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Toolbox of Countermeasures and Their Potential Effectiveness for Roadway Departure Crashes

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August 2008

Introduction

This issue brief documents estimates of the crash reduction that might be expected if a specific countermeasure or group of countermeasures is implemented with respect to roadway departure crashes and other non-intersection crashes. The crash reduction estimates are presented as Crash Reduction Factors (CRFs).

Traffic engineers and other transportation professionals can use the information contained in this issue brief when asking the following types of question: Which countermeasures might be considered along a particular section of a highway that is experiencing a high number of roadway departure crashes? What changes in the number of roadway departure crashes can be expected with the implementation of the various countermeasures?

When selecting countermeasures to reduce the number and/or severity of roadway departure crashes, the practitioner should first consider countermeasures designed to reduce the likelihood of vehicles leaving the roadway. Next, the practitioner should select strategies which minimize the likelihood of crashing into an object or overturning if the vehicle travels beyond the edge of the shoulder. Finally, the practitioner should consider countermeasures which reduce the severity of the crash such as improving the design and application of barrier and attenuation systems.

When selecting countermeasures to reduce the number and/or severity of crashes associated with hazardous roadside obstacles, the practitioner should refer to the AASHTO Roadside Design Guide which recommends these design options in order of preference:

  1. Remove the obstacle;
  2. Redesign the obstacle so it can be safely traversed;
  3. Relocate the obstacle to a point where it is less likely to be struck;
  4. Reduce impact severity by using an appropriate breakaway device;
  5. Shield the obstacle with a longitudinal traffic barrier designed for redirection or use a crash cushion; and
  6. Delineate the obstacle if the above alternatives are not appropriate.

Crash Reduction Factors

A CRF is the percentage crash reduction that might be expected after implementing a given countermeasure. In some cases, the CRF is negative, i.e. the implementation of a countermeasure is expected to lead to a percentage increase in crashes.

One CRF estimate is provided for each countermeasure. Where multiple CRF estimates were available from the literature, selection criteria were used to choose which CRFs to include in the issue brief:

Where these criteria could not be met, a CRF may still be provided. In these cases, it is recognized that the reliability of the estimate of the CRF is low, but the estimate is the best available at this time. The CRFs in this issue brief may be periodically updated as new information becomes available.

The Desktop Reference for Countermeasures lists all of the CRFs included in this issue brief, and alis many other CRFs available in the literature. A few CRFs found in the literature were not included in the Desktop Reference. These CRFs were considered to have too large a range or too large a standard error to be meaningful, or the original research did not provide sufficient detail for the CRF to be useful.

A CRF should be regarded as a generic estimate of the effectiveness of a countermeasure. The estimate is a useful guide, but it remains necessary to apply engineering judgment and to consider site-specific environmental, traffic volume, traffic mix, geometric, and operational conditions which will affect the safety impact of a countermeasure. The user must ensure that a countermeasure applies to the particular conditions being considered. The reader is also encouraged to obtain and review the original source documents for more detailed information, and to search databases such as the National Transportation Library (ntlsearch.bts.gov) for information that becomes available after the publication of this issue brief.

Presentation of the Crash Reduction Factors

In the Tables presented in this issue brief, the crash reduction estimates are provided in the following format:

CRF(standard error)REF

The CRF is the value selected from the literature.

The standard error is given where available. The standard error is the standard deviation of the error in the estimate of the CRF. The true value of the CRF is unknown. The standard error provides a measure of the precision of the estimate of the true value of the CRF. A relatively small standard error indicates that a CRF is relatively precisely known. A relatively large standard error indicates that a CRF is not precisely known. The standard error may be used to estimate a confidence interval of the true value of the CRF. (An example of a confidence interval calculation is given below.)

The REF is the reference number for the source information.

As an example, the CRF for the countermeasure remove or relocate fixed objects outside of clear zone for all crashes is:

38(10)17

The following points should be noted:

Using the Tables

The CRFs for roadway departure crashes and other non-intersection crashes are presented in six tables which

summarize the available information. The Tables are:

The following points should be noted:


Legend

CRF(standard error)REF
CRF is a crash reduction factor, which is an estimate of the percentage reduction that might be expected after implementing a given countermeasure. A number in bold indicates a rigorous study methodology and a small standard error in the value of the CRF.
Standard error, where available, is the standard deviation of the error in the estimate of the CRF.
REF is the reference number for the source information.

Additional crash types identified in the Other Crashes column:

a: sideswipe b: night c: right-angle d: left-turn e: Wet pavement f: overturn g: Pedestrian h: right-turn i: animal
j: Parking k: Wet weather l: Head-on/sideswipe m: snow n: truck-related o: speed related p: Pedestrian walking along the roadway only

Table 1: Barrier Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed Object Crashes Other Crashes Daily Traffic Volume (vehicles/day)
Improve guardrail All     189     419 239 f    419 <5,000/lane
All     99 329   279 189 f    279 >5,000/lane
All       269          
Fatal   All 501            
Injury     359            
Install animal fencing All               i    809  
Injury               i    919  
PDO               i    619  
Install barrier (concrete) inside and outside curve Fatal/Injury     399            
Install guardrail (as shield for rocks and posts) All     149       1009    
Injury     319            
Install guardrail (as shield for trees) Fatal     659            
Injury     519            
Install guardrail (at culvert) All     279            
Install guardrail (at ditch) Injury     269            
Install guardrail (at embankment) All   All   7(31)4          
Fatal   All   44(10)4          
Injury     429            
Injury   All   47(5)4          
Install guardrail (inside curves) Fatal/Injury     289            
Install guardrail (outside curves) Fatal/Injury     639            
Install impact attenuators All     299 459          
Fatal All All 751       69(28)4    
Injury All All 501       69(10)4    
PDO             46(30)4    
Replace guardrail with a softer material (concrete -> steel -> wire) Fatal   All   41(31)4          
Injury   All   32(10)4          

Table 2: Bridge Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed ObjectCrashes Other Crashes Daily Traffic Volume (vehicles/day)
Install bridge lighting All     599            
Install delineators (on bridges) All     439            
Install guardrail (at bridge) All     229     379   f    419 <5,000/lane
All     209     329   f    329 >5,000/lane
All               k    509  
Fatal     909            
Injury     459            
Repair bridge deck All     149            
Replace bridge (general) All   All 451            
Replace bridge (2-lane) All     459            
Upgrade bridge parapet All     59            
Upgrade bridge railing All     209            
Fatal     769            
Injury     619            
PDO     509            
Widen bridge All     459 449 459   459 a    499  
Fatal/Injury     929            
PDO     959            
Widen bridge (18 to 24 ft) All     689            
Widen bridge (18 to 30 ft) All     939            
Widen bridge (20 to 24 ft) All     569            
Widen bridge (20 to 30 ft) All     909            
Widen bridge (22 to 24 ft) All     369            
Widen bridge (22 to 30 ft) All     869            

Table 3: Geometric Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed ObjectCrashes Other Crashes Daily Traffic Volume (vehicles/day)
Flatten crest vertical curve All All All 20(19)17            
Fatal/Injury All All 51(19)17            
Fatal/Injury Rural 2-lane 5018            
Flatten horizontal curve All     399            
All       909 679 739 689 f    739 <5,000/lane
All       799 649 249 879 f    249 >5,000/lane
Flatten horizontal curves (10 to 5 degrees) All     459            
Flatten horizontal curves (15 to 5 degrees) All     639            
Flatten horizontal curves (20 to 10 degrees) All     489            
Flatten side slopes All     439           <5,000/lane
All     459           >5,000/lane
All       109     629  
Flatten side slopes (11 to 8 degrees) All     89         g    149  
All               h    149  
Flatten side slopes (14 to 9 degrees) Injury Rural 2-lane 22(4)4            
PDO Rural 2-lane 24(2)4            
All     79         g    129  
All               h    129  
Flatten side slopes (18 to 9 degrees) All Rural 2-lane 119         g    199  
All               h    199  
Flatten side slopes (18 to 11 degrees) All     89         g    149  
All               h    149  
Flatten side slopes (18 to 14 degrees) Injury Rural 2-lane 42(4)4            
PDO Rural 2-lane 29(4)4            
All     59         g    89  
All               h    89  
Flatten side slopes (27 to 9 degrees) All     129         g    219  
All               h    219  
Flatten side slopes (27 to 11 degrees) All     99         g    159  
All               h    159  
Flatten side slopes (27 to 14 degrees) All     69         g    109  
All               h    109  
Flatten side slopes and remove guardrail All All All 42(58)17            
Improve gore area All     259            
Improve horizontal and vertical alignments All     589            
Improve longitudinal grade All     499            
Fatal/Injury     879            
PDO     839            
Improve superelevation All     409 509          
Improve superelevation (for drainage) All     459            
Increase number of lanes All               d    719  
All     209   389 429   a    389 <5,000/lane
All               c    359 <5,000/lane
All               f    429 <5,000/lane
All     319   449 529   a    449 >5,000/lane
All               c    459 >5,000/lane
All               f    529 >5,000/lane
Fatal     399            
Injury     239            
Increase number of lanes (continued) PDO     279 509 509 539   a    649  
PDO               c    469  
PDO               d    679  
Install acceleration/deceleration lanes All     269     759   a    759  
Install channelized lane All     679     939      
PDO     629            
Install climbing lane (where large difference between car and truck speed) Fatal/Injury Rural 2-lane 3318            
Install passing/climbing lane All All All 201            
Fatal/Injury Rural 2-lane 3318            
Install shoulder All     99            
Install shoulder bus lanes Fatal/Injury         509     a    279  
Fatal/Injury               c    349  
Fatal/Injury               d    429  
PDO       279 869     a    89  
PDO               c    319  
PDO               d    579  
Install truck escape ramp All     189 759   339      
Lengthen culverts All     449            
Narrow cross section (4 to 3 lanes with two-way left turn lane) All Urban 4-lane highway 37(1)11     31(2)11   c 37(1)11 8,000 - 17,400
All Urban 4-lane highway           d 24(2)11 8,000 - 17,400
Fatal/Injury Urban 4-lane highway 0(2)11           8,000 - 17,400
PDO Urban 4-lane highway 46(1)11           8,000 - 17,400
Reduce horizontal curve angle All     389            
Reduce shoulder width (6 ft to 0 ft) All Rural 2-lane -12(3)14            
Reduce shoulder width (6 ft to 1 ft) All Rural 2-lane -17(6)14            
Reduce shoulder width (6 ft to 2 ft) All Rural 2-lane -11(2)14            
Reduce shoulder width (6 ft to 4 ft) All Rural 2-lane -6(2)14            
Reduce shoulder width (6 ft to 5 ft) All Rural 2-lane -2(2)14            
Resurface pavement and improve superelevation All     289         e   519  
Stabilize shoulder All     259            
Stabilize shoulder and dropoff All All All 251            
Widen lane (add 1 ft to both sides) All       129 129     a    129  
Widen lane (add 2 ft to both sides) All       239 239     a    239  
Widen lane (add 3 ft to both sides) All       329 329     a    329  
Widen lane (add 4 ft to both sides) All       409 409     a    409  
Widen lane (initially less than 9 ft) Fatal/Injury Rural 2-lane 2818           400 - 2,000
Widen lane (initially between 9 ft and 10.75 ft) Fatal/Injury Rural 2-lane 1618           400 - 2,000
Widen lanes All     509 499 709   59 a    529  
All               f    59  
Widen shoulder (from 6 to 7 ft) All Rural 2-lane -1(4)14            
Widen shoulder (from 6 to 8 ft) All Rural 2-lane 4(2)14            
Widen shoulder (from 6 to 9 ft) All Rural 2-lane 21(6)14            
Widen shoulder (from 6 to >9 ft) All Rural 2-lane 18(3)14            
Widen shoulder (initially less than 1 ft) Fatal/Injury Rural 2-lane 2518           400 - 2,000
Widen shoulder (initially between 1 ft and 3.3 ft) Fatal/Injury Rural 2-lane 1318           400 - 2,000
Widen shoulder (paved)(from 0 to 2 ft) All       169     169    
Widen shoulder (paved)(from 0 to 4 ft ) All       299     299    
Widen shoulder (paved)(from 0 to 6 ft ) All       409     409    
Widen shoulder (paved)(from 0 to 8 ft ) All       499     499    
Widen shoulder (unpaved)(from 0 to 2 ft ) All       139     139    
Widen shoulder (unpaved)(from 0 to 4 ft ) All       259     259    
Widen shoulder (unpaved)(from 0 to 6 ft) All       349     349    
Widen shoulder (unpaved)(from 0 to 8 ft) All       439     439    

Table 4: Median Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed ObjectCrashes Other Crashes Daily Traffic Volume (vehicles/day)
Install median All All All 151            
Injury Rural Multilane 12(3)4            
Fatal/Injur y Rural 2-lane -94(56)4            
Injury Urban Multilane 22(2)4            
Fatal/Injur y Urban 2-lane 39(10)4            
PDO Rural Multilane 18(3)4            
PDO Rural 2-lane -128(55)4            
PDO Urban Multilane -9(2)4            
Install median (flush) All     449         d   729 <5,000/lane
All     529         d   789 >5,000/lane
Fatal     909            
Install median barrier All               c   589 <5,000/lane
All               c   549 >5,000/lane
All     199 359          
All All All 86(3)17            
All   Multilane divide d -24(3)4            
Fatal   Multilane divide d 43(10)4            
Injury     409            
Fatal/Injury All All 88(5)17            
Injury   Multilane divide d 30(6)4            
Install median barrier (cable) All   Highway (3-lane ) -34(74)4            
Fatal Rural Highway     926        
Injury   Highway (3-lane ) 26(84)4            
Injury   Multilane divided 29(11)4            
Install median barrier (concrete) Injury   Multilane divided -15(36)4            
Fatal     909            
Injury     109            
Install median barrier (steel) Injury   Multilane divided 35(8)4            
Install or upgrade median barrier near gore area All     179 569   399     <5,000/lane
Install raised median All     209   759     g   259  

Table 5: Roadside Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed ObjectCrashes Other Crashes Daily Traffic Volume (vehicles/day)
Install frontage road All     409            
Install snow fencing All               m   539  
Remove poles by burying utility lines All     409            
Remove obstacles on curves to improve sight distance Fatal/Injury Rural 2-lane 518            
Remove or relocate fixed objects outside of clear zone All All All 38(10)17            
All     189         f    429 <5,000/lane
All     179         f    449 >5,000/lane
All             659    
All Urban           209    
All       719          
Fatal/Injury All All 38(13)17            
Widen clear zone (add 5 ft) All             139    
Widen clear zone (add 8 ft) All             219    
Widen clear zone (add 10 ft) All             259    
Widen clear zone (add 15 ft) All             359    
Widen clear zone (add 20 ft) All             449    

Table 6: Sign/Marking/Operational Countermeasures

Countermeasure(s) Crash Severity Area Type Road Type All Crashes Run-off-Road Crashes Head-on Crashes Rear-end Crashes Fixed ObjectCrashes Other Crashes Daily Traffic Volume (vehicles/day)
SIGNS
Implement sign corrections to MUTCD standards Injury Urban Local 15(10)4            
PDO Urban Local 7(6)4            
Install chevron signs on horizontal curves All     359            
Fatal/Injury Rural 2-lane 2018            
Install curve advance warning signs All     309 309 299        
Fatal     559            
Fatal/Injury Rural 2-lane 1018            
Injury     30(71)4            
PDO     8(76)4            
Install curve advance warning signs (advisory speed) All     299            
Injury     13(9)4            
PDO     29(23)4            
Install curve advance warning signs (flashing beacon) All     309            
Install delineators (general) All     119 349 679     a    679  
                   
Install dynamic/variable accident warning signs Injury   Freeway 44(17)4     16(10)4      
Install dynamic/variable queue warning signs PDO   Freeway       -16(15)4      
Install dynamic/variable speed warning signs All     46(17)4            
Injury     41(62)4            
Install guide signs (general) All     159            
Install guideposts or barrier reflectors Fatal/Injury Rural 2-lane 818            
Install illuminated signs All     159            
Install lane assignment signs All           109   a    209  
Install nonvehicular (animal) reflectors All     109         b    259  
Install pavement condition warning signs All All All           k    201  
All     59         e    209  
Install post-mounted delineators (curves) All All All           b    301  
All     259            
Install post-mounted delineators (tangents and curves combined) Injury Rural 2-lane -4(10)4            
PDO Rural 2-lane -5(7)4            
PAVEMENT
Improve pavement friction (groove shoulder) All     229            
Improve pavement friction (grooving) All     379 419   549 369 f   549 <5,000/lane
All     219 409   359 199 f    359 >5,000/lane
All               e   649 <5,000/lane
All               e   549 >5,000/lane
Improve pavement friction (increase skid resistanc Fatal/Injury Rural 2-lane           e   3018  
MARKINGS
Delineate multiple lanes (painted lane lines) All Urban Multilane 8(22)8            
Install centerline markings All     339            
Injury All 2-lane 1(6)8            
PDO All 2-lane -1(5)8            
Install chevron converging pattern markings on pavement All Urban   38(6)12            
Injury   Freeway 56(26)4            
Install edgelines and centerlines All Rural Undivided -3(21)2           1,000 - 4,000
Injury All All 24(11)8            
Install edgelines, centerlines and delineators Injury All All 45(11)8            
Install edgeline markings All     449     459 669 f   459 <5,000/lane
All     389     509 599 f   509 >5,000/lane
All       309          
Injury     159            
PDO     89            
Install edgeline markings (from 4 to 6 in) Injury Rural 2-lane 3(4)8            
PDO Rural 2-lane 3(11)8            
Install edgeline markings (8 in) Injury Rural 2-lane -5(8)8            
PDO Rural 2-lane 1(15)8            
Install raised pavement markers (snowplowable) where DOC = degree of curvature All Mostly Rural 4-lane freeway           b   -13(14)3 ≤20,000
All Mostly Rural 4-lane freeway           b   33(21)3 <60,000
All Mostly Rural 4-lane freeway           b   6(21)3 20,001 - 60,000
All Mostly Rural 2-lane, DOC>3.5           b   -43(9)3 ≤5,000
All Mostly Rural 2-lane, DOC>3.5           b -26(10)3 5,001 - 15,000
All Mostly Rural 2-lane, DOC>3.5           b   -3(11)3 15,001 - 20,000
All Mostly Rural 2-lane, DOC<3.5           b   -16(3)3 ≤5,000
All Mostly Rural 2-lane, DOC<3.5           b    1(5)3 5,001 - 15,000
All Mostly Rural 2-lane, DOC<3.5           b   24(7)3 15,001 - 20,000
REGULATORY
Install no-passing line All     539   409     a    409  
Prohibit on-street parking All Urban Arterial (64ft) 42(8)4           30,000
All     229       409    
Injury Urban Arterial 20(5)4            
Injury Urban Arterial (64ft) 35(14)4           30,000
PDO Urban Arterial 27(2)4            
PDO Urban Arterial (64ft) 48(1)4           30,000
Reduce mean speed by 5% through speed limit change and enforcement Fatal All All 17(5)4            
Injury All All 7(3)4            
PDO All All 5(4)4            
Reduce mean speed by 10% through speed limit change and enforcement Fatal All All 32(9)4            
Injury All All 15(5)4            
PDO All All 10(8)4            
Reduce mean speed by 15% through speed limit change and enforcement Fatal All All 44(14)4            
Injury All All 22(8)4            
PDO All All 15(12)4            
LIGHTING
Improve lighting All               b    379  
Fatal All Freeway 73(71)4            
Fatal All Highway 69(36)4            
Fatal Rural Highway 73(72)4            
Fatal Urban Highway 63(52)4            
Injury All Freeway 27(12)4            
Injury All Highway 28(6)4            
Injury Rural Highway 20(12)4            
Injury Urban Highway 31(7)4            
PDO All Freeway 32(26)4            
PDO All Highway 18(7)4            
PDO Rural Highway 30(43)4            
PDO Urban Highway 16(8)4            
Install lighting All     622         b   2022  
Injury     822         b   2922  
Install lighting at interchanges All All All 50(17)17            
Fatal/Injury All All 26(38)17            
OPERATIONAL
Add two-way left-turn lane All   All 8(16)17            
All       379 369 369   c    209  
All               d    339  
All               g    199  
Fatal/Injury   All 20(25)17 909 679 329   a    329  
Fatal/Injury               c    319  
Fatal/Injury               d    179  
Injury     209            
PDO     359 169 649 389   a    379  
PDO               c    239  
PDO               d    389  
Convert from two-way to one-way traffic All     439            
Implement crossover at work zone All   4-lane divided 07           6,800 - 38,000
Implement single lane closure at work zone All   4-lane divided -567           20,000 - 41,500
Improve drainage patterns All     329            
All               e    409  
Install sidewalk All               p   8823  
Reconfigure lanes within existing pavement width (two to three in one direction) All   2-lane 329     469   a    469  
All   2-lane           d    469  
Injury   2-lane 599            
Reconfigure lanes within existing pavement width (four to five in one direction) All Urban Freeway -11(5)4           77,000 - 126,000
Fatal/Injury Urban Freeway -11(8)4           77,000 - 126,000
Reconfigure lanes within existing pavement width (five to six in one direction) All Urban Freeway -3(8)4           77,000 - 126,000
Fatal/Injury Urban Freeway -7(13)4           77,000 - 126,000
Remove unwarranted signals (one-way streets) All               g   1720  

References

  1. Agent, K. R., Stamatiadis, N., and Jones, S., “Development of Accident Reduction Factors.” KTC-96-13, Kentucky Transportation Cabinet, (1996)
  2. Al-Masaeid, H. R. and Sinha, H., “An Analysis of Accident Reduction Potentials of Pavement Marking.” Journal of Transportation Engineering, ASCE, (1993) pp. 723-736.
  3. Bahar, G., Mollett, C., Persaud, B., Lyon, C., Smiley, A., Smahel, T., and McGee, H., “NCHRP Report 518: Safety Evaluation of Permanent Raised Pavement Markers.”Washington, D.C., Transportation Research Board, National Research Council, (2004)
  4. Bahar, G., Parkhill, M., Hauer, E., Council, F., Persaud, B., Zegeer, C., Elvik, R., Smiley, A., and Scott, B. “Prepare Parts I and II of a Highway Safety Manual: Knowledge Base for Part II”. Unpublished material from NCHRP Project 17-27. (May 2007)
  5. Carrasco, O., McFadden, J., and Chandhok, P., “Evaluation of the Effectiveness of Shoulder Rumble Strips on Rural Multi-lane Divided Highways In Minnesota.” 83rd Transportation Research Board Annual Meeting, Washington D.C., (2004)
  6. Chandler, B., “Eliminating Cross-Median Fatalities: Statewide Installation of Median Cable Barrier in Missouri.”TR News, No. 248, Washington, D.C., Transportation Research Board of the National Academies, (2007) pp. 29-31 .
  7. Dudek, C. L., Richards, S. H., and Buffington, J. L., “Some Effects of Traffic Control on Four-Lane Divided Highways.”Transportation Research Record 1086, Washington, D.C., Transportation Research Board, National Research Council, (1986) pp. 20-30.
  8. Elvik, R. and Vaa, T., “Handbook of Road Safety Measures.” Oxford, United Kingdom, Elsevier, (2004)
  9. Gan, A., Shen, J., and Rodriguez, A., “Update of Florida Crash Reduction Factors and Countermeasures to Improve the Development of District Safety Improvement Projects.” Florida Department of Transportation, (2005)
  10. Garder, P. and Davies, M., “Safety Effect of Continuous Shoulder Rumble Strips on Rural Interstates in Maine.” 2006 TRB 85th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#06-2219, Washington, D.C., (2006)
  11. Gates, T. J., Noyce, D. A., Talada, V., and Hill, L., “The Safety and Operational Effects of “Road Diet” Conversion in Minnesota.” 2007 TRB 86th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#07-1918, Washington, D.C., (2007)
  12. Griffin, L. I. and Reinhardt, R. N., “A Review of Two Innovative Pavement Patterns that Have Been Developed to Reduce Traffic Speeds and Crashes.” Washington, D.C., AAA Foundation for Traffic Safety, (1996)
  13. Griffith, M. S., “Safety Evaluation of Rolled-In Continuous Shoulder Rumble Strips Installed on Freeways.”Transportation Research Record 1665, Washington, D.C., Transportation Research Board, National Research Council, (1999) pp. 28-33.
  14. Gross, F. and Jovanis, P. P., “Estimation of Safety Effectiveness of Changes in Shoulder Width using Case-Control and Cohort Methods.” 2007 TRB 86th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#07-2762, Washington, D.C., (2007)
  15. Harwood, D. W., Council, F. M., Hauer, E., Hughes, W. E., and Vogt, A., “Prediction of the Expected Safety Performance of Rural Two-Lane Highways.” FHWA RD-99-207, McLean, Va., Federal Highway Administration, (2000)
  16. Hirasawa, M., Takuda, T., Asano, M., and Saito, K., “Developing Optimal Centerline Rumble Strips and Evaluating Their Safety Benefits on National Highways in Hokkaido, Japan.” 2006 TRB 85th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#06-1968, Washington, D.C. , (2006)
  17. Hovey, P. W. and Chowdhury, M., “Development of Crash Reduction Factors.” 14801(0), Ohio Department of Transport, (2005)
  18. Montella, A., “Safety Reviews of Existing Roads: a Quantitative Safety Assessment Methodology.” 2005 TRB 84th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#05-1295, Washington, D.C., (2005)
  19. Patel, R. B., Council, F. M., and Griffith, M. S., “Estimating the Safety Benefits of Shoulder Rumble Strips on Two Lane Rural Highways in Minnesota: An Empirical Bayes Observational Before-After Study.” 2007 TRB 86th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#07-1924, Washington,
  20. Persaud, B., Hauer, E., Retting, R. A., Vallurupalli, R., and Mucsi, K., “Crash Reductions Related to Traffic Signal Removal in Philadelphia.” Accident Analysis and Prevention, Vol. 29, No. 6, Oxford, N.Y., Pergamon Press, (1997) pp. 803-810.
  21. Smith, E. B. and Ivan, J. N., “Evaluation of Safety Benefits and Potential Crash Migration Due to Shoulder Rumble Strip Installation on Freeways in Connecticut.” 2005 TRB 84th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#05-1299, Washington, D.C., (2005)

    Updated August 2008

  22. Harkey, D., Srinivasan, R., Baek, J., Council, F. M., Eccles, K., Lefler, N., Gross, F., Persaud, B., Lyon, C., Hauer, E., and Bonneson, J. A., “Crash Reduction Factors for Traffic Engineering and ITS Improvements,” NCHRP Report No. 617, (2008)
  23. McMahon, P., Zegeer, C., Duncan, C., Knoblauch, R., Stewart, R., and Khattak, A., “An Analysis of Factors Contributing to ‘Walking Along Roadway’ Crashes: Research Study and Guidelines for Sidewalks and Walkways,” FHWA-RD-01-101, (March 2002)
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