Desktop Reference for Crash Reduction Factors

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Tables for Roadway Departure Crash Reduction Factors

Table 4. Barrier Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
BARRIER COUNTERMEASURES
Improve guardrail All All     <5,000/lane (Total) 15 18        
All All     >5,000/lane (Total) 15 9        
All All All All   1 5        
All All       15 5        
All All       15 6        
All All       15 7        
All All       15 7        
All All       15 11        
All All       15 15        
All All       15 15        
All All       15 20        
All Fatal All All   1 50        
All Injury       15 35        
All Injury All All   1 35        
Fixed object All     <5,000/lane (Total) 15 23        
Fixed object All     >5,000/lane (Total) 15 18        
Fixed object All       15 21        
ROR All       15 26        
ROR All     >5,000/lane (Total) 15 32        
ROR All       15 28        
Overturn All     <5,000/lane (Total) 15 41        
Overturn All     >5,000/lane (Total) 15 27        
Overturn All       15 34        
Rear-end All     <5,000/lane (Total) 15 41        
Rear-end All     >5,000/lane (Total) 15 27        
Rear-end All       15 34        
Install animal fencing Animal All       15 80        
Animal All All All   1 90        
Animal All       15 70        
Animal All       15 90        
Animal Injury       15 91        
Animal PDO       15 61        
Animal head-on All       15 61        
Install barrier (concrete) inside and outside curve All Fatal/Injury       15 39        
Install guardrail (as shield for rocks and posts) All All       15 14        
All Injury       15 31        
Fixed object All       15 100        
Install guardrail (as shield for trees) All Fatal       15 65        
All Injury       15 51        
Install guardrail (at culvert) All All       15 27        
All All       15 24        
All All       15 30        
Install guardrail (at ditch) All Injury       15 26        
Install guardrail (at embankment) All Injury       15 42        
ROR All   All   5 7 31     Meta-analysis
ROR Fatal   All   5 44 10     Meta-analysis
ROR Injury   All   5 47 5     Meta-analysis
Install guardrail (inside curves) All Fatal/Injury       15 28        
Install guardrail (outside curves) All Fatal/Injury       15 63        
Install impact attenuators All All       15 29        
All All All All   1 5        
All All       15 5        
All All       15 20        
All All       15 20        
All All       15 35        
All All       15 41        
All All       15 50        
All Fatal All All   1 75        
All Fatal       15 75        
All Fatal       15 83        
All Fatal       15 90        
All Injury All All   1 50        
All Injury All All   15 50        
Fixed Object Fatal All All   5 69 28     Meta-analysis
Fixed Object Injury All All   5 69 10     Meta-analysis
Fixed Object PDO       5 46 30     Meta-analysis
ROR All       15 45        
Replace guardrail with a softer material (concrete→steel→wire) ROR Fatal   All   5 41 31     Meta-analysis
ROR Injury   All   5 32 10     Meta-analysis

Table 5. Bridge Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
BRIDGE COUNTERMEASURES
Install bridge lighting All All       15 59        
Install delineators (on bridges) All All       15 43        
All All       15 39        
All All       15 40        
All All       15 50        
Install guardrail (at bridge) All All     <5,000/lane (Total) 15 22        
All All     >5,000/lane (Total) 15 20        
All All       15 11        
All All       15 24        
All All       15 24        
All All       15 44        
All Fatal       15 90        
All Injury       15 45        
Overturn All     <5,000/lane (Total) 15 41        
Overturn All     >5,000/lane (Total) 15 32        
Rear-end All     <5,000/lane (Total) 15 37        
Rear-end All     >5,000/lane (Total) 15 32        
Wet All       15 50        
Repair bridge deck All All       15 14        
All All       15 13        
All All       15 15        
Replace bridge (general) All All All All   1 45        
Replace bridge (2-lane) All All       15 45        
Upgrade bridge parapet All All       15 5        
Upgrade bridge railing All All       15 20        
All All All All   1 5        
All Fatal       15 76        
All Fatal       15 60        
All Fatal       15 92        
All Injury       15 61        
All Injury All All   1 30        
All Injury       15 30        
All Injury       15 92        
All PDO       15 50        
Vary bridge width All All Rural Rural Highway   6 100(1-(EXP(-0.135Ibr(Wb-12)-1.0)Ps+1.0)); Ibr=presence of bridges (1 if one or more bridges present, 0 if not), Wb=bridge width – approach traveled-way width (ft), Ps=proportion of crash type subset (for values of Ps, refer to source).  
Vary horizontal bridge radius All All Urban Urban Street   6 100(1-(2.30(EXP(-2298/R)+343.8/R)(1-Poffroad)+ 0.781(EXP(320.9/R)Poff-road))); Poffroad= proportion of crashes that occur off the roadway.  
Widen bridge All All       15 45        
All All All All   1 45        
All All       15 36        
All All       15 40        
All All       15 45        
All All       15 47        
All All       15 48        
All All       15 55        
All Fatal/Injury       15 92        
All PDO       15 95        
Fixed Object All       15 45        
Fixed Object All       15 40        
Fixed Object All       15 50        
Head-on All       15 45        
Head-on All       15 40        
Head-on All       15 50        
ROR All       15 44        
Sideswipe All       15 49        
Sideswipe All       15 40        
Sideswipe All       15 50        
Sideswipe All       15 57        
Widen bridge (18 to 24 ft) All All       15 68        
Widen bridge (18 to 30 ft) All All       15 93        
Widen bridge (20 to 24 ft) All All       15 56        
Widen bridge (20 to 30 ft) All All       15 90        
Widen bridge (22 to 24 ft) All All       15 36        
Widen bridge (22 to 30 ft) All All       15 86        

Table 6. Geometric Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
GEOMETRIC COUNTERMEASURES
Change shoulder type and/or width All All Rural     21 100(1-((AMFWRA x AMFTRA- 1.0)PRA+1.0)), AMFWRA=accident modification factor for related accidents based on shoulder width (for values of AMfWRA, refer to source), AMFTRA=accident modification factor for related accidents based on shoulder type (for values of AMFTRA, refer to source), PRA=proportion of total crashes constituted by related crashes. Expert Panel
Flatten crest vertical curve All All All All   27 20 19     EB Before-After
All Fatal/Injury All All   27 51 19     EB Before-After
All Fatal/Injury Rural 2-lane   38 50        
Flatten horizontal curve All All       15 39        
All All All All   1 40        
All All       15 35        
All All Rural     21 100(1-((1.55Lc+80.2/R-0.012Is)/1.55Lc)); Lc=length of horizontal curve (mi) without spirial curve length, R=curve radius (ft), Is=presence of a spiral transition curve (1 if a spiral transition is present, 0 otherwise). Expert Panel
All Fatal       15 87        
All Injury       15 87        
All PDO       15 87        
Fixed Object All     <5,000/lane 15 68        
Fixed Object All     >5,000/lane 15 87        
Head-on All     <5,000/lane 15 67        
Head-on All     >5,000/lane 15 64        
ROR All     <5,000/lane 15 90        
ROR All     >5,000/lane 15 79        
Overturn All     <5,000/lane 15 73        
Overturn All     >5,000/lane 15 24        
Rear-end All     <5,000/lane 15 73        
Rear-end All     >5,000/lane 15 24        
Rear-end All       15 49        
Flatten horizontal curves (10 to 5 degrees) All All       15 45        
Flatten horizontal curves (15 to 5 degrees) All All       15 63        
Flatten horizontal curves (20 to 10 degrees) All All       15 48        
Flatten side slopes All All     <5,000/lane 15 43        
All All     >5,000/lane 15 45        
All All All All   1 30        
All All       15 25        
All All       15 30        
All All       15 32        
All All       15 35        
Fixed object All       15 62        
ROR All       15 10        
Flatten side slopes (11 to 8 degrees) All All       15 8        
Ped All       15 14        
Right-turn All       15 14        
Flatten side slopes (14 to 9 degrees) All All       15 7        
All Injury Rural 2-lane   5 22 4     Meta-analysis
All PDO Rural 2-lane   5 24 2     Meta-analysis
Ped All       15 12        
Right-turn All       15 12        
Flatten side slopes (18 to 9 degrees) All All Rural 2-lane   15 11        
ROR All Rural 2-lane   5 24 21     Cross-section
Ped All Rural 2-lane   15 19        
Right-turn All       15 19        
Flatten side slopes (18 to 11 degrees) All All       15 8        
Ped All       15 14        
Right-turn All       15 14        
Flatten side slopes (18 to 14 degrees) All All       15 5        
All Injury Rural 2-lane   5 42 4     Meta-analysis
All PDO Rural 2-lane   5 29 4     Meta-analysis
ROR All Rural 2-lane   5 18 16     Cross-section
Ped All       15 8        
Right-turn All       15 8        
Flatten side slopes (27 to 9 degrees) All All       15 12        
Ped All       15 21        
Right-turn All       15 21        
Flatten side slopes (27 to 11 degrees) All All       15 9        
Ped All       15 15        
Right-turn All       15 15        
Flatten side slopes (27 to 14 degrees) All All       15 6        
Ped All       15 10        
Right-turn All       15 10        
Flatten side slopes and remove guardrail All All All All   27 42 58     EB Before-After
Improve curve superelevation All All Rural All   21 0       Expert Panel
All All Rural     21 100(1-(1.00+6(SD-0.01))); SD=superelevation deficiency between 0.01 and 0.02 Expert Panel
All All Rural     21 100(1-(1.06+3(SD-0.02))); SD=superelevation deficiency greater than 0.02 Expert Panel
Improve gore area All All       15 25        
All All All All   1 25        
Improve horizontal and vertical alignments All All       15 58        
All All All All   1 50        
All All       15 50        
All All       15 50        
All All       15 73        
Improve longitudinal grade All All       15 49        
All All All All   1 40        
All All       15 40        
All All       15 57        
All Fatal/Injury       15 87        
All PDO       15 83        
Improve superelevation All All       15 40        
All All       1 40        
ROR All       15 50        
Improve superelevation (for drainage) All All       15 45        
All All       15 40        
All All       15 49        
Increase number of lanes All All     <5,000/lane 15 20        
All All     >5,000/lane 15 31        
All All       15 10        
All All       15 20        
All All       15 22        
All All       15 25        
All All       15 25        
All All       15 25        
All Fatal       15 39        
All Injury       15 23        
All PDO       15 27        
Head-on All     <5,000/lane 15 38        
Head-on All     >5,000/lane 15 44        
Head-on All       15 53        
Head-on All       15 53        
Head-on PDO       15 50        
Left-turn All       15 71        
Left-turn PDO       15 67        
ROR All       15 44        
ROR All       15 26        
ROR All       15 44        
ROR All       15 44        
ROR PDO       15 50        
Overturn All     <5,000/lane 15 42        
Overturn All     >5,000/lane 15 52        
Rear-end All     <5,000/lane 15 42        
Rear-end All     >5,000/lane 15 52        
Rear-end All       15 32        
Rear-end All       15 32        
Rear-end All       15 40        
Rear-end All       15 53        
Rear-end PDO       15 53        
Right-angle All     <5,000/lane 15 35        
Right-angle All     >5,000/lane 15 45        
Right-angle All       15 15        
Right-angle PDO       15 46        
Sideswipe All     <5,000/lane 15 38        
Sideswipe All     >5,000/lane 15 44        
Sideswipe All       15 44        
Sideswipe All       15 30        
Sideswipe All       15 30        
Sideswipe All       15 35        
Sideswipe PDO       15 64        
Increase vertical grade by 1% All All Rural 2-lane   23 -1.6P; P=percent grade (absolute value)  
Install acceleration/ deceleration lanes All All       15 26        
All All All All   1 10        
All All       15 10        
All All       15 10        
All All       15 10        
All All       15 25        
All All       15 75        
Rear-end All       15 75        
Sideswipe All       15 75        
Install channelized lane All All       15 67        
All PDO       15 62        
Rear-end All       15 93        
Install climbing lane (where large difference between car and truck speed) All Fatal/Injury Rural 2-lane   38 33        
Install passing/climbing lane All All All All   1 20        
All Fatal/Injury Rural 2-lane   38 33        
Install shoulder All All       15 9        
Install shoulder bus lanes Head-on Fatal/Injury       15 50        
Head-on PDO       15 86        
Left-turn Fatal/Injury       15 42        
Left-turn PDO       15 57        
ROR PDO       15 27        
Right-angle Fatal/Injury       15 34        
Right-angle PDO       15 31        
Sideswipe Fatal/Injury       15 27        
Sideswipe PDO       15 8        
Install truck escape ramp All All       15 18        
ROR All       15 75        
Rear-end All       15 33        
Lengthen culverts All All       15 44        
All All       15 40        
All All       15 48        
All All       15 30        
Narrow cross section (4 to 3 lanes with two way left-turn lane) All All Urban 4-lane highway 8,000-17,000 17 37 1     EB Before-After
All All   4-lane   42 26   23 28  
All Fatal/Injury Urban 4-lane highway 8,000-17,000 17 0 2     EB Before-After
All PDO Urban 4-lane highway 8,000-17,000 17 46 1     EB Before-After
Left-turn All Urban 4-lane highway 8,000-17,400 17 24 2     EB Before-After
Rear-end All Urban 4-lane highway 8,000-17,400 17 31 2     EB Before-After
Right-angle All Urban 4-lane highway 8,000-17,400 17 37 1     EB Before-After
Reduce horizontal curve angle All All       15 38        
All All       15 40        
Reduce shoulder width (6 ft to 0 ft) All All Rural 2-lane   20 -12 3     Cohort
Reduce shoulder width (6 ft to 1 ft) All All Rural 2-lane   20 -17 6     Cohort
Reduce shoulder width (6 ft to 2 ft) All All Rural 2-lane   20 -11 2     Cohort
Reduce shoulder width (6 ft to 4 ft) All All Rural 2-lane   20 -6 2     Cohort
Reduce shoulder width (6 ft to 5 ft) All All Rural 2-lane   20 -2 2      
Reduce vertical grade by 1% All All Rural 2-lane   23 1.6P; P=percent grade (absolute value) Expert Panel
Resurface pavement and improve superelevation All All       15 26        
Wet pavement All       15 51        
Stabilize shoulder All All       15 25        
Stabilize shoulder and dropoff All All All All   1 25        
Vary grade All All   Freeway   6 100(1-((EXP(bPg)-1.0)Ps+1.0)); b=regression coefficient (for values of b, refer to source), Pg=percent grade(absolute value), Ps=proportion of crash type subset (for values of Ps, refer to source).  
All All Rural Rural Highway   6 100(1-(EXP(bPg-1.0)1.0+1.0)); b=regression coefficient (for values of b, refer to source)., Pg=percent grade (absolute value).  
Vary horizontal curvature All All Rural Rural Highway   6 100(1-((1.55Lc+80.2/R-0.012Is)/1.55Lc)); Lc=length of horizontal curve (mi), R=curve radius (ft), Is=presence of a spiral transition curve (1 if a spiral transition is present, 0 otherwise).  
Vary inside shoulder width All All   Freeway   6 100(1-((EXP(-0.021(Wis-Wsb))- 1.0)(Pi/0.15)+1.0)); Wis=inside shoulder width (ft), Wsb=base inside shoulder width (ft) (=4.0 for four lanes, 10.0 for six or more lanes), Pi=proportion of crash type subset (for values of Pi, refer to source).  
All All Rural Rural Highway   6 100(1-((EXP(-0.021(Wis-4))- 1.0)(Pi/0.16)+1.0)); Wis=inside shoulder width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
Vary lane width All All   Freeway   6 100(1-((EXP(-0.047(Wl-12))- 1.0)(Pi/0.37)+1.0)); Wl=lane width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
All All Rural Rural Highway   6 100(1-((EXP(-0.047(Wl-12))- 1.0)(Pi/0.36)+1.0)); Wl=lane width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
All All Urban Urban Street   6 100(1-((EXP(-0.040(Wl-12))- 1.0)(Pi/0.24)+1.0)); Wl=lane width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source)  
Vary outside shoulder width All All   Freeway   6 100(1-((EXP(-0.021(Ws-10))- 1.0)(Pi/0.15)+1.0)); Ws=outside shoulder width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
All All Rural Rural Highway   6 100(1-((EXP(-0.021(Ws-8))- 1.0)(Pi/0.16)+1.0)); Ws=outside shoulder width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
Vary shoulder width All All Urban Urban Street   6 100(1-((EXP(-0.014(Ws-1.5))- 1.0)(Pi/0.088)+1.0)); Ws=shoulder width (ft), Pi=proportion of crash type subset (for values of Pi, refer to source).  
Vary side slopes All All Rural Rural Highway   6 100(1-((EXP(0.692(1/Ss-0.25))- 1.0)Ps+1.0)), Ss= horizontal run for a 1ft change in elevation (average for length of segment, ft), Ps=proportion of crash type subset (for values of Ps, refer to source).  
Vary spiral transition curvature All All Rural Rural Highway   6 100(1-((1.55Lc+80.2/R- 0.012)/(1.55Lc+80.2/R))); Lc=length of horizontal curve (mi), R=curve radius (ft).  
Vary superelevation All All Rural Rural Highway   6 0 through -15 according to the superelevation deficiency (refer to source).  
Vary uncurbed crosssections All All Urban Urban Street   6 100(1-((EXP(-0.074)(1-Poff-road))+EXP(- 0.225)Poff-road)); Poff-road=proportion of off-road crashes.  
Widen lane (add 1 ft to both sides) Head-on All       15 12        
ROR All       15 12        
Sideswipe All       15 12        
Widen lane (add 2 ft to both sides) Head-on All       15 23        
ROR All       15 23        
Sideswipe All       15 23        
Widen lane (add 3 ft to both sides) Head-on All       15 32        
ROR All       15 32        
Sideswipe All       15 32        
Widen lane (add 4 ft to both sides) Head-on All       15 40        
ROR All       15 40        
Sideswipe All       15 40        
Widen lane (initially less than 9 ft) All Fatal/Injury Rural 2-lane 400-2,000 38 28   5 50  
Widen lane (initially between 9 ft and 10.75 ft) All Fatal/Injury Rural 2-lane 400-2,000 38 16   2 30  
Widen lanes All All All     15 56        
All All Rural     21 100(1-((AMFRA-1.0)PRA+1.0)); AMFRA=accident modification factor for related accidents (for values of AMFRA, refer to source), PRA=proportion of total crashes constituted by related crashes. Expert Panel
All All       15 50        
Fixed Object All       15 5        
Head-on All       15 70        
Head-on All       15 5        
Head-on All       15 70        
ROR All       15 49        
Overturn All       15 5        
Sideswipe All       15 52        
Sideswipe All       15 5        
Sideswipe All       15 52        
Widen shoulder (from 6 to 7 ft) All All Rural 2-lane   20 -1 4      
Widen shoulder (from 6 to 8 ft) All All Rural 2-lane   20 4 2      
Widen shoulder (from 6 to 9 ft) All All Rural 2-lane   20 21 6      
Widen shoulder (from 6 to >9 ft) All All Rural 2-lane   20 18 3      
Widen shoulder All All All All   1 20        
Widen shoulder (initially less than 1 ft) All Fatal/Injury Rural 2-lane 400-2,000 38 25   9 40  
Widen shoulder (initially between 1 ft and 3.3 ft) All Fatal/Injury Rural 2-lane 400-2,000 38 13   6 20  
Widen shoulder (initially less than or equal to 4 ft) All All All All   1 20        
Widen shoulder (initially more than 4 ft) All All All All   1 35        
Widen shoulder (paved) All All       15 29        
All All       15 57        
All All       15 20        
All All       15 8        
All All       15 32        
All All       15 50        
Fixed Object All       15 15        
Head-on All       15 45        
Head-on All       15 75        
Head-on All       15 15        
ROR All       15 60        
Ped All       15 71        
Sideswipe All       15 28        
Sideswipe All       15 41        
Sideswipe All       15 15        
Widen shoulder (paved) (from 0 to 2 ft) Fixed Object All       15 16        
ROR All       15 16        
Widen shoulder (paved) (from 0 to 4 ft) Fixed Object All       15 29        
ROR All       15 29        
Widen shoulder (paved) (from 0 to 6 ft) Fixed Object All       15 40        
ROR All       15 40        
Widen shoulder (paved) (from 0 to 8 ft) Fixed Object All       15 49        
ROR All       15 49        
Widen shoulder (unpaved) All All Rural 2-lane   15 15        
All All       15 22        
Widen shoulder (unpaved) (from 0 to 2 ft) Fixed Object All       15 13        
ROR All       15 13        
Widen shoulder (unpaved) (from 0 to 4 ft) Fixed Object All       15 25        
ROR All       15 25        
Widen shoulder (unpaved) (from 0 to 6 ft) Fixed Object All       15 34        
ROR All       15 34        
Widen shoulder (unpaved) (from 0 to 8 ft) Fixed Object All       15 43        
ROR All       15 43        

Table 7. Median Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
MEDIAN COUNTERMEASURES
Install median All All All All   1 15        
All Fatal/Injury Rural 2-lane   5 -94 56     Meta-Analysis
All Fatal/Injury Urban 2-lane   5 39 10     Meta-Analysis
All Injury Rural Multilane   5 12 3     Meta-Analysis
All Injury Urban Multilane   5 22 2     Meta-Analysis
All PDO Rural Multilane   5 18 3     Meta-Analysis
All PDO Rural 2-lane   5 -128 55     Meta-analysis
All PDO Urban Multilane   5 -9 2     Meta-analysis
Install median (flush) All All     <5,000/lane 15 44        
All All     >5,000/lane 15 52        
All All All All   1 25        
All All       15 15        
All All       15 15        
All Fatal       15 90        
Left-turn All     <5,000/lane 15 72        
Left-turn All     >5,000/lane 15 78        
Install median barrier All All All All   27 86 3     EB Before-After
All All   Multilane   5 -24 3     Meta-Analysis
All All       15 19        
All All All All   1 5        
All All       15 5        
All All       15 15        
All All       15 19        
All All       15 20        
All All       15 25        
All All       15 25        
All All       15 36        
All Fatal   Multilane divided   5 43 10     Meta-Analysis
All Fatal All All   1 65        
All Fatal       15 65        
All Fatal/Injury All All   27 88 5     EB Before-After
All Injury   Multilane divided   5 30 6     Meta-Analysis
All Injury All All   1 40        
All Injury       15 40        
ROR All       15 35        
Right-angle All     <5,000/lane 15 58        
Right-angle All     >5,000/lane 15 54        
Install median barrier (cable) All All   Highway (three-lane)   5 -34 74     Meta-Analysis
All Fatal   Highway (three-lane)   5 100 254     Meta-Analysis
All Injury   Highway (three-lane)   5 26 84     Meta-Analysis
All Injury   Multilane divided   5 29 11     Meta-Analysis
Head-on Fatal Rural Highway   9 92       Simple Before-After
Install median barrier (concrete) All Fatal       15 90        
All Injury   Multilane divided   5 -15 36     Meta-Analysis
All Injury       15 10        
Install median barrier (steel) All Injury   Multilane divided   5 35 8     Meta-Analysis
Install or upgrade median barrier near gore area All All     <5,000/lane 15 17        
All All     >5,000/lane 15 17        
All All       15 17        
ROR All     <5,000/lane 15 56        
ROR All     >5,000/lane 15 56        
ROR All       15 56        
Rear-end All     <5,000/lane 15 39        
Rear-end All     >5,000/lane 15 39        
Rear-end All       15 39        
Install raised median All All       15 20        
All All       15 25        
Head-on All       15 75        
Ped All       15 25        
Vary median width All All Urban Urban Street   6 100(1-((b0(EXP(b1Wm^b2)- 1.0)+1.0)/(b0(EXP(b1x16b^b2)-1.0)+1.0))); b0, b1, and b2=regression coefficients (for values of b0, b1, and b2, refer to source), Wm=median width (ft).  
All All Rural Rural Highway   6 100(1-((b0(EXP(b1Wm^b2)- 1.0)+1.0)/(b0(EXP(b1Wmb^b2)-1.0)+1.0))); b0, b1, and b2=regression coefficients (for values of b0, b1, and b2, refer to source), Wm=median width (ft), Wmb=base median width (ft) (16 for surfaced median, 76 for depressed median).  
All All   Freeway   6 100(1-((b0(EXP(b1Wm^b2)- 1.0)+1.0)/(b0(EXP(b1Wmb^b2)-1.0)+1.0))); b0, b1, and b2=regression coefficients (for values of b0, b1, and b2, refer to source), Wm=median width (ft), Wmb=base median width (ft) (24 for surfaced median, 76 for depressed median).  

Table 8. Roadside Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
ROADSIDE COUNTERMEASURES
Install frontage road All All       15 40        
All All All All   1 40        
Install snow fencing Snow All       15 53        
Snow All       15 71        
Snow All       15 35        
Remove poles by burying utility lines All All       15 40        
Remove obstacles on curves to improve sight distance All Fatal/Injury Rural 2-lanes   38 5        
Remove or relocate fixed objects outside of clear zone All All All All   27 38 10     EB Before-After
All All     <5,000/lane 15 18        
All All     >5,000/lane 15 17        
All All All All   1 30        
All All All All   1 25        
All All       15 29        
All All       15 35        
All All       15 61        
All All       15 20        
All All       15 25        
All All       15 30        
All All       15 30        
All All       15 55        
All All       15 25        
All Fatal All All   1 50        
All Fatal All All   1 40        
All Fatal       15 40        
All Fatal       15 50        
All Fatal       15 40        
All Fatal       15 50        
All Fatal/Injury All All   27 38 13     EB Before-After
All Injury All All   1 30        
All Injury All All   1 25        
All Injury       15 25        
All Injury       15 30        
All Injury       15 25        
All Injury       15 30        
Fixed object All       15 65        
Fixed Object Injury Urban     15 20        
Fixed Object All     <400 15 40        
Fixed Object All       15 88        
Fixed Object All       15 90        
Fixed Object All       15 100        
Fixed Object All       15 75        
ROR All       15 71        
Overturn All     <5,000/lane 15 42        
Overturn All     >5,000/lane 15 44        
Vary horizontal clearance All All Rural Rural Highway   6 100(1-((EXP(-0.0137(Whc-30))- 1.0)Ps+1.0)); Whc=horizontal clearance (average for length of segment, ft), Ps=proportion of crash type subset (for values of Ps, refer to source).  
Vary utility pole density All All   Freeway   6 100(1-((fp-1.0)Ps+1.0)); fp=((0.0000984ADT+0.0354Dp)Wo^-0.6- 0.04)/(0.0000128ADT+0.075); Dp=utility pole density (two-way total) (pole/mi), Wo =average pole offset from nearest edge of traveled way (ft), Ps=proportion of crash type subset (for values of Ps, refer to source).  
All All Rural Rural Highway   6 100(1-((fp-1.0)Ps+1.0)); fp=((0.0000984ADT+0.0354Dp)Wo^-0.6- 0.04)/(0.0000128ADT+0.075); Dp=utility pole density (two-way total) (pole/mi), Wo =average pole offset from nearest edge of traveled way (ft), Ps=proportion of crash type subset (for values of Ps, refer to source)  
All All Urban Urban Street   6 100(1-(0.022(fp-1.0)+1.0)), fp=((0.0000984ADT+0.0354Dp)Wo^-0.6- 0.04)/(0.0000649ADT+1.128); Dp=utility pole density (two-way total) (poles/mi), Wo=average pole offset from nearest edge of traveled way (ft)  
Widen clear zone (add 5 ft) Fixed Object All       15 13        
Widen clear zone (add 8 ft) Fixed Object All       15 21        
Widen clear zone (add 10 ft) Fixed Object All       15 25        
Widen clear zone (add 15 ft) Fixed Object All       15 35        
Widen clear zone (add 20 ft) Fixed Object All       15 44        

Table 9. Signs/Markings/Operational Countermeasures

Countermeasures Crash Type Crash Severity Area Type Road Type Daily Traffic Volume (veh/day) Ref Effectiveness Study Type
Crash Reduction Factor/Function Std Error Range
Low High
SIGNS
Implement sign corrections to MUTCD standards All Injury Urban Local   5 15 10     Meta-Analysis
All PDO Urban Local   5 7 6     Meta-Analysis
Install chevron signs on horizontal curves All Fatal/Injury Rural 2-lane   38 20        
All All       15 35        
All All Urban Arterial (urban)   5 64 49     Simple Before-After
All All       15 20        
All All       15 35        
All All       15 50        
Install curve advance warning signs All Fatal/Injury Rural 2-lane   38 10        
All Injury       5 30 71     Meta-Analysis
All PDO       5 8 76     Meta-Analysis
All All       15 30        
All Fatal       15 55        
All All       15 30        
All All       15 23        
All Injury       15 20        
Head-on All       15 29        
ROR Fatal/Injury       15 30        
ROR All All All   1 30        
Install curve advance warning signs (advisory speed) All Injury       5 13 9     Meta-Analysis
All PDO       5 29 23     Meta-Analysis
All All       15 29        
All All       15 20        
Install curve advance warning signs (flashing beacon) All All       15 30        
Install delineators (general) All All       15 11        
Head-on All       15 67        
Night All       15 25        
ROR All       15 34        
Sideswipe All       15 67        
Install dynamic/variable accident warning signs All Injury   Freeways   5 44 17     Meta-Analysis
Rear-end Injury   Freeways   5 16 10     Meta-Analysis
Install dynamic/variable queue warning signs Rear-end PDO   Freeways   5 -16 15     Meta-Analysis
Install dynamic/variable speed warning signs All All       5 46 17     Meta-Analysis
All Injury       5 41 62     Meta-Analysis
Install guide signs (general) All All All     15 15        
Install guideposts or barrier reflectors All Fatal/Injury Rural 2-lane   38 8        
Install illuminated signs All All       15 15        
Install lane assignment signs Rear-end All       15 10        
Sideswipe All       15 20        
Install nonvehicular (animal) reflectors All All       15 10        
Night All       15 25        
Install pavement condition warning signs All All       15 5        
Wet pavement All       15 20        
Wet pavement All       15 20        
Wet pavement All All All   1 20        
Install post-mounted delineators (curves) All All       15 25        
All All       15 20        
All All       15 25        
All All       15 30        
Night All All All   1 30        
Install post-mounted delineators (tangents and curves combined) All Injury Rural 2-lane   5 -4 10     Meta-Analysis
All PDO Rural 2-lane   5 -5 7     Meta-Analysis
All All       15 25        
PAVEMENT
Improve pavement friction All All       15 13        
Ped All       15 10        
Improve pavement friction (groove shoulder) All All       15 22        
All All All All   1 25        
All All       15 18        
All All       15 25        
All All       15 25        
All Fatal/Injury       15 18        
All PDO       15 17        
ROR All       15 27        
ROR All       15 27        
Improve pavement friction (grooving) All All       15 21        
All All     <5,000/lane 15 37        
All All     >5,000/lane 15 21        
All All All All   1 25        
All All       15 10        
All All       15 14        
All All       15 25        
Fixed Object All     <5,000/lane 15 36        
Fixed Object All     >5,000/lane 15 19        
ROR All     <5,000/lane 15 41        
ROR All     >5,000/lane 15 40        
Overturn All     <5,000/lane 15 54        
Overturn All     >5,000/lane 15 35        
Rear-end All     <5,000/lane 15 54        
Rear-end All     >5,000/lane 15 35        
Wet pavement All       15 60        
Wet pavement All     <5,000/lane 15 64        
Wet pavement All     >5,000/lane 15 54        
Wet pavement All All All   1 60        
Improve pavement friction (increase skid resistance) Wet pavement All All All   1 45        
Wet pavement Fatal/Injury Rural 2-lane   38 30        
Improve pavement friction (overlay) All All     <5,000/lane 15 13        
All All     >5,000/lane 15 20        
Fixed Object All     <5,000/lane 15 43        
Fixed Object All     >5,000/lane 15 34        
Head-on All     <5,000/lane 15 43        
Head-on All     >5,000/lane 15 61        
Head-on Fatal/Injury       15 19        
Head-on PDO       15 30        
Left-turn Fatal/Injury       15 41        
Left-turn PDO       15 34        
ROR Fatal/Injury       15 28        
ROR PDO       15 29        
Rear-end Fatal/Injury       15 12        
Rear-end PDO       15 21        
Right-angle All       15 23        
Right-angle Fatal/Injury       15 11        
Right-angle PDO       15 31        
Sideswipe All     <5,000/lane 15 43        
Sideswipe All     >5,000/lane 15 61        
Sideswipe Fatal/Injury       15 12        
Sideswipe PDO       15 27        
Wet pavement All     <5,000/lane 15 23        
Wet pavement All     >5,000/lane 15 50        
Improve pavement friction (curve overlay) All All       15 17        
All All       15 10        
All All       15 24        
Head-on All       15 86        
Wet pavement All       15 51        
Improve pavement friction (resurface with deicing additives) Head-on All       15 31        
Improve pavement friction (resurface with open-graded mix) All All       15 75        
Fixed object All       15 93        
Head-on All       15 90        
Sideswipe All       15 90        
Wet pavement All       15 91        
Improve pavement friction (skid treatment with overlay) Ped Fatal/Injury       15 3        
Install centerline rumble strips All All Rural 2-lane 5,000-22,000 5 14 5     EB Before-After
All Injury Rural 2-lane 5,000-22,000 5 15 8     EB Before-After
Head-on All Rural 2-lane highway   26 55       Simple Before-After
Head-on Fatal Rural 2-lane highway   26 68       Simple Before-After
Head-on Injury (minor) Rural 2-lane highway   26 26       Simple Before-After
Head-on Injury (major) Rural 2-lane highway   26 33       Simple Before-After
Head-on/Sideswipe All Rural 2-lane 5,000-22,000 5 21 12     EB Before-After
Head-on/Sideswipe Injury Rural 2-lane 5,000-22,000 5 25 15     EB Before-After
Install or upgrade curbing Fixed object All       15 50        
Install shoulder rumble strips All All Rural Multilane divided   8 16       Simple Before-After
All Injury Rural Multilane divided   8 17       Simple Before-After
ROR All Rural 2-lane >4,000 41 13 8      
ROR All Rural Multilane divided   8 10       Simple Before-After
ROR All Rural Highway   16 27 22 22 33  
ROR All Rural Freeway   19 18 7     Comparison Group Before-After
ROR All Rural Freeway   19 21 10     Comparison Group Before-After
ROR All Rural All   57 34        
ROR All Rural Arterial   57 16        
ROR All Rural Between ramps   57 34        
ROR All Rural Highway   57 38        
ROR All Rural 3-lane   57 36        
ROR All Rural 2-lane   57 32        
ROR Fatal/Injury Rural 2-lane >4,000 41 18 12      
ROR Injury Rural Multilane divided   8 22       Simple Before-After
ROR Injury All Freeway   19 13 12     Comparison Group Before-After
ROR Injury Rural Freeway   19 7 16     Comparison Group Before-After
Install shoulder rumble strips on illuminated highways ROR All Rural All   57 41        
Install shoulder rumble strips on unilluminated highways ROR All Rural All   57 31        
Pave shoulder All All       15 15        
Head-on All       15 86        
Night All       15 62        
Vary centerline rumble strip width All All Rural Rural Highway   6 12 6      
Vary shoulder rumble strips All All Rural Rural Highway   6 100(1-(-0.07Pi+1.0)); Pi=proportion of crash type subset (for values of Pi, refer to source).  
All All   Freeway   6 100(1-(-0.12Pi+1.0)); Pi=proportion of influential crashes that occur on roadway type i  
MARKINGS
Delineate multiple lanes (painted lane lines) All All Urban Multilane   13 18 22     Meta-Analysis
Install centerline markings All All       15 33        
All All All All   1 36        
All All       15 35        
All All       15 30        
All Injury All 2-lane   13 1 6     Meta-Analysis
All PDO All 2-lane   13 -1 5     Meta-Analysis
Install chevron converging pattern markings on pavement All All Urban     18 38 6     Simple Before-After
All Injury   Freeways   5 56 26     Meta-Analysis
Install edgelines and centerlines All All Rural Undivided 1,000-1,400 2 -3 21     EB Before-After
All Injury All All   13 24 11     Meta-Analysis
Install edgelines, centerlines and delineators All Injury All All   13 45 11     Meta-Analysis
Install edgeline markings All All     <5,000/lane 15 44        
All All     >5,000/lane 15 38        
All All All All   1 20        
All All       15 24        
All All       15 30        
All All       15 4        
All All       15 15        
All All       15 15        
All All       15 25        
All Injury       15 15        
All PDO       15 8        
Fixed object All     <5,000/lane 15 66        
Fixed object All     >5,000/lane 15 59        
ROR All       15 30        
ROR All All All   1 25        
Overturn All     <5,000/lane 15 45        
Overturn All     >5,000/lane 15 50        
Rear-end All     <5,000/lane 15 45        
Rear-end All     >5,000/lane 15 50        
Install edgeline markings (from 4 to 6 in) All Injury Rural 2-lane   13 3 4     Meta-Analysis
All PDO Rural 2-lane   13 3 11     Meta-Analysis
Install edgeline markings (8 in) All Injury Rural 2-lane   13 -5 8     Meta-Analysis
All PDO Rural 2-lane   13 1 15     Meta-Analysis
Install raised pavement markers (snowplowable) where DOC = Degree of Curvature Night All Rural 4-lane freeway <20,000 4 -13 14     EB Before-After
Night All Rural 4-lane freeway <60,000 4 33 21     EB Before-After
Night All Rural 4-lane freeway 20,001-60,000 4 6 21     EB Before-After
Night All Rural 2-lane, DOC>3.5 <5,000 4 -43 9     EB Before-After
Night All Rural 2-lane, DOC>3.5 5,001-15,000 4 -26 10     EB Before-After
Night All Rural 2-lane, DOC>3.5 15,001-20,000 4 -3 11     EB Before-After
Night All Rural 2-lane, DOC>3.5 <5,000 4 -16 3     EB Before-After
Night All Rural 2-lane, DOC>3.5 5,001-15,000 4 1 5     EB Before-After
Night All Rural 2-lane, DOC>3.5 15,001-20,000 4 24 7     EB Before-After
REGULATORY
Install no-passing line All All       15 53        
Head-on All       15 40        
Sideswipe All       15 40        
Lower posted speed All All All All   40 -7       Paired comparison
Fatal/Injury All All All   40 -5       Paired comparison
Lower posted speed by 5 mph All All All All   40 -44       Paired comparison
Lower posted speed by 10 mph All All All All   40 7       Paired comparison
Lower posted speed by 15-20 mph All All All All   40 5       Paired comparison
Prohibit on-street parking All All Urban Arterial (urban) 30,000 5 42 8     Simple Before-After
All All       15 22        
All All       15 8        
All All       15 35        
All Injury Urban Arterial   5 20 5     Meta-Analysis
All Injury Urban Arterial (64ft) 30,000 5 35 14     Simple Before-After
All PDO Urban Arterial   5 27 2     Meta-Analysis
All PDO Urban Arterial (64ft) 30,000 5 48 1     Simple Before-After
Fixed object All       15 40        
Raise posted speed All All All All   40 11       Paired comparison
Fatal/Injury All All All   40 7       Paired comparison
Raise posted speed by 5 mph All All All All   40 8       Simple Before-After
Raise posted speed by 10-15 mph All All All All   40 15       Simple Before-After
Reduce mean speed by 5% through speed limit change and enforcement All Fatal All All   5 17 5     Meta-Analysis
All Injury All All   5 7 3     Meta-Analysis
All PDO All All   5 5 4     Meta-Analysis
Reduce mean speed by 10% through speed limit change and enforcement All Fatal All All   5 32 9     Meta-Analysis
All Injury All All   5 15 5     Meta-Analysis
All PDO All All   5 10 8     Meta-Analysis
Reduce mean speed by 15% through speed limit change and enforcement All Fatal All All   5 44 14     Meta-Analysis
All Injury All All   5 22 8     Meta-Analysis
All PDO All All   5 15 12     Meta-Analysis
Vary curb parking extent All All Urban Urban Street   6 100(1-(1+Ppk(Bpk-1))), Bpk=(1.10+0.365Iu2+0.609Pb/o)((fap/pp- 1.0)Pap+1.0); Ppk=proportion of street segment length with parallel or angle parking (=0.5 Lpk/L), Lpk=curb miles allocated to parking (mi), Iu2=indicator variable for cross section(1 for two-lane street; 0 otherwise), Pb/o=for that part of the street with parking, the proportion that has business or office as an adjacent land use, fap/pp=ratio of crashes on streets with angle parking to those on streets with parallel parking, Pap= for that part of the street with parking, the proportion with angle parking  
Vary speed limit All All   Freeway   6 100(1-EXP(-0.012(V-55))); V=speed limit (mph)  
All All Urban Urban Street   6 100(1- ((EXP(0.252IV<=30+0.318IV>=45)Poffroad+ 1.15((V^2.066)(Exp(-0.0689V)))(1-Poffroad)))); Poff-road=proportion of crashes that occur off the roadway, for values of IV<=30 and IV>=45, refer to source; 100(1- (EXP(b(V-40)))); b= vary per roadway type, V=Speed limit (mph).  
LIGHTING
Improve lighting All All All All   1 25        
All All       15 23        
All All       15 20        
All All       15 25        
All Fatal All Freeway   5 73 71     Meta-Analysis
All Fatal All Highway   5 69 36     Meta-Analysis
All Fatal Rural Highway   5 73 72     Meta-Analysis
All Fatal Urban Highway   5 63 52     Meta-Analysis
All Injury All Freeway   5 27 12     Meta-Analysis
All Injury All Highway   5 28 6     Meta-Analysis
All Injury Rural Highway   5 20 12     Meta-Analysis
All Injury Urban Highway   5 31 7     Meta-Analysis
All PDO All Freeway   5 32 26     Meta-Analysis
All PDO All Highway   5 18 7     Meta-Analysis
All PDO Rural Highway   5 30 43     Meta-Analysis
All PDO Urban Highway   5 16 8     Meta-Analysis
Night All       15 37        
Night All       15 20        
Night All       15 45        
Night All       15 45        
Install lighting All All       62 6       Meta-Analysis/Expert Panel
All Injury       62 8       Meta-Analysis/Expert Panel
Night All       62 20       Meta-Analysis/Expert Panel
Night Injury       62 29       Meta-Analysis/Expert Panel
Install lighting at interchanges All All All All   27 50 17     EB Before-After
All Fatal/Injury All All   27 26 38     EB Before-After
OPERATIONAL
Add two-way left-turn lane All All   All   27 8 16     EB Before-After
All All   All   1 34   25 45  
All All       15 30       Simple Before-After
All All       15 25       Simple Before-After
All All       15 35       Cross-section
All All       15 34       Simple Before-After
All All       15 25       Simple Before-After
All Fatal/Injury   All   27 20 25     EB Before-After
All Injury       15 20       Cross-section
All PDO       15 35       Cross-section
Head-on All       15 36        
Head-on Fatal/Injury       15 67       Simple Before-After
Head-on PDO       15 64       Simple Before-After
Left-turn All       15 33        
Left-turn All       15 33       Simple Before-After
Left-turn Fatal/Injury       15 17       Simple Before-After
Left-turn PDO       15 38       Simple Before-After
ROR All       15 37        
ROR Fatal/Injury       15 90       Simple Before-After
ROR PDO       15 16       Simple Before-After
Ped All       15 19        
ROR PDO       15 16       Simple Before-After
Rear-end All       15 36        
Rear-end All       15 36       Simple Before-After
Rear-end All       15 36       Cross-section
Rear-end Fatal/Injury       15 32       Simple Before-After
Rear-end PDO       15 38       Simple Before-After
Right-angle All       15 20       Simple Before-After
Right-angle Fatal/Injury       15 31       Simple Before-After
Right-angle PDO       15 23       Simple Before-After
Sideswipe Fatal/Injury       15 32       Simple Before-After
Sideswipe PDO       15 37       Simple Before-After
Convert from two-way to one-way traffic All All       15 43        
All All All All   1 33        
Implement crossover at work zone All All   4-lane divided 6,800-38,000 12 0       Simple Before-After
Implement maintenance and bituminous overlay Head-on All       15 31        
Left-turn Fatal/Injury       15 37        
Left-turn PDO       15 13        
ROR Fatal/Injury       15 19        
ROR PDO       15 30        
Ped Fatal/Injury       15 33        
Ped PDO       15 42        
Rear-end Fatal/Injury       15 21        
Right-angle Fatal/Injury       15 16        
Right-angle PDO       15 23        
Sideswipe PDO       15 29        
Implement single lane closure at work zone All All   4-lane divided 20,000-41,500 12 -56       Simple Before-After
Improve drainage patterns All All       15 32        
All All All All   1 20        
All All       15 20        
Wet pavement All       15 40        
Install sidewalk (to avoid walking along roadway) Ped All       15 74        
Ped All       15 75        
Ped All       15 89        
Ped All       15 65        
Ped All       15 65        
Reconfigure lanes within existing pavement width (two to three in one direction) All All   2-lane   15 32        
All Injury   2-lane   15 59        
Left-turn All   2-lane   15 46        
Rear-end All   2-lane   15 46        
Sideswipe All   2-lane   15 46        
Reconfigure lanes within existing pavement width (four to five in one direction) All All Urban Freeway 77,000-126,000 5 -11 5     EB Before-After
All Fatal/Injury Urban Freeway 77,000-126,000 5 -11 8     EB Before-After
All Fatal/Injury/PDO Urban Freeway 77,000-126,000 5 -10 7     EB Before-After
Reconfigure lanes within existing pavement width (five to six in one direction) All All Urban Freeway 77,000-126,000 5 -3 8     EB Before-After
All Fatal/Injury Urban Freeway 77,000-126,000 5 -7 13     EB Before-After
All Fatal/Injury/PDO Urban Freeway 77,000-126,000 5 -4 11     EB Before-After
Reduce driveway density (general) All All Urban Urban Street   6 100(1-(EXP(0.008(Dd,b/o-50)))); Dd,b/o = density of driveways serving business of office land uses (driveways/mi)  
Remove unwarranted signals (one-way streets) Ped All       46 17       Comparison Group Before-After
Vary passing lanes All All Rural Rural Highway   6 0.25 for one direction with three lane; 0.35 for two direction with four lane  
Vary truck presence All All Urban Urban Street   6 100(1-((ftk-1.0)(1-Poff-road)+1.0)), ftk=(2EXP(-0.059Pt)+0.017Pt)/1.506; Poffroad= proportion of crashes that occur off the roadway, Pt=percent of truck presence; 100(1-(1.0+Truck/Basei)), for values of Truck and Basei, refer to source.  

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