Students will be reading and gathering notes from a set of three (3) articles. When gathering notes, students should avoid simply copying and pasting passages from the journal articles but rather focus on expressing the thoughts in the students’ own words. While doing this, passages may be copy and pasted (within quotes) and properly referenced but these must accompany an explanation of the passage/section as developed by the student. The point is to display knowledge and understanding.Design Guidance for J-Turns
on Rural High-Speed Expressways
Boris Claros, Zhongyuan Zhu, Praveen Edara, and Carlos Sun
conflict between minor and major road vehicles by forcing the minor
road vehicles to use a U-turn downstream of the main intersection.
As shown in Figure 1, the median opening at the main intersection is
closed to all minor road movements (i.e., through and left). The left
turns from the major road onto the minor road may still be permitted
at the main intersection.
The J-turn design has been in use in many states, including
Michigan, North Carolina, and Maryland (as a restricted crossing
U-turn). In the past decade, the Missouri Department of Transportation has replaced several high-crash intersections on rural
high-speed expressways with J-turns. In Missouri, all J-turns are
two-way, stop-controlled intersection replacements on rural highspeed expressway intersections. Much of the research done to
date on J-turns has involved unsignalized J-turns, typically installed
in urban areas. Studies that have evaluated the performance of
unsignalized J-turns on rural high-speed expressways are fewer.
One recent study quantified the overall safety benefits of J-turns in
Missouri (2). Hummer et al. documented the safety of unsignalized
superstreet intersections in North Carolina (3), and Inman and Haas
reported on the safety performance of restricted crossing U-turn
intersections in Maryland (4).
Despite the J-turn’s long existence, little research stands behind
some of the J-turn design criteria. For example, limited research has
been done on the effect of spacing between the main intersection and
the U-turn on safety and operations. Similarly, it is not clear when
acceleration lanes are beneficial at J-turn sites (i.e., at what traffic
volume). Thus this present study used a two-pronged approach to
develop some guidance to J-turn design. First, a thorough analysis
of crashes that occurred at existing J-turn sites in Missouri was conducted. The objective of this analysis was to identify how the crash
frequencies and the types of crashes were influenced by design
parameters. Second, the safety effects of different design parameters
and traffic volumes were examined further through traffic simulation. The simulation experiments measured the safety effect of two
design considerations: (a) the presence of acceleration lanes and
(b) the spacing between the main intersection and the U-turn. Various
combinations of minor road and major volumes were analyzed for a
J-turn, with and without acceleration lanes, and for different spacing
values. Vehicle trajectory data obtained from microsimulation were
used to derive safety conflict measures such as time to collision, postencroachment time, and conflict angle, which in turn were used to
quantify the number of conflicts. The crash and simulation analyses
complemented each other. The crash analysis used field crash data
but was limited in sample size. The simulation, however, involved
many more vehicles and events, and made it possible to conduct sensitivity analysis, but it did not involve actual crashes. The scope of
this study was limited to four-lane, rural, divided expressways with
speed limits over 60 mph.
Owing to the J-turn’s safety effectiveness, it has become a viable alternative to replace high-crash, two-way, stop-controlled intersections on
high-speed expressways. National guidance on the design of J-turns
on high-speed highways is limited. What is the safety effect of spacing
between the intersection and the U-turn? Under what circumstances is
the provision of acceleration lanes recommended? This study answered
these questions through a safety assessment on the basis of (a) an examination of crashes that occurred at 12 J-turn sites in Missouri and (b) a
simulation-based assessment of the effect of various design variables
and traffic flows. The crash review revealed the proportions of the five
most frequently occurring crash types at J-turn sites: (a) major road
sideswipe (31.6%), (b) major road rear-end (28.1%), (c) minor road
rear-end (15.8%), (d) loss of control (14%), and (e) merging from U-turn
(10.5%). The crash rates, accounting for exposure, decreased with the
increase in the spacing to the U-turn for sideswipe and rear-end crashes;
J-turns with a spacing of 1,500 ft or greater experienced the lowest crash
rates. The crash rates were lower for J-turn sites with acceleration lanes
for minor road traffic merging onto the major road than for sites without
acceleration lanes. A calibrated simulation model analysis revealed that
the presence of acceleration lanes reduced conflicts for all volumes and
designs, including low volumes. The simulation analysis also reinforced
the crash analysis results that safety improved with an increase in spacing
between the main intersection and the U-turn.
How dangerous are two-way, stop-controlled intersections on
high-speed rural highways? Maze et al. reported that most crashes
that occurred at unsignalized intersections on high-speed rural
expressways were right-angle crashes that resulted from turning
movements (1). They found that right-angle crashes resulted in
a higher proportion of fatal and serious injuries and that the proportion of right-angle crashes on rural high-speed expressways in
Minnesota, Utah, and Iowa were 57%, 69%, and 52%, respectively
(1). What are transportation agencies doing to mitigate these rightangle crashes? Treatments (e.g., enhancement of the intersection
sight distance, provision of minor road gap selection assistance, and
alerting vehicles to the presence of entering traffic) all contribute
to right-angle crash mitigation. However, these treatments do not
address the fundamental minor road conflicting movements. Alternative intersection designs, such as the J-turn, eliminate the right-angle
B. Claros and P. Edara, C2640 Lafferre Hall; C. Sun, E2509 Lafferre Hall, and
Z. Zhu, Department of Civil and Environmental Engineering, University of
Missouri (the school at Columbia), Columbia, MO 65211. Corresponding author:
P. Edara, edarap@missouri.edu.
Transportation Research Record: Journal of the Transportation Research Board,
No. 2618, 2017, pp. 69–77.
http://dx.doi.org/10.3141/2618-07
69
70
Transportation Research Record 2618
conducted one of the few studies to evaluate the effect of U-turn
spacing and acceleration lanes at J-turns (9). They found that the
provision of a right-turn acceleration lane decreased fatal and injury
crashes regardless of the U-turn spacing or annual average daily
traffic.
Methodology
FIGURE 1 J-turn vehicle movements.
Synthesis of Existing Guidance
What spacing between the intersection and the U-turn currently is
found at J-turns across the country? Does any guidance exist on
when acceleration lanes are recommended at a J-turn site? Before
these questions can be answered, it is useful to examine the current
guidance available on J-turn design. The AASHTO Green Book does
not provide guidance on the J-turn design. The closest design with
elements similar those of a J-turn is the median U-turn (Chapter 9,
p. 162) (5). However, the median U-turn design is different from
the J-turn design in an important way. The median U-turn design
prohibits only major road left-turn movements at the main inter
section. The primary purpose of the J-turn is to prohibit minor road
through and left-turn movements at the intersection. The multiple
lane changes that minor road vehicles need to complete their movement in a J-turn are not a consideration in the median U-turn design.
Consequently, the U-turn spacing in a median U-turn has been found
to be shorter than at J-turns. On the basis of FHWA’s Signalized
Intersections: Informational Guide (6), the AASHTO Green Book
recommends spacing of 660 ft for U-turns in urban areas and 1,320 ft
for rural medians (5). FHWA’s Restricted Crossing U-Turn Informational Guide explains that these values likely were derived under
the assumption of a posted speed limit of 45 mph, which would
be lower than the 60 to 70 mph posted speed limits found on rural
expressways (7). Guidance from various states describes a wide
range of spacing from 560 to 3,000 ft (8). Zhang and Kronprasert
This section presents the methodology used for safety analysis and
simulation analysis of J-turn sites. The crash analysis focused on
sampling, site characteristics, crash data collection, and collision
diagrams. The simulation analysis included model development,
calibration, and evaluation of scenarios.
Crash Analysis
Sampling
The criteria used to select sites for collision diagram analysis consisted
of crash data availability, pre-J-turn intersection configuration, the
absence of influence from other facilities, and no significant geometric
or other changes during the post-J-turn analysis period. A master list
of J-turns in Missouri was developed and consisted of 18 facilities
that were in operation as of 2015. Twelve of the 18 facilities satisfied the site selection criteria. These 12 facilities are listed in Table 1.
The table shows the following site characteristics: location, urban or
rural classification, opening date, U-turn spacing, and major and minor
road annual average daily traffic.
The geometric layouts of the 12 J-turns are shown in Figure 2.
Seven sites restricted left turns from the major road to the minor road
at the main intersection (J-turns 1, 3 to 6, 9, and 10), while the other
five sites (J-turns 2, 7, 8, 11, and 12) permitted them. Except at one
site (J-turn 1), all other sites consisted of four legs. Half of the sites
(J-turns 2 to 6, and 12) provided loons at the U-turn to accommodate
the wider-turning radii of trucks. Five sites (J-turns 2, 7, 8, 9, and 11)
had acceleration lanes for the minor road traffic that turned right onto
TABLE 1 Description of J-Turn Sites
U-Turn Distance
(ft)
JTa
Location
City
Area
Open
1
2
1
2
3
4
5
6
7
8
9
10
11
12
RT-M and Old Lemay Ferry Co.
MO-13 and Old MO-13 (364 E)
US-65 and MO-215
US-65 and MO-38
US-65 and Ash St.
US-65 and RT-AA
US-54 and Route E
US-54 and Honey Creek Rd.
US-63 and Route AB
US-63 and B. F. Church Rd.
MO-30 and Upper Byrnes Mill Rd.
US-65 and Rochester Rd.
Imperial
Osceola
Sheridan
Jackson
Jackson
Sheridan
Jefferson City
Jefferson City
Columbia
Columbia
Byrnes Mill
Ridgedale
Urban
Rural
Rural
Rural
Rural
Rural
Rural
Rural
Rural
Urban
Urban
Rural
Sept. 07
July 09
Nov. 09
Nov. 09
Nov. 09
Nov. 09
Oct. 11
Nov. 11
Nov. 12
Nov. 12
Dec. 12
Dec. 12
800
1,100
630
630
630
650
1,700
1,900
2,300
900
1,500
730
1,900
980
630
630
630
1,300
na
1,900
3,000
1,400
1,700
990
Note: AADT = annual average daily traffic; na = not applicable.
a
J-turn reference number.
AADT by Road
Speed Limit
(mph)
Major
Minor
60
60
65
65
70
70
65
65
65
65
65
65
9,320
11,109
7,573
6,975
6,631
9,407
15,097
18,213
26,956
26,388
23,091
11,584
358
467
982
822
524
932
1,017
435
1,020
1,504
2,226
486
Claros, Zhu, Edara, and Sun
71
JT-2
JT-1
800 ft
1,100 ft
1,900 ft
JT-3
980 ft
JT-4
630 ft
630 ft
630 ft
630 ft
JT-6
JT-5
630 ft
630 ft
650 ft
1,300 ft
1,900 ft
1,900 ft
900 ft
1,400 ft
JT-8
JT-7
1,700 ft
JT-10
JT-9
2,300 ft
3,000 ft
JT-11
JT-12
1,500 ft
1,700 ft
FIGURE 2 Layouts of all J-turn sites. Diagrams not to scale.
730 ft
990 ft
72
Transportation Research Record 2618
the major road. These dozen sites provided a good variety of geometric
layouts.
Crash Data Collection, Review, and Diagramming
Crash data were collected for the entire footprint of the J-turn (U-turn
to U-turn) and additional areas of influence. The influence area
upstream of the U-turn in each direction captured the area where
mainline traffic was influenced by traffic that was merging after
completion of a U-turn. The influence areas consisted of (a) 1,000 ft
beyond the U-turn in each direction for the major road and (b) 250 ft
from the intersection in each direction on the minor road. Crashes
within this footprint were investigated with the accident browser
from the Missouri Department of Transportation’s transportation
management system. For each site, data were obtained from the date
the site opened to traffic until December 2014. Within the extended
J-turn footprint, 183 crashes occurred at all facilities. All 183 police
crash reports were reviewed manually to land the crashes precisely
within the J-turn footprint. This review found that only 90 of the
183 crashes were J-turn–related and occurred within its footprint.
The remaining 93 crashes occurred completely outside the J-turn
footprint and were not of interest in the study. In the next step, weatherrelated, animal-related, and other non-J-turn–related crashes were
removed; these crashes numbered 36. The remaining 57 crashes were
determined to be J-turn–related and were considered for further
analysis of the effect of spacing. These crashes were then plotted
with computer-aided design within each J-turn site. The crash report
review involved the careful examination of the location fields, collision
diagram, and narratives and statements.
Crash Analysis Results
The J-turn–related crashes were separated into five types: (a) major
road sideswipe, (b) major road rear-end, (c) minor road rear-end,
(d) loss of control, and (e) merging from U-turn. The crashes were
aggregated across all sites, and the percentage of each crash type
was computed. Figure 3 shows these percentages. The most frequent
crash types at a J-turn in Missouri were sideswipe (31.6%) and rearend (28.1%) on major roads. According to the descriptions in the crash
reports, most of these crashes occurred while vehicles were merging
with traffic or changing lanes to enter the deceleration lane to complete
a U-turn. Driver inattention also was cited as a common circumstance
in the crash reports.
The rear-end crashes on minor roads occurred when vehicles
collided with a leading vehicle that had stopped suddenly or slowed
down to look for a gap in the traffic on a major road. Most of the loss
of control crashes involved driver inattention, improper lane use, or
high speed. For the top two crash types on major roads (i.e., sideswipe
and rear-end), crash rates were computed with the use of Equation 1.
The crash rate was calculated as a function of traffic exposure and
segment length between the minor road intersection and the U-turn.
Thus, if a J-turn site had a U-turn on each side of the main inter
section, the crash rate was computed for two segments: the segment
that encompassed the left U-turn and the segment that encompassed
the right U-turn. This computation was done to account for the
fact that J-turns can be asymmetrical, (i.e., different spacing from
the intersection to each of the two U-turns).
crashes per million vehicle miles traveled =
A = annual number of crashes occurring over the segment,
L = length of the segment from minor road to U-turn, in
miles, and
AADT = annual average daily traffic for total entering vehicles
per year.
Figure 4 presents the computed crash rates categorized by the
segment length between the minor road and the U-turn. Both sideswipe and rear-end crash rates on the major roads decreased with
an increase in the distance to the U-turn. The longer distance helped
merging vehicles to accelerate and reach the prevailing speed of
Type of Crash
Major road sideswipe
Major road rear-end
Minor road rear-end
Loss of control
Merging from U-turn
3
2
5
L
1
FIGURE 3 Percentage of crashes by type.
(1)
where
1
2
3
4
5
4
A × 1,000,000
L × AADT × 365
Crashes
18 31.6%
16 28.1%
9
15.8%
8
14.0%
6
10.5%
Claros, Zhu, Edara, and Sun
73
Several parameters in VISSIM were optimized to accurately simulate vehicles at a J-turn. These parameters included reduced speed
areas (length and magnitude), desired speed decisions, and lane
change distance upstream of a connector. For example, the lane change
distance parameter specifies the upstream distance from a connector
where vehicles start to look for lane-changing gaps to stay on their
desired path. This parameter value was calibrated with the use of field
videos by matching the visual simulation output with the field video.
The speed calibration procedure in this study used disaggregated
data on individual vehicle speeds measured in the field (2). Thus the
calibration procedure was more robust than the state of practice that
relied on aggregated sensor speeds on a roadway. A map of the field
data collection equipment, radar speed guns, and cameras is shown
in Figure 7. Several cameras and radar guns were used to extract
vehicle speeds and traffic volumes. Peak period data were collected
in the southbound direction for the morning peak and northbound
direction for the evening.
The speed distribution of merging vehicles from the minor and
major roads was extracted from field data and was used to create
the desired speed distributions in VISSIM, as shown in Figure 8.
The 85th percentile speeds of passenger cars and trucks on the major
roads were 75 mph and 70 mph, and the speed for merging vehicles
was 64 mph.
Distance Minor Road to U-Turn (L)
1,500 ft
Crashes per MVMT
2.0
1.5
1.0
1.606
1.490
0.671
0.5
0.290
0.042
0.161
0.0
Sideswipe
Rear-end
FIGURE 4 Major road sideswipe and rear-end crash rates.
MVMT = million vehicle miles traveled.
major road traffic. J-turn sites with a spacing of 1,500 ft or greater
experienced the lowest crash rates per million vehicle miles traveled.
The effect of the acceleration lane on crash rate also was examined.
Two sets of comparisons were made: (a) designs with and without
acceleration lanes for minor road traffic merging onto the major road
and (b) designs with and without acceleration lanes for the U-turn
traffic merging onto a major road. The crash rates for these two sets are
shown in Figure 5. The results showed that the crash rates were lower
for sites with acceleration lanes. This finding was further investigated
with simulation for various volume and design combinations.
Simulation Scenarios
Different volume scenarios were generated to analyze the J-turn
performance. The base condition volumes shown in Table 2 were
obtained from the field data discussed earlier. The field-observed
minor road volumes were low and did not generate enough conflicts
to be useful for safety analysis. Thus higher values were used to
analyze the combined effect of traffic volume and design parameters.
Twelve major road and minor road volume combinations were generated, as shown in Table 3. The minor road crossing flow column
includes minor road left-turn and through movements. The volume
scenarios ranged from low volume to high volume. These 12 volume
scenarios were then examined for the two U-turn distances of 1,000
and 2,000 ft, and for the presence and absence of acceleration lanes,
which resulted in 48 (12 × 2 × 2) combinations. The design with
acceleration lanes consisted of an acceleration lane on a major road
for turning movements from a minor road and another acceleration lane after the U-turn of vehicles to merge into the major road.
Simulation Analysis
The VISSIM microscopic traffic simulation was used to analyze
the effect of the same two J-turn design considerations: presence or
absence of acceleration lanes and the distance between the minor
road and the U-turn. The simulation model used in this research was
calibrated with the field data collected at a J-turn near Deer Park Road
on Highway 63, south of Columbia, Missouri (2). This section of
Highway 63 is a rural, four-lane highway with a speed limit of 70 mph
and consists mainly of tangents with no sharp horizontal curves
or steep vertical grades. The satellite image and the corresponding
VISSIM simulation model layout are shown in Figure 6.
0.0
0.2
Crashes per MVMT
0.4
0.6
Acceleration lane, minor road
1.0
0.63
No acceleration lane, minor road
Acceleration lane after U-turn
0.8
0.84
0.15
No acceleration lane after U-tur…
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