Safety Evaluation of Multiple

Strategies at Stop-Controlled 

Intersections

PUBLICATION NO. FHWA-HRT-17-086 JANUARY 2018

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296
FOREWORD

The research documented in this report was conducted as part of the Federal Highway 

Administration’s (FHWA) Evaluation of Low-Cost Safety Improvements Pooled Fund Study 

(ELCSI-PFS). FHWA established this PFS in 2005 to conduct research on the effectiveness of 

the safety improvements identified by the National Cooperative Highway Research Program

Report 500 Guides as part of the implementation of the American Association of State Highway 

and Transportation Officials Strategic Highway Safety Plan.

(1) The ELCSI-PFS studies provide a 

crash modification factor and benefit–cost economic analysis for each of the targeted safety 

strategies identified as priorities by the pooled fund member States.

This study evaluated multiple low-cost safety improvements at stop-controlled intersections that 

included basic signing and pavement markings. This strategy is intended to reduce the frequency 

and severity of crashes at stop-controlled intersections by alerting drivers approaching a stopcontrolled intersection. The results indicate reductions for all crash types (i.e., total, fatal and

injury, rear-end, right-angle, and nighttime crashes). The economic analysis results suggest that 

the multiple low-cost treatments at stop-controlled intersections, even with conservative 

assumptions on cost, service life, and the value of a statistical life, can be cost effective. This 

report is intended for safety engineers, highway designers, planners, and practitioners at State and 

local agencies involved with AASHTO Strategic Highway Safety Plan implementation.

Jonathan Porter, Ph.D.

Acting Director, Office of Safety

Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) in the interest of information exchange. The U.S. Government assumes no liability for 

the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts its programs and processes to 

ensure continuous quality improvement.
TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.

FHWA-HRT-17-086

2. Government 

Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Safety Evaluation of Multiple Strategies at Stop-Controlled Intersections

5. Report Date

January 2018

6. Performing Organization Code

7. Author(s) 

Thanh Le, Frank Gross, Bhagwant Persaud, Kimberly Eccles, and 

Jonathan Soika

8. Performing Organization Report No.

9. Performing Organization Name and Address

VHB Persaud and Lyon, Inc 

8300 Boone Blvd., Ste. 700 87 Elmcrest Road

Vienna, VA 22182-2626 Toronto, Ontario M9C 3R7

10. Work Unit No.

11. Contract or Grant No.

DTFH61-13-D-00001

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

Federal Highway Administration 

1200 New Jersey Avenue, SE

Washington, DC 20590

13. Type of Report and Period Covered

Safety Evaluation Final Report; October

2010–September 2017

14. Sponsoring Agency Code

HRDS-20

15. Supplementary Notes.

FHWA Office of Safety Research and Development managed this study under the Development of Crash 

Modification Factors program. The FHWA Office of Safety Research and Development Program and Task 

Manager was Roya Amjadi (HRDS-20).

16. Abstract

The Development of Crash Modification Factors program studied the safety performance of various stop-controlled 

intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated the 

safety effectiveness of multiple low-cost treatments at stop-controlled intersections. Improvements included basic 

signing and pavement markings. This strategy is intended to reduce the frequency and severity of crashes at stopcontrolled intersections by alerting drivers to the presence and type of approaching intersection. Geometric, traffic, 

and crash data were obtained at three- and four-legged, two- and four-lane major road, and urban and rural stopcontrolled intersections in South Carolina. To account for potential selection bias and regression to the mean, an 

empirical Bayesian before–after analysis was conducted, using reference groups of untreated intersections with 

similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes throughout

time and time trends in crash counts unrelated to the treatments. The aggregate results indicate reductions for all 

crash types analyzed (i.e., total, fatal and injury, rear-end, right-angle, and nighttime). The reductions are 

statistically significant at the 95-percent confidence level for all crash types. For all crash types combined, the crash 

modification factors (CMFs) are 0.917 for all severities and 0.899 for fatal and injury crashes. The CMFs for rearend, right-angle, and nighttime crashes are 0.933, 0.941, and 0.853, respectively. The benefit–cost ratio estimated 

with conservative cost and service life assumptions is 12.4 to 1 for total crashes at unsignalized intersections. The 

results suggest that the multiple low-cost treatments, even with conservative assumptions on cost, service life, and 

the value of a statistical life, can be cost effective.

17. Key Words

Stop-controlled, unsignalized, intersection, low cost, 

safety improvements, safety evaluations, empirical 

Bayesian, before–after, multi-strategy, multiple 

treatments

18. Distribution Statement

No restrictions. This document is available to the public 

through the National Technical Information Service, 

Springfield, VA 22161.

http://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages:

99

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized.
ii
iii

TABLE OF CONTENTS

EXECUTIVE SUMMARY............................................................................................................1

CHAPTER 1. INTRODUCTION .................................................................................................3

BACKGROUND ON MULTIPLE STRATEGIES AT STOP-CONTROLLED 

INTERSECTIONS.....................................................................................................................3

BACKGROUND ON STUDY...................................................................................................4

DOUBLING AND OVERSIZING ADVANCE WARNING SIGNS, STOP SIGNS, AND 

YIELD SIGNS ............................................................................................................................7

FLUORESCENT YELLOW SHEETING...............................................................................7

RETROREFLECTIVE SIGN POSTS .....................................................................................8

REFRESHING EXISTING PAVEMENT MARKINGS .......................................................8

STOP LINES ..............................................................................................................................8

LIMITATIONS OF PREVIOUS RESEARCH.......................................................................9

CHAPTER 4. STUDY DESIGN .................................................................................................13

SAMPLE SIZE ESTIMATION OVERVIEW ......................................................................13

REFERENCE GROUP OVERVIEW....................................................................................18

CHAPTER 5. METHODOLOGY ..............................................................................................19

CHAPTER 6. DATA COLLECTION........................................................................................21

TREATMENT SITES..............................................................................................................21

REFERENCE SITES...............................................................................................................25

TRAFFIC DATA......................................................................................................................26

CRASH DATA .........................................................................................................................27

TREATMENT COST DATA..................................................................................................28

DATA CHARACTERISTICS AND SUMMARY.................................................................29

CHAPTER 7. DEVELOPMENT OF SPFs................................................................................31

SPFs FOR 3 X 22 INTERSECTIONS....................................................................................32

SPFs FOR 4 X 22 INTERSECTIONS....................................................................................34

SPFs FOR 3 X 42 INTERSECTIONS....................................................................................36

SPFs FOR 4 X 42 INTERSECTIONS....................................................................................38

BEFORE–AFTER ADJUSTMENT FACTORS ...................................................................40

CHAPTER 8. BEFORE–AFTER EVALUATION RESULTS................................................43

AGGREGATE ANALYSIS.....................................................................................................43

DISAGGREGATE ANALYSIS..............................................................................................43

CHAPTER 9. ECONOMIC ANALYSIS ...................................................................................49

CHAPTER 10. SUMMARY AND CONCLUSIONS................................................................51

APPENDIX. ADDITIONAL INSTALLATION DETAILS.....................................................53

EXAMPLE OF DOCUMENTS USED DURING THE LOW-COST INTERSECTION 

IMPROVEMENT PROJECT.................................................................................................53

GENERAL SIGNING AND PAVEMENT MARKING NOTES FOR ALL 

INTERSECTIONS...................................................................................................................54
iv

Remark all existing stop lines, crosswalks, arrows and word messages unless:.............54

STANDARD MARKINGS FOR INTERSECTIONS...........................................................55

Application of Markings at Intersections...........................................................................55

Arrows and Word Messages................................................................................................57

Additional Guidance through Intersections ......................................................................57

Crosswalks ............................................................................................................................57

TYPICAL MARKINGS FOR TURN LANE INSTALLATIONS.......................................58

Notes ......................................................................................................................................58

STANDARD PAVEMENT MARKINGS ..............................................................................61

ADDITIONAL SIGN INVENTORY FOR REPLACEMENT............................................67

RETROREFLECTIVE SIGN POST PANELS.....................................................................71

STANDARD REVIEW GUIDELINES..................................................................................79

General Notes........................................................................................................................79

Non‐Signalized Locations ....................................................................................................80

Signalized Locations.............................................................................................................81

Field Notes.............................................................................................................................82

Final Plans.............................................................................................................................82

Submissions...........................................................................................................................83

Checklist for Submitting Packets........................................................................................84

ACKNOWLEDGEMENTS.........................................................................................................85

REFERENCES.............................................................................................................................87
v

LIST OF FIGURES

Figure 1. Illustration. Example of stop-controlled intersection improvements................................3

Figure 2. Equation. Estimated change in safety.............................................................................19

Figure 3. Equation. EB estimate of expected crashes....................................................................19

Figure 4. Equation. EB weight.......................................................................................................20

Figure 5. Equation. Index of effectiveness.....................................................................................20

Figure 6. Equation. Standard deviation of index of effectiveness .................................................20

Figure 7. Screenshot. Example 1 of check and verify treatment site in Google® EarthTM 

(original image modified with circle around intersection) ...................................................23

Figure 8. Screenshot. Example 2 of check and verify treatment site in Google® EarthTM 

(original image modified with circle around intersection) ...................................................24

Figure 9. Screenshot. Example 3 check and verify treatment site in Google® EarthTM 

(original image modified with circle around intersection) ...................................................25

Figure 10. Example of collecting number of legs for reference site from Google® EarthTM........26

Figure 11. Equation. Total crash SPF for 3 x 22 intersections.......................................................32

Figure 12. Equation. Fatal and injury crash SPF for 3 x 22 intersections......................................33

Figure 13. Equation. Rear-end crash SPF for 3 x 22 intersections ................................................33

Figure 14. Equation. Right-angle crash SPF for 3 x 22 intersections............................................34

Figure 15. Equation. Total crash SPF for 4 x 22 intersections.......................................................34

Figure 16. Equation. Fatal and injury crash SPF for 4 x 22 intersections......................................35

Figure 17. Equation. Rear-end crash SPF for 4 x 22 intersections ................................................35

Figure 18. Equation. Right-angle crash SPF for 4 x 22 intersections............................................36

Figure 19. Equation. Nighttime crash SPF for 4 x 22 intersections...............................................36

Figure 20. Equation. Total crash SPF for 3 x 42 intersections.......................................................36

Figure 21. Equation. Rear-end crash SPF for 3 x 42 intersections ................................................37

Figure 22. Equation. Right-angle crash SPF for 3 x 42 intersections............................................37

Figure 23. Equation. Total crash SPF for 4 x 42 intersections.......................................................38

Figure 24. Equation. Fatal and injury crash SPF for 4 x 42 intersections......................................38

Figure 25. Equation. Rear-end crash SPF for 4 x 42 intersections ................................................39

Figure 26. Equation. Right-angle crash SPF for 4 x 42 intersections............................................39

Figure 27. Equation. Nighttime crash SPF for 4 x 42 intersections...............................................40

Figure 28. Equation. Before–after adjustment factor calculation ..................................................40

Figure 29. Chart. Relationship between CMF (total crashes) and total intersection AADT .........47

Figure 30. Chart. Relationship between CMF (fatal and injury crashes) and total 

intersection AADT................................................................................................................47

Figure 31. Chart. Relationship between CMF (total crashes) and expected total crashes per 

year during before period......................................................................................................48

Figure 32. Chart. Relationship between CMF (fatal and injury crashes) and expected fatal 

and injury crashes per year during before period .................................................................48

Figure 33. Illustration. SCDOT Standard Drawing 625-305-00 excerpts for application of 

markings at intersections ......................................................................................................56

Figure 34. Illustration. SCDOT Standard Drawing 625-305-00 excerpt for guidance 

through intersections.............................................................................................................57

Figure 35. Illustration. SCDOT Standard Drawing 625-305-00 excerpts for crosswalk 

markings ...............................................................................................................................58
vi

Figure 36. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 1)..............................................................................................................59

Figure 37. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 2)..............................................................................................................59

Figure 38. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 3)..............................................................................................................60

Figure 39. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for chevron 

marking details......................................................................................................................61

Figure 40. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for straight arrow 

standard pavement marking..................................................................................................62

Figure 41. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right or left turn 

arrow and combination straight and left or right turn arrow standard pavement 

marking.................................................................................................................................63

Figure 42. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right lane drop 

arrow and left lane drop arrow standard pavement marking ................................................64

Figure 43. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for “ONLY” 

standard pavement marking..................................................................................................65

Figure 44. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right or left turn 

markings application.............................................................................................................66

Figure 45. Illustration. Additional sign inventory for replacement (part 1)...................................67

Figure 46. Illustration. Additional sign inventory for replacement (part 2)...................................68

Figure 47. Illustration. Additional sign inventory for replacement (part 3)...................................69

Figure 48. Illustration. Additional sign inventory for replacement (part 4)...................................70

Figure 49. Illustration. SCDOT nonsignalized intersection design for pavement marking 

and sign installations.............................................................................................................73

Figure 50. Illustration. SCDOT traffic engineering rumble strip typical.......................................74

Figure 51. Illustration. SCDOT typical for a signalized intersection.............................................75

Figure 52. Illustration. SCDOT typical for a four-way stop controlled intersection .....................76

Figure 53. Illustration. SCDOT typical for a cross-type stop controlled intersection ...................77

Figure 54. Illustration. SCDOT typical for a t-type stop controlled intersection...........................78

Figure 55. Illustration. SCDOT street name sign typical...............................................................79
vii

LIST OF TABLES

Table 1. Phase V safety strategies and participating States .............................................................5

Table 2. Before-period crash rate assumptions for four-legged stop-controlled intersections ......14

Table 3. Minimum required before period intersection-years for treated sites—total crashes......15

Table 4. Minimum required before period intersection-years for treated sites—fatal and 

injury crashes........................................................................................................................15

Table 5. Minimum required before period intersection-years for treated sites—rear-end 

crashes...................................................................................................................................15

Table 6. Minimum required before period intersection-years for treated sites—right-angle 

crashes...................................................................................................................................16

Table 7. Sample analysis for crash effects* (rural two-lane intersections)....................................16

Table 8. Sample analysis for crash effects* (urban two-lane intersections)..................................17

Table 9. Sample analysis for crash effects* (rural four-lane intersections)...................................17

Table 10. Sample analysis for crash effects* (urban four-lane intersections) ...............................17

Table 11. p-value for 10-percent change in crashes.......................................................................18

Table 12. Reference groups and desirable sample sizes ................................................................18

Table 13. Definitions of crash types...............................................................................................28

Table 14. Treatment cost summary................................................................................................28

Table 15. Data summary for treatment sites ..................................................................................29

Table 16. Data summary for reference sites...................................................................................30

Table 17. SPF parameters for total crashes at 3 x 22 intersections................................................33

Table 18. SPF Parameters for fatal and injury crashes at 3 x 22 intersections ..............................33

Table 19. SPF Parameters for rear-end crashes at 3 x 22 intersections .........................................34

Table 20. SPF parameters for right-angle crashes at 3 x 22 intersections .....................................34

Table 21. SPF parameters for total crashes at 4 x 22 intersections................................................35

Table 22. SPF Parameters for fatal and injury crashes at 4 x 22 intersections ..............................35

Table 23. SPF Parameters for rear-end crashes at 4 x 22 intersections .........................................35

Table 24. SPF parameters for right-angle crashes at 4 x 22 intersections .....................................36

Table 25. SPF Parameters for nighttime crashes at 4 x 22 intersections .......................................36

Table 26. SPF parameters for total crashes at 3 x 42 intersections................................................37

Table 27. SPF parameters for rear-end crashes at 3 x 42 intersections..........................................37

Table 28. SPF parameters for right-angle crashes at 3 x 42 intersections .....................................38

Table 29. SPF parameters for total crashes at 4 x 42 intersections................................................38

Table 30. SPF parameters for fatal and injury crashes at 4 x 42 intersections...............................39

Table 31. SPF parameters for rear-end crashes at 4 x 42 intersections..........................................39

Table 32. SPF parameters for right-angle crashes at 4 x 42 intersections .....................................39

Table 33. SPF parameters for nighttime crashes at 4 x 42 intersections........................................40

Table 34. Before–after adjustment factor for total crashes............................................................41

Table 35. Before–after adjustment factor for fatal and injury crashes...........................................41

Table 36. Before–after adjustment factor for rear-end crashes......................................................42

Table 37. Before–after adjustment factor for right-angle crashes..................................................42

Table 38. Before–after adjustment factor for nighttime crashes....................................................42

Table 39. Aggregate results for EB before–after study..................................................................43

Table 40. Disaggregate results by area type...................................................................................44

Table 41. Disaggregate results by number of legs.........................................................................44

Table 42. Disaggregate results by number of lanes .......................................................................45
viii

Table 43. Disaggregate results for three-legged intersections by number of lanes........................46

Table 44. Disaggregate results for four-legged intersections by number of lanes.........................46

Table 45. B/C ratios .......................................................................................................................50

Table 46. Recommended CMFs.....................................................................................................51

Table 47. Advance placement distance for signal ahead, stop, or intersection warning signs ......71
ix

LIST OF ABBREVIATIONS

AADT annual average daily traffic 

B/C benefit–cost

CMF crash modification factor

EB empirical Bayesian

ELCSI‐PFS Evaluation of Low‐Cost Safety Improvements Pooled Fund Study 

FHWA Federal Highway Administration 

MUTCD Manual on Uniform Traffic Control Devices

NCHRP National Cooperative Highway Research Program

PDO property damage only

PE preliminary engineering

RTM regression to the mean

SCDOT South Carolina Department of Transportation

SPF safety performance function

USDOT U.S. Department of Transportation

1

EXECUTIVE SUMMARY

The Federal Highway Administration (FHWA) established the Development of Crash 

Modification Factors (DCMF) program in 2012 to address highway safety research needs for 

evaluating new and innovative safety strategies (improvements) by developing reliable 

quantitative estimates of their effectiveness in reducing crashes. The ultimate goal of the DCMF 

program is to save lives by identifying new safety strategies that effectively reduce crashes and 

promote those strategies for nationwide implementation by providing measures of their safety 

effectiveness and benefit–cost (B/C) ratios through research. State transportation departments and 

other transportation agencies need to have objective measures for safety effectiveness and B/C 

ratios before investing in broad applications of new strategies for safety improvements. Forty 

State transportation departments provided technical feedback on safety improvements to the 

DCMF program and implemented new safety improvements to facilitate evaluations. These 

States are members of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study

(ELCSI-PFS), which functions under the DCMF program.

This study evaluated multiple low-cost treatments at stop-controlled intersections in South 

Carolina. Improvements included basic signing and pavement markings. The purpose of this 

study was to quantify the safety effectiveness of these treatments. The treatments were installed 

as part of the South Carolina Department of Transportation (SCDOT) systemic intersection 

improvement program. The results provide evidence for others to consider as they make datadriven decisions about the type of treatments to implement. 

Both urban and rural stop-controlled intersections on divided and undivided State-maintained 

roads (nonfreeways) were selected as locations for treatments. Preliminary study results have 

shown that, by making improvements such as those listed above, SCDOT was able to achieve a 

small but statistically significant crash reduction. While the expected crash savings per location 

were not as large as for some higher cost treatments (e.g., converting conventional intersections 

to roundabouts), the low cost of these treatments allows many more locations to be treated.

Geometric, traffic, and crash data were obtained at three- and four-legged, two- and four-lane 

major road, and urban and rural stop-controlled intersections in South Carolina. To account for 

potential selection bias and regression to the mean (RTM), an empirical Bayesian (EB) before–

after analysis was conducted, using reference groups of untreated intersections with similar 

characteristics to the treated sites. The analysis also controls for changes in traffic volumes 

throughout time and time trends in crash counts unrelated to the treatments. 

The aggregate results indicate reductions for all crash types analyzed (i.e., total, fatal and injury,

rear-end, right-angle, and nighttime). The reductions are statistically significant at the 95-percent 

confidence level for all crash types. For all crash types combined, the crash modification factors

(CMFs) are 0.917 for all severities and 0.899 for fatal and injury crashes. The CMFs for rear-end, 

right-angle, and nighttime crashes are 0.933, 0.941, and 0.853, respectively.

The disaggregate analysis identified those conditions under which the multiple low-cost 

treatments are most effective. Variables of interest included area type (urban or rural), number of 

legs (three or four), lane configuration of the mainline and the cross street, traffic volumes, and 

expected crashes without treatment. The disaggregate analysis indicated larger crash reductions 
2

of all types for rural areas, four-legged intersections, and intersections with two-lane major roads. 

For total entering volume and expected crashes before treatment, the disaggregate analysis 

indicated the strategy is more effective on average for intersections with lower traffic volumes 

and fewer expected crashes per year.

Assuming a 3-year service life, conservative costs, and the benefits for total crashes, the B/C ratio 

is 12.4 to 1. With the U.S. Department of Transportation (USDOT) recommended sensitivity

analysis, these values could range from 7.1 to 1 up to 17.5 to 1. Assuming a 7-year service life, 

and the same conservative costs and benefits for total crashes, the B/C ratio is 25.5 to 1. With the 

USDOT recommended sensitivity analysis, these values could range from 14.5 to 1 up to 35.9 to 

1. These results suggest that the multiple low-cost treatments, even with conservative 

assumptions on cost, service life, and the value of a statistical life, can be cost-effective in 

reducing crashes at stop-controlled intersections.
3

CHAPTER 1. INTRODUCTION

BACKGROUND ON MULTIPLE STRATEGIES AT STOP-CONTROLLED 

INTERSECTIONS

In recent years, there has been an increased interest in systemic installations of low-cost safety 

treatments throughout an entire jurisdiction. The South Carolina Department of Transportation 

(SCDOT) embraced this approach in its intersection safety improvement plan and identified a 

number of low-cost strategies for implementation at stop-controlled and signalized intersections 

statewide. Typical low‐cost treatments at stop-controlled intersections in South Carolina included 

improvements to basic signing and pavement markings. Figure 1 illustrates typical improvements 

at a four-legged, stop-controlled intersection with two-lane major road.

© SCDOT.

Figure 1. Illustration. Example of stop-controlled intersection improvements.
4

The following is an overview of the types of basic signing and pavement markings 

improvements, and the appendix provides further details and considerations. Each treatment was 

installed when appropriate. Each intersection received a unique package of improvements suited 

for implementation at that site, which included the following:

• Signing improvements included the following:

o Double‐up (i.e., both right- and left-side, shoulder mounted) 36 inches by 36 inches

intersection warning signs (W2-series) on fluorescent yellow sheeting. Figure 1 shows 

examples of applicable intersection warning signs for stop-controlled intersections.

o Advance street name plaque (W16‐8) on fluorescent yellow sheeting accompanying 

each right‐side intersection warning sign.

o Double-up (i.e., both right- and left-side, shoulder mounted) 48 inches by 48 inches

stop (R1‐1) and yield (R1‐2) signs.

o Retroreflective strips on sign posts for the above signs.

• Pavement marking improvements included the following:

o Stop lines within 4 to 10 ft of the edge of the nearest through lane along the major 

road.

o Yield lines at all lanes having yield conditions.

o Dashed white edge-lines through intersections along major roads.

o Remarking of all existing stop lines, crosswalks, arrows, and word messages unless:

▪ The roadway had been resurfaced within one calendar year and new 

thermoplastic markings had been applied.

▪ Existing markings were uniformly reflective, and the above ground 

thickness was 90 mm or greater.

▪ Otherwise directed by a district representative.

o Marking of all turn lanes to include the pattern of lane arrows and accompanying word 

message “ONLY” based on the turn-lane length, in accordance with Standard 

Drawing 625-410-00.

BACKGROUND ON STUDY

The goal of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI‐PFS)

is to develop reliable estimates of the effectiveness of the safety improvements that are identified 

as strategies in the National Cooperative Highway Research Program (NCHRP) Report 500 

Guides.

(1) These estimates are determined by conducting scientifically rigorous evaluations at 

sites in the United States where these strategies are being implemented. The study has spanned 
5

multiple phases. In March 2005, the first Technical Advisory Committee Meeting of the ELCSI‐

PFS was held at the Turner‐Fairbank Highway Research Center. The purpose of the meeting was 

to discuss the study and applicable strategies from the NCHRP Report 500 Guides and to develop 

a prioritization of those strategies for potential evaluation in the study.(1) Since this initial 

meeting, several phases have been undertaken to evaluate strategies.

Phase V of the ELCSI‐PFS is a “build‐to‐evaluate” effort in which States have volunteered to 

install a variety of promising low‐cost safety countermeasures and contribute the appropriate data 

to allow a rigorous crash‐based evaluation of their safety effectiveness. This phase has a two‐part 

nature and consists of an implementation part and an evaluation part. The implementation portion 

(Part 1) defined the before period, including installation data (location and date), roadway data, 

traffic data, and crash data. The evaluative portion (Part 2) began within 3 years of the conclusion 

of the installation phase. Four safety strategies were identified for implementation and evaluation 

in Phase V. Five States volunteered and provided data for the Phase V evaluations. Table 1 shows 

these safety improvement strategies and the volunteering States.

Table 1. Phase V safety strategies and participating States.

Safety 

Strategy/Participating 

State

Combination 

of Cable 

Median 

Barrier and 

Rumble 

Strips

Combination 

of Centerline 

Rumble 

Strips and 

Edge-Line 

Rumble 

Strips

Multi‐Strategy 

Improvements 

at Signalized 

Intersections

Multi‐Strategy 

Improvements 

at StopControlled 

Intersections

Illinois X — — —

Kentucky X X — —

Missouri X X — —

Pennsylvania — X — —

South Carolina — — X X

—Not used. 

As a volunteering State, SCDOT initiated a project to improve safety at more than 2,200 

intersections statewide through low‐cost engineering techniques focused primarily on signing and 

markings in 2009. These intersections—600 of which were classified as rural—comprise only 2 

percent of all State‐maintained intersections but account for nearly half of all intersection crashes 

and fatalities. It was envisioned that the project would span 3 years and implement improvements 

at approximately 700 to 800 intersections each year.

This report documents the safety effectiveness evaluations of multiple strategies at stopcontrolled intersections implemented in South Carolina. The evaluation of multiple strategies at 

signalized intersections can be found in the companion report entitled Safety Evaluation of 

Multiple Strategies at Signalized Intersections.

(6)

7

CHAPTER 2. LITERATURE REVIEW

Literature on the stop-controlled intersection strategies of interest is limited. The following 

provides a summary of the salient research related to specific strategies. There were very few 

studies identified that investigated the effects of multiple strategies.

DOUBLING AND OVERSIZING ADVANCE WARNING SIGNS, STOP SIGNS, AND 

YIELD SIGNS 

The Institute of Transportation Engineers published the results of two evaluations concerning 

doubling stop signs (i.e., placement of a stop sign on the left side of the stop approach road to 

complement the existing stop sign on right side).(7) The first evaluation was solely for the 

installation of double stop signs. This countermeasure had an estimated reduction of 11 percent 

on total crashes. The study neglected to estimate a standard error for this crash reduction. The 

other evaluation was for a combination of treatments. The combination was adding a centerline, 

moving the stop line to the extended curb lines, and doubling stop signs. The estimated effect on 

total crashes was a nine percent decrease, and there was no observed change in right-angle 

crashes. 

Polanis conducted an evaluation of another combination of intersection treatments.(8) The 

combination was adding a centerline, adding a stop line, and replacing existing 24-inch stop signs 

with 30-inch stop signs. The results indicate a 55-percent reduction in right-angle crashes with a 

standard error of 52 percent. Therefore, the reductions were not statistically significant. Not only 

were the results of Polanis’s study statistically insignificant, the design of the study was not 

rigorous. The study employed a simple before–after methodology, which fails to account for 

traffic volume changes, RTM, and a host of other potentially confounding factors. Furthermore, 

only 10 sites were used in the study, and these sites were all from the same municipality in North 

Carolina: Winston-Salem.(8)

A case study by the Federal Highway Administration (FHWA) further examined the effect of 

doubling and oversizing stop signs at intersections in Winston-Salem, NC.(9) At four stopcontrolled intersections with a history of high crash frequency, stop signs were doubled using 30-

inch signs as opposed to the conventional 24-inch variety. Based on a simple before–after 

comparison, the results estimated a 48-percent reduction in total crashes. As with the Polanis

study, this case study employs a weak study methodology (i.e., simple before–after) and uses a 

small sample size, which lacks geographic diversity. Furthermore, this case study exhibits a clear 

selection bias, making the regression to the mean (RTM) phenomenon a serious concern.

FLUORESCENT YELLOW SHEETING 

There have been multiple studies that examined the use of fluorescent yellow sheeting on 

warning signs. Eccles and Hummer focused on the use of fluorescent yellow sheeting as an 

inexpensive method of increasing the conspicuity of signs without violating the provisions 

contained in the Manual on Uniform Traffic Control Devices (MUTCD).

(10) Multiple studies 

confirm the superiority of fluorescent signs in terms of conspicuity. Jenssen et al. conducted a 

comparative evaluation of fluorescent and nonfluorescent signs on a closed track in Norway.(11)

Subjects seated in moving railcars were asked to indicate when they could detect and recognize 
8

the size, shape, and content of fluorescent and nonfluorescent signs. The performance of the 

fluorescent signs proved to be superior because the subjects were able to detect and recognize the 

fluorescent signs well before they could detect and recognize the nonfluorescent signs. Burns and 

Johnson studied fluorescent and nonfluorescent materials and found that the photometric 

properties of fluorescent materials explained their superior visibility and conspicuity.(12)

RETROREFLECTIVE SIGN POSTS

A recent study by the Virginia Department of Transportation directly relates to the retroreflective 

sign post strategy.(13) This study examined the effectiveness of retroreflective material on stop 

sign posts with respect to visibility and driver compliance. The authors measured performance 

with respect to visibility using a video survey in which participants were asked to pinpoint when 

a stop sign with retroreflective material on the post and another without retroreflective material 

on the post could be detected. The results indicated that during daytime conditions, the vast 

majority of participants could detect the stop sign without retroreflective material on the post 

sooner than the stop sign with retroreflective material on the post. In contrast, during nighttime 

conditions, the vast majority of participants could detect the stop sign when retroreflective 

material is on the post sooner than the stop sign without retroreflective material on the post. In 

terms of compliance, the behavior of drivers approaching a stop sign with retroreflective material 

on the post was not observed to be different from that of a driver approaching a stop sign without 

retroreflective material on the post.

REFRESHING EXISTING PAVEMENT MARKINGS 

The research team did not identify any existing studies on the safety effects of refreshing existing 

pavement markings at stop-controlled intersections. 

STOP LINES

The installation of a stop line has also been studied in recent years. The installation of a stop line

on the minor approach of an unsignalized intersection is intended to address angle crashes in 

which drivers are unaware of the presence of an intersection or fail to stop at the stop sign. 

Golembiewski and Chandler estimated that this countermeasure reduced total crashes by 19 

percent.(14) This study did not provide an estimate of the standard error of the crash reduction.

The Institute of Transportation Engineers estimated that the installation of stop lines on minor 

road approaches with short segments of centerline reduced total crashes by 19 percent and 

reduced right-angle crashes by 47 percent. Once again, the standard errors of these crash 

reductions were not estimated.(7)

Polanis evaluated the combination of adding a centerline, adding a stop line, and replacing a 24-

inch stop sign with a 30-inch stop sign.(8) This combination of treatments was estimated to reduce 

right-angle crashes by 67 percent with a standard error of 11 percent. Therefore, the reduction is 

statistically significant. 

A FHWA study analyzed the effects of installing stop lines and a short interval of double yellow 

centerlines at intersections in Winston-Salem, NC.(9) The treatment group consisted of four stopcontrolled intersection with a history of high crash frequency. The study used a simple before–
9

after method to estimate the crash effects on total crash frequency. The results indicated that total 

crashes decreased by 53 percent. It should be noted that this study employed a weak study design 

(i.e., simple before–after) and a small sample size.

This strategy is a potentially effective countermeasure at locations with a history of crashes in 

which drivers are unaware of the presence of the intersection. However, the authors noted that the 

stop line should be installed in such a way that it can be seen from a significant distance by 

approaching drivers.(14) Aside from its significant crash reduction potential, this countermeasure 

is appealing because of its relatively low cost. 

LIMITATIONS OF PREVIOUS RESEARCH 

Literature on the stop-controlled intersection strategies of interest was scarce in some cases and 

nonexistent in others. In the cases of fluorescent yellowing sheeting, retroreflective sign posts, 

and refreshing existing pavement markings, the research team did not identify studies that 

quantify the effect on crashes of implementing the strategies. With regard to the strategy of 

doubling and oversizing advance warning signs, stop signs, and yields signs, the research team 

identified several studies that estimate crash effects. However, the studies employed study 

designs that lacked statistical rigor and frequently neglected to estimate standard errors for the 

crash reductions. The standard error of a crash reduction enables one to judge the statistical 

significance of the crash effect. Therefore, the omission of standard errors in these studies poses a 

major obstacle to a meaningful interpretation of the results. With respect to the strategy of 

installing stop lines, some of the studies also lacked standard error estimates. Furthermore, none 

of the previous studies conducted a comprehensive evaluation with regard to crash type and 

severity. The previous studies generally reported the effect on total crashes or angle crashes, and 

virtually none estimated the effect on injury crashes. Thus, there is a need for additional research 

of the stop-controlled strategies of interest that employs rigorous study designs and analyzes a 

full range of crash types and severities.

11

CHAPTER 3. OBJECTIVE

This research examined the safety impacts of multiple strategies implemented at stop-controlled 

intersections throughout South Carolina. The objective was to estimate the safety effectiveness of 

this strategy as measured by crash frequency. Target crash types included the following: 

• Total crashes (all types and severities combined).

• Injury crashes (fatal injury, incapacitating injury, nonincapacitating injury, and possible 

injury).

• Rear-end crashes (all severities combined).

• Right-angle crashes (all severities combined).

• Nighttime crashes (all severities combined).

A further objective was to address the following questions:

• Do effects vary by area type (i.e., urban versus rural)?

• Do effects vary by approach configuration of intersection (i.e., three-legged versus fourlegged)?

• Do effects vary by lane configuration of intersection (e.g., four mainline lanes and two

cross-street lanes versus two mainline lanes and two cross-street lanes)?

• Do effects vary by traffic volume?

• Do effects vary by expected crashes?

The evaluation of overall effectiveness included the consideration of the installation costs and 

crash savings in terms of the benefit–cost (B/C) ratio. 

Meeting these objectives placed some special requirements on the data collection and analysis 

tasks, including the need to do the following:

• Select a large enough sample size to detect, with statistical significance, what may be 

small changes in safety for some crash types.

• Identify appropriate untreated reference sites.

• Properly account for changes in safety because of changes in traffic volume and other 

factors unrelated to the strategy.

13

CHAPTER 4. STUDY DESIGN

The study design involved a sample size analysis and prescription of needed data elements. The 

sample size analysis assessed the size of sample required to statistically detect an expected 

change in safety and determined what changes in safety could be detected with available sample 

sizes.

SAMPLE SIZE ESTIMATION OVERVIEW

When planning a before–after safety evaluation study, it is vital to ensure that enough data are 

included such that the expected change in safety can be statistically detected. Even though in the 

planning stage the expected change in safety is unknown, it is still possible to make a rough 

estimate of how many sites would be required based on the best available information about the 

expected change in safety. Alternatively, one could estimate, for the number of available sites, the 

change in safety that could be statistically detected. For a detailed explanation of sample size 

considerations, as well as estimation methods, see chapter 9 of Hauer.(15) The sample size analysis 

presented here is limited to two cases: (1) how large a sample would be required to statistically 

detect an expected change in safety; and (2) what changes in safety could be detected with 

available sample sizes.

For case 1, it was assumed that a conventional before–after study with comparison group design 

would be used because available sample size estimation methods were based on this assumption. 

The sample size estimates from this method would be conservative in that the empirical Bayesian 

(EB) methodology would likely require fewer sites. To facilitate the analysis, it was also assumed 

that the number of comparison sites was equal to the number of installation sites and the duration 

of the before and after periods were equal, which, again, was a conservative assumption.

Table 2 provides the crash rate assumptions. It shows the average number of crashes per year per 

intersection in the before period for each combination of crash type and intersection 

configuration. The locations of interest for this strategy were three- and four-legged, stopcontrolled intersections. Intersection crash rates differ substantially depending on a number of 

factors (e.g., traffic control, traffic volume, geometric configuration, and area type). Therefore, 

the intersection crash rates assumed for these computations represented a general estimate based 

on the reference sites identified for this study. Rates A and B represent rural and urban, fourlegged, stop-controlled intersections with two-lane major roads, respectively. Rates C and D 

represent rural and urban, stop-controlled intersections with four-lane major roads, respectively.
14

Table 2. Before-period crash rate assumptions for four-legged stop-controlled intersections.

Crash Type

Rate A (SC)

Rural StopControlled 

Intersections 

with 2-Lane 

Major Roads

Rate B (SC)

Urban StopControlled 

Intersections 

with 2-Lane 

Major Roads

Rate C (SC)

Rural StopControlled 

Intersections 

with 4-Lane 

Major Roads

Rate D (SC)

Urban StopControlled 

Intersections 

with 4-Lane 

Major Roads

Total 1.400 1.966 1.752 2.232

Injury 0.542 0.625 0.669 0.692

Rear-end 0.253 0.633 0.309 0.718

Right-angle 0.460 0.761 0.706 0.927

Crash rate = crashes/intersection/year.

Table 3 to table 6 provide estimates of the required number of before- and after-period 

intersection-years for total, fatal and injury, rear-end, and right-angle crashes, respectively, at 

four-legged stop-controlled intersections assuming both 90- and 95-percent confidence levels. 

Columns labeled “A-95%” and “A-90%” indicate Rate A (rural four-legged, stop-controlled with 

two-lane major roads) with 95- and 90-percent confidence levels, respectively. Similarly, 

columns labeled “B-95%,” “C-95%,” and “D-95%” indicate rates B, C, and D at the 95-percent 

confidence level. Columns labeled “B-90%,” “C-90%,” and “D-90%” indicate rates B, C, and D 

at the 90-percent confidence level. The minimum sample indicates the amount of data necessary 

to detect the safety effects with a desirable level of statistical significance. Larger safety effects 

require less data to achieve the same confidence level. These sample size calculations were based 

on specific assumptions regarding the number of crashes per intersection and years of available 

data. Intersection-years were the number of intersections where the strategy was implemented 

multiplied by the number of years of data before or after implementation. For example, if a 

strategy was implemented at nine intersections and data were available for three years since 

implementation, then there would be a total of 27 intersection-years of after period data available 

for the study. The number of intersection-years was estimated by first estimating the required 

number of intersection-related crashes and then dividing by the appropriate intersection crash 

rate.
15

Table 3. Minimum required before period intersection-years for treated sites—total 

crashes.

Expected 

Percent 

Reduction 

in 

Crashes A-95% B-95% C-95% D-95% A-90% B-90% C-90% D-90%

10 1,325 944 1,059 831 824 586 658 517

15 420 299 336 263 284 202 227 178

20 199 142 159 125 138 98 110 86

25 111 79 89 70 78 55 62 49

Note: Assumes equal number of site-years for treatment and comparison sites and equal length of before and after 

periods.

Table 4. Minimum required before period intersection-years for treated sites—fatal and 

injury crashes.

Expected 

Percent 

Reduction 

in 

Crashes A-95% B-95% C-95% D-95% A-90% B-90% C-90% D-90%

10 3,423 2,968 2,773 2,681 2,127 1,845 1,723 1,666

15 1,085 941 879 850 734 637 595 575

20 515 446 417 403 356 309 288 279

25 288 250 233 225 201 174 163 158

Note: Assumes equal number of site-years for treatment and comparison sites and equal length of before and after 

periods.

Table 5. Minimum required before period intersection-years for treated sites—rear-end 

crashes.

Expected 

Percent 

Reduction 

in 

Crashes A-95% B-95% C-95% D-95% A-90% B-90% C-90% D-90%

10 7,332 2,930 6,003 2,584 4,557 1,821 3,731 1,606

15 2,324 929 1,903 819 1,573 629 1,288 554

20 1,103 441 903 389 763 305 625 269

25 617 246 505 217 431 172 353 152

Note: Assumes equal number of site-years for treatment and comparison sites and equal length of before and after 

periods.
16

Table 6. Minimum required before period intersection-years for treated sites—right-angle

crashes.

Expected 

Percent 

Reduction 

in 

Crashes A-95% B-95% C-95% D-95% A-90% B-90% C-90% D-90%

10 4,033 2,438 2,627 2,001 2,507 1,515 1,633 1,244

15 1,278 773 833 634 865 523 564 429

20 607 367 395 301 420 254 273 208

25 339 205 221 168 237 143 154 118

Note: Assumes equal number of site-years for treatment and comparison sites and equal length of before and after 

periods.

Case 2 considers the data collected for both the before and after periods. The statistical accuracy 

attainable for a given sample size is described by the standard deviations of the estimated percent 

change in safety. From this, p-values are estimated for various sample sizes and expected changes 

in safety for a given crash history. A set of such calculations is shown in Table 7 through table 

10. The calculations are based on the methodology in Hauer.(15) The tables indicate the total 

intersection-years of data available in the before and after period.

Table 7. Sample analysis for crash effects* (rural two-lane intersections).

Crash Type

Intersection-Years 

in Before Period

Intersection-Years in 

After Period

(Assumes 2-Year 

After Period for Each 

Site)

Minimum 

Percent 

Reduction 

p = 0.10**

Minimum 

Percent 

Reduction

p = 0.05**

Total 3,195 1,278 10 10

Fatal and injury 3,195 1,278 10 15

Rear-end 3,195 1,278 15 15

Right-angle 3,195 1,278 10 15

*Results are to nearest 5-percent interval.

**Minimum percent reduction detectable for crash rate assumption. Crash rate assumption is based on actual crash 

rate for the before period from table 2.
17

Table 8. Sample analysis for crash effects* (urban two-lane intersections).

Crash Type

Intersection-Years 

in Before Period

Intersection-Years in 

After Period

(Assumes 2-Year 

After Period for Each 

Site)

Minimum 

Percent 

Reduction

p = 0.10**

Minimum 

Percent 

Reduction

p = 0.05**

Total 3,195 1,278 10 10

Fatal and injury 3,195 1,278 10 10

Rear-end 3,195 1,278 10 10

Right-angle 3,195 1,278 10 10

*Results are to nearest 5-percent interval.

**Minimum percent reduction detectable for crash rate assumption. Crash rate assumption is based on actual crash 

rate for the before period from table 2.

Table 9. Sample analysis for crash effects* (rural four-lane intersections).

Crash Type

Intersection-Years 

in Before Period

Intersection-Years in 

After Period

(Assumes 2-Year 

After Period for Each 

Site)

Minimum 

Percent 

Reduction

p = 0.10**

Minimum 

Percent 

Reduction

p = 0.05**

Total 3,195 1,278 10 10

Fatal/injury 3,195 1,278 10 10

Rear-end 3,195 1,278 15 15

Right-angle 3,195 1,278 10 10

*Results are to nearest 5-percent interval.

**Minimum percent reduction detectable for crash rate assumption. Crash rate assumption is based on actual crash 

rate for the before period from table 2.

Table 10. Sample analysis for crash effects* (urban four-lane intersections).

Crash Type

Intersection-Years 

in Before Period

Intersection-Years in 

After Period

(Assumes 2-Year 

After Period for Each 

Site)

Minimum 

Percent 

Reduction

p = 0.10**

Minimum 

Percent

Reduction

p = 0.05**

Total 3,195 1,278 5 10

Fatal and injury 3,195 1,278 10 10

Rear-end 3,195 1,278 10 10

Right-angle 3,195 1,278 10 10

*Results are to nearest 5-percent interval.

**Minimum percent reduction detectable for crash rate assumption. Crash rate assumption is based on actual crash 

rate for the before period from table 2.

Another strategy is to estimate the level of significance (i.e., the p-value) for which a minimum 

desired effect can be detected. For instance, assume the minimum desired level of effect is ten

percent for total and target crashes. Based on the current knowledge of available data, table 11
18

indicates the p-value associated with a 10-percent change in crashes based on the before period 

data. These calculations use the crash rates from table 2. Given the existing sample size, it is 

likely this study can detect moderate treatment effects (e.g., a 10-percent change in total crashes) 

at the 10-percent level of significance.

Table 11. p-value for 10-percent change in crashes.

Crash Type Rural 2-Lane Urban 2-Lane Rural 4-Lane Urban 4-Lane

Total 0.03 0.02 0.02 0.01

Fatal and injury 0.12 0.10 0.09 0.09

Rear-end 0.27 0.10 0.22 0.09

Right-angle 0.15 0.08 0.09 0.06

REFERENCE GROUP OVERVIEW

A reference group is required for the various intersection groups, including rural and urban, threeand four-legged, stop-controlled intersections with two- and four-lane major roads. Each 

reference group should consist of untreated sites adjacent to or in the vicinity of the treated sites. 

The untreated sites in each reference group should have geometric, traffic, and crash data for the 

same years as treated sites. Each reference group should be similar to its corresponding treatment 

group—particularly in terms of area type (e.g., urban or rural), geometric configuration (e.g.,

number of legs and number of through lanes), and annual average daily traffic (AADT)—except 

that these intersections were not treated during the study period. These sites are used in the 

calibration of safety performance functions (SPFs). Based on previous experience in similar 

analyses, the research team determined that at least 30 intersections for each intersection type in 

reference group would be desirable, as shown in table 12. Where it is impractical or infeasible to 

obtain the required sample size for one or more intersection groups, it is possible to combine 

groups and account for the differences through statistical modeling during the development of 

SPFs. 

Table 12. Reference groups and desirable sample sizes.

Number 

of Legs

Number of Through 

Lanes on Major Road Rural Urban Total

3 2-lane 30 30 60

3 4-lane 30 30 60

4 2-lane 30 30 60

4 4-lane 30 30 60

— Total 120 120 240

—Not applicable.
19

CHAPTER 5. METHODOLOGY

This study employed the EB methodology for observational before–after studies. The EB method

was considered rigorous in that it accounted for RTM using a reference group of similar but 

untreated sites. In the process, SPFs were used for the following reasons:

• They overcome the difficulties of using crash rates in normalizing for volume differences 

between the before and after periods.

• They can account for time trends. (The final SPFs did not use yearly indicator variables to 

account for time trend, and more detailed discussions are provided in Before-After 

Adjustment Factors in chapter 7.)

• They reduce the level of uncertainty in the estimates of safety effect.

• They properly account for differences in crash experience and reporting practice in 

amalgamating data and results from diverse jurisdictions.

• They provide a foundation for developing guidelines for estimating the likely safety 

consequences of a contemplated strategy.

In the EB approach, the change in safety ( ) for a given crash type at a site is given by figure 2.

Figure 2. Equation. Estimated change in safety.

Where:

= expected number of crashes that would have occurred in the after period without the 

strategy.

= number of reported crashes in the after period. 

In estimating , the effects of RTM and changes in traffic volume were explicitly accounted for 

using SPFs, relating crashes of different types to traffic flow and other relevant factors for each 

jurisdiction based on reference sites. Annual SPF multipliers were calibrated to account for 

temporal effects on safety (e.g., variation in weather, demography, and crash reporting).

In the EB procedure, the SPF was used to first estimate the number of crashes that would be 

expected in each year of the before period at locations with traffic volumes and other 

characteristics similar to the one being analyzed (i.e., reference sites). The sum of these annual 

SPF estimates (P) was then combined with the count of crashes (x) in the before period at a 

treatment site to obtain an estimate of the expected number of crashes (m) before installation, as 

shown in figure 3. 

m  w(P)  (1w)(x)

Figure 3. Equation. EB estimate of expected crashes.

∆Safety = λ − π
20

Where w is estimated from the mean and variance of the SPF estimate, as shown in figure 4.

w =

1

1+ kP

Figure 4. Equation. EB weight.

Where k is constant for a given model, which is estimated from the SPF calibration process with 

the use of a maximum likelihood procedure. In that process, a negative binomial distributed error 

structure is assumed with k being the overdispersion parameter of this distribution.

A factor was then applied to m to account for the length of the after period and differences in 

traffic volumes between the before and after periods. This factor was the sum of the annual SPF 

predictions for the after period divided by P, the sum of these predictions for the before period. 

The result, after applying this factor, was an estimate of . The procedure also produced an 

estimate of the variance of .

The estimate of was then summed over all treatment sites in a group of interest (to obtain 

sum) and compared with the count of crashes observed during the after period in that group 

( sum). The variance of was also summed over all sites in the treatment group. 

The index of effectiveness ( ) is estimated in figure 5.

















2

( )

1

sum

sum

sum

sum

Var











Figure 5. Equation. Index of effectiveness.

Where Var is variance.

The standard deviation of is given in figure 6.

2

2

2 2

2

( )

1

( ) ( )

( )







































sum

sum

sum

sum

sum

sum

Var

Var Var

StDev

















Figure 6. Equation. Standard deviation of index of effectiveness.

The percent change in crashes was calculated as 100(1  ); thus, a value of  0.7 with a 

standard deviation of 0.12 indicates a 30-percent reduction in crashes with a standard deviation of 

12 percent.
21

CHAPTER 6. DATA COLLECTION

SCDOT provided the majority of data for this study. The dataset included the following data 

elements:

• Treatment implementation data: SCDOT provided information related to treatment sites 

and start and completion dates for each improvement. SCDOT also provided the research 

team with work orders, drawings, and sketches for these locations. The research team 

used some of these additional data to verify the intersection configurations.

• Reference site data: SCDOT provided a list of intersections that had not been treated. The 

research team used these intersections as potential reference sites.

• Traffic data: SCDOT provided a statewide AADT data file for 2014. This file has 

information for almost all mainline routes and cross streets. The research team obtained 

additional AADT files for 2006 to 2014 from SCDOT’s website. These publicly available 

files do not have all the details necessary (many AADT for minor routes are missing). The 

research team used these files to calculate traffic growth factors and estimated AADTs for 

other years.

• Crash data: SCDOT provided the research team with crash data files for 2005 to 2014.

The research team collected additional data using Google® EarthTM and Google® MapsTM.

TREATMENT SITES

SCDOT provided the research team with a list of all intersections under the ground-level contract

that includes signing and pavement marking installation (a total of 918 locations.) Because the 

ground-level contract covers both the improvements at signalized and stop-controlled 

intersections, the first step was to separate stop-controlled intersections from the file. Key pieces 

of information from this data file included county, route designations and numbers for both 

mainline and cross street (e.g., US 25, SC 12), start and completion dates of installation, number 

of lanes (e.g., two or four lanes on the mainlines, two lanes on the cross street), and area type 

(i.e., urban, rural). The first step of processing the data was to convert route designation and 

number for both mainline and cross street into three identification codes as follows:

• Route type code (i.e., US = 2, SC = 4, and S = 7).

• Route number.

• Route auxiliary (i.e., Mainline = 0, Alternate = 2, and Business = 7).

These three identifiers would later be used to link the crash and traffic data files to each 

intersection. Once crash and traffic data were linked to each intersection, the research team 

summarized the number of crashes per year by type for each location.

The start and completion dates allowed the team to identify the before and after periods. Before 

and after periods included complete calendar years during which there was no installation 

activity. For example, if the work at a given intersection started in December 2009 and was not 

completed until January 2010, two full calendar years of 2009 and 2010 were considered 
22

“installation years” and removed from the dataset. The before period in this research is from 2005 

(the first year of available data) to 2008 (the last full year of no construction activity). Similarly, 

the after period is from 2011 to 2014 (the last year of available data).

The result of this process was a list of stop-controlled intersections with location identifiers in 

uniform format across different data files. This list included the before and after periods. These 

intersections were candidates for the treatment group used in the EB evaluation. The research

team checked all work orders and work plans to collect number of legs and verify number of 

lanes for each intersection. The research team conducted a manual process of verifying candidate 

intersections in Google® EarthTM (i.e., visual verification) to select the final treatment group. The 

research team flagged intersections—and later dropped treatment sites from the list of 

candidates—based on the following criteria:

1. The intersection is located close to another intersection or facility (e.g., railroad crossing) 

and it was not possible to separate crashes and operations, as seen in figure 7. The 

candidate treatment site is highlighted, however, it is located next to a railroad crossing 

and what appears to be a major signalized intersection. In this case, the research team 

determined that it would be difficult to know if a crash occurred because of the 

intersection of interest or something else. In these cases, the research team dropped the 

site from the candidate pool.

2. The intersection has an abnormal configuration, and the data fail to reflect the anomaly. 

This is often the case where an intersection has an extreme skew angle or it is an exit 

ramp from a limited-access highway. Figure 8 and figure 9 are two examples. Both 

intersections were coded in the installation data file as three-legged, stop-controlled 

intersections between the surface street and the limited-access highway above (i.e., US 

178 and US 123-Calhoun Memorial Hwy, US 378-Sunset Blvd and SC 12-Jarvis 

Klapman Blvd). There is no indication in the data file that these are exit ramps. The traffic 

volumes associated with these locations are for the major limited-access highways, not the 

ramps themselves. All intersections similar to these were flagged and later dropped from 

the treatment group.

Following SCDOT’s advice, the research team decided to exclude all intersections in Beaufort 

County because there were changes in route names and numbers in this county that could lead to 

inaccurate matching of traffic and crash data.
23

Imagery ©2016 Google®, Map data ©2016 Google®.

Figure 7. Screenshot. Example 1 of check and verify treatment site in Google® EarthTM

(original image modified with circle around intersection).

(16)
24

Imagery ©2016 Google®, Map data ©2016 Google®.

Figure 8. Screenshot. Example 2 of check and verify treatment site in Google® EarthTM

(original image modified with circle around intersection).

(17)
25

Imagery ©2016 Google®, Map data ©2016 Google®.

Figure 9. Screenshot. Example 3 check and verify treatment site in Google® EarthTM

(original image modified with circle around intersection).

(18)

REFERENCE SITES

SCDOT provided the research team with a list of more than 3,000 intersections—both stopcontrolled and signalized—for reference sites. Similar to the installation data, this list of 

intersections included key location identifiers (e.g., county, route designations, and numbers) and 

intersection characteristics (e.g., number of lanes on the mainline and cross street, area type, and 

type of traffic control). Therefore, the research team followed similar steps to process the raw 

data. The route identifiers were converted to a common format to link crash and traffic data for 

each intersection from different files. However, this data file did not provide number of legs, a 

key variable for these potential reference sites.

The research team decided to collect number of legs using Google® EarthTM and Google®

MapsTM. It was infeasible to locate and collect number of legs from Google® EarthTM for every 

intersection because of resource constraints. Instead, the research team randomly sampled at least 

30 intersections for each group from the pool of candidate reference sites, and took the following 

steps:
26

1. Separate the pool of stop-controlled intersections into different categories using the 

available information (e.g., rural intersections with two lanes on the mainline and two

lanes on the cross street, urban intersections with four lanes on the mainline).

2. Randomize the order in each intersection category using a random number generator.

3. Start from the top of the list for each category, locate the intersection in Google® MapsTM

and Google® EarthTM, and determine the number of legs and verify the number of lanes.

The research team repeated these steps until there were at least 30 sites for each group (e.g.,

three-legged, rural intersections with two mainline lanes and two cross street lanes). Figure 10

shows a screenshot of a four-legged, rural intersection between US 76 (Garners Ferry Rd) and S69 (Congress Rd) in Richland County, located in Google® MapsTM in satellite image mode.

Imagery ©2016 Google®, Map data ©2016 Google®.

Figure 10. Example of collecting number of legs for reference site from Google®

EarthTM.

(19)

TRAFFIC DATA

SCDOT provided the research team with a statewide traffic volume data file for 2014. The 

research team used data in this file and merged with both candidate treatment and reference sites. 

This data file had more details with AADT information for both mainline and cross street for 

most intersections. The research team made a request but SCDOT was not able to provide similar 

data for other years. With SCDOT’s advice, the research team downloaded AADT files for 2006 

to 2014 publicly available on SCDOT’s website. However, these data files were much less 
27

detailed than the 2014 file the research team received from SCDOT staff. AADT information 

from these files was not available for many intersection mainlines and a majority of intersection 

cross streets. The research team used these data files to create growth factors by county. The 

research team used the growth factors and the detailed 2014 data file to estimate AADT 

information for 2006 to 2013. AADT for 2005 was not available from SCDOT’s website, so the 

research team extrapolated 2005 AADT based on data for 2006 to 2008. If AADT for either the 

mainline or cross street was still missing after the data processing, the research team dropped the 

intersections from the pools of treatment or reference sites. Note that there were few intersections 

that fell into this group. 

CRASH DATA

SCDOT provided 10 years of crash data (2005 to 2014). A unique accident number identifies 

each crash in the data files. A combination of the following variables was used to identify the 

location of each crash:

• County number (e.g., 1 = Abbeville, 2 = Aiken, and 3 = Allendale).

• Route type code (e.g., 2 = US, 4 = SC, and 7 = S).

• Route number.

• Route auxiliary (e.g., 0 = Mainline, 2 = Alternate, and 7 = Business).

• Crossing route type code (e.g., 2 = US, 4 = SC, and 7 = S).

• Crossing route number.

• Crossing route auxiliary (e.g., 0 = Mainline, 2 = Alternate, and 7 = Business).

• Base distance offset from the intersection (e.g., 1 = 0.01 mi, 5 = 0.05 mi, and

10 = 0.1 mi).

Note that the research team used crossing route in this context as a reference point, and the offset 

determined the distance from that reference point to the crash location. Route and crossing route 

in crash data files do not necessarily mean the mainline and minor routes in the same context of 

an intersection. The route indicates the roadway on which the crash occurred, and the crossing 

route indicates the crossing street at the nearest intersection (reference point). Both can be the 

mainline or the minor roads of the intersection used as the reference point.

The research team screened crash location information to identify and count crashes at each 

intersection. The crash data files did not provide a specific code to determine “intersectionrelated” crashes. Therefore, the process of locating and counting crashes at each intersection 

relied solely on crash location. The research team considered a crash “intersection-related” and 

counted it toward the number of crashes at an intersection if the location information indicated 

the crash occurred within 0.05 mi (264 ft), as was recommended by SCDOT staff.
28

The research team used number of fatalities and injuries coded for each crash to determine crash 

severity. Manner of collision determined rear-end and right-angle crashes. Light condition 

information was also available and identified nighttime crashes.

Table 13 presents the crash type definitions for South Carolina crash data.

Table 13. Definitions of crash types.

Total Fatal and Injury Rear-End Right-Angle Nighttime

Crashes of all 

types and 

severity 

levels

One of the 

following 

conditions:

• At least one 

fatality (fat ≥ 1)

• At least one 

injury (inj ≥ 1)

Manner of 

collision coded 

as “rear-end” 

(rims_mac = 10)

Manner of 

collision coded 

as “Angle 1” 

(rims_mac = 41), 

“Angle 2” 

(rims_mac = 42), 

or “Angle 3” 

(rims_mac = 43)

Light Condition 

coded as 

anything other 

than “Daylight” 

(alc = 1).

TREATMENT COST DATA

SCDOT provided actual construction cost data for improvements at more than 800 unsignalized 

intersections. Intersection construction costs were separated into subtotal pavement marking and 

signing treatment costs. Each intersection received a package of those treatments appropriate for 

implementation at the site out of the list of potential treatments. The treatment costs varied at 

each intersection based on the unique package of treatments it received. Table 14 summarizes the 

treatment costs.

Table 14. Treatment cost summary.

Statistic Pavement Marking Signing Total

Minimum $374.14 $426.05 $430.14

Average $2,958.10 $3,181.10 $5,874.01

Maximum $26,524.98 $18,530.21 $33,196.54

Note that some intersections only had pavement marking or signing improvements, but all 

intersections had at least some of one type of treatment installed.

Maintenance costs are dependent on the countermeasures installed at a given intersection. 

Without a record of the countermeasures installed at each intersection, it is difficult to estimate 

maintenance costs and service life. In addition, preliminary engineering (PE) costs were not 

supplied by SCDOT. For systemic projects, PE costs often represent 10 to 30 percent of the total 

project costs.
29

DATA CHARACTERISTICS AND SUMMARY

Table 15 and table 16 provide summary information for the data collected for the treatment and 

reference sites. The information in table 15 should not be used to make simple before–after 

comparisons of crashes per site-year since it does not account for factors, other than the strategy, 

that may cause a change in safety between the before and after periods. Such comparisons are 

properly done with the EB analysis as presented later.

Table 15. Data summary for treatment sites.

Data Element Before Period After Period

Number of sites 434 434

Three-legged, two lanes on the mainline and 

two lanes on the cross street

126 126

Four-legged, two lanes on the mainline and two

lanes on the cross street

131 131

Three-legged, four lanes on the mainline and 

two lanes on the cross street

116 116

Four-legged, four lanes on the mainline and two

lanes on the cross street

60 60

Number of site-years 2,438 1,389

Total crashes 8,514 4,231

Fatal and injury crashes 2,841 1,290

Right-angle crashes 3,538 1,840

Rear-end crashes 2,401 1,472

Nighttime crashes 2,193 915

Max mainline AADT (vehicles per day) 41,731 41,755

Average mainline AADT (vehicles per day) 11,042 10,437

Min mainline AADT (vehicles per day) 641 631

Max minor road AADT (vehicles per day) 8,436 8,400

Average minor road AADT (vehicles per day) 1,453 1,539

Min minor road AADT (vehicles per day) 102 100
30

Table 16. Data summary for reference sites.

Data Element Value

Number of sites 568

Number of site-years 5,680

Total crashes 9,095

Fatal and injury crashes 3,122

Right-angle crashes 3,952

Rear-end crashes 2,266

Nighttime crashes 2,382

Max mainline AADT (vehicles per day) 51,589

Average mainline AADT (vehicles per day) 8,495

Min mainline AADT (vehicles per day) 121

Max minor road AADT (vehicles per day) 8,100

Average minor road AADT (vehicles per day) 1,203

Min minor road AADT (vehicles per day) 102
31

CHAPTER 7. DEVELOPMENT OF SPFs

This section presents the SPFs developed for each crash type. The SPFs support the use of the EB 

methodology to estimate the safety effectiveness of this strategy.(15) The research team developed

negative binomial regression models to predict the number of crashes. In specifying a negative 

binomial error structure, the dispersion parameter, k, was estimated iteratively from the model 

and the data. For a given dataset, smaller values of k indicate relatively better models. The

research team developed one SPF for each of the following intersection configurations:

• 3 x 22: Three-legged intersections with two lanes on the mainline and two lanes on the 

cross street.

• 4 x 22: Four-legged intersections with two lanes on the mainline and two lanes on the 

cross street.

• 3 x 42: Three-legged intersections with four lanes on the mainline and two lanes on the 

cross street.

• 4 x 42: Four-legged intersections with four lanes on the mainline and two lanes on the 

cross street.

The research team developed correlation matrices for variables and used them as guide for the 

SPF development process. This helped the research team avoid highly correlated variables in the 

models. The model development followed a process of forward selection for selecting variables 

with the best fit. The research team started with mainline and cross street traffic volumes and 

their variants (e.g., natural logarithm, ratio of cross street AADT, and mainline AADT). Other 

candidate explanatory variables were then added, one by one, to the model. The model was reestimated and the goodness of fit was reevaluated with each variable addition.

The research team initially included annual adjustment variables (i.e., indicators for years 2005 to 

2014) in the SPFs during the first iteration of model development. However, most of these 

variables did not result in statistically significant parameters or help improve the fit of the SPFs. 

The inclusion of annual adjustment variables also led to heavily under-predicted crashes for some 

years (i.e., small coefficients on the negative side and far from being well fit), especially for the 

later years that cover the after period. The team eventually decided to drop these annual 

adjustment variables from the models and considered another approach to account for the annual 

trend (discussed later in this chapter).

In some cases, the research team could not develop an adequate model for a specific crash type. 

In these cases, the team used the SPF for total crashes and adjusted by the proportion of the 

number of crashes for the given crash type in total crashes.

The definition of variables included in the final SPFs are as follows:

• Totalaxbc = the predicted number of total crashes (all types and severity levels) for 

intersection with “a” legs, “b” lanes on the mainline, and “c” lanes on the cross street 

(e.g., 3 x 42 for three-legged intersections with four lanes on the mainline and two lanes 

on the cross street).
32

• FIaxbc = the predicted number of fatal and injury crashes for intersection with “a” legs, “b” 

lanes on the mainline, and “c” lanes on the cross street.

• Rear-Endaxbc = the predicted number of rear-end crashes for intersection with “a” legs, 

“b” lanes on the mainline, and “c” lanes on the cross street.

• Right-Angleaxbc = the predicted number of right-angle crashes for intersection with “a” 

legs, “b” lanes on the mainline, and “c” lanes on the cross street.

• Nightaxbc = the predicted number of nighttime crashes for intersection with “a” legs, “b” 

lanes on the mainline, and “c” lanes on the cross street.

• ml_aadt = AADT on the mainline (vehicles/day).

• xst_aadt = AADT on the cross street (vehicles/day).

• aadt = ml_aadt + xst_aadt, total traffic of intersection (vehicles/day).

• ratio1 = ln(xst_aadt)/ln(ml_aadt), with ln(xst_aadt) being the natural logarithm of AADT

on cross street and ln(ml_aadt) being the natural logarithm of AADT on mainline.

• ratio2 = xst_aadt/ml_aadt, with xst_aadt and ml_aadt being the AADT on cross street and 

mainline, respectively.

• ratio3 = xst_aadt/(xst_aadt + ml_aadt), with xst_aadt and ml_aadt being the AADT on 

cross street and mainline, respectively.

• ratio4 = ln(xst_aadt)/ln(xst_aadt + ml_aadt), with ln(xst_aadt) being the natural 

logarithm of AADT on cross street and ln(xst_aadt + ml_aadt) being the natural logarithm 

of total traffic at intersection.

• urban = urban/rural indicator for the intersection (= 1 for urban, = 0 otherwise).

• β1, β2, β3, β4 = parameters estimated in the SPF development process using maximum 

likelihood method.

• k = overdispersion parameter.

SPFs FOR 3 X 22 INTERSECTIONS

The SPF for total crashes at three-legged intersections with two lanes on the mainline and two

lanes on the cross street is shown in figure 11.

Figure 11. Equation. Total crash SPF for 3 x 22 intersections.

Total3×22 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4 
33

Table 17 presents the total crash SPF parameters for three-legged intersections with two lanes on 

the mainline and two lanes on the cross street.

Table 17. SPF parameters for total crashes at 3 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.285 0.049

β2 Coefficient of cross street AADT 0.081 0.025

β3 Coefficient for urban/rural indicator 0.270 0.068

β4 Intercept term –2.814 0.439

k Overdispersion parameter 0.128 0.032

The SPF for fatal and injury crashes at three-legged intersections with two lanes on the mainline 

and two lanes on the cross street is shown in figure 12.

Figure 12. Equation. Fatal and injury crash SPF for 3 x 22 intersections.

Table 18 presents the fatal and injury crash SPF parameters for three-legged intersections with 

two lanes on the mainline and two lanes on the cross street.

Table 18. SPF Parameters for fatal and injury crashes at 3 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1

Coefficient of total intersection 

AADT (mainline AADT + cross 

street AADT) 0.329 0.069

β4 Intercept term –3.641 0.614

k Overdispersion parameter 0.125 0.088

The SPF for rear-end crashes at three-legged intersections with two lanes on the mainline and two 

lanes on the cross street is shown in figure 13.

Figure 13. Equation. Rear-end crash SPF for 3 x 22 intersections.

Table 19 presents the rear-end crash SPF parameters for three-legged intersections with two lanes 

on the mainline and two lanes on the cross street.

FI3×22 = aadt

β1 eβ4

Rear End3×22 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4 
34

Table 19. SPF Parameters for rear-end crashes at 3 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 1.033 0.092

β2 Coefficient of cross street AADT 0.093 0.040

β3 Coefficient for urban/rural indicator 0.378 0.119

β4 Intercept term –10.550 0.844

k Overdispersion parameter 0.351 0.082

The SPF for right-angle crashes at three-legged intersections with two lanes on the mainline and 

two lanes on the cross street is shown in figure 14.

Figure 14. Equation. Right-angle crash SPF for 3 x 22 intersections.

Table 20 presents the right-angle crash SPF parameters for three-legged intersections with two 

lanes on the mainline and two lanes on the cross street.

Table 20. SPF parameters for right-angle crashes at 3 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of intersection AADT 0.264 0.109

β2

Coefficient for ratio1 = 

ln(xst_aadt)/ln(ml_aadt)

1.758 0.427

β3 Coefficient for urban/rural indicator 0.461 0.140

β4 Intercept term –5.101 1.015

k Overdispersion parameter 0.375 0.145

The research team could not develop a statistically significant model for nighttime crashes. The 

SPF for total crashes was used with an adjustment factor to predict nighttime crashes.

SPFs FOR 4 X 22 INTERSECTIONS

The SPF for total crashes at four-legged intersections with two lanes on the mainline and two 

lanes on the cross street is shown in figure 15.

Figure 15. Equation. Total crash SPF for 4 x 22 intersections.

Table 21 presents the total crash SPF parameters for four-legged intersections with two lanes on 

the mainline and two lanes on the cross street.

Right Angle3×22 = aadt

β1 × e

 β2×ratio 1+β3×urban +β4 

Total4×22 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4 
35

Table 21. SPF parameters for total crashes at 4 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.227 0.030

β2 Coefficient of cross street AADT 0.082 0.025

β3 Coefficient for urban/rural indicator 0.081 0.050

β4 Intercept term –2.041 0.253

k Overdispersion parameter 0.169 0.028

The SPF for fatal and injury crashes at four-legged intersections with two lanes on the mainline 

and two lanes on the cross street is shown in figure 16.

Figure 16. Equation. Fatal and injury crash SPF for 4 x 22 intersections.

Table 22 presents the fatal and injury crash SPF parameters for four-legged intersections with two 

lanes on the mainline and two lanes on the cross street.

Table 22. SPF Parameters for fatal and injury crashes at 4 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.106 0.048

β2 Coefficient of cross street AADT 0.086 0.042

β3 Coefficient for urban/rural indicator –0.165 0.079

Β4 Intercept term –2.005 0.398

k Overdispersion parameter 0.240 0.078

The SPF for rear-end crashes at four-legged intersections with two lanes on the mainline and two 

lanes on the cross street is shown in figure 17.

Figure 17. Equation. Rear-end crash SPF for 4 x 22 intersections.

Table 23 presents the rear-end crash SPF parameters for four-legged intersections with two lanes 

on the mainline and two lanes on the cross street.

Table 23. SPF Parameters for rear-end crashes at 4 x 22 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 1.133 0.080

β2 Coefficient of cross street AADT 0.130 0.057

β3 Intercept term –11.721 0.731

k Overdispersion parameter 0.869 0.172

The SPF for right-angle crashes at four-legged intersections with two lanes on the mainline and 

two lanes on the cross street is shown in figure 18.

FI4×22 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4

 

Rear End4×22 = ml_aadt

β1 × xst_aadtβ2 × eβ3
36

Figure 18. Equation. Right-angle crash SPF for 4 x 22 intersections.

Table 24 presents the right-angle crash SPF parameters for four-legged intersections with two 

lanes on the mainline and two lanes on the cross street.

Table 24. SPF parameters for right-angle crashes at 4 x 22 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT 

(Mainline AADT + Cross street AADT) 0.166 0.044

β2

Coefficient for ratio4 =

(xst_aadt)/(ml_aadt) 1.397 0.329

β3 Coefficient for urban/rural indicator 0.172 0.066

β4 Intercept term –2.817 0.470

k Overdispersion parameter 0.266 0.051

The SPF for nighttime crashes at four-legged intersections with two lanes on the mainline and 

two lanes on the cross street is shown in figure 19.

Figure 19. Equation. Nighttime crash SPF for 4 x 22 intersections.

Table 25 presents the nighttime crash SPF parameters for four-legged intersections with two lanes 

on the mainline and two lanes on the cross street.

Table 25. SPF Parameters for nighttime crashes at 4 x 22 intersections.

Parameter Description

Estimated 

Value Standard Error

β1 Coefficient for natural mainline AADT 0.153 0.058

β2 Coefficient of cross street AADT 0.100 0.050

β3 Coefficient for urban/rural indicator –0.217 0.095

β4 Intercept term –2.784 0.481

k Overdispersion parameter 0.459 0.119

SPFs FOR 3 X 42 INTERSECTIONS

The SPF for total crashes at three-legged intersections with four lanes on the mainline and two 

lanes on the cross street is shown in figure 20.

Figure 20. Equation. Total crash SPF for 3 x 42 intersections.

Right Angle4×22 = aadt

β1 × e

 β2×ratio 4+β3×urban +β4

 

Night Time4×22 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4 

Total3×42 = aadt

β1 × e

 β2×ratio 3+β4 
37

Table 26 presents the total crash SPF parameters for three-legged intersections with four lanes on 

the mainline and two lanes on the cross street.

Table 26. SPF parameters for total crashes at 3 x 42 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT (mainline 

AADT + cross street AADT) 0.356 0.056

β2

Coefficient for ratio3 =

xst_aadt/(xst_aadt + ml_aadt) 1.164 0.294

β4 Intercept term –2.950 0.548

k Overdispersion parameter 0.185 0.032

The research team could not develop a statistically significant model for fatal and injury crash 

SPF at three-legged intersections with four lanes on the mainline and two lanes on the cross 

street. The SPF for total crashes was used with an adjustment factor to predict the number of fatal 

and injury crashes.

The SPF for rear-end crashes at three-legged intersections with four lanes on the mainline and 

two lanes on the cross street is shown in figure 21.

Figure 21. Equation. Rear-end crash SPF for 3 x 42 intersections.

Table 27 presents the rear-end crash SPF parameters for three-legged intersections with four lanes 

on the mainline and two lanes on the cross street.

Table 27. SPF parameters for rear-end crashes at 3 x 42 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT (mainline 

AADT + cross street AADT) 0.345 0.115

β3 Coefficient for urban/rural indicator 0.289 0.121

β4 Intercept term –4.325 1.076

k Overdispersion parameter 0.799 0.162

The SPF for right-angle crashes at three-legged intersections with four lanes on the mainline and 

two lanes on the cross street is shown in figure 22. 

Figure 22. Equation. Right-angle crash SPF for 3 x 42 intersections.

Table 28 presents the right-angle crash SPF parameters for three-legged intersections with four 

lanes on the mainline and two lanes on the cross street.

Rear End3×42 = aadt

β1 × e

 β3×urban +β4 

Right Angle3×42 = aadt

β1 × e

 β2×ratio 3+β3×urban +β4 
38

Table 28. SPF parameters for right-angle crashes at 3 x 42 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT (mainline 

AADT + cross street AADT) 0.428 0.095

β2

Coefficient for ratio3 =

(xst_aadt)/(xst_aadt + ml_aadt) 2.582 0.439

β3 Coefficient for urban/rural indicator 0.180 0.092

β4 Intercept term –4.815 0.914

k Overdispersion parameter 0.411 0.084

The research team could not develop a statistically significant model for nighttime crashes. The 

SPF for total crashes was used with an adjustment factor to predict nighttime crashes.

SPFs FOR 4 X 42 INTERSECTIONS

The SPF for total crashes at four-legged intersections with four lanes on the mainline and two 

lanes on the cross street is shown in figure 23.

Figure 23. Equation. Total crash SPF for 4 x 42 intersections.

Table 29 presents the total crash SPF parameters for four-legged intersections with four lanes on 

the mainline and two lanes on the cross street.

Table 29. SPF parameters for total crashes at 4 x 42 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.149 0.039

β2 Coefficient of cross street AADT 0.147 0.024

β3 Coefficient for urban/rural indicator 0.157 0.054

β4 Intercept term –1.878 0.402

k Overdispersion parameter 0.197 0.029

The SPF for fatal and injury crashes at four-legged intersections with four lanes on the mainline 

and two lanes on the cross street is shown in figure 24.

Figure 24. Equation. Fatal and injury crash SPF for 4 x 42 intersections.

Table 30 presents the fatal and injury SPF parameters for four-legged intersections with four 

lanes on the mainline and two lanes on the cross street.

Total4×42 = ml_aadt

β1 × xst_aadtβ2 × e

 β3×urban +β4 

FI4×42 = ml_aadt

β1 × xst_aadtβ2 × eβ4
39

Table 30. SPF parameters for fatal and injury crashes at 4 x 42 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.100 0.055

β2 Coefficient of cross street AADT 0.089 0.037

β4 Intercept term –1.949 0.579

k Overdispersion parameter 0.272 0.075

The SPF for rear-end crashes at four-legged intersections with four lanes on the mainline and two 

lanes on the cross street is shown in figure 25.

Figure 25. Equation. Rear-end crash SPF for 4 x 42 intersections.

Table 31 presents the rear-end SPF parameters for four-legged intersections with four lanes on 

the mainline and two lanes on the cross street.

Table 31. SPF parameters for rear-end crashes at 4 x 42 intersections.

Parameter Description Estimated Value Standard Error

β1 Coefficient of mainline AADT 0.521 0.093

β2

Coefficient for ratio3 =

xst_aadt/(xst_aadt + ml_aadt)

1.430 0.412

β3 Coefficient for urban/rural indicator 0.538 0.111

β4 Intercept term –6.372 0.880

k Overdispersion parameter 0.262 0.109

The SPF for right-angle crashes at four-legged intersections with four lanes on the mainline and 

two lanes on the cross street is shown in figure 26. 

Figure 26. Equation. Right-angle crash SPF for 4 x 42 intersections.

Table 32 presents the right-angle SPF parameters for four-legged intersections with four lanes on 

the mainline and two lanes on the cross street.

Table 32. SPF parameters for right-angle crashes at 4 x 42 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT (mainline 

AADT + cross street AADT) 0.123 0.067

β2 Coefficient ratio4 = (xst_aadt)/(ml_aadt) 1.660 0.324

β3 Coefficient for urban/rural indicator 0.205 0.077

β4 Intercept term –2.620 0.714

k Overdispersion parameter 0.375 0.065

Rear End4×42 = mlaadt

β1 × e

 β2×ratio 3+β3×urban +β4

 

Right Angle4×42 = aadt

β1 × e

 β2×ratio 4+β3×urban +β4 
40

The SPF for nighttime crashes at four-legged intersections with four lanes on the mainline and 

two lanes on the cross street is shown in figure 27.

Figure 27. Equation. Nighttime crash SPF for 4 x 42 intersections.

Table 33 presents the nighttime SPF parameters for four-legged intersections with four lanes on 

the mainline and two lanes on the cross street.

Table 33. SPF parameters for nighttime crashes at 4 x 42 intersections.

Parameter Description

Estimated 

Value

Standard 

Error

β1

Coefficient of intersection AADT (mainline 

AADT + cross street AADT) 0.554 0.087

β2

Coefficient for ratio3 = xst_aadt/(xst_aadt +

ml_aadt) 1.167 0.386

β3 Coefficient for urban/rural indicator –0.233 0.097

β4 Intercept term –6.062 0.825

k Overdispersion parameter 0.240 0.105

BEFORE–AFTER ADJUSTMENT FACTORS

SPFs may include annual factors to account for potential time trends, as discussed in the first 

section of chapter 5. In this study, however, the SPFs did not include yearly indicator variables 

because after numerous attempts, the research team could not achieve a reasonable level of 

statistical significance for these individual variables. The research team decided to account for the 

time trend by using an aggregate before-to-after adjustment factor. Instead of using annual 

adjustment factors (i.e., one for each year), the research team used a single adjustment factor to 

account for the difference (i.e., crash trend) between the before and after periods. Because 

SCDOT did not install the treatment at all sites in the same year, the installation periods varied. 

For this reason, the team calculated one adjustment factor for each installation period (i.e., all 

intersections for which treatments were implemented in 2009–2010 have the same adjustment 

factor). Using these adjustment factors, the assumption is that all safety effects of unknown or 

immeasurable factors (e.g., weather) do not differ among reference and treatment sites or across 

intersection configurations. These factors were calculated based on the observed and predicted 

crashes at all reference sites. Figure 28 shows the equation used to calculate the before-after 

adjustment factors.

Figure 28. Equation. Before–after adjustment factor calculation.

Night Time4×42 = aadt

β1 × e

 β2×ratio 3+β3×urban +β4 

Adj_Factor =

Obsafter

Predafter

Obsbefore

Predbefore
41

Where:

Adj_Factor = the factor for adjusting the difference between the before and after period.

Obs_before = observed number of crashes at reference sites during the before period.

Predbefore = predicted number of crashes at reference sites during the before period (calculated 

by SPF).

Obs_after = observed number of crashes at reference sites during the after period.

Predafter = predicted number of crashes at reference sites during the after period (calculated by 

SPF).

Table 34 to table 38 present the before–after adjustment factors for each installation time frame 

and crash type.

Table 34. Before–after adjustment factor for total crashes.

Installation 

Year(s)

Observed 

Crashes—

Before

Observed 

Crashes—

After

Predicted 

Crashes—

Before

Predicted 

Crashes—

After

Adjustment 

Factor

2009 3,894 4,321 3,648 4,540 0.892

2009–2010 3,894 3,426 3,648 3,634 0.883

2010 4,774 3,426 4,552 3,634 0.899

2010–2011 4,774 2,641 4,552 2,724 0.925

2011 5,669 2,641 5,458 2,724 0.934

2011–2012 5,669 1,759 5,458 1,814 0.934

2012 6,454 1,759 6,368 1,814 0.957

Table 35. Before–after adjustment factor for fatal and injury crashes.

Installation 

Year(s)

Observed 

Crashes—

Before

Observed 

Crashes—

After

Predicted 

Crashes—

Before

Predicted 

Crashes—

After

Adjustment 

Factor

2009 1,346 1,462 1,251 1,559 0.872

2009–2010 1,346 1,124 1,251 1,248 0.837

2010 1,660 1,124 1,562 1,248 0.848

2010–2011 1,660 871 1,562 936 0.876

2011 1,998 871 1,874 936 0.873

2011–2012 1,998 557 1,874 623 0.838

2012 2,251 557 2,186 623 0.868
42

Table 36. Before–after adjustment factor for rear-end crashes.

Installation 

Year(s)

Observed 

Crashes—

Before

Observed 

Crashes—

After

Predicted 

Crashes—

Before

Predicted 

Crashes—

After

Adjustment 

Factor

2009 912 1,144 909 1,119 1.019

2009–2010 912 943 909 895 1.050

2010 1,122 943 1,132 895 1.063

2010–2011 1,122 727 1,132 668 1.098

2011 1,323 727 1,356 668 1.115

2011–2012 1,323 487 1,356 440 1.133

2012 1,539 487 1,583 440 1.137

Table 37. Before–after adjustment factor for right-angle crashes.

Installation 

Year(s)

Observed 

Crashes—

Before

Observed 

Crashes—

After

Predicted 

Crashes—

Before

Predicted 

Crashes—

After

Adjustment 

Factor

2009 1,695 1,887 1,585 1,974 0.894

2009–2010 1,695 1,512 1,585 1,580 0.895

2010 2,065 1,512 1,979 1,580 0.917

2010–2011 2,065 1,171 1,979 1,185 0.947

2011 2,440 1,171 2,373 1,185 0.961

2011–2012 2,440 772 2,373 789 0.951

2012 2,781 772 2,768 789 0.974

Table 38. Before–after adjustment factor for nighttime crashes.

Installation 

Year(s)

Observed 

Crashes—

Before

Observed 

Crashes—

After

Predicted 

Crashes—

Before

Predicted 

Crashes—

After

Adjustment 

Factor

2009 1,049 1,096 956 1,188 0.841

2009–2010 1,049 857 956 951 0.821

2010 1,286 857 1,193 951 0.836

2010–2011 1,286 652 1,193 713 0.849

2011 1,525 652 1,430 713 0.858

2011–2012 1,525 416 1,430 475 0.822

2012 1,730 416 1,669 475 0.846
43

CHAPTER 8. BEFORE–AFTER EVALUATION RESULTS

AGGREGATE ANALYSIS

Table 39 provides the estimates of expected crashes in the after period without treatment, the 

observed crashes in the after period, and the estimated crash modification factor (CMF) and its 

standard error for each crash type considered in this study. The results in table 39 indicate 

reductions for all crash types analyzed in this study. The reductions are statistically significant at 

the 95-percent confidence level for all crash types. For all crash types combined, the CMFs are 

0.917 for all severities and 0.899 for fatal and injury crashes. The crash type with the smallest 

CMF (which translates to the greatest reduction) is nighttime crashes with a CMF of 0.853 (or 

14.7-percent reduction). The CMFs for rear-end and right-angle crashes are 0.933 and 0.941, 

respectively.

Table 39. Aggregate results for EB before–after study.

Statistic Total

Fatal and

Injury

RearEndRightAngle Nighttime

EB estimate of crashes expected 

in the after period without the 

systemic improvement 4,614 1,434 1,577 1,955 1,072

Count of crashes observed in 

the after period 4,231 1,290 1,472 1,840 953

Estimated CMF 0.917* 0.899* 0.933* 0.941* 0.853*

Standard error of the estimated 

CMF 0.017 0.028 0.030 0.026 0.031

*Statistically significant results at the 95-percent confidence level.

DISAGGREGATE ANALYSIS

The disaggregate analysis identified specific CMFs by crash type and different conditions. The 

process also revealed those conditions under which the multiple low-cost treatments are more

effective. The research team identified several variables of interest, including: area type (urban or 

rural), number of legs (three or four), lane configuration of the mainline and the cross street, 

traffic volumes, and expected crashes without treatment. All of these variables are likely 

correlated, and caution should be exercised in interpreting and applying the disaggregate analysis 

results. The team did not conduct a disaggregate analysis on individual treatments or groups of 

treatments because no detailed information on type of treatment that each intersection received 

was available. Although we knew these intersections received at least some or all of the 

treatments, we did not know exactly what treatments were applied.

Table 40 presents the disaggregate results by area type (urban or rural), indicating the sample size 

(number of sites), CMF, and standard error of the CMF (in parentheses) by group for each crash 

type considered in this study. For the 188 urban intersections, the results in table 40 indicate 

increases in all crash types analyzed in this study. Specifically, the CMFs for total and fatal and

injury crashes are 1.066 and 1.095, respectively, which are statistically significant at the 95-

percent confidence level. The CMFs for rear-end, right-angle, and nighttime crashes are 1.006, 

1.025, and 1.013, respectively, which are not statistically significant at the 95-percent confidence 
44

level. For the 245 rural intersections, the results in table 40 indicate reductions for all crash types 

analyzed in this study, which are all statistically significant at the 95-percent confidence level. 

Based on the disaggregate analysis by area type, it appears this strategy is highly effective at rural 

intersections, but there is the potential to increase crashes at urban intersections. However, as 

noted above, this effect may be due to other correlated variables.

Table 40. Disaggregate results by area type.

Statistic Urban

Standard 

Error Rural

Standard 

Error

Number of intersections 188 N/A 245 N/A

Total CMF 1.066 0.025 0.748* 0.022

Fatal and injury CMF 1.095 0.047 0.734* 0.034

Rear-end CMF 1.006 0.040 0.811* 0.044

Right-angle CMF 1.025 0.037 0.833* 0.037

Nighttime CMF 1.013 0.051 0.718* 0.039

*Statistically significant results at the 95-percent confidence level.

Table 41 presents the disaggregate results by number of legs, indicating the sample size (number 

of sites), CMF, and standard error of the CMF (in parentheses) by group for each crash type 

considered in this study. For the 242 three-legged intersections, the results in table 41 indicate 

reductions in all crash types analyzed in this study. The CMFs for total, fatal and injury, rear-end, 

and right-angle crashes are not statistically significant at the 95-percent confidence level. The 

CMF for nighttime crashes is 0.902 and is statistically significant at the 95-percent confidence 

level. For the 191 four-legged intersections, the results in table 41 indicate reductions for all crash 

types analyzed in this study, which are all statistically significant at the 95-percent confidence 

level. Based on the disaggregate analysis by number of legs, it appears this strategy is more 

effective at four-legged intersections than three-legged intersections. However, as noted above, 

this effect may be due to other correlated variables.

Table 41. Disaggregate results by number of legs.

Statistic 3-Legged

Standard 

Error 4-Legged

Standard 

Error

Number of intersections 242 N/A 191 N/A

Total CMF 0.958 0.022 0.854* 0.025

Fatal and injury CMF 0.949 0.039 0.836* 0.041

Rear-end CMF 0.962 0.036 0.862* 0.052

Right-angle CMF 0.977 0.037 0.902* 0.037

Nighttime CMF 0.902* 0.041 0.780* 0.048

*Statistically significant results at the 95-percent confidence level.

Table 42 presents the disaggregate results by number of lanes, indicating the sample size (number 

of sites), CMF, and standard error of the CMF (in parentheses) by group for each crash type 

considered in this study. For the 257 intersections with two-lane major roads, the results in table 

42 indicate reductions in all crash types analyzed in this study, which are all statistically 

significant at the 95-percent confidence level. For the 176 intersections with four-lane major 

roads, the results in table 42 indicate reductions in total, rear-end, right-angle, and nighttime 

crashes, and an increase in fatal and injury crashes. None of the CMFs associated with four-lane 
45

major roads are statistically significant at the 95-percent confidence level. Based on the 

disaggregate analysis by number of lanes, it appears this strategy is more effective at two-lane 

major road intersections than four-lane major road intersections. However, as noted above, this 

effect may be due to other correlated variables.

Table 42. Disaggregate results by number of lanes.

Statistic

2 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

4 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

Number of intersections 257 N/A 176 N/A

Total CMF 0.879* 0.022 0.960 0.025

Fatal and injury CMF 0.814* 0.035 1.013 0.047

Rear-end CMF 0.919* 0.041 0.948 0.043

Right-angle CMF 0.925* 0.037 0.956 0.037

Nighttime CMF 0.806* 0.040 0.916 0.050

*Statistically significant results at the 95-percent confidence level.

Table 43 presents the disaggregate results by number of legs and number of lanes, indicating the 

sample size (number of sites), CMF, and standard error of the CMF (in parentheses) by group for 

each crash type considered in this study. 

For the 126 three-legged intersections with two-lane major roads, the results in table 43 indicate 

reductions in all crash types analyzed in this study. The CMFs for total, fatal and injury, and 

nighttime crashes are 0.902, 0.811, and 0.828, respectively, which are statistically significant at 

the 95-percent confidence level. The CMFs for rear-end and right-angle crashes are not 

statistically significant at the 95-percent confidence level. For the 116 three-legged intersections 

with four-lane major roads, none of the CMFs are statistically significant at the 95-percent 

confidence level.

For the 131 four-legged intersections with two-lane major roads, the results in table 43 and table 

44 indicate reductions in all crash types analyzed in this study. The CMFs for total, fatal and

injury, right-angle, and nighttime crashes are 0.854, 0.816, 0.892, and 0.779, respectively, which 

are statistically significant at the 95-percent confidence level. The CMF for rear-end crashes is 

not statistically significant at the 95-percent confidence level, but is statistically significant at the 

90-percent confidence level. 

For the 60 four-legged intersections with four-lane major roads, the results in table 43 indicate 

reductions in all crash types analyzed in this study. The CMFs for total, rear-end, and nighttime 

crashes are 0.854, 0.838, and 0.780, respectively, which are statistically significant at the 95-

percent confidence level. The CMFs for fatal and injury and right-angle crashes are not 

statistically significant at the 95-percent confidence level.

Based on the disaggregate analysis by number of legs and number of lanes, it appears this 

strategy is effective for most combinations of legs and lanes. It is least effective at three-legged 

intersections with four-lane major roads (i.e., 3 x 42). It is most effective at four-legged 
46

intersections with two-lane major roads (i.e., 4 x 22). However, as noted above, this may be due 

to other correlated variables.

Table 43. Disaggregate results for three-legged intersections by number of lanes.

Statistic

3-Legged with 

2 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

3-Legged with 

4 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

Number of 

intersections 126 N/A 116 N/A

Total CMF 0.902* 0.032 1.003 0.031

Fatal and Injury CMF 0.811* 0.050 1.082 0.059

Rear-end CMF 0.940 0.051 0.982 0.052

Right-angle CMF 0.990 0.066 0.970 0.045

Nighttime CMF 0.828* 0.054 0.979 0.063

*Statistically significant results at the 95-percent confidence level.

Table 44. Disaggregate results for four-legged intersections by number of lanes. 

Statistic

4-Legged with 

2 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

4-Legged with 

4 Mainline 

Lanes and 2 

Cross Street 

Lanes

Standard 

Error

Number of 

intersections 131 N/A 60 N/A

Total CMF 0.854* 0.032 0.854* 0.043

Fatal and injury CMF 0.816* 0.049 0.878 0.074

Rear-end CMF 0.875 0.069 0.838* 0.078

Right-angle CMF 0.892* 0.044 0.924 0.064

Nighttime CMF 0.779* 0.060 0.780* 0.081

*Statistically significant results at the 95-percent confidence level.

Figure 29 and figure 30 show the individual CMFs for total crashes and fatal and injury crashes, 

respectively, for each treatment site compared to the total entering traffic volume associated with 

the intersection. The linear trend line suggests the multiple low-cost treatments are more effective 

on average for intersections with lower traffic volumes, and the effectiveness decreases (i.e., 

CMF increases) as traffic volume increases. The CMFs in both figure 29 and figure 30 appear to 

cross 1.0 when AADT is around 20,000. This suggests that the crash reduction potential is better 

for intersections with total entering AADT under 20,000. Again, the perceived relationship may 

also be due to correlations with other variables.
47

Source: FHWA.

Figure 29. Chart. Relationship between CMF (total crashes) and total intersection AADT.

Source: FHWA.

Figure 30. Chart. Relationship between CMF (fatal and injury crashes) and total 

intersection AADT.

Figure 31 and figure 32 show the individual CMFs for total crashes and fatal and injury crashes, 

respectively, for each treatment site compared to the expected crashes per year in the before 

period. The linear trend line suggests the multiple low-cost treatments are more effective on 

average for intersections with fewer expected crashes per year in the before period, and the 

effectiveness decreases (i.e., CMF increases) as expected crashes increase. Note that this trend is 

consistent with the relationship for traffic volume as shown in figure 29 and figure 30, which 

makes sense because expected crashes increase as traffic volume increases. This confirms the 

need for caution when interpreting the results of the univariate analyses. Specifically, the net 
48

effect of the multiple correlations among variables investigated is a negligible effect on the 

expected number of crashes, which collectively captures the effects of those variables.

Source: FHWA.

Figure 31. Chart. Relationship between CMF (total crashes) and expected total crashes per 

year during before period.

Source: FHWA.

Figure 32. Chart. Relationship between CMF (fatal and injury crashes) and expected fatal 

and injury crashes per year during before period.
49

CHAPTER 9. ECONOMIC ANALYSIS

An economic analysis was conducted to estimate the B/C ratio for implementing various low-cost 

pavement marking and signing improvements at stop-controlled intersections. The statistically 

significant aggregate reduction in total crashes was used to calculate the benefits for an average 

intersection. The research team performed the economic analysis of total crashes as a 

conservative estimate of the economic benefit.

Based on work order cost data for over 800 unsignalized intersections provided by SCDOT, the 

economic analysis assumed an average total construction cost of $5,900. In addition, annual 

maintenance and operations costs were not available and are assumed to be zero (i.e., these costs

will not be incurred within the service life). PE, project management, and other general costs 

were not provided; however, a large portion of project planning was completed by State forces,

and other costs for two contractors would have been split across all intersections if the costs were 

available. In future economic analyses of similar projects, all of these preliminary costs should be 

added to the construction costs.

The analysis assumed the useful service life for safety benefits was approximately 7 years. 

Pavement markings were assumed to last roughly 4 years and signs roughly 10 years for an 

approximate average of 7 years for the overall project. A conservative analysis using a service 

life of 3 years was also conducted. 

The FHWA Office of Safety Research and Development suggested using the Office of 

Management and Budget Circular A-4 as a resource for the real discount rate of seven percent to 

calculate the present value benefits and costs of the treatment over the service life.(20) With this 

information, the capital recovery factor was computed for all intersection types as 2.62 for a 

service life of 3 years and 5.39 for a service life of 7 years.

For the benefit calculations, the most recent FHWA mean comprehensive crash costs 

disaggregated by crash severity and location type were used as a base.(1) These costs were 

developed based on 2001 crash costs and the unit cost (in 2001 dollars) was $158,177 for fatal 

and injury crashes and $7,428 for property damage only (PDO) crashes. This was updated to 

2015 dollars by applying the ratio of the USDOT 2015 value of a statistical life of $9.4 million to 

the 2001 value of $3.8 million.(1,22) Applying this ratio of 2.474 to the unit costs for fatal and

injury and PDO crashes yields values of $391,280 and $18,375, respectively. The research team 

then weighted the values at approximately 30 percent fatal and injury crashes in the after period, 

which resulted in a total crash cost of $132,071 in 2015 dollars. 

All project costs were brought forward to 2015 dollars for consistency with crash cost values 

based on the same 7-percent discount rate, assuming original project costs are in 2011 dollars.

The total crash reduction was calculated by subtracting the actual crashes in the after period from 

the expected crashes in the after period had the intersection treatments not been implemented. 

The total crash reduction was then divided by the average number of after period years per site to 

compute the total crashes saved per year. The treatments saved 119.7 crashes per year for the 

sample sites, or an average reduction of 0.3 crashes per site per year across the 434 treatment 

sites. Similarly, the treatments reduced fatal and injury crashes by 45 crashes per year across the 

sample sites, or an average reduction of 0.1 fatal and injury crashes reduced per site per year.
50

The annual economic benefits were calculated by multiplying the crash reduction per site per 

year by the cost of a crash. Total crash reduction and total crash cost were used in the calculation. 

The B/C ratio was calculated as the ratio of the present value of benefits to the present value of 

all costs. USDOT recommended a sensitivity analysis be conducted assuming values of a 

statistical life of 0.57 and 1.41 times the recommended 2015 value.(22) These factors can be 

applied directly to the estimated B/C ratios to obtain a lower and upper bound of the B/C ratios. 

Table 45 presents the resulting B/C ratios.

Table 45. B/C ratios.

Service Life Lower Bound Average B/C Upper Bound

3 years 7.1 12.4 17.5

7 years 14.5 25.5 35.9

These results suggest that the unsignalized intersection treatments, even with conservative 

assumptions of service life and the value of a statistical life, can be cost effective in reducing total 

crashes at stop-controlled intersections.
51

CHAPTER 10. SUMMARY AND CONCLUSIONS

The objective of this study was to undertake a rigorous before–after evaluation of the safety 

effectiveness, as measured by crash frequency, of systemic low-cost improvements at stopcontrolled intersections. The study used data from South Carolina to examine the effects for the 

specific crash types total, fatal and injury, rear-end, right-angle, and nighttime crashes. Based on 

the aggregate results, table 46 presents the recommended CMFs for the various crash types. 

Table 46. Recommended CMFs.

Variable Total

Fatal and

Injury Rear-End Right-Angle Nighttime

CMF 0.917 0.899 0.933 0.941 0.853

Standard Error 0.017 0.028 0.030 0.026 0.031

The disaggregate analysis sought to identify those conditions under which the multiple low-cost 

treatments are most effective. Variables of interest included area type (urban or rural), number of 

legs (three or four), lane configuration of the mainline and the cross street, traffic volumes, and 

expected crashes without treatment. The disaggregate analysis indicated larger crash reductions 

of all types for rural areas, four-legged intersections, and intersections with two-lane major roads.

For total entering volume and expected crashes before treatment, the disaggregate analysis 

indicated the strategy is more effective on average for intersections with lower traffic volumes 

and fewer expected crashes per year. However, it is important to cautious in interpreting and 

applying the results of the other univariate comparisons, which are likely confounded my 

multiple correlative effects.

The B/C ratio, estimated with conservative costs and 3-year service life, considering the benefits 

for total crashes, is 12.4 to 1. With the USDOT recommended sensitivity analysis, these values 

could range from 7.1 to 1 up to 17.5 to 1. These results suggest that the multiple low-cost 

treatments, even with conservative assumptions on cost, service life, and the value of a statistical 

life, can be cost effective in reducing crashes at stop-controlled intersections.

This research demonstrates the potential effect of a systemic intersection improvement program 

by evaluating a systemic program where each site received an individualized version of a 

package of intersection treatments with some differences in application at each individual 

intersection. Although information regarding the exact treatments installed at each site was not 

available to the research team, such data would have value in future evaluations of multiplestrategy improvement projects. Agencies should consider how to best document and track the 

improvements at each site to facilitate more complete and rigorous disaggregate analyses. 

However, the approach used in this research is able to quantify the overall effects of an 

improvement program and suggests the expected effectiveness of similar future programs.

53

APPENDIX. ADDITIONAL INSTALLATION DETAILS

This appendix provides a description and examples of the general work completed by SCDOT to 

implement the multiple-strategy improvements at signalized intersections and illustrations of the 

SCDOT Standard Drawings used in the project. The appendix concludes with a list of general 

notes related to standard review guidelines, field notes, final plans, and submissions. Most of the 

following text is excerpted from SCDOT project guidelines. For explanatory purposes, the 

authors of this report added the text in brackets.

EXAMPLE OF DOCUMENTS USED DURING THE LOW-COST INTERSECTION 

IMPROVEMENT PROJECT(19)

[SCDOT used the following documents during the project:]

• General Signing & Pavement Marking Notes for all Intersections. SCDOT included 

this document in each work order sent to the contractors. It contains general notes and 

instructions that pertain to all intersections.

• SCDOT Standard Drawing 625-305-00. This document shows the standard pavement 

markings for intersections.

• SCDOT Standard Drawing 625-310-00. This document shows the standard pavement 

markings for turn lanes.

• SCDOT Standard Drawing 625-410-00. This document shows the standard pavement 

markings for arrows and the word message “Only.”

• Additional Sign Inventory for Replacement. SCDOT decided to replace additional 

warning and regulatory signs (in addition to the typical) from this table to include signs 

near the intersection that were considered to have notable safety impacts.

• Unsignalized Intersection Design. This document shows general pavement marking and 

sign installation information for unsignalized intersections.

• SCDOT Traffic Engineering Guideline 20. SCDOT Traffic Engineering designed this 

document to provide information on the installation of retroreflective sign post panels.

• SCDOT Guidelines for Advance Placement of Warning Signs. SCDOT revised this 

document from the Table 2C-4 from the 2009 MUTCD to show suggested placement of 

advanced warning signs. Proper staking has been one of the biggest issues to date so this 

document was used to serve as a guideline. 100 feet was added to Condition B (0) to 

provide additional advance notice needed for the added street name sign.

• Intersection Typicals. These documents are examples of intersection typicals provided to 

the contractor by SCDOT. They include typicals for a signalized intersection, a four-way 

stop controlled intersection, a cross-type stop controlled intersection, and a t-type stop 

controlled intersection. These typicals are revised after field inspection to create a final 

plan.
54

• Street Name Sign Typical. This document is an example of the SignCADD layout 

provided with each intersection typical.

• Placement Dimensions for Stop Ahead. [This document shows dimensions for 

placement of rumble strips preceding a Stop sign.]

GENERAL SIGNING AND PAVEMENT MARKING NOTES FOR ALL 

INTERSECTIONS(19)

[SCDOT used the following guidance for signing and pavement marking for all intersections.]

Remark all existing stop lines, crosswalks, arrows and word messages unless:

• The roadway has been resurfaced within one calendar year and new thermoplastic 

markings have been applied.

• Existing markings are uniformly reflective and above ground thickness is ≥ 90 mils.

• Otherwise directed by a district representative.

Individual typicals in work orders may not show all desired markings; therefore, all turn lanes 

shall be marked to include the pattern of lane arrows and accompanying word message “ONLY” 

based on the turn lane length, in accordance with Standard Drawing 625-410-00.

As referenced in Standard Drawing 625-410-00 for signalized intersections, combination Straight 

and Left or Right Turn arrows shall be added on all shared usage lanes where there are two or 

more through lanes (exclusive or shared). For example, if an approach has an exclusive through 

lane AND a shared through/right turn lane, the shared lane shall have two through/right turn 

arrows installed in accordance with Standard Drawing 625-410-00.

Additional pavement marking details for intersections shall be followed in accordance with 

Standard Drawing 625-305-00 and 625-310-00. Note that all turn bays should be delineated with 

an extended dashed edgeline as shown in the standard drawings.

If existing lane markings and word messages are in good condition but not compliant with the 

typical, retain the existing marking scheme and do not install the typical layout.

For fabrication of D series signs, utilize appendix C of the blue MUTCD with 8” capital letters 

for 4-lane divided roadways and 6” capital letters for all other roadways.

Opposite side signs should be placed adjacent to the existing sign within a 30’ tolerance.

If “STOP” pavement marking is used, place 8’ letters approximately 10’ in advance of stop limit 

line.

Install retroreflective sign post panels only on signs as indicated on Traffic Engineering Guideline 

TG-20 that are shown on the original typicals. Additional signs will not require sign post panels.
55

Do not replace Junction signs with blue border and lettering.

For electric sign mounted flashers, contact the RCE for disconnect of electric power to convert to 

solar flasher.

Replace all other existing signs within 500’ of the intersection that are included in the attached 

table entitled “Additional Sign Inventory for Replacement.”

Reinstall all pavement markings to match the existing field markings unless otherwise noted, i.e., 

TWLT markings should not be remarked as double yellow, dashed edge lines should not be 

installed for single turn lanes, etc.

STANDARD MARKINGS FOR INTERSECTIONS(19)

[The following text is transcribed from SCDOT Standard Drawing 625-305-00. Excerpts of 

details from the standard drawing are included as figures.]

Application of Markings at Intersections

1. Stop lines are to be applied at all signalized intersections. 

2. At non-signalized intersections, the roadways which must stop are to have stoplines if 

centerlines are present. 

3. Where stoplines are used, lane lines and center lines will terminate at the stopline. They do 

not extend across stoplines nor do they terminate prior to stoplines. Location of stoplines 

should be determined prior to marking longitudinal lines. 

4. Lane lines terminating at a stopline should not be less than 10 ft in length, however they may 

be longer. The last lane line will be 10 to 40 ft long. The following procedure will aid in this 

determination: 

a. Mark a spot 50 ft in advance of stopline of each lane line approach. 

b. If a line is being applied when the spot is crossed, the striper operator permits 

automatic cut-off and the following 30 gap. When the next line begins, the striper 

operator will manually override the automatic cut-off and will extend the line to 

the stopline. 

c. If a line is not being applied when the spot is crossed, when the next line begins 

the striper operator will manually override the automatic cut-off and will extend 

the line to the stopline. 

5. At all intersections, lane lines will normally be omitted within the intersection area where 

turning vehicles must maneuver.

[Figure 33 shows a detail of standard markings for intersections.]
56

©SCDOT

Figure 33. Illustration. SCDOT Standard Drawing 625-305-00 excerpts for application of 

markings at intersections.
57

Arrows and Word Messages

Arrows and word messages are not typical at all turn lanes and will be placed only at locations 

shown on the plans or where directed by the engineer. In the absence of a marked crosswalk the 

stopline should be placed at a distance of no less than 4 ft and no more than 30 ft from the where 

arrows supplement signs to prohibit a movement that would otherwise be legal from that lane, the 

arrow must be accompanied by the word ‘only.’ All arrows and word messages shall be as 

indicated on standard drawings 625-410-00.

Additional Guidance through Intersections

[Figure 34 shows guidelines for applying dashed-line pavement markings through intersections.]

© SCDOT

Figure 34. Illustration. SCDOT Standard Drawing 625-305-00 excerpt for guidance through 

intersections.

Crosswalks

All crosswalks are to be marked with 8” solid white lines. Crosswalk lines are to be spaced not 

less than 6 feet apart. [Figure 35 shows standards for an unsignalized school crosswalk.]
58

© SCDOT

Figure 35. Illustration. SCDOT Standard Drawing 625-305-00 excerpts for crosswalk 

markings.

TYPICAL MARKINGS FOR TURN LANE INSTALLATIONS

(19)

[The following text is transcribed from SCDOT Standard Drawing 625-310-00. Excerpts of 

details from the standard drawing are included as figures.]

Notes

[The following notes relate to installing typical markings for turn lanes:]

Length of tapers and chevrons vary. See plan sheets for dimensions. 

Apply arrows, see Standard Drawing number 625-410-00. 

Apply ‘only’ copy, see Standard Drawing number 625-410-00. 

No raised markers are to be applied on chevrons. 
59

Stoplines shown on mainline are to be applied only at signalized intersections.

[Figure 36 through figure 39 show details for turn lane markings from SCDOT Standard Drawing 

625-310-00.]

© SCDOT

Figure 36. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 1).

© SCDOT

Figure 37. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 2).
60

© SCDOT

Figure 38. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for turn lane 

installations (part 3).
61

© SCDOT

Figure 39. Illustration. SCDOT Standard Drawing 625-310-00 excerpts for chevron 

marking details.

STANDARD PAVEMENT MARKINGS(19)

[Figure 40 through figure 44 are excerpts of details from SCDOT Standard Drawing 625-410-00.]
62

© SCDOT

Figure 40. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for straight arrow 

standard pavement marking.
© SCDOT

Figure 41. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right or left turn arrow and combination straight 

and left or right turn arrow standard pavement marking.

6

3
© SCDOT

Figure 42. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right lane drop arrow and left lane drop arrow 

standard pavement marking.

6

4
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© SCDOT

Figure 43. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for “ONLY” 

standard pavement marking.
© SCDOT

Figure 44. Illustration. SCDOT Standard Drawing 625-410-00 excerpt for right or left turn markings application.

6

6
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ADDITIONAL SIGN INVENTORY FOR REPLACEMENT(19)

[SCDOT replaced additional warning and regulatory signs (in addition to the typical) shown in 

figure 45 through figure 48, including signs near the intersection that were considered to have 

notable safety impacts.]

© SCDOT

Figure 45. Illustration. Additional sign inventory for replacement (part 1).
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© SCDOT

Figure 46. Illustration. Additional sign inventory for replacement (part 2).
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© SCDOT

Figure 47. Illustration. Additional sign inventory for replacement (part 3).
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© SCDOT

Figure 48. Illustration. Additional sign inventory for replacement (part 4).

[Table 47 shows the advance placement distance at different posted speed limits or 85thprecentile speeds.] 

This chart is intended as a reference with adjustments expected due to field conditions and

engineering judgment.
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Table 47. Advance placement distance for signal ahead, stop, or intersection warning signs.

Posted or 85th-Percentile 

Speed (mi/hr)

Multilane Approach* (ft) Single Lane Approach** (ft)

20 225 200

25 325 200

30 460 200

35 565 200

40 670 225

45 775 275

50 885 350

55 990 425

60 1,100 500

65 1,200 575

70 1,250 650

75 1,350 750

Note: * These values reflect condition A from table 2C-4 of the 2009 MUTCD and should be used as a reference for 

designated signs on multilane approaches.

** These values reflect condition B from table 2C-4 of the 2009 MUTCD plus 100 ft due to the chart representing 

minimum guidelines and the additional advance notice needed due to the supplemental street name signs added to 

these sign assemblies.

RETROREFLECTIVE SIGN POST PANELS(19)

[The following guidelines on the use of retroreflective signpost panels were signed and approved 

by South Carolina’s Director of Traffic Engineering on June 24, 2008:]

Number: TG-20

Subject: Retroreflective Sign Post Panels

Background: Section 2A.21 of the MUTCD provides guidance on the use of 

Retroreflective Sign Post Panels. This section states that these panels 

can be applied to regulatory and warning signs where engineering 

judgment indicates a need for additional target enhancement during 

nighttime conditions. Therefore, these panels will generally be 

applied where crash history indicates a relatively high percentage of 

nighttime crashes.

Guideline: The panels shall be constructed of a nonmetallic composite or 3mm 

aluminum composite material approved by the SCDOT covered with 
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a 3-inch wide type III sheeting. The panel shall be placed for the full 

length of the support from the sign except that the color for the 

“Yield” and “Do Not Enter” signs shall be red. If there are two posts 

supporting the sign, panels should be added to both posts.

To avoid excessive use of the Retroreflective Sign Post Panel, it is 

suggested that panels only be applied when needed to the regulatory 

signs below:

• Red Regulatory Signs. Stop, Yield, Do Not Enter, and Wrong 

Way signs—Red Panels.

• Horizontal Alignment Signs. Chevrons, Curve, Turn, and Large 

Arrow signs—Yellow Panels.

• Advance Traffic Control Signs. Stop Ahead, Yield Ahead, and 

Signal Ahead signs—Yellow Panels.

• Intersection Warning Signs. Cross Road, Side Road, and TwoDirection Large Arrow signs—Yellow Panels.

• Pedestrian Signs and School Area Signs. W11-2 and S1 

Series—Fluorescent Yellow Green Panels.

[Figure 49 and figure 50 show standards for pavement marking and rumble strip placement at 

unsignalized intersections.]
© SCDOT

Figure 49. Illustration. SCDOT nonsignalized intersection design for pavement marking and sign installations.

7

3
74

© SCDOT

Figure 50. Illustration. SCDOT traffic engineering rumble strip typical.

[Figure 51 through figure 54 are examples of intersection typicals that SCDOT provided to the 

contractor, including a signalized intersection, a four-way stop-controlled intersection, a crosstype controlled intersection, and a t-type strop-controlled intersection.]
75

© SCDOT

Figure 51. Illustration. SCDOT typical for a signalized intersection.
76

© SCDOT

Figure 52. Illustration. SCDOT typical for a four-way stop controlled intersection.
77

© SCDOT

Figure 53. Illustration. SCDOT typical for a cross-type stop controlled intersection.
78

© SCDOT

Figure 54. Illustration. SCDOT typical for a t-type stop controlled intersection.

[Figure 55 shows a street name sign typical layout.]
79

© SCDOT

Figure 55. Illustration. SCDOT street name sign typical.

STANDARD REVIEW GUIDELINES(20)

[The following is an excerpt from an internal SCDOT document containing standard review 

guidelines for reviewing installations of the treatments in this project.]

General Notes

• Speed limit signs are not to be replaced as part of this project. 

• Additional Advisory Speed plaques (such as speed plaques on “Trucks Entering Hwy” 

sign, etc.) will not be addressed as a part of this project. 

• Do not list info for retroreflective sign post panels on the plans. 

• Left Turn arrow Pavement Markings shall be installed in TWLTL’s. 

• Show all signs as proposed; do not shade anything to represent existing conditions. 

• Any non‐standard intersections, i.e., free flow interchanges or roundabouts should be sent 

to SCDOT Safety Office for verification and instruction. 

• No Pavement Markings or signs shall be applied to routes that are not state maintained. 

• All Illumination shall be upgraded to LED. 

• Yield conditions shall receive yield line and skip line pavement markings. 

• Place note “retain existing” for all non‐MUTCD signs. 
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• A photo of the current street name signs in the field trumps all spelling of the street name. 

• No signs should be placed in paved radii.

• Limit sign placement for dead ends, short routes, grid systems, etc. 

• Engineering judgment should be used when placing all warning signs.

o Under urban grid conditions cross road warning signs (or signal ahead signs) should 

not be placed.

o Signs should not be placed near driveways (where it would obstruct sight distance) or 

in citizen’s front yard.

o Signs should not be placed when an object would obscure their view (i.e., a large tree, 

shrubs, bridge columns, etc.).

o Use caution when placing signs in historic districts.

o Use caution when placing signs on interchange entrance and exit ramps.

• Guidelines for placing opposite side intersections (or signal) warning signs.

o Do not place on roadways with more than three‐lanes (three‐lanes meaning two 

through lanes and a paved median).

o On four‐lane divided highways signs should be placed in the median.

• We will not be making upgrades to existing ramps at crosswalks.

Non‐Signalized Locations

• Include estimated quantities for crosswalk, stop lines, yield lines, and skip lines on final 

sheet for non‐signalized locations. 

• Left turn Arrows and ONLY’s: 

o Less than 250’ – arrow ONLY arrow.

o 250’ or more – arrow ONLY arrow ONLY. 

• D‐Signs – Make a note of the size of the letters on the signs: 

o Only need to note of existing 8” letters on 4‐lane divided. 

• Do not show junction signs unless they are attached to a D‐sign that is being moved or

replaced. 

• Skip lines and yield lines must be shown at all yields. 

• Overhead Flashers at a stop intersection should be treated as a signalized location and 

have plans made for both pavement markings/signs and signals. All flashers will be 

replaced with LED casings and modules. NOTE: this does not include pole‐mounted 

flashers on a Stop sign, Stop Ahead sign or intersection warning sign. 
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• No NEW Flashers will be installed on Stop controlled intersections.

• All Signal Ahead, Stop Ahead, Yield and Stop signs shall be 48”. Stop and Yield signs in 

the median or in exclusive turn lanes can be 30”. Use engineering judgment to determine. 

• Intersection warning signs shall be 36”.

• Guidelines for placing street name signs on intersection warning signs: 

o On all undivided roadways street name signs should be placed on only the right side 

intersection warning sign (no opposite side sign placement).

o On four‐lane divided highways street name signs should be placed on both the right 

side and opposite side intersection warning signs (if they are both used).

o Word messages (such as “STOP” and “STOP AHEAD”) should be used sparingly. 

Only when currently in the field or engineering judgment warrants their placement 

(i.e., no warning signs or opposite side signs can be placed).

Signalized Locations

• All signal ahead signs must have street names. 

• Yield and stop lines must be behind crosswalk. Indicate on plans that the stop lines/yield 

lines need to be eradicated and new ones installed to accommodate the crosswalk. 

• Show piano lines in crosswalk only if they currently exist. 

• Ramps will be counted as 2 if crosswalks don’t connect at the corner and 1 if they do. 

• Left Turn Yield on Green (ball) sign ‐ only installed when protected/permissive left turn 

(5‐signal face, dog‐house style head). 

• There should be one 3‐signal face head located in the center of each thru lane, as a 

minimum. A 5‐signal face PT/PM head counts as one thru lane signal. 

• Skip lines and yield lines must be shown at all yields. 

• No NEW flashers will be installed at signalized locations. 

• At intersections where Ped Heads are currently installed, if the “Walk” symbol appears 

automatically, then no Push Buttons are required. 

• All Ped Heads shall be Countdown. 

• If Ped Heads are present, propose crosswalks. 

• If Push Buttons are present a crosswalk is not required. 
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• If a crosswalk is required, show ramps. If ramps cannot be installed mark on field notes 

why (i.e., catch basin). 

• If ped BUTTONS are present (or proposed) = cross walks are not required.

• If ped HEADS are present (or proposed) = cross walks are required.

• If cross walks are present (or proposed) = ped heads should be present. 

• Quantities for pedestrian equipment will be estimated based on the number of NEW 

pedestrian equipment installed. 

• Number of signal heads: With permitted/protected left ‐ 1 signal head per thru lane (5 

signal face, dog‐house style counts as one). With protected only left ‐ 4 signal face, red 

arrows for left lane + 1 signal face per thru lane.

Field Notes

• Location information (Street names, county, etc.) 

• Indicate reasons for not following regular guidelines so we know that it was not just 

overlooked... ped treatments, crosswalk, ramps, signs, etc. 

• Any information or recommendations that may be helpful that you happen to notice while 

you are in the field. 

• If “Signal Ahead” or “Stop Ahead” signs are determined not to be necessary, put note on 

field sheet as to why. 

• On field notes, make mention of conflicting signs. For example, a Stop controlled 

intersection located between a signalized intersection and its coordinating “Signal Ahead” 

sign. Locations of the proposed intersection warning signs should be discussed with 

SCDOT. 

• On field notes, note if JCT signs are black or blue. 

• Note on field sheets any landscaped areas where proposed signs are to be located as well 

as any historic districts. 

• Note on field sheets if medians or islands are pavement markings or raised. If raised, note 

if it is earthen or concrete. 

• Street name signs on Mast Arms and Span Wire to be noted in field notes but not to be 

replaced. 

Final Plans

• Name the intersections as they are in the list given by SCDOT. 
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• Consultant Company logos.

• Note NOT TO SCALE.

• Speeds from each approach. 

• North arrow.

• Any changes that are made to a signalized location must be called out with an arrow 

pointing and a note indicating a change, i.e., Install new ped treatments (with arrows to 

new ped treatments only), Install NEW near‐side head (with arrows to new near‐side 

heads only), Install NEW ramp (...), Install NEW overhead signs (...), Install NEW red 

arrow LED head (...), etc.).

• These changes may or may not require a new PE’d plan. At a minimum, they will require 

an update to the signal plan if one exists. Please supply a list of signalized locations that 

will require a new plan to be drawn and which additions there were to the plan. (See 

checklist for submitting packets.)

• Example list: 

o US1 @ SC12 – nearside head, ped treatments. 

o US1 @ S‐35 – ped treatments, ramps.

o US1 @ S‐1298 – additional thru lane head, ramps.

• Small maps are not necessary on Final plans (per example plan set for LCSI letting.pdf).

• Right of way does not need to be shown on plans. 

• Signal Equipment box is not necessary on the Final plans.

Submissions

• Round 2 and 3 signals and stops can be submitted at the same time to cover the area all at 

once. 

• Submit packets of approximately 50 locations at a time. 

• If at all possible, do not split up a single county into two different submittals; it’s best to 

have all locations in each county together. 

• Submittals should include two packets: 

o Signal group – this packet will go to the signal group for review and contain all 

necessary documents spelled out below. 

o Safety group – this packet will go to the safety group for review and contain all 

necessary documents spelled out below. 
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Checklist for Submitting Packets

Initial Signal Group: 

_____ Final plan – electronic version printout, may have pavement markings and signs on them 

_____ Field notes plan – can be hand drawn plan or notes handwritten on electronic print, make 

notes for all decisions that are not following the standard recommendations (i.e., no signal 

ahead sign because signal nearby, no sidewalk ramp because gutter under curb, no double 

up on signal ahead because of somebody’s beautiful garden, etc.) 

_____ Quantities form – can be hand written from field as long as legible, include color of signal 

head/ped head casing, whether there are mast arms or not 

_____ Electronic photos or ftp 

_____ Electronic plans on disk or ftp 

_____ Electronic list of locations needing updated signal plan 

Final Signal Group Construction Packet: 

_____ Coversheet 

_____ Quantity sheets 

_____ Drawing for each location 

_____ Construction specifications with specific location information for the district 

Safety Group: 

_____ Electronic Documents (submitted on CD is fine) ‐ Microstation file for each location, 

PDF of field notes and quantities sheet, PDF of final plan and any photos taken during the

site review 

_____ Cover sheet – this should include a list of all locations included in the packet (along with 

their signalized or stop controlled status) and all locations omitted from the packet along 

with the reason for omission (current project, interchange, etc.). Please also note the 

locations where overhead flashers (mounted on span wire or mast arms) are present. 

These will need to be included in both the signalized and safety packets. 

_____ For signalized locations: include a hard copy of the final signing and marking plan 

(without signal information), a copy of the field notes and a copy of the quantities sheet. 

_____ For stop controlled locations: include a hard copy of the final signing and marking plan, a 

copy of the field notes and a copy of the quantities sheet. 

_____ For stop controlled locations with overhead flashers: include a hard copy of the final 

signing and marking plan (include flasher information on both the safety and signal 

copies for overhead flashers only), a copy of the field notes and a copy of the quantities 

sheet.
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ACKNOWLEDGEMENTS

This report was prepared for the FHWA Office of Safety Research and Development under 

Contract DTFH61-13-D-00001. The FHWA Program and Task Manager for this project was 

Roya Amjadi. 

The research team gratefully acknowledges the participation of SCDOT for their assistance in this 

study.

87

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HRDS-20/01-18(200)E