APPENDIX D. FIELD DATA COLLECTION FOR GEOMETRIC DESIGN
AND TRAFFIC CONTROL FEATURES
This appendix documents the definitions and codes used to record geometric
and traffic control data during the field data collection. Data for each intersection
visited in the field were recorded on a standard form (figure D-1). Most data
items were recorded for each of the three or four approaches to the intersection.
A few items (angle of intersection, lighting, character of development, and
level of pedestrian activity) apply to the intersection as a whole, rather than
to any specific approach. Location information was also collected on the form.
More types of data were gathered in the field than were used in the final
analyses. The intent was to collect as broad a set of geometric and traffic
control data as feasible during the initial field visits so that, if a question
arose during the analysis about the geometrics or traffic control of a specific
intersection, data from the field would be available to answer the question.
This would eliminate the need to make additional field visits during the latter
stages of the project. Photographs were also taken in the field on each intersection
approach.
Some data items were gathered solely for site selection purposes. For example,
data were recorded on whether each intersection leg had one-way or two-way operation.
In fact, all legs of the study intersections had two-way operation. However,
if one-way operation had been present, this data item would have alerted the
research team to that fact.
Each data item in figure D-1 is discussed below:
- Number of through lanes:
Number of lanes used by through traffic on each approach. This included
all lanes used exclusively by through traffic and lanes shared by through
traffic and right- or left-turning traffic.
- Number of left-turn lanes:
Number of lanes used exclusively by left-turning traffic. A shared
lane used by both through traffic and left-turning traffic was counted as
a through lane, not as a left-turn lane.
- Number of right-turn lanes:
Number of exclusive right-turn lanes on the approach. A shared lane
used by both through and right-turning traffic was counted as a through lane,
not as a right-turn lane. If there was a separate right-turn roadway created
by a channelizing island, the number of right-turn lanes was recorded as 1
or more, even if vehicles entered the channelizing roadway from a lane shared
with through traffic (i.e., even if there was no exclusive right-turn lane
upstream of the right-turn roadway created by the channelizing island).
Figure D-1. Key Intersection Geometric
and Traffic Control Variables.
Site Number |
County |
Data Collector Name |
Intersection |
B |
A |
C |
Date |
Time |
|
Acceptable Codes |
Major Road
NB or EB |
Crossroad
NB or EB |
Major Road
SB or WB |
Crossroad
SB or WB |
Comments
(use back if needed) |
Name of Street: |
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1. Number of through lanes |
Numeric |
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2. Number of left-turn lanes |
Numeric |
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3. Number of right-turn lanes |
Numeric |
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4. Type of left-turn treatment |
N,C,P |
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5. Type of right-turn treatment |
N,I,L,R |
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6. Horizontal alignment |
T,G,M,S |
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7. Approach grades |
L,M,S / U,D |
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8. Crest/sag vertical curves |
N,C,S |
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9. Total through-lane width (ft) |
Numeric |
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10. Right shoulder type |
P,G,T,C |
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11. Right shoulder width (ft) |
Numeric |
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12. Total LTL width (ft) |
Numeric |
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13. Total LTL length (ft) |
Numeric |
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14. Total RTL width (ft) |
Numeric |
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15. Total RTL length (ft) |
Numeric |
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16. Divided/undivided |
D,U |
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17. Median width (ft) |
Numeric |
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18. Median type |
N,R,D,F |
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19. One-way/two-way |
1 or 2 |
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20. Left-turn prohibition |
N,A,M,E,B |
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21. Number of driveways within 250 ft |
Numeric |
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22. Type of driveways |
N,C,I,R |
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23. Curb parking within 250 ft |
N,P,A |
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24. Traffic control |
N,ST,SG |
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25. Left-turn phasing (arrows) |
N,A,B |
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26. Pedestrian signals |
Y,N |
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27. Painted crosswalk on approach |
Y,N |
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28. Advance warning signs |
Y,F,N |
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29. Posted speed limit (mph) |
Numeric |
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30. Angle of intersection |
Numeric |
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31. Lighting |
N,H,S,I/Y,N |
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32. Character of development |
C,B,I,M,R,X |
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33. Level of pedestrian activity |
L,M,H |
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- Type of left-turn treatment:
N = No left-turn lanes.
C = Left-turn channelization defined by raised (curbed) or depressed median.
P = Painted left-turn channelization (no median or flush median).
Note: If number of left-turn lanes was zero, the type of left-turn treatment
was N.
- Type of right-turn treatment:
N = None.
I = Right-turn roadway created by a channelizing island without an
exclusive right-turn lane upstream of it (i.e., traffic entered the right-turn
roadway from a shared lane used by both through and right-turning traffic).
L = Right-turn roadway created by a channelizing island with an exclusive
right-turn lane upstream of it (i.e., traffic entered the right-turn roadway
from an exclusive right-turn lane).
R = Conventional exclusive right-turn lane with no channelizing island.
- Horizontal alignment (of approach):
T = Tangent.
G = Gentle curve (radius over 600 m or 2,000 ft).
M = Moderate curve (radius from 150 to 600 m or 500 to 2,000 ft).
S = Sharp curve (radius less than 600 m or 500 ft).
NOTE: The G, M, and S codes were used if the intersection was located on a
horizontal curve or if there was a horizontal curve on the approach within
250 feet of the intersection. The curve radius was estimated visually in the
three categories shown.
- Approach grades (within 75 m or 250 ft of the intersection):
L = Level (less than 2 percent grade).
M = Moderate grade (2 to 4 percent grade).
S = Steep grade (over 4 percent grade).
NOTE: The percent grade was estimated visually.
- Crest/sag vertical curve (on approach):
N = None.
C = Crest vertical curve on approach.
S = Sag vertical curve on approach.
NOTE: Recorded presence of crest and sag vertical curves that extended through
the intersection or were within 75 m (250 ft) of the intersection.
- Total through-lane width (ft):
Combined total width of all the through lanes, including both shared
left-turn and right-turn lanes. Widths of exclusive right- and left-turn lanes
were not included in the total through-lane width. The number of lanes whose
widths were measured matched the number of through lanes recorded.
NOTE: The through-lane width was measured at the stop line or crosswalk with
a measuring wheel. The total through-lane width was recorded such that the
total through-lane width divided by the number of through lanes equaled the
average lane width for the through lanes.
- Right shoulder type:
P = Paved.
G = Gravel.
T = Turf.
C = Curb.
- Right shoulder width (ft):
Measured from the outside edge of the through lane or right-turn
lane to the outside edge of the shoulder. This measurement was made with a
measuring wheel.
- Total LTL width (ft):
Combined total width of all exclusive left-turn lanes. The number
of lanes whose widths were measured matched the total number of exclusive
left-turn lanes recorded.
NOTE : The total left-turn lane width was measured at the stop line or crosswalk.
This measurement was made with a measuring wheel. The total left-turn lane
width was recorded such that the total left-turn lane width divided the total
number of exclusive left-turn lanes equaled the average left-turn lane width.
- Total LTL length (ft):
Total length of all exclusive left-turn lanes.
NOTE: The total left-turn lane length was measured from the stop line or crosswalk
to the upstream end of the left-turn lane(s). This measurement was made with
a measuring wheel. If the left-turn lane included a taper at its upstream
end, the length of the left-turn lane was measured to the last point at which
the left-turn lane had its full width.
- Total RTL width (ft):
Combined total width of all right-turn lanes. The number of lanes
whose widths were measured matched the total number of right-turn lanes recorded.
NOTE: The total right-turn lane width was measured at the stop line or crosswalk.
This measurement was made with a measuring wheel. The total right-turn lane
width was recorded such that the total right-turn lane width divided by the
total number of right-turn lanes equaled the average right-turn lane width.
- Total RTL length (ft):
Total length of all right-turn lanes.
NOTE: The total right-turn lane length was measured from the stop line or
crosswalk to the upstream end of the right-turn lane(s). This measurement
was made with a measuring wheel. If the right-turn lane included a taper at
its upstream end, the length of the right-turn lane was measured to the last
point at which the right-turn lane had its full width.
- Divided/undivided:
D = Divided (a raised or depressed median, or a flush median at
least 1.2 m (4 ft) in width, was present between the lanes in opposing direction
of travel).
U = Undivided (no median present; a roadway with a flush median less than
1.2 m (4 ft) in width.
- Median width (ft):
Measured from inside edge of the through lane to
inside edge of through lane in the opposite direction of travel (i.e., left-turn
lanes cut into the median were included in the median width). This measurement
was made with a measuring wheel. If the approach was undivided, the median
width as recorded as 0 m (0 ft).
- Median type:
N = No median.
R = Raised median (curbed with turf or pavement in the median).
D = Depressed median (turf median with no curbs). This type of median typically
had a ditch or swale below roadway grade.
F = Flush median (paved median that was flush with the roadway grade).
- One-way/two-way operation:
1 = One-way traffic operation on the intersection leg containing
the approach.
2 = Two-way traffic operation on the intersection leg containing the approach.
- Left-turn prohibition:
N = No left-turn prohibition on this approach.
A = Left turns prohibited from this approach at all times.
M = Left turns prohibited from this approach during the morning peak period
only, but not at other times.
E = Left turns prohibited from this approach during the evening peak period
only, but not at other times.
B = Left turns prohibited from this approach during both peak periods, but
not at other times.
- Number of driveways within 75 m or 250 ft:
Total number of driveways within 75 m (250 ft) of the intersection
on both sides of the street on the intersection leg containing the approach
in question.
- Type of driveways:
N = No driveways (recorded as such if the number of driveways was
equal to zero).
C = One or more commercial driveways included in the driveway count for this
leg of the intersection.
I = One or more industrial/institutional driveways included in the driveway
count for this leg, but no commercial driveways.
R = One or more residential driveways included in the driveway count for this
leg, but no commercial or industrial/institutional driveways.
NOTE: This category was intended to establish a hierarchy in which the driveway
type for the most heavily used driveway(s) was recorded. Commercial driveways
are usually more heavily used throughout the day than industrial/institutional
driveways, which in turn are usually more heavily used than residential driveways.
Industrial/institutional driveways include those that serve factories, non-retail
businesses, government buildings, hospitals, schools, churches, and apartment
complexes (with more than 10 apartments).
- Curb parking within 75 m or 250 ft:
N = No curb parking on the right side of the intersection approach
within 250 ft of the intersection.
P = Parallel parking on the right side of the intersection approach within
250 ft of the intersection.
A = Angle parking on right side of the intersection approach within 250 ft
of the intersection.
NOTE: Width of angle parking area was not included in width of through lanes.
- Traffic control:
N = None.
ST = STOP controlled.
SG = Signalized.
- Left-turn phasing (arrows):
N = No protected left-turn phase (i.e., there was no green arrow
so all left turns were made on the green ball).
A = Protected left-turn phase with left turns allowed only during the protected
phase (i.e., all left turns were made with a green arrow, while no left turns
were allowed on green ball).
B = Protected left-turn phase with left turns permitted both during the protected
phase and on the green ball (i.e., protected/permissive operation).
- Pedestrian signals:
Y = Pedestrian signals (WALK/DON'T WALK) present for crossing the
approach in question.
N = No pedestrian signals for crossing the approach.
- Painted crosswalk on approach:
Y = Painted or marked pedestrian crosswalk present on the approach
in question.
N = No painted crosswalk on the approach in question.
- Advance warning signs:
Y = Advance warning signs (e.g., SIGNAL AHEAD) present on the approach
in question.
F = Advance warning signs present AND the warning signs were accompanied by
flashing beacons.
N = No advance warning signs on the approach.
NOTE: If there was an advance warning sign with any legend other than SIGNAL
AHEAD (or the SIGNAL AHEAD symbol sign), the sign legend was noted as a comment.
Advisory speed limits are not typically used in conjunction with SIGNAL AHEAD
signs; however, if an advisory speed limit was used on the approach (except
for a temporary work zone speed limit), the magnitude of the advisory speed
limit was noted as a comment.
- Posted speed limit (mph):
The posted regulatory speed limit (mph) on each approach.
NOTE: Regulatory speed limit signs are normally repeated at intervals to make
sure that drivers are aware of the speed limit. If there were no speed limit
signs within the immediate vicinity of the intersection, data collectors drove
up to 1.6 km (1 mile) upstream to check for speed limit signs that applied
to the approach in question. If there were no regulatory speed limits signs
on the street, the following default speed limits were used:
25 mph = Business or residential district on a non-state highway.
55 mph = State highways or outside of business and residential areas on non-State
highways.
- Angle of intersection:
The angle between the intersecting approaches. The angle entered
was the smallest angle between the intersecting approaches (i.e., entered
as 90 degrees or an acute angle between 0 and 90 degrees).
NOTE: If the angle was other than 90 degrees, a sketch was made of the three
or four approaches to illustrate which approaches intersected at acute, right,
and obtuse angles.
- Lighting:
N = None.
H = High-mast lighting (not expected at conventional highway intersections;
more typical of freeway interchanges).
S = Street lighting (individual luminaires) continuously along one or both
intersecting streets.
I = Street lighting (individual luminaires) at the intersection, but not along
the intersecting streets.
NOTE: Ambient light sources other than street lighting present at the intersection
were noted by a supplementary code of Y (Yes) or N (No).
- Character of development:
A = Agricultural area.
C = Central business district/downtown.
B = Outlying commercial business district.
I = Industrial district.
M = Mixed commercial and residential development.
R = Residential development.
X = Other (describe in comment).
- Level of pedestrian activity:
L = Low (almost no pedestrian activity).
M = Medium (pedestrian activity with some frequency).
H = High (pedestrian activity with some frequency).
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