Intersection Safety Case Study

This case study is one in a series documenting successful 

intersection safety treatments and the crash reductions that 

were experienced. Traffic engineers and other transportation 

professionals can use the information contained in the case 

study to answer the following questions:

•	 Whataresomeinexpensivetreatmentoptions toconsider that can reduce

crashesat stopsign-controlledintersections?

•	 How manycrashesdidthetreatments reduce?

•	 Arethereanyimplementation issuesassociated with these

treatments,andif so, how can theybeovercome?

FHWA-SA-09-010

U.S. Department of Transportation

Federal Highway Administration

Stop Sign-Controlled 

Intersections:

Enhanced Signs and Markings

A Winston-Salem Success Story
2 FHWA | Stop Sign-Controlled Intersections

Treatment Summary

All intersection examples used in this report are from WinstonSalem, NC. Existing intersection treatments met minimum 

Manual on Uniform Traffic Control Devices (MUTCD) standards. 

This case study examines the application of four successful 

combinations of intersection treatment enhancements that 

reduced crashes at stop sign-controlled intersections:

1) Larger (30-inch) stop signs with “Stop Ahead” advance traffic 

control sign and added pavement markings (double-yellow 

centerline and stop bars) to help delineate traffic at the 

intersection 

2) Added pavement markings (double-yellow centerline and 

stop bars) to existing (24-inch) stop signs

3) Additional and larger (30-inch) stop signs 

4) Additional and larger (30-inch) stop signs and added pavement 

markings (double-yellow centerline and stop bars).

(Note: Complete tables for each set of enhanced treatments appear at the end of this document.)

“The benefits to the city are 

clear. By taking an active 

role in roadway safety, and 

using simple low-cost traffic 

engineering solutions, WinstonSalem has created a much 

safer driving environment for 

motorists. These improvements 

will continue to yield positive 

results as the city population 

grows and average daily traffic 

(ADT) continues to rise.” 

Stanley F. Polanis 

Director of Transportation 

City of Winston-Salem, NC

Objective

The following case study showcases four successful and effective low-cost strategies that measurably improved safety at 

stop sign-controlled intersections in Winston-Salem, NC. The treatments included adding larger and additional stop signs, 

“Stop Ahead” advance traffic control signs, and enhanced pavement markings.

Introduction

One-third of all intersection crashes in the United States, and more than 40 percent of fatal 

crashes, occur at stop sign-controlled intersections1

. A major problem is failure to see the stop 

sign and/or to know where to stop. Past research has shown that simple, low-cost treatment 

enhancements such as increasing the visibility of stop signs, and/or adding pavement 

markings, can improve driver compliance with the stop sign and reduce the number and 

severity of crashes2

.
FHWA | Stop Sign-Controlled Intersections 3

Results

1. Larger (30-inch) stop signs with “Stop Ahead” 

advance traffic control sign and added 

pavement markings

Problem: Drivers were violating stop-controls in four

Winston-Salem stop sign-controlled intersections due 

to poor visibility of the signs and markings, leading to 

higher numbers of crashes at these intersections.

Solution: The city sought to reduce crashes by 

improving visibility of the stop-controls through 

enhanced low-cost signs and markings that were 

easy to implement. The posted speed limit on all the 

approaches was 35 mph except for the intersection of 

Buena Vista Road and Oaklawn Avenue which was 

25 mph. The updated countermeasures included:

•	 Replaced the existing 24-inch stop signs with larger

30-inch signs (the MUTCD specifies 24-inch as the 

minimum size).

•	 Placed stop bars, consisting of a solid 12-inch white

line extending across the approach lanes, to indicate

the point behind which vehicles are required to stop,

in compliance with a stop sign.

•	 Placed a short segment of double-yellow centerlines

(the two-directional no-passing zone markings, up to

50 feet in length) prohibiting crossing the centerline 

markings for passing in either direction.

•	 Installed“Stop Ahead” advance traffic control signs

(30-inch) on the approaches for two of the 

intersections (Cameron and Ivy Streets).

These relatively inexpensive treatments have proven 

effective in mitigating crashes and enhancing safety. 

The city experienced an average crash reduction 

of 56.9 percent per year at these intersections. 

“Stop Ahead” signs, although not independently 

evaluated, seem to have contributed to the crash 

reductions. See Appendix A for a more detailed tabular 

summary of these treatments.

Evaluation Methodology

This case study examines 16 stop sign-controlled intersections in Winston-Salem, NC, with a high incidence of crashes (many 

with injuries) due to driver violation of the stop-control condition.* Crash reduction results were based on a review of “before 

and after” data from these intersections during a minimum of three years, between 1988—2002.** (The “before” and “after” 

observation periods ranged between 39-55 months depending on the intersection).

* These intersections did not experience a significant number of fatalities.

**Note that crash reduction averages in this report reflect the percent reduction 

per year based on the difference between the total number of “before” and 

“after” crashes. Injury reductions per year are noted where supporting data 

was available.

2. Added pavement markings (double-yellow centerline 

and stop bars) to existing (24-inch) stop signs

Problem: Four two-way, two-lane stop sign-controlled 

intersections of minor arterial roads with a posted speed limit of 

35 mph or less were experiencing a high number of crashes. Stop 

signs were in place, visible and in good condition. However, there 

were no pavement markings on the approaches.

Table 1: Larger (30-inch) stop signs with “Stop Ahead” advance traffic control sign 

and added pavement markings (treatment data and results)

Treatment Location

Reduction 

in Crashes 

Per Year

•	 30-inch stop signs

(replaced 24-inch signs)

•	 “Stop Ahead” advance

traffic control sign

•	 Double-yellow centerline

and stop bars

•	 30-inch stop signs

(replaced 24-inch signs)

•	 “Stop Ahead” advance

traffic control sign

•	 Double-yellow centerline

and stop bars

•	 30-inch stop signs

(replaced 24-inch signs)

•	 Double-yellow centerline

and stop bars

•	 30-inch stop signs

(replaced 24-inch signs)

•	 Double-yellow centerline

and stop bars

Twelfth Street & 

Cameron Avenue 

(Stop sign on 

Cameron Avenue)

Thirtieth Street &

Ivy Avenue (Stop

sign on Ivy Avenue)

Twentieth Street & 

Thurmond Street 

(Stop sign on 

20th Street)

75%

90.7%

74.6%

6.7%

Average 56.9%

Buena Vista Road

& Oaklawn Avenue 

(All-way stop)
Treatment Location

Reduction 

in Crashes 

Per Year

Double-yellow centerline and 

stop bars

Double-yellow centerline and 

stop bars

Double-yellow centerline and 

stop bars

Double-yellow centerline and 

stop bars

Second Street and Spring 

Street (Stop sign on 

Spring Street)

Cameron Avenue and 

Mt. Zion Place (Stop sign

on Mt. Zion Place)

Thirtieth Street & Bon 

Air Avenue (Stop sign 

on Bon Air Avenue)

Brindle Street and 

Sprague Street/Willard 

Road (Stop sign on

Brindle Street)

51.4%

83.3%

40%

41.7%

Average 52.7%

Treatment Location

Reduction 

in Crashes 

Per Year

Dual 30-inch stop signs

Dual 30-inch stop signs

Dual 30-inch stop signs

Dual 30-inch stop signs

Reynolds Road & West

End Blvd (Stop sign on 

West End Blvd)

Broad Street & Brookstown 

Avenue (Stop sign on 

Brookstown Avenue)

Third Street & Cameron 

Avenue (Stop sign on 

Cameron Avenue)

Sixteenth Street & Ivy

Avenue (Stop sign on 

16th Street)

71.4%

33.8%

80%

28.6%

Average 48.3%

Table 3: Additional and larger (30-inch) stop signs (treatment data and results)

Table 2: Added pavement markings (double-yellow centerline and stop bars) to 

existing (24-inch) stop signs (treatment data and results)

4 FHWA | Stop Sign-Controlled Intersections

Solution: The city sought to reduce crashes by clarifying 

the proper stopping position for vehicles through 

enhanced pavement markings that were easy to 

implement. The updated countermeasures included:

•	 Placing a short interval of double-yellow centerlines

(up to 50-feet).

•	 Placing stop bars (12-inches wide).

These pavement marking treatments were designed to 

make the intersection and proper stop position more 

conspicuous to drivers, and thereby increase the driver 

alertness to the intersection control. These simple, lowcost countermeasure enhancements significantly reduced 

injury and overall crashes, as shown in the table to the 

right. These countermeasures resulted in an average 

crash reduction of 52.7 percent and reduced injuries 

by 70 percent per year. See Appendix A for a more 

detailed tabular summary of these treatments.

3. Additional and larger (30-inch) stop signs 

Problem: Four two-way, two-lane stop sign-controlled 

intersections of minor arterial roads with a posted speed 

limit of 35 mph or less were experiencing a high number 

of crashes. The causes of these crashes could not be 

readily determined from the crash reports—i.e., it was not 

clear whether motorists were running the stop signs or 

stopping but then pulling into the path of an oncoming 

vehicle.

Solution: The city decided to visually emphasize the 

required stop by:

•	 Placing an additional stop sign on the left side of the stop

approach roadway. 

•	 Using larger (30-inch) stop signs for the intersection.

These countermeasure enhancements were aimed to 

better alert drivers and thus enhance their ability to safely 

navigate through the intersection. At these locations the 

city experienced an average crash reduction of 48.3 

percent per year. See Appendix A for a more detailed 

tabular summary of these treatments.

4. Additional and larger (30-inch) stop signs with 

added pavement markings

Problem: Four two-way, two-lane stop sign-controlled 

intersections of minor arterial roads with a posted speed 

limit of 45 mph or less were experiencing a high number 

of crashes. While existing stop signs were in place, drivers 

did not always have an adequate view of approaching 

traffic from the cross-streets.

Solution: The city decided to implement a set of low-cost 

signs and markings countermeasure enhancements to 

heighten the awareness of the intersection control and 

Double-yellow centerline and stop bars added to existing (24-inch) stop sign.
Treatment Location

Reduction 

in Crashes 

Per Year

•	Dual 30-inch stop signs

•	Double-yellow centerline

and stop bars 

•	Dual 30-inch stop signs

•	Double-yellow centerline

and stop bars 

•	Dual 30-inch stop signs

•	Stop bars

•	Dual 30-inch stop signs

•	Stop bars

Twentieth Street & 

Cherry Street (Stop sign 

on Cherry Street)

Greenwich Road &

Knollwood Street/Hanover 

Arms Court (Stop sign on 

Greenwich Road)

Indiana Avenue &

Motor Road (Stop sign

on Motor Road)

Fifth Street & Lowery 

Court (Stop sign on 

Lowery Court)

78.6%

66.7%

63.6%

50%

Average 65.9%

Table 4: Additional and larger (30-inch) stop signs with added pavement markings 

(treatment data and results)

FHWA | Stop Sign-Controlled Intersections 5

Summary of Results

The “before” conditions at all 16 of these intersections met minimum 

MUTCD standards. The safety enhancements discussed in this 

case study were added to reduce crashes. The combinations of 

enhanced countermeasures installed in these Winston-Salem 

stop sign-controlled intersections reduced total crashes at these 

intersections by approximately 55 percent, and total injuries by 

an average of 70 percent per year. The average reductions in 

crashes achieved by the treatments are consistent with the overall 

crash reductions mentioned in the Desktop Reference for Crash 

Reduction Factors by the Department of Transportation (USDOT) 

Federal Highway Administration (FHWA)8. The findings also indicate 

that installing stop signs larger than the minimum size of 24-inches, 

as specified in the MUTCD, helps to increase driver awareness of the 

stopped condition.

References

1)	 InsuranceInstitutefor HighwaySafety, Volume37, No9, October26,2000.

2)	 Douglas A. Ripley.“QuantifyingtheSafety BenefitsofTrafficControl Devices – Benefit-Cost AnalysisofTrafficSign

Upgrades.”Mid-ContinentTransportation Research Symposium, Ames, Iowa, August2005.

3)	 BrigliaJr.,P.m. (1982). An evaluation of4-waystopsign-control. ITEJournal,52,16-19.

4)	 Hauer,E.,andLovell, J. (1986).Thesafetyaffectof conversion toall-waystop-control.Transportation Research

Record,vol.1068,103-107.

5)	 Gattis, J.“SupplementalSigningforStopSigns.”Universityof Arkansas.Fayetteville, AR. October1995.

6)	 Von Houten, R., & Retting, R.A. (2001). Increasing motorist complianceandcaution at stopsigns. Journalof Applied

Behavior Analysis,34,185-193.

7)	 Retting. R.A., Helen B.Weinstein, Mark G.Solomon.“Analysisof motorvehiclecrashesat stopsigns in four U.S.

cities”. JournalofSafety Research 34(2003)485-489.

8)	 Desktop ReferenceforCrash Reduction Factors,FHWA-SA-07-015, USDOTFHWA September2007(Pg37,38).

9)	 NCHRP Report500.Volume05: A Guidefor Addressing UnsignalizedIntersection Collisions,v-73,Transportation

Research Board,Washington, D.C,2003.

encourage drivers to stop in a position that provided 

an effective view of approaching traffic. The improved 

countermeasures included:

•	 Placing an additional stop sign on the left side of the

stop approach roadway and use of larger (30-inch) 

stop signs for the intersection at all stop sign-controlled 

approaches.

•	 Placing 12-inch stop bars at all stop sign-controlled

approaches.

•	 Installation of short segments of double-yellow

centerlines (up to 50-feet) at two of the approaches 

(Cherry Street and Greenwich Road).

At these locations the city experienced an average 

crash reduction of 65.9 percent with injuries down by 

65 percent per year as well. See Appendix A for a more 

detailed tabular summary of these treatments.

Discussion

Implementation Issues

Winston-Salem experienced no implementation issues 

with these countermeasures.

Cost

The costs for implementing the countermeasure 

enhancements were low: Approximately $350 for a 

30-inch stop sign or a “Stop Ahead” advance warning 

sign, and approximately $1,250 for the enhanced 

pavement markings (centerlines and stop bars).

Time Frame

The signing and pavement marking treatments were 

implemented within 3 months.

Effectiveness 

The combinations of enhanced treatments discussed 

have been effective in reducing crashes at these stop 

sign-controlled intersections. The city attributes its success 

to targeting appropriate intersection approaches that 

would benefit from enhanced treatments—specifically, 

intersections where conditions allow an approaching driver 

to see the enhanced treatments at a distance, in time to 

respond. In addition, the city was committed to adequately 

maintain the signs and markings.

Additional (left and right side of street) and larger (30-inch) stop signs with stop bars.
Appendix A

Treatment Location

Percent 

Reduction in 

Crashes/Year 

(Injuries/Year)

Before

MonthsCrashesFatalitiesInjuriesMonthsCrashesFatalitiesInjuries

After Implementation 

Date

•	30-inch stop signs

(replaced 24-inch signs)

•	“Stop Ahead”advanced

traffic control sign

•	Double-yellowcenterline

and stop bars

•	30-inch stop signs

(replaced 24-inch signs)

•	Double-yellow centerline

and stop bars

Twelfth Street 

and Cameron 

Avenue 

(Stop sign 

on Cameron 

Avenue)

Apr-88 52

50

52

50

12

15

3

14

0

0

0

N/A

6

9

N/A

N/A

75%

(unknown)

6.7%

(unknown)

•	30-inch stop signs

(replaced 24-inch signs)

•	“Stop Ahead”advanced

traffic control sign

•	Double-yellowcenterline

and stop bars

51 11 0 11 50 1 0 N/A 90.7%

(unknown)

Thirtieth 

Street and Ivy

Avenue (Stop 

sign on Ivy

Avenue)

Apr-89

•	30-inch stop signs

(replaced 24-inch signs)

•	Double-yellow centerline

and stop bars

48 7 1 12 54 2 N/A N/A 74.6%

(unknown)

Buena Vista 

Road and

Oaklawn 

Avenue (Allway stop)

Dec-87

Twentieth 

Street and 

Thurmond 

Street (Stop 

sign on 20th 

Street)

Mar-91

Double-yellow centerline 

and stop bars

Second Street 

and Spring 

Street (Stop 

sign on Spring 

Street)

Cameron 

Avenue and 

Mt. Zion Place

(Stop sign on 

Mt. Zion Place)

Thirtieth Street 

& Bon Air 

Avenue (Stop 

sign on Bon Air 

Avenue)

Brindle Street 

and Sprague 

Street/Willard 

Road (Stop

sign on Brindle 

Street)

Double-yellow centerline 

and stop bars

Double-yellow centerline 

and stop bars

Double-yellow centerline 

and stop bars

46

39

49

50

22

6

5

12

0

0

0

0

6

6

7

14

43

39

49

50

10

1

3

7

N/A

0

0

0

N/A

0

2

6

83.3% 

(100%)

40% 

(71%)

51.4%

(unknown

41.7% 

(57%)

Nov-89

Apr-02

Jul-02

Jun-02

1. Larger (30-inch) stop signs with “Stop Ahead” advance traffic control sign and added pavement markings 56.9%

2. Added pavement markings (double-yellow centerline and stop bars) to existing (24-inch) stop signs 52.7% (70%)

6 FHWA | Stop Sign-Controlled Intersections
Treatment Location

Percent 

Reduction in 

Crashes/Year 

(Injuries/Year)

Before

MonthsCrashesFatalitiesInjuries

MonthsCrashesFatalitiesInjuries

After Implementation 

Date

Dual 30-inch stop signs

•	Dual 30-inch stop signs

•	Double-yellowcenterline

and stop bars 

Twentieth 

Street & 

Cherry Street 

(Stop sign on 

Cherry Street)

Greenwich 

Road &

Knollwood 

Street/Hanover 

Arms Court 

(Stop sign on 

Greenwich 

Road)

Fifth Street & 

Lowery Court 

(Stop sign on 

Lowery Court)

•	Dual 30-inch stop signs

•	Double-yellowcenterline

and stop bars 

•	Dual 30-inch stop sign

•	Stop bars

Dual 30-inch stop signs

Dual 30-inch stop signs

Dual 30-inch stop signs

Reynolds Road

& West End 

Blvd (Stop sign 

on West End 

Blvd)

Dec-88 47

52

47

55

44

44

55

47

51

47

55

14

37

10

7

14

6

10

4

24

2

5

0

0

0

0

0

0

0

N/A

N/A

N/A

0

5

13

3

4

12

5

8

44

44

55

3

2

5

N/A

0

0

N/A

2

3

N/A

N/A

N/A

0

66.7% 

(60%)

71.4%

(unknown)

78.6%

(unknown)

33.8%

(unknown)

80%

(unknown)

28.6%

(100%)

50% 

(62%)

Broad Street 

& Brookstown 

Avenue 

(Stop sign on 

Brookstown 

Avenue)

Apr-93

Third Street 

& Cameron 

Avenue 

(Stop sign 

on Cameron 

Avenue)

Nov-98

Sixteenth 

Street & Ivy

Avenue 

(Stop sign on 

16th Street)

Jul-02

Aug-89

May-02

Indiana

Avenue & 

Motor Road

(Stop sign on 

Motor Road)

•	Dual 30-inch stop signs

•	Stop bars

43 11 0 7 43 4 0 2 63.6% 

(71%)

Jul-02

Jun-02

3. Additional and larger (30-inch) stop signs

4. Additional and larger (30-inch) stop signs with added pavement markings

48.3%

65.9% (65%)

FHWA | Stop Sign-Controlled Intersections 7
FHWA-SA-09-010 June 2009

U.S. Department of Transportation

Federal Highway Administration

For More Information

Ed Rice

Intersection Safety Team Leader, 

FHWA Office of Safety

202.366.9064

ed.rice@dot.gov

Stanley F. Polanis

Director of Transportation, 

City of Winston-Salem, NC

336.747.6867

stanp@cityofws.org

Visit FHWA’s intersection safety web site to download this and 

other case studies highlighting proven intersection safety 

treatments from across the country:

http://safety.fhwa.dot.gov/intersection