SUMMARY

REPORT Evaluation of Sign and 

Marking Alternatives for 

Displaced Left-Turn Lane 

Intersections 

FHWA Publication No.: FHWA-HRT-08-071 

FHWA Contact: Joe Bared, HRDS-05, (202) 493-3314, 

joe.bared@fhwa.dot.gov

This document describes research conducted by the Federal 

Highway Administration (FHWA) to support guidance on the 

signing and marking of displaced left-turn lane intersections 

(DLT)—also known as continuous flow intersections (CFI).

Introduction

In recent years, the FHWA has advocated certain novel 

intersection designs as a means to promote intersection 

safety while meeting the often conflicting demands to increase 

capacity, decrease travel time, and minimize the cost of new 

infrastructure. One of these designs, the DLT, is in the early 

stages of deployment in the United States.

The DLT is an at-grade intersection that is intended to support 

high-traffic flow where there is a large volume of left turns 

and heavy through volumes. Its design permits the use of 

two- or three-phase traffic signals at the junction of two roads, 

while still providing at-grade protected left-turn movements. 

Two-phase signals are enabled by having left-turning traffic 

cross over opposing lanes to the left side of the roadway in 

advance of the main intersection. The turn onto the cross 

street can then be made at the same time as the opposing 

through movements on the originating road. This eliminates 

possible conflicts with the through movement. Timing of the 

signals at the crossover points and at the main intersection can 

help to ensure that vehicles, whether through or turning, stop 

just once at the intersection. Figure 1 shows the direction of 

travel for left-turn traffic (yellow arrows) and opposing through 

traffic (blue arrows) at a partial DLT in Baton Rouge, LA. A 

partial DLT is designed with two opposing displaced left-turn 

bays on the major road, while the left-turn traffic of the cross 

street is kept at the main intersection.

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov
2

Several studies have shown the benefits of the 

DLT design over other signalized intersection 

designs in terms of increased capacity(1,2,3) and 

efficiency of land use.(1,4) Because it uses a twophase signal, the DLT results in less delay, fewer 

pollutants, and lower fuel consumption than 

conventional at-grade intersections that have 

three or more signal phases.(5)

Some evidence suggests that the DLT may also 

provide a safety benefit relative to conventional 

intersections with protected left turns. In the 

absence of crash data, the safety of an intersection design may be estimated by counting 

the number and type of potential conflict 

points. This method identifies three types 

of potential conflict points: (1) diverging, 

(2) merging, and (3) crossing. Diverging conflicts occur where vehicle paths split or diverge 

and may occur where some vehicles slow down 

to turn onto another roadway while others 

maintain their speed on the current roadway. 

Merging conflicts occur where two traffic 

paths come together and may result in sideswipe collisions or rear-end collisions if 

vehicles in the converging paths are traveling 

at different speeds. Crossing conflicts are 

potentially the most dangerous, as these

occur where two traffic paths cross at right, or 

nearly right, angles. 

Figure 2 shows the conflict points for a 

conventional four-legged signalized intersection. Thirty-two conflict points are depicted: 

8 diverging, 8 merging, and 16 crossing 

conflicts—most of which are associated with 

left-turn movements.

Figure 3 shows a conflict diagram for a DLT of

the type examined in this study—a partial 

DLT with crossovers on the two opposing 

approaches. There are 30 conflict points in

this DLT, 2 fewer than for the conventional 

intersection. The importance of this 6-percent 

reduction in the number of conflict points 

may be greater than the numerical reduction 

because it is a reduction in the most serious 

conflict type—the crossing conflict. 

Figure 1. Left-turn and through movements at a DLT in Baton Rouge, LA.
3

In this summary report, the road with the crossover left-turn movements will be referred 

to as the major road. The road without crossovers for the left-turn movements will be 

referred to as the minor road. It should be 

noted that a full DLT with crossovers for all 

left-turn movements would have 12 crossing 

path conflicts, 2 fewer than for the partial DLT 

examined in this report.

Although the number of conflict points is widely 

used as a safety assessment tool, a literature 

review revealed little empirical support for a 

relationship between the number of conflict 

points and crashes.(6) Similarly, although the 

frequency of actual conflicts (also known as 

near crashes or near misses) and the frequency 

of actual crashes would seem to be related, the 

literature is not clear on that either. While some 

authors report a positive correlation between 

observed conflicts and crashes(7,8) and others 

report a positive correlation between conflicts 

in microsimulations and real-world crashes,(9)

the complexities of driver behavior and 

observer judgment make interpretation of 

actual conflicts and crashes difficult.(10)

Nevertheless, the reduction in severe conflict 

Figure 2. Conflict diagram for a conventional fourlegged at-grade intersection.

Figure 3. Conflict diagram for a partial DLT.
4

points provided by the DLT design offers the 

potential for increased safety. The present 

study was intended to provide an increased 

understanding of motorist behavior at DLT 

intersections and to provide some insight into 

signing and marking techniques to enhance 

DLT safety performance.

Goal

Only a few DLT intersections exist in the United 

States; therefore, the DLT is not familiar to 

most motorists. Furthermore, the techniques 

for signing and marking DLTs have yet to be 

standardized. The research reported here 

is intended to provide an empirical basis for 

development of DLT signing and marking 

guidance. 

Specific objectives of the study were as follows:

1. Provide recommendations for signing DLT 

crossovers.

2. Provide recommendations for mitigation 

of stop line overruns at the displaced left-turn 

terminal on the minor street DLT approaches.

3. Assess the extent to which naïve drivers 

are able to navigate a DLT properly the first time 

they encounter it.

Background

When this study began, the partial DLT in Baton 

Rouge, LA (depicted in figure 1), had been 

in operation for almost 1 year. The questions 

addressed in this study were partly based on 

experience at that intersection. 

At the Baton Rouge DLT, the left-turn crossovers occur about 152 m (500 ft) before the 

main intersection. To alert drivers who intend 

to go left of the need to begin their left-turn 

movement earlier than they might otherwise 

expect, the Louisiana transportation department 

decided to install large and conspicuous 

overhead signs (see figure 4). Such overhead 

signs are much more expensive than roadside ground-mounted signs, so the question 

arose whether ground-mounted signs might 

be just as effective as overhead signs. 

Three navigation sign conditions were 

implemented in the FHWA Highway Driving 

Simulator: (1) an overhead sign similar to the 

one in Baton Rouge, (2) ground-mounted signs 

both in the median and on the right side of the 

road, and (3) only one ground-mounted sign on 

the right side of the road. 

Figure 4. Overhead sign for a left-turn crossover at the Baton Rouge DLT.
5

Also at the Baton Rouge DLT, some drivers 

on the minor road were observed stopping 

beyond the stop line and in the path of the 

left-turn movement from the major street. This 

area of potential conflict is indicated in figure 5, 

in which the photograph of the DLT has 

been shaded yellow to show the area where 

vehicles on the minor street sometimes overran the stop line. Arrows in figure 5 show the 

path of potentially conflicting turning vehicles.

Approach

A partial DLT was modeled in the FHWA 

Highway Driving Simulator. Three alternative 

signing, marking, and traffic signal locations 

were implemented. The behaviors of volunteer 

drivers recruited from the Washington, DC, 

metropolitan area were then recorded as they 

navigated through the simulated intersections. 

For comparison, the conventional design of 

the same intersection was also implemented. 

All designs, whether conventional or DLT, had 

three through lanes in each direction, two leftturn lanes for each approach, and one right-turn 

lane for each approach.

The performance measures were as follows:

•	 Navigation errors.

•	 Late lane changes. 

•	 Stop location relative to stop line on the 

minor street approach.

Navigation errors were recorded when drivers 

failed to turn left in accordance with the route 

instructions. Late changes into turn lanes 

were recorded if participants were still in the 

through lanes when they could have been in 

either of the two left-turn lanes. 

The stopping location was of interest on the 

minor street approach to the intersection 

because of the stop line overrun problem that 

had been observed at the Baton Rouge DLT. 

Method

Simulator Description

FHWA’s Highway Driving Simulator is a 

relatively high fidelity research simulator. 

Simulator components include a 1998 Saturn 

SL1 chassis, five projectors, and a cylindrical 

projection screen. Each of the projectors has 

a resolution of 2,048 by 1,536 pixels, and 

the image on the screen wraps 240 degrees 

around the forward view. Measured horizontally, the projection screen is 2.7 m (9 ft) from 

the driver design eye point. The vehicle chassis 

Figure 5. The potential conflict between stopped vehicles and left-turning vehicles from the major 

(crossover) approach.
6

is mounted on a three degree-of-freedom 

motion system. A sound system provides 

engine, wind, tire, and other sounds. 

The vehicle dynamics model is calibrated 

to approximate the characteristics 

of a small passenger sedan. Data 

capture is synchronized to the frame 

rate (mean ≈ 100 fps) of the graphics cards. 

Data recorded from the vehicle dynamics model 

included speed, longitudinal acceleration, 

lateral acceleration, throttle position, brake 

force, vehicle position, and heading.

Simulated Roadways

Between intersections, both major and minor 

roads consisted of six lanes, three in each 

direction. At conventional intersections and 

DLTs, there were two left-turn lanes and one 

right-turn lane.

Treatment Conditions

There were three signing treatments on the 

major road approaches to the DLT crossover 

and three treatments on the minor road 

approaches to the DLT. For the conventional 

comparison intersections, signs and markings 

did not vary.

Major Road Treatments

A plan view of approach to the DLT is illustrated 

in figure 6. The three treatment conditions 

were implemented on the major road approach 

in the circled area in figure 6. The treatments 

were labeled overhead sign, two groundmounted signs, and one ground-mounted sign.

Overhead Sign. The overhead sign treatment, 

which is illustrated in figure 7, consisted of two 

signs. At 108 m (354 ft) before the flair of the 

upstream left-turn lane, there was a groundmounted KEEP LEFT sign (MUTCD, D3-2). Then 

centered over the two left-turn lanes and at 

the end of the flair for the turn-lane lanes, 

there was an overhead sign with the street 

name and left slanted arrows positioned 

above the lanes. A third sign, a groundmounted NEXT SIGNAL sign (MUTCD, D3-2) 

on the right side of the road, is also shown 

in figure 8. This sign was present in all three 

main road treatment conditions and was 

placed 230 m (754 ft) before the flair of the 

upstream left-turn lane.

Two Ground-Mounted Signs. The two groundmount signs treatment is illustrated in figure 9. 

This treatment replaced the overhead sign with 

two signs that gave the street name and route 

number and had a left slanted arrow. The NEXT 

SIGNAL and KEEP LEFT advance signs for the 

left turn were in the same locations as they were 

in the overhead sign treatment.

One Ground-Mounted Sign. The one groundmounted sign treatment, which is illustrated in 

figure 10, differed from the two ground-mounted 

Figure 6. The approach to the DLT crossover with the area where the signing differed between major road 

treatments is circled.
7

signs treatment in two ways. First, the street 

name and route number sign in the median 

was removed. Second, there was no upstream 

KEEP LEFT sign.

Minor Road Treatments

On the minor road approach to the DLT, there 

were also three treatment conditions. These 

were labeled high, medium, and low in 

accordance with the amount of signing 

and marking that was used. The purpose of 

these treatments was to determine the extent 

of signing and marking needed to minimize 

stop line overruns, such as those observed in 

Baton Rouge.

High. The high treatment is shown in 

figure 11. It consisted of KEEP CLEAR painted 

Figure 7. The overhead sign treatment.

Figure 8. Progression of signs in the overhead treatment for the DLT crossover.
8

on the pavement beyond the stop line, 

staggered stop lines, STOP HERE ON RED 

(MUTCD R10-6a) signs mounted on the right 

side of the road and in the median, a 

crosswalk marked with parallel transverse

lines, and a near-side traffic signal head 

located to the right of the intersection stop line.

Medium. The medium treatment, shown in 

figure 12, was the same as in the high treatment, except for the removal of the near-side 

traffic signal. The STOP HERE ON RED sign 

was mounted on a sign post instead of on the 

traffic signal post.

Low. In the low treatment there was no crosswalk, and there were no STOP HERE ON 

RED signs. In addition, a single stop line 

Figure 9. The two ground-mounted signs treatment.

Figure 10. The one ground-mounted sign treatment.
9

served all lanes, as was the case at the Baton 

Rouge DLT. Except for the KEEP CLEAR 

pavement marking, the low treatment 

resembled the conditions at the Baton Rouge 

DLT, where overrunning of the stop line had 

been observed. The low treatment is shown in 

figure 13.

Participants

Ninety-six participants were recruited through 

an FHWA participant database and through the 

use of ads in local newspapers and on the 

Internet. Participants were required to have a 

valid driver’s license and were tested to verify 

Figure 11. High treatment on minor street approach.

Figure 12. Medium treatment on the minor road approach.
10

that their visual acuity was at least 20/40 vision 

in at least one eye. One-third of the participants 

were assigned to each of three treatment 

combinations: (1) overhead and high, 

(2) two-ground mounted and medium, or 

(3) one ground-mounted and low. Within these 

groups of 32 participants, there were equal 

numbers of males and females over and under 

the age of 65.

Research Design

Table 1 summarizes the research design. 

The Simulation Scenarios

All participants drove through a series of 

eight intersections. At the beginning of the 

experimental session and each time they passed 

through an intersection, they were given an 

instruction of the form, “follow the signs to 

state route [xx], [street name].” For example, 

“Follow the signs to state route 61, Airline 

Highway.” If the instructions were followed, a 

left turn was made at every other intersection. 

The second and sixth intersections were 

always one of the minor street approaches. 

Half the participants encountered the minor 

street approach to the DLT first and the minor 

Figure 13. Low treatment on the minor street approach.

Table 1. Research design and sample size for the major road signing variable.

Overhead sign 

and high

Two ground-mounted 

signs and medium

One ground-mounted 

sign and low

Participant total

Females under 65 8 8 8 24

Females 65 and 

above 

8 8 8 24

Males under 65 8 8 8 24

Males 65 and above 8 8 8 24

Total 32 32 32 96
11

street approach to the conventional intersection 

second, and the other half encountered these 

intersections in the reverse order. The fourth 

and eighth intersections were on the major 

road approaches. Half of the participants 

encountered the DLT crossover first (at the 

fourth intersection) and the conventional 

intersection second (at the eighth intersection), and half encountered those 

intersections in the reverse order. The signal 

was always red when participants arrived at 

the second and sixth intersections (the minor 

street approaches). The signal was always 

green for the major street approaches at the 

fourth and eighth intersections. The counterbalancing scheme for controlling the order 

of occurrence of conventional and DLT 

intersections is shown in table 2. Groups of 

24 participants received each order, with equal 

numbers of males and females in each group.

Whenever participants failed to make the 

correct maneuver at any intersection, they were 

allowed to proceed through the intersection 

before being given verbal instructions to make 

a U-turn. They were then guided back onto 

the intended route. The first, third, fifth, and 

seventh intersections were conventional and 

signalized, and the signals always showed 

green. If participants correctly followed the 

navigation instructions, no turns were made 

at these intersections. The posted speed 

limit on major road approaches was 80 km/h 

(50 mi/h), and the posted speed limit on minor 

road approaches was 56 km/h (35 mi/h).

Preexperiment Familiarization Drives

Before beginning to drive through the eight 

intersections that represented the main part 

of the experiment, participants were allowed 

to familiarize themselves with the handling of 

the simulator vehicle on a wide multilane road 

where they accelerated, braked, and changed 

lanes. This was followed by an additional 

drive through three conventional signalized 

intersections. At two of these intersections, 

participants made left turns. At the remaining 

intersection, they encountered a red traffic 

signal where they stopped and waited for a 

green signal.

Findings

The findings for the major and minor road 

approaches were analyzed separately as they 

addressed different questions and are assessed 

by different measures.

Major Road Approach

The question of interest on the approach to 

the crossovers was the type and quantity of 

signage that would be needed to ensure that 

most drivers recognized the need to merge 

into a left-turn lane well upstream of the 

main intersection. The primary measure of 

effectiveness was the location on the approach 

to the crossover where participants entered 

the left-turn lanes. A secondary measure 

was whether the driver missed the crossover 

entirely and whether an illegal left turn was 

made at the main intersection.

Table 2. Four combinations of DLT and conventional intersection orders used.

2nd intersection

(Minor approach)

4th intersection

(Major approach)

6th intersection

(Minor approach)

8th intersection 

(Major approach)

Conventional Conventional DLT DLT

Conventional DLT DLT Conventional

DLT Conventional Conventional DLT

DLT DLT Conventional Conventional
12

Lane position was first assessed when the 

participant’s vehicle was 273 m (895 ft) upstream 

from the crossover stop line and 177 m (580 ft) 

upstream of the beginning of the flair for the 

turn lanes. At this point, there were three 

through lanes and no turn lanes or flairs. 

Drivers could see the navigation signs ahead 

but could not yet read them. In the overhead 

and two ground-mounted signs treatments, drivers could have read an advance 

navigation sign that indicated that their 

intended destination was the next left. It 

appears that the NEXT LEFT sign, which was 

not in the one ground-mounted sign treatment, 

was effective. There were fewer drivers in the 

left lane in the one ground-mounted sign treatment than in the other two treatments, which 

resulted in a significant lane by treatment 

interaction, χ2

(4) = 15.2, p < 0.01. Table 3 shows 

lane position counts for the three signing 

treatments at this upstream location.

The lane occupancy of participants was 

classified at four locations on the approach to 

the crossover: (1) at the end of the left-turn 

flair where two turn lanes were fully available, 

(2) at the beginning of the painted gore for the 

turn lanes, (3) half the distance between the 

beginning of the painted gore and the stop 

line, and (4) at the upstream stop line. These 

points are depicted in figure 14. At each of 

these points, participants were classified 

as either in the turn lanes or in the through 

lanes. As can be seen in table 4, participants 

in the one ground-mounted sign treatment 

were late entering the crossover lanes 

relative to participants in the other two 

treatment conditions. Where the two turn 

lanes were first available and at the gore, the 

differences between treatment groups were 

significant, χ2

(2) = 9.8, p < 0.01, and χ2(2) = 11.1, 

p < 0.01, respectively. Once the halfway point 

between the beginning of the gore and the 

stop line was reached, there was no longer 

a significant difference between treatment 

groups (p > 0.05).

Five of the participants missed the left-turn 

crossover entirely. Three of these drivers 

were in the one ground-mounted sign group, 

and one was in each of the other two groups. 

The difference in the number of drivers 

missing the left turn as a function of signing 

was not statistically significant. Of the drivers 

who missed the crossover, only one made an 

illegal left turn at the main intersection. That 

driver was in the overhead sign condition. 

The other four drivers went through the main 

intersection and were then instructed to make 

a U-turn to and return to the planned route.

For comparison, the participants’ lane was 

also classified for the major road approach 

to the conventional intersection. Because 

of geometric differences between DLT and 

conventional intersection design, the points 

of comparison were only approximate. The 

left-turn lanes of the conventional intersection 

were much longer than the lanes on the 

approach to the crossover. As can be seen in 

table 5, most drivers were in the conventional 

intersection turn lanes as soon as the lanes 

were available, and there were no differences 

in the number of drivers in these lanes as a 

function of the approach signage treatment. 

The lack of difference among groups should 

not be surprising as there were no differences 

in signing at the conventional intersections.

Minor Road Approach

The main concern at the minor road crossing 

was whether some drivers might stop beyond 

Table 3. Vehicle lane positions upstream of the 

crossover.

Signing Left lane Center lane Right lane

Overhead 

sign

16 14 2

Two groundmounted 

signs

19 13 0

One groundmounted 

sign

7 18 7
13

the stop line at red traffic signals. If they did this, 

they could potentially obstruct the left-turning 

traffic that had crossed over to the left side of 

the major road.

Only one driver, who was in the high treatment 

condition, failed to stop behind or near the stop 

line. Instead, at the stop line, the driver straddled 

the gore line between the through and left-turn 

lanes and did not come to a full stop until 10 m 

(33 ft) beyond the stop line. When the protected 

left-turn signal turned green, the driver began 

to move to the right and into the through traffic 

lane, which still had a red signal indication, and 

then swerved to the left and made the left turn.

The behavior of that participant clearly indicated 

that the driver was confused as to whether to go 

straight or turn left. 

Figure 14. Approach to DLT crossover with reference points measured from the stop line for the assessment 

of lane occupancy.

Table 4. Number of drivers (out of 32) in each signing group who were in the left-turn lanes at four points on 

the approach to the left-turn crossover.

Measurement location Distance to 

stop line

Overhead sign Two groundmounted signsOne groundmounted sign

Two turn lanes first available 95 m 17 20 8

Gore between through and 

turn lanes begins

78 m 19 26 13

Halfway between beginning 

of gore and stop line

39 m 29 29 27

Stop line at crossover 0 m 31 31 29

1 m = 3.28 ft
14

There was no difference between treatment 

groups in average stopping distance relative 

to the stop line, F (2, 86) = 0.05, p > 0.5. The 

overall mean stopping distance behind the 

stop line was 5.3 m (17.4 ft). This stopping 

distance was significantly further upstream of 

the stop line than for the minor street approach 

to the conventional intersection, F (1, 81) = 

7.3, p < 0.01. In the conventional intersection, 

the mean distance to the stop line was 

4.1 m (13.4 ft). Although both of these distances 

are greater than might be expected in the real 

world, they are consistent with the results of 

previous studies in the FHWA Highway Driving 

Simulator. In the simulator, participants tend to 

perceive that they are at the stop line as soon as 

the stop line cannot be seen over the hood of the 

car, at which point they are still about one car 

length upstream of the virtual stop line.

Discussion

This study had three purposes: (1) to inform 

recommendations for signing DLT crossovers, 

(2) to inform recommendations for mitigation of 

stop line overruns on minor street approaches 

to DLTs, and (3) to assess the extent to which 

naïve drivers are able to navigate a DLT the first 

time they encounter it.

Signing at Crossovers

With respect to DLT crossovers, the results 

show that advance signing is important and 

that overhead signing is not necessarily more 

effective than ground-mounted signs. On the 

three-lane approach to the crossovers, a KEEP 

LEFT sign 108 m (384 ft) upstream of the 

beginning of the taper for the left-turn lanes 

was effective in getting participants to move to 

the left lane. Ground-mounted signs on both 

sides of the road were effective in guiding 

drivers into the turn lanes. The relative importance of the advance KEEP LEFT and the street 

name navigation signs to prompt entry into the 

left-turn lanes remains to be determined in 

future studies. 

The absence of a significant difference in the 

effectiveness of the overhead sign compared 

to that of the dual ground-mounted signs 

suggests that where ground-mounted signs on 

both sides of the road are feasible, the additional expense of an overhead guide sign might 

not be necessary. These results do not suggest 

that overhead signs should not be considered, 

but rather that in some situations groundmounted signs may be sufficient.

Stop Line Overrun Mitigation

Regardless of treatment condition, overrun of 

the stop line on the minor street approach to 

the DLT was not a problem. All three treatments 

employed the KEEP CLEAR pavement marking. 

Whether the KEEP CLEAR marking was 

responsible for the lack of stop line overruns 

in this study is uncertain. However, this 

pavement-marking treatment is relatively 

inexpensive and should be considered, 

particularly at reconstructed intersections 

Table 5. Number of drivers (out of 32) in each signing group who were in the left-turn lanes at four points on 

the approach to the conventional intersection.

End of flair Begin gore Halfway Stop line

Distance to stop line 365 m 208 m 98 m 0 m 

Overhead 27 30 30 30

Two ground-mounted 28 30 32 32

One ground-mounted 27 31 32 32

1 m = 3.28 ft
15

where drivers may tend to stop at the 

main intersection because of habit or 

experience. Because drivers in the low 

condition did not overrun the stop line, this 

study does not permit evaluation of the 

potential effectiveness of near-side signals or 

the STOP HERE ON RED traffic control device.

Naïve Driver Navigation

Even though participants had no introduction 

to or previous experience with a DLT, all 

drivers who entered the DLT crossover lanes 

crossed to the left side of the road. No driver 

turned into the oncoming lanes rather than 

crossing them. It is also of note that in more 

than a year since its opening, no crashes have 

resulted from this driver error at the Baton 

Rouge DLT. Proper geometric design, signing, 

and marking seem sufficient to minimize the 

occurrence of this particular driver error. 

The participants in this study showed no 

confusion when confronted with a DLT for 

the first time. This finding adds to the evidence 

cited in the introduction of this summary 

report that the DLT design may be expected 

to promote intersection safety while 

meeting the demands for increased capacity, 

decreased travel time, and reduced cost of 

new infrastructure. 

Recommendations

Because the crossover lanes for the DLT are 

upstream of where drivers might be expecting 

to begin their left-turn maneuver, conspicuous 

advance and navigation guide signing is 

recommended. In cases where conspicuous 

ground-mounted signs with good sight 

distance are feasible, overhead signing may 

not provide additional benefit. Where advance 

signing is not used, as was the case in with 

the one ground-mounted sign treatment, the 

frequency of last-minute lane changes may 

increase, and this might introduce a higher 

crash risk than otherwise. Therefore, advance 

signing is recommended to encourage drivers 

who intend to turn left to move to the left lane 

well before the taper for the left-turn lanes. 

References

1. Reid, J.D., and Hummer, J.E. (2001). 

Travel Time Comparisons Between 

Seven Unconventional Arterial 

Intersection Designs. Transportation 

Research Record: Journal of the 

Transportation Research Board, 1751, 

p. 56–66.

2. Chick, M.J. (2001). The Displaced Right Turn 

Junction. Unpublished Dissertation, The 

University of Leeds, Leeds, U.K.

3. El Asawey, M., and Sayed, T. (2007). 

Comparison of Two Unconventional 

Intersection Schemes: The Crossover 

Displaced Left-Turn (XDL) Intersection 

and the Upstream Signalized Crossover 

(USC) Intersection. Paper presented at the 

Transportation Research Board 86th Annual 

Meeting, Washington, DC.

4. Simmonite, B.F., and Chick, M.J. (2004). 

Development of The Displaced Right-Turn 

Intersection. Transportation Research 

Record: Journal of the Transportation 

Research Board, 1881, p. 11–18.

5. Jagannathan, R. (2003). Evaluation of 

Crossover Displaced Left-turn (XDL) 

Intersections and Real-Time Signal Control 

Strategies with Artificial Intelligence 

Techniques. Unpublished Masters Thesis, 

Virginia Polytechnic Institute and State 

University, Falls Church, VA.
16

Researchers—This study was performed by the Human Centered Systems Team of FHWA’s Office of 

Safety Research and Development. Vaughan W. Inman of SAIC was the Principal Investigator. Megan 

Pavlok, Erin Dagnall, and Pascal Beuse conducted the experiment. Jason Williams, Peter Chou, Ryan 

Cartwright, and Mike Baumgartner of AAI Engineering Support prepared and operated the Highway 

Driving Simulator. For information about this research, contact Joe G. Bared, FHWA Task Manager, HRDS, 

(202) 493-3314, joe.bared@dot.gov. 

Distribution—This Summary Report is being distributed according to a standard distribution. Direct 

distribution is being made to the FHWA Divisions and Resource Centers.

Availability—The report can be obtained from the FHWA Product Distribution Center by sending a 

request by e-mail to report.center@fhwa.dot.gov, by fax to (301) 577-1421, by phone to (301) 577-0818, or 

online at http://www.tfhrc.gov/safety/intersect.htm.

Key Words—Continuous Flow Intersection; Displaced Left-Turn; unconventional intersections; 

novel intersections; driving simulation; intersection safety; navigation signs; intersection markings; 

KEEP CLEAR. 

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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.

February 2009 FHWA-HRT-08-071

HRDS-05/2-09(3M)E

6. Simodynes, T., Welch, T., and Kuntemeyer, M. 

(2000). Effects of Reducing Conflict Points 

on Reducing Accidents (ABSTRACT ONLY). 

Paper presented at the Third National Access 

Management Conference.

7. Dadic, I., Badanjak, D., Scukanec, A., and 

Brlek, P. (2000). Dependence of Conflict 

Intensity Between Traffic Flows and Traffic 

Safety. Traffic Safety on Two Continents 

Publication of: Swedish National Road and 

Transport Research Institute, p. 217–226.

8. Hydén, C. (1987). The Development of a 

Method for Traffic Safety Evaluation: The 

Swedish Traffic Conflicts Technique. Lund: 

Lund Institute of Technology.

9. Gettman, D., and Head, L. (2008). Surrogate 

Safety Assessment Model (SSAM) (No. 

FHWA-HRT-08-049): Federal Highway 

Administration.

10. Davis, G.A., Hourdos, J., and Xiong, H. 

(2008). Outline of Causal Theory of Traffic 

Conflicts and Collisions. Paper presented 

at the Transportation Research Board 87th 

Annual Meeting, Washington, DC.