TECHBRIEF Safety Evaluation of Turning 

Movement Restrictions at 

Stop-Controlled Intersections

FHWA Publication No.: FHWA-HRT-17-065

FHWA Contact: Roya Amjadi, HRDS-20, (202) 493-3383, 

roya.amjadi@dot.gov

This document is a technical summary of the Federal 

Highway Administration report Safety Effects of 

Turning Movement Restrictions at Stop-Controlled 

Intersections (FHWA-17-064).

Objective

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 goal of the 

DCMF program is to save lives by identifying new 

safety strategies that effectively reduce crashes 

and to 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 provide technical 

feedback on safety improvements to the DCMF 

program and implement new safety improvements 

to facilitate evaluations. These States are members 

of the Evaluation of Low-Cost Safety Improvements 

Pooled Fund Study, which functions under the 

DCMF program. 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research
2

This study evaluated the safety 

effects of converting three-legged, full 

movement intersections to right-in/

right-out (RIRO) operations using 

physical barriers. The intent of this 

strategy is to reduce the frequency and 

severity of crashes by eliminating 

left turns into and out of target 

intersections, which are the highest 

severity conflicts at an intersection.

Studies have explored various access 

management techniques and the 

installation of median barriers at the 

corridor level. However, no information 

is available to quantify the safety 

effects of restricting left turns at specific 

intersections and the effects of shifting 

traffic to downstream intersections. 

Introduction

Improving access management near 

unsignalized intersections and reducing the frequency and severity of 

intersection conflicts are two objectives to improve unsignalized intersection safety in the National Cooperative 

Highway Research Program (NCHRP) 

Report 500 Guide, Volume 5: A Guide for 

Addressing Unsignalized Intersection 

Collisions.

(1) Restricting or eliminating 

turning maneuvers is a key element of 

several related strategies.

Turning movement restrictions are a type 

of access management strategy used 

to improve the safety of stop-controlled 

intersections and driveways. Restricted 

and prohibited turn movements reduce 

the number of turning conflict points at 

intersections, which are generally known 

to reduce crash risk.(2) RIRO eliminates left 

turns into and out of the minor road. A 

positive or curbed median barrier on the 

mainline is a common strategy, creating 

an RIRO at minor road stop-controlled 

intersections. The median physically 

blocks left turns into and out of the 

intersecting street. Figure 1 presents 

a photograph of a stop-controlled 

intersection with RIRO operations.

While restricting turns is expected to 

provide a safety improvement in most 

cases, limited information is available 

about the quantitative safety effects 

of these practices and their effects 

on downstream intersections. The 

full report serves to address the need 

for research into the safety effects of 

turning movement restrictions at stopcontrolled intersections.

A literature review focused on the 

safety effects of RIRO operations, which 

are most commonly implemented with 

a raised median preventing all left 

turns. Most or all evaluations to date 

have examined corridor and segment 

impacts of installing raised medians 

rather than the effects of turning 

restrictions at treated and adjacent full 

movement intersections.

Research by Schultz, Braley, and Boschert 

in Correlating Access Management 

to Crash Rate, Severity, and Collision 

Type indicated the presence of a raised 

median corresponded to a reduction of 

1.23 crashes per million vehicle miles 

traveled (MVMT).(3) In addition, raised 

medians were negatively correlated with 

right-angle collisions.
3

In NCHRP Report 420, Gluck, Levinson, 

and Stover also investigated the 

relationship between median type and 

crash rates.(4)

NCHRP Report 395 compared outcomes 

from a number of crash prediction 

models developed by researchers.(5) A 

composite finding suggested that, in 

general, a raised median is safer than 

undivided roadways, especially on roads 

with more than 20,000 vehicles per day.

Eisele and Frawley, in “Estimating 

the Safety and Operational Impact 

of Raised Medians and Driveway 

Density: Experiences From Texas and 

Oklahoma Case Studies,” investigated 

the relationship between access 

density and crash rate for raised median 

and nonraised median corridors 

separately.(6) Both relationships were 

positively correlated, but the trend 

line was slightly steeper for nonraised 

median corridors than raised median 

corridors. The researchers concluded 

that the reduced slope of the regression 

line for raised median corridors demonstrated there were relatively low crash 

rates in corridors with raised medians 

due to reduced conflict points.

Hallmark et al. indicated in the 

Toolbox to Assess Tradeoffs Between 

Safety, Operations, and Air Quality for 

Figure 1. Photo. RIRO stop-controlled intersection.

© VHB
4

Intersection and Access Management 

Strategies: Final Report that an FHWA 

evaluation involving data from seven 

States suggested raised medians 

reduced crashes at least 40 percent in 

urban settings.(7)

Methodology

This research examined the safety 

impacts of restricting turning movements to RIRO from full movements 

at stop-controlled intersections 

in California. The objective was to 

estimate the safety effectiveness of 

this strategy as measured by crash 

frequency. Target crash types included 

the following:

• Total: all crashes within 100 ft of an 

intersection (all types and severities 

combined).

• Intersection-related: as termed by 

the reporting officer, all crashes 

within 100 ft of an intersection (all 

types and severities combined).

• Fatal and injury: all injury 

crashes defined as “intersectionrelated” (fatal, incapacitating, 

non-incapacitating, and possible 

injuries).

• Multivehicle: all multivehicle 

crashes defined as “intersectionrelated” (all types and severities 

combined). (Note: all “intersectionrelated” crashes included multiple 

vehicles; therefore, the project team 

dropped this category from the 

remainder of the analysis as it was 

redundant.)

A further objective was to address the 

following ways in which effects might 

have varied:

• Lane configuration of intersection 

(i.e., four mainline lanes and 

two cross-street lanes versus six 

mainline lanes and two cross-street 

lanes).

• Level of traffic volume.

• Design speed on the major route.

• Type of traffic control at downstream intersections (i.e., signalized 

or minor road stop control).

• Presence of turn lanes at downstream intersections.

The evaluation of overall effectiveness 

included consideration of installation 

costs and crash savings in terms of the 

B/C ratio.

For strategies such as restricting turning movements, there is often insufficient information to determine the exact 

location and timing of the treatment, 

which precludes the use of an empirical 

Bayes before–after study design. Using 

FHWA’s A Guide to Developing Quality 

CMFs, the project team determined that 

a rigorous cross-sectional study design 

would serve as a suitable alternative.(8) 

A cross-sectional study design is a type 

of observational study used to analyze 

a representative sample at a specific 

point in time. Using this method, 

researchers estimate the safety effect 

by taking the ratio of the average crash 

frequency for two groups—one with the 
5

feature of interest and the other without 

the feature of interest. In this case, the 

feature of interest was RIRO operations. 

For this method to work, the two groups 

should be similar in all regards except 

for the feature of interest.

Finding two groups of subjects that fit 

this criterion is difficult to accomplish 

in practice. The project team adopted 

multivariate regression to develop 

the statistical relationships between 

the dependent variables and a set 

of predictor variables. In this case, 

crash frequency was the dependent 

variable, and the team considered 

several predictor variables, including 

treatment presence, traffic volume, 

and other roadway characteristics. 

The project team estimated regression 

coefficients during the modeling 

process for each predictor variable. 

The coefficients represent the expected 

change in crash frequency due to a unit 

change in the predictor variable, with all 

else being equal.

The project team applied generalized 

linear modeling techniques to develop 

the crash prediction models and specified a log-linear relationship using a 

negative binomial error structure. The 

negative binomial error structure has 

advantages over the Poisson distribution in that it allows for overdispersion 

of the variance that is often present in 

crash data.

The full report contains a detailed explanation of the methodology, including 

a description of how the estimate of 

safety effects for target crashes was 

calculated.

Results

Results are presented in two parts. 

The first part contains aggregate results, 

and the second part is based on a disaggregate analysis that sought to identify 

those conditions under which the strategy is most effective.

Aggregate Analysis

Aggregate results indicated reductions 

for all crash types analyzed (i.e., total, 

all intersection-related, and fatal and 

injury intersection-related) at the stopcontrolled intersections with RIRO 

operations compared to intersections 

with full movement (table 1). Reductions were statistically significant at 

the 95-percent confidence level for all 

crash types. Crash modification factors (CMFs) for total, all intersectionrelated, and fatal and injury 

intersection-related crashes, were 

0.55, 0.32, and 0.20, respectively.

Crash migration is a potential issue 

related to restricted turning movements 

at a given access point. This occurs when 

crashes at a treated site shift to another 

site. While RIRO operations eliminate 

left turns at the subject location, U-turn 

movements and related crashes potentially increase at the next intersection 

downstream that allows U-turns. As 

such, at a full movement signalized intersection within a corridor, there could 

be an increase in U-turn movements 

from both directions along the mainline 
6

if the stop-controlled intersections are 

converted to RIRO along the corridor. 

To account for this in this analysis, only 

U-turns at one intersection (the downstream intersection) were paired with 

the RIRO intersection because U-turn 

movements at the upstream intersection 

were paired with another RIRO intersection, and the effect was counted. This 

avoided double counting U-turns and 

overestimating the effect.

Table 2 and table 3 present the estimated CMFs and related standard errors 

for each target crash type and traffic 

control type combination at the downstream intersections. CMFs represent 

the change in crashes at the immediate 

downstream full movement intersection 

from RIRO locations compared to an 

immediate downstream full movement 

intersection from full movement locations. 

Disaggregate Analysis

The disaggregate analysis sought 

to identify those conditions under 

which the strategy was most effective. 

The project team considered several 

variables in the disaggregate 

analysis, including major and minor 

road traffic volume, number of 

mainline lanes, and design speed. 

Variable Total Intersection-Related Fatal and Injury

Estimate of CMF

(parent RIRO = 1; 

downstream SIGNAL = 1)

1.10 1.02 0.94

Standard error of CMF

(parent RIRO = 1; 

downstream SIGNAL = 1)

0.20 0.24 0.26

Table 2. Results for urban signal control intersections downstream from stop-controlled intersections with RIRO 

compared to full movement.

Variable Total Intersection-Related Fatal and Injury

Observed crashes per 

site-year with RIRO 0.86 0.21 0.06

Observed crashes per siteyear with full movement 1.39 0.68 0.38

Estimate of CMF 0.55* 0.32* 0.20*

Standard error of CMF 0.09 0.08 0.07

Table 1. Results for urban, three-legged, stop-controlled intersections with RIRO compared to full movement.

*Indicates statistically significant results at the 95-percent confidence level.
7

The multivariable regression models 

included interaction terms to 

investigate the potential differential 

effects of RIRO with respect to the 

interacted variable. For example, the 

interaction term for major road traffic 

volume and RIRO was the product 

of the two variables. A statistically 

significant interaction term indicated 

an apparent differential effect of RIRO 

across different traffic volumes.

The results indicated that interaction 

terms were not statistically significant 

at even an 80-percent confidence level 

for any of these interactions between 

RIRO and major road traffic volume, 

minor road traffic volume, design 

speed, and number of lanes on the 

mainline. This was consistent for all 

crash types.

Based on the disaggregate results, it 

did not appear that RIRO operations 

had differing effects for different levels 

of traffic on both mainline and cross 

street, design speed, or number of 

lanes on the mainline.

Economic Analysis

For this analysis, the project team used 

sites with physical barriers to provide 

the RIRO operations. Other agencies 

might have used other means to implement RIRO operations, such as cable 

barrier, rigid barrier, or with signs only.

For estimating treatment costs, the 

project team’s assumptions included 

an average median width of 4 ft at an 

average cost of $6 per sq ft.(9) (Note: the 

median may be 6 ft wide for a portion 

of the length between full movement 

intersections with narrow sections at 

the ends to facilitate turning lanes.)

Given these assumptions, implementation cost was approximately $24 per 

linear ft (or $126,720 per mi). For cost 

estimation purposes, the project team 

assumed a distance of 1,210 ft, which 

represented the average distance 

between the centers of signalized intersections evaluated in this study, minus 

100 ft to account for the intersection 

area. Given these assumptions, the 

average cost per installation between 

Variable Total Intersection-Related Fatal and Injury

Estimate of CMF (parent 

RIRO = 1; downstream 

SIGNAL = 0)

1.64* 2.55** 1.56

Standard error of 

CMF (parent RIRO = 1; 

downstream SIGNAL = 0)

0.33 0.39 0.45

*Indicates statistically significant result at the 90-percent confidence level.

**Indicates statistically significant result at the 95-percent confidence level.

Table 3. Results for urban stop-controlled intersections downstream from stop-controlled intersections with RIRO 

compared to full movement.
8

signalized intersections was approximately $26,500.

The analysis assumed the useful service 

life for safety benefits was 20 years. 

Based on Michigan and Ohio data, 

annual maintenance costs per lanemile for area mowing, curb sweeping, 

and curb and gutter repairs were less 

than $60 annually. Given the relatively 

low cost for these services, the analysis 

assumed these costs were negligible 

compared to the installation costs over 

the service life.(10)

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 7 percent to calculate the present value benefits and 

costs of the treatment over the service 

life.(11) With this information, the analysis computed the capital recovery factor as 10.59.

For benefit calculations, the project 

team used the most recent FHWA mean 

comprehensive crash costs disaggregated by crash severity and location 

type as a base.(12) FHWA developed these 

costs based on 2001 crash costs, and 

the unit cost (in $U.S. 2001) for fatal 

and injury crashes was $158,177. At the 

time of analysis, this was updated to 

2015 dollars by applying the ratio of 

the U.S. Department of Transportation 

(USDOT) 2015 value of a statistical life 

of $9.4 million to the 2001 value of 

$3.8 million.(12,13) Applying this ratio of 

2.47 to the unit cost for fatal and injury 

crashes resulted in an aggregate 2015 

unit cost of $391,280.

To estimate the safety benefits of 

implementing RIRO operations, the 

project team analyzed two hypothetical 

sections: (1) a single stop-controlled 

intersection leading to a signalized 

intersection, and (2) a more complex 

corridor example with multiple 

intersections. The team calculated 

the net change in crashes by adding 

the expected change in crashes at 

RIRO intersections to the expected 

change in crashes at the downstream 

intersections. In some cases, there 

was an expected increase in crashes 

at downstream intersections from 

conversion of upstream full movement 

stop-controlled intersections to RIRO 

intersections.

The project team calculated the annual 

economic benefits by multiplying the 

crash reduction per site per year by the 

average cost of a fatal and injury crash. 

The team calculated the B/C ratio of 

9.6:1 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 

0.55 and 1.38 times the recommended 

2015 value.(13) These factors can be 

applied directly to the estimated B/C 

ratios to get a range from 5.4:1 to 13.5:1. 

Results of this hypothetical example 

suggest the RIRO strategy, with reasonable assumptions in cost, service life, 

and value of a statistical life, can be cost 

effective for reducing fatal and injury 
9

Variable Total All Intersection-Related Fatal and Injury

Estimate of CMF 0.55* 0.32* 0.20*

Standard error of CMF 0.09 0.08 0.07

*Indicates statistically significant results at the 95-percent confidence level.

crashes at similar stop-controlled intersections; however, there is a need to 

consider potential costs and benefits 

with site-specific values on a case-bycase basis.

Summary and Conclusions

The objective of this study was to 

undertake a rigorous cross-sectional 

evaluation of the safety effectiveness—

as measured by crash frequency—of 

turning movement restrictions at stopcontrolled intersections. The study 

compared RIRO to full movement 

access using California data to examine 

effects for specific crash types: total, 

intersection-related, and fatal and 

injury intersection-related crashes. 

Based on the aggregate results, table 4 

presents recommended CMFs for 

various crash types for urban, threelegged, stop-controlled intersections 

with RIRO compared to full movement. 

Aggregate results indicated reductions 

for all crash types analyzed, and all 

reductions were statistically significant 

at the 95-percent confidence level.

While results indicated crash reductions 

at stop-controlled intersections with 

RIRO compared to full movement, there 

is a need to consider the potential for 

crash migration in determining net 

benefits. Table 5 and table 6 present the 

recommended CMFs for various crash 

types for downstream intersections from 

urban, three-legged, stop-controlled 

intersections with RIRO compared 

to full movement. Table 5 presents 

results for downstream intersections 

with signal control. Changes were not 

statistically significant, even at the 

90-percent confidence level; however, 

there was potential for increased total 

and intersection-related crashes at 

downstream signalized intersections. 

Table 6 presents the results for 

downstream intersections with stop 

control. Increases were statistically 

significant at the 90-percent confidence 

level for total crashes and statistically 

significant at the 95-percent confidence 

level for intersection-related crashes. 

All three CMFs indicated potential for 

increased total, intersection-related, 

and fatal and injury intersection-related 

crashes at downstream stop-controlled 

intersections.

The disaggregate analysis sought 

to identify those conditions under 

which the strategy was most effective. 

Table 4. Recommended CMFs for urban, three-legged, stop-controlled intersections with RIRO compared to 

full movement.
10

Variable Total All Intersection-Related Fatal and Injury

Estimate of CMF 1.64* 2.55** 1.56

Standard error of CMF 0.33 0.39 0.45

Variables of interest included number of 

lanes on the mainline and cross street, 

traffic volumes, and design speed. 

For major road traffic volume, minor 

road traffic volume, and design speed, 

the disaggregate analysis indicated 

no statistically significant differences 

in effects for various levels of these 

variables.

The B/C ratio for converting a hypothetical stop-controlled intersection 

from full movement to RIRO, estimated 

with conservative cost and service 

life assumptions, and considering 

the change in fatal and injury crashes 

with potential for crash migration at 

a downstream signalized intersection, 

was 9.6:1. With USDOT recommended 

sensitivity analysis, these values 

could range from 5.4:1 to 13.5:1. The 

economic analysis was based on a 

single hypothetical stop-controlled 

intersection and a downstream 

signalized intersection. The RIRO 

operation was more cost beneficial 

when the target stop-controlled 

intersections had relatively high 

safety risk compared to downstream 

intersections, particularly downstream 

stop-controlled intersections. While 

these results suggest the strategy can 

be cost effective in reducing crashes at 

stop-controlled intersections, potential 

costs and benefits need to be analyzed 

on a case-by-case basis with sitespecific values.

Table 6. Recommended CMFs for urban stop-controlled intersections downstream from stop-controlled intersections with 

RIRO compared to full movement.

Variable Total All Intersection-Related Fatal and Injury

Estimate of CMF 1.10 1.02 0.94

Standard error of CMF 0.20 0.24 0.26

Note: Apply CMFs once for each upstream intersection converted from full movement to RIRO.

Note: Apply CMFs once for each upstream intersection converted from full movement to RIRO.

*Indicates statistically significant result at the 90-percent confidence level.

**Indicates statistically significant result at the 95-percent confidence level.

Table 5. Recommended CMFs for urban signalized intersections downstream from stop-controlled intersections with 

RIRO compared to full movement.
11

REFERENCES

1. Neuman, T.R., et al. (2003). Guidance 

for the Implementation of AASHTO 

Strategic Highway Safety Plan: 

Volume 5: A Guide for Addressing 

Unsignalized Intersection Collisions, National Cooperative 

Highway Research Program Report 

500, National Academies Press, 

Transportation Research Board, 

Washington, DC.

2. Simodynes, T., Welch, T., and 

Kuntemeyer, M. (2000). Effects of 

Reducing Conflict Points on Reducing 

Accidents (Abstract), Third National 

Access Management Conference, p. 

141, Federal Highway Administration, 

Washington, DC.

3. Schultz, G.G., Braley, K.T., and 

Boschert, T. (2008). “Correlating 

Access Management With Crash 

Rate, Severity, and Collision Type,” 

Presented at the 84th Annual Meeting 

of the Transportation Research Board, 

Washington, DC.

4. Gluck, J.S., Levinson, H.S., and 

Stover, V. (1999). Impact of Access 

Management Techniques, NCHRP 

Report 420, National Research 

Council, Transporation Research 

Board, Washington, DC.

5. Bonneson, J.A. and McCoy, P.T. 

(1997). Capacity and Operational 

Effects of Midblock Left-Turn 

Lane, NCHRP Report 395, National 

Research Council, Transportation 

Research Board, Washington, DC.

6. Eisele, W.L. and Frawley, W.E. 

(2005). “Estimating the Safety 

and Operational Impact of Raised 

Medians and Driveway Density: 

Experiences From Texas and 

Oklahoma Case Studies,” Transportation Research Record, 1931, 

Transportation Research Board, 

Washington, DC.

7. Hallmark, S., Plazak, D., Fitzsimmons, 

E., Hoth, K., and Isebrands, H. (2008). 

Toolbox to Assess Tradeoffs Between 

Safety, Operations, and Air Quality 

for Intersection and Access Management Strategies: Final Report, MTC 

Project 2007-02, Transportation 

Research Board, Washington, DC.

8. Gross, F., Persaud, B., and Lyon, 

C. (2010). A Guide to Developing 

Quality Crash Modification Factors, 

FHWA-SA-10-032, Federal Highway 

Administration, Washington, DC.

9. Bushell, M.A., Poole, B.W., Zegeer 

C.V., and Rodriguez, D.A. (2013). 

Costs for pedestrian and bicyclist 

infrastructure improvements, UNC 

Highway Safety Research Center, 

Chapel Hill, NC.

10. Adams, T. M. (2011). Estimating Cost 

per Lane Mile for Routine Highway 

Operations and Maintenance, 

MRUTC 07-12, Midwest Regional 

University Transportation Center 

Madison, WI.

11. Office of Management and Budget. 

(2003). Circular A-4: Regulatory 

Analysis, Office of Management and 

Budget, Washington, DC.

12.Council, F., Zaloshnja, E., Miller, T., 

and Persaud, B. (2005). Crash Cost 
12

DECEMBER 2017 FHWA-HRT-17-065

HRDS-20/12-17(200)E

Researchers—Thanh Le, Frank Gross, Tim Harmon, and Kimberly Eccles.

Distribution—This TechBrief is being distributed according to a standard 

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Center by e-mail to report.center@dot.gov, fax to (814) 239-2156, phone to (814) 

239-1160, or online at http://www.fhwa.dot.gov/research.

Key Words—Turning movement restrictions, low-cost, safety improvements, safety 

evaluations.

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Estimates by Maximum PoliceReported Injury Severity Within 

Selected Crash Geometries, FHWAHRT05-051, Federal Highway 

Administration, Washington, DC.

13.U.S. Department of Transportation. 

(2015). Guidance on Treatment of the 

Economic Value of a Statistical 

Life (VSL) in U.S. Department of 

Transportation Analyses—2015 

Adjustment, Memorandum, U.S. 

Department of Transportation, 

Washington, DC. Available online: 

https://cms.dot.gov/sites/dot.gov/

files/docs/VSL2015_0.pdf, last accessed May 9, 2016.