
Npredicted-rs = Nspf-rs(CMF1r x CMF2r x CMF6r x CMF9r
x CMF10r)
Where:
CMF1r is for Lane Width
CMF2r is for Shoulder Width and Type
CMF6r is for Driveway Density
CMF9r is for Two-Way Left-Turn Lanes
CMF10r is for Roadside Design
2-21
Rural Two-Lane Highway Segment CMFs
2-22
Crash Modification Factor for
Lane Width (CMF1r)
CMF1r = (CMFra – 1.0)pra + 1.0
CMFra for lane width
1.23
• ‘Base condition’ is 12ft lanes
• CMFs for ADT >2000
based on Zegeer
• CMFs for ADT <400
based on studies by
Griffin and Mak
• Expert panel
developed transition
lines, referencing other
research
2-23
Crash Modification Factor for
Lane Width (CMF1r)
CMF1r = (CMFra – 1.0)pra + 1.0
Note equations for ADT’s between 400 and 2000
2-24
CMF - Lane and Shoulder Width Adjustment
for Related Crashes
Table 10-4
- Adjust for (Run
off Road + Headon + Sideswipes)
to total crashes
pra = 0.574
CMF1r = (CMFra –
1.0)pra + 1.0
2-25
Calculation for Lane Width (CMF1r): Example
For 3,500 AADT for a 10 foot wide lane:
From Table 10-8: CMFra = 1.30
► Adjustment for lane width and shoulder width
related crashes (Run off Road + Head-on +
Sideswipes) to obtain total crashes using default
value for pra = 0.574
CMF1r = (CMFra - 1.0) pra + 1.0
= (1.30 - 1.0) * 0.574 + 1.0
= (0.30) (0.574) + 1.0
= 1.172
2-26
Calculation for Shoulder Width and Type
(CMF2r)
CMF2r = (CMFwra CMFtra– 1.0)pra + 1.0
CMFwra for shoulder width:
• Base condition is 6-ft
shoulders
• CMFs for ADT >2000
based on Zegeer
(FHWA)
• CMFs for ADT <400
based on other studies
by Zegeer (NCHRP
362)
• Expert panel
developed transition
lines, referencing
other research
2-27
Crash Modification Factor for Shoulder
Width (CMFwra)
CMF2r = (CMFwra CMFtra– 1.0)pra + 1.0
Note equations for ADT’s between 400 and 2000
2-28
Crash Modification Factor for Shoulder
Type (CMFtra)
2-29
CMF – Lane and Shoulder Width Adjustment
for Related Crashes
Table 10-4
- Adjust for (Run
off Road + Headon + Sideswipes)
to total crashes
pra = 0.574
CMF2r = (CMFwraCMFtra
– 1.0)pra + 1.0
2-30
Calculation for Shoulder Width and Type
(CMF2r): Example
For 3,500 AADT with a 2 ft wide aggregate
shoulder:
CMFwra = 1.30 (Table 10-9) and CMFtra = 1.01 (Table 10-10)
► Adjustment from crashes related to lane and
shoulder width (Run off Road + Head-on +
Sideswipes) to total crashes using default value for
pra = 0.574
CMF2r = (CMFwra CMFtra - 1.0) pra + 1.0
= ((1.30)(1.01) - 1.0) * 0.574 + 1.0
= (0.313) (0.574) + 1.0
= 1.180
2-31
Crash Modification Factors
Lane and Shoulder Width – Example:
For 1,500 AADT 10’
lane and no shoulder:
What is CMF1r&2r?
 Lane Width = 10’
(From Table 10-8) CMFra =
1.213
CMF1r = (1.213 - 1.0)x
0.574 + 1.0 = 1.122
 Shoulder Width = 0’
(From Table 10-9)
Combined CMF:
CMFwra = 1.375
CMF1r&2r = 1.122x 1.215
CMF2r= (((1.375 x 1.00) = 1.363
1.0)x 0.574) + 1.0 = 1.215
2-32
Crash Modification Factors
Example: Combination Shoulder Type
6 ft Shoulder, AADT > 2,000 vpd
From Table 10-10:
• CMF6’ paved = 1.00
• CMF6’ gravel = 1.02
6 ft
4’
2’
Combination
Shoulder Type
CMFtra Calculation:
 CMFtra = (4’/6’)x1.00
+ (2’/6’) x 1.02 = 1.007
2-33
Some Insights
Review of CMFs for Lane Width and Shoulders
► Not much difference between 11and 12-ft lanes
► Lane width is less important for
very low volume roads
► Incremental width for shoulders
is much more sensitive than for
lanes
► Shoulder width effectiveness
increases significantly as AADT
increases
2-34
CMF for % Grade for Roadway Segments
(CMF5r)
For Roadway Segment on 4% Grade:
CMF5r = ?1.10
2-35
CMF for Driveway Density (Access) (CMF6r)
0.322 + (0.05-0.005Ln(AADT))*DD
_____________________
CMF6r =
0.322 + (0.05-0.005*Ln(AADT))*5
Where:
CMF6r = effect of driveway density on total crashes
DD = Driveway Density (driveways per mile)
AADT = Average Annual Daily Traffic
2-36
Calculation for Driveway Density (CMF6r):
Example
Where:
AADT = 3,500
Access is 31 driveways in 5.02 miles
DD = 31/5.02
= 6.17 driveways per mile
CMF6r =
=
0.322 + (0.05-0.005*Ln(AADT))*DD
_____________________
0.322 + (0.05-0.005*Ln(AADT))*5
0.322 + (0.05-0.005*Ln(3,500))*6.17
0.322 + (0.05-0.005*Ln(3,500))*5
= 1.029
2-37
CMF for Installing Centerline Rumble
Strips (CMF7r)
2-38
Safety Effects of Installing Shoulder Rumble
Strips: Two-Lane Rural Roads
* Not in HSM
*CRFrumble = 13% reduction in total crashes
CMF = 1 – *CRF
CMFrumble = 1- 0.13
= 0.87
*From FHWA CMF Clearinghouse
http://www.cmfclearinghouse.org
2-39
CMF for Passing Lane/Climbing Lane (CMF8r)
2-40
CMF for Rural Two-Way Left Turn Lanes
(CMF9r)
Most effective where one direction flow rate
> 300 vph and in rural areas
2-41
CMF for TWLTL Lanes (CMF9r)
CMF9r = 1.0 – 0.7 PD * PLT/D
Where:
Pdwy = Driveway-related crashes as a proportion of
total crashes
Pdwy =
(0.0047 DD + 0.0024 DD2)
(1.199 + 0.0047 DD + 0.0024 DD2)
DD = drive density (driveways/mi > 5/mile)
PLT/D = Left turn crashes susceptible to correction by a
TWLTL as a proportion of driveway related crashes
(estimated as 0.50)
2-42
Example Calculation for TWLTL (CMF9r)
CMF9r = 1.0 – (0.7 Pdwy x PLT/D)
For 35 driveways in 0.8 mile long segment
DD = 35/0.8 = 43.47 driveways/mi
Pdwy =
(0.0047(43.47)) + 0.0024(43.472)
(1.199 + 0.0047(43.47) + 0.0024(43.472)
= 0.80
CMF9r = 1.0 – (0.7 x 0.80 x 0.50)
= 0.72
2-43
Roadside Quality is Strongly Linked to
Related Crashes
Roadside Design (CMF10r)
Roadside Design is based on Roadside Hazard
Ratings that are dependent on the roadside
environment
Ratings range from 1 to 7:
• 1 = forgiving roadside environment
• 7 = unforgiving roadside environment
2-44
Roadside Hazard Ratings
Base condition is Hazard Rating = 3
2-45
Roadside Hazard Rating of 1
► Wide clear zones
greater than or
equal to 30 ft from
the pavement
edgeline.
► Sideslopes flatter
than 1:4
► Recoverable
sideslope
2-46
Roadside Hazard Rating of 2
4
1
► Clear zone between 20 and 25 ft
from pavement edgeline
► Sideslope about 1:4
► Recoverable sideslope
2-47
Roadside Hazard Rating of 3
3
1
► Clear zone about 10 ft from pavement
edgeline
► Sideslope about 1:3 or 1:4
► Rough roadside surface
► Marginally recoverable
2-48
Roadside Hazard Rating of 4
► Clear zone between 5 and 10 ft from pavement edgeline
► Sideslopes about 1:3 or 1:4
► May have guardrail (5 to 6.5 ft from pavement edgeline).
► May have exposed trees, poles, or other objects (about 10 ft
from pavement edgeline)
► Marginally forgiving, but increased chance of a reportable
roadside crash
2-49
Roadside Hazard Rating of 5
►
Clear zone between 5
and 10 ft from
pavement edgeline
► Sideslope about 1:3
► Virtually nonrecoverable
► May have guardrail (0
to 5 ft from edgeline)
► May have exposed
trees, poles, or other
objects (about 10 ft
from pavement
edgeline)
2-50
Roadside Hazard Rating of 6
2
1
► Clear zone less than or equal to 5 ft
► Sideslope about 1:2, Non-recoverable
► No guardrail
► Exposed rigid obstacles within 0 to 6.5 ft
of the pavement edgeline
2-51
Roadside Hazard Rating of 7
► Clear zone less than or equal to 5 ft
► Sideslope 1:2 or steeper, Non-recoverable
► Cliff or vertical rock cut
► No guardrail
► High likelihood of severe injuries from a
roadside crash
2-52
CMF for Roadside Hazard Rating for Roadside
Design (CMF10r)
CMF10r =
e(-0.6869 + (0.0668 x RHR))
e(-0.4865)
Where:
CMF10r = CMF for the effect of roadside design
RHR = Roadside Hazard Rating
2-53
Calculation for Roadside Design
(CMF10r): Example
Where:
RHR = 5
CMF10r = e(-0.6869 + (0.0668xHR)) /e-0.4865
= e(-0.6869 + (0.0668x5)) /e-0.4865
= 1.143
2-54
Calculated CMFs for Roadside Hazard
Ratings
HAZARD RATING CMF'S (calculated)
Clear zone width
Roadside Obstacles
(ft)
Roadside Slope
Hazard Rating
CMF10r
None within clear Zone
30 or more
Flatter than 1:4
1
0.875
None within clear Zone
30 or more
1:4
1.5
0.905
None within clear Zone
20 to 30
1:4
2
0.935
None within clear Zone
20 to 30
1:3
2.5
0.967
None within clear Zone
10 to 20
1:4
2.5
0.967
None within clear Zone
10 to 20
1:3
3
1.000
None within clear Zone
10 to 20
1:2 or steeper
3.5
1.034
None within clear Zone
5 to 10
1:4
4
1.069
None within clear Zone
5 to 10
1:3
5
1.143
None within clear Zone
5 to 10
1:2 or steeper
5.5
1.182
None within clear Zone
0 to 5
N/A
6
1.222
Barrier 5-6.5 ft fro edge of travel way
None
N/A
4
1.069
Barrier 0-5 ft from edge of travel way
None
N/A
5
1.143
Rock cut or cliff with no barrier
None
N/A
7
1.306
2-55
CMF for Lighting (CMF11r)
CMF11r = 1.0 – [(1.0 – 0.72pinr – 0.83 ppnr ) pnr]
Where:
CMF11r = effect of lighting on total crashes
► pinr = proportion of total nighttime crashes for
unlighted roadway segments that involve a fatality
or injury
► ppnr = proportion of total nighttime crashes for
unlighted roadway segments that involve PDO
crashes only
► pnr = proportion of total crashes for unlighted
roadway segments that occur at night
2-56
CMF for Lighting
CMF11r = 1.0- [(1.0 – 0.72 pinr – 0.83 ppnr ) pnr ]
► These are default values for nighttime crash
proportions; replace with local values if
available
2-57
Calculation for Lighting (CMF11r) for Total
Crashes
Example: Two-Lane Undivided:
Obtaining coefficients from Table 10-12
CMF11r = 1.0- [(1.0 – 0.72 pinr – 0.83 ppnr ) pnr ]
CMF11r = 1.0 – [(1.0 – 0.72(0.382) – 0.83(0.618))(0.370)]
= 1.0 – [(1.0 – 0.275 – 0.513)(0.370)]
= 1.0 - (0.212)(0.370)
= 0.922
2-58
CMF for Lighting for Nighttime Crashes
2-59
Safety Effects of Automated Speed
Enforcement (CMF12r)
Use of video or photographic identification in
conjunction with radar or lasers to detect
speeding drivers:
CMF12r = 0.93 for Total Crashes
2-60
CMFs of Other Roadway Elements
►*Horizontal Curves & Superelevation
►Flattening Side Slopes
►Centerline Pavement Markings
►Edgeline Pavement Markings
►Post Mounted Delineators
► Installing Combination
Horizontal/Advisory Speed Signs
► Raised Pavement Markers
2-61
CMF for Flattening Sideslopes for Total
Crashes
2-62
CMF for Flattening Sideslopes for Single
Vehicle Related Crashes
2-63
Safety Effects of Placing Standard
Edgeline Markings
► combining Injury (32.1%)and Non-Injury
(67.9%) into an CMF for total crashes:
CMFedgeline = 0.97*0.321 + 0.97*0.679 = 0.97
2-64
CMF for Placing Standard Centerline
Markings
► combining Injury (32.1%)and Non-Injury
(67.9%) into an CMF for total crashes:
CMFcenterline = 0.99*0.321 + 1.01*0.679 = 1.004
2-65
CMF for Placing Standard Centerline and
Edgeline Markings
► using Injury (32.1%)and Non-Injury (67.9%)
into an CMF for total crashes:
CMFcenterline+Edge = (CMF-1.0) x 0.321 + 1
= (0.76-1.0) x 0.321 + 1 = 0.923
2-66
CMF for Placing Standard Centerline and
Edgeline Markings and Post Mounted
Delineators
► using Injury (32.1%)and Non-Injury (67.9%) into
an CMF for total crashes:
CMFcenterline+Edge+Del = (CMF-1.0) x 0.321 + 1
= (0.55-1.0) x 0.321 + 1 = 0.856
2-67
Applying CMFs to the SPF Base
Prediction Model
Npredicted-rs = Nspf-rs x (CMF1r x…CMFxr) Cr
Where:
Npredicted-rs = predicted average crash frequency for an
individual roadway for a specific year (crashes/year)
Nspf-rs = predicted average crash frequency for base
conditions for an individual roadway segment (crashes
per year)
CMF1r ... CMFxr = Crash Modification Factors for
individual design elements
Cr = calibration factor
2-68
Applying CMFs to the SPF Base
Prediction Model: Example
From Example
Calculations:
Rural Two-Lane
Road:
AADT = 3,500 vpd,
Length = 5.02 mi,
31 Driveways,
RHR = 5,
Nspf-rs = 4.69
Lane Width = 10 ft
CMF1r = 1.172
Shoulder Width = 2 ft gravel
CMF2r = 1.180
Segments on Grade (none)
CMF5r = 1.000
Driveway Density (6.17/mi)
CMF6r = 1.029
Centerline Rumble, None
CMF7r = 1.000
Edgeline Rumble
CMF7re = 0.870
Passing/Climbing Lanes, None CMF8r = 1.000
TWLTLs, None
CMF9r = 1.000
Roadside Design, RHR = 5
CMF10r = 1.143
Lighting, None
CMF11r = 1.000
Automated Enforcement, None CMF12r = 1.000
2-69
Applying CMFs to the SPF Base
Prediction Model: Example
Npredicted-rs = Nspf-rs x (CMF1rx … CMFxr) Cr
From example calculations (letting Cr = 1.0):
Npredicted-rs =
4.69 x (1.172 x 1.180 x 1.000 x 1.029 x
1.00 x 0.870 x 1.000 x 1.000 x 1.143 x
1.000 x 1.000) x 1.000
= 4.69 x1.415
= 6.64 crashes per year
2-70
Predicting Highway Safety for Two-Lane
Rural Highway Segments
Learning Outcomes:
► Described the Safety Performance
Function (Base) equation for prediction of
Crash Frequency
► Described the Quantitative Safety Effects
of Crash Modification Factors (CMFs)
► Applied CMFs to the Base Equation
2-71
HSM Practitioner’s Guide for Two-Lane Rural
Highways Workshop
Questions and Discussion:
2-72