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Publication Number: FHWA-RD-02-089
Date: July 2002

Safety Effectiveness of Intersection Left- and Right-Turn Lanes

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:

  1. 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.

  2. 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.

  3. 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:            
1. Number of through lanes
Numeric          
2. Number of left-turn lanes
Numeric          
3. Number of right-turn lanes
Numeric          
4. Type of left-turn treatment
N,C,P          
5. Type of right-turn treatment
N,I,L,R          
6. Horizontal alignment
T,G,M,S          
7. Approach grades
L,M,S / U,D          
8. Crest/sag vertical curves
N,C,S          
9. Total through-lane width (ft)
Numeric          
10. Right shoulder type
P,G,T,C          
11. Right shoulder width (ft)
Numeric          
12. Total LTL width (ft)
Numeric          
13. Total LTL length (ft)
Numeric          
14. Total RTL width (ft)
Numeric          
15. Total RTL length (ft)
Numeric          
16. Divided/undivided
D,U          
17. Median width (ft)
Numeric          
18. Median type
N,R,D,F          
19. One-way/two-way
1 or 2          
20. Left-turn prohibition
N,A,M,E,B          
21. Number of driveways within 250 ft
Numeric          
22. Type of driveways
N,C,I,R          
23. Curb parking within 250 ft
N,P,A          
24. Traffic control
N,ST,SG          
25. Left-turn phasing (arrows)
N,A,B          
26. Pedestrian signals
Y,N          
27. Painted crosswalk on approach
Y,N          
28. Advance warning signs
Y,F,N          
29. Posted speed limit (mph)
Numeric          
30. Angle of intersection
Numeric    
31. Lighting
N,H,S,I/Y,N    
32. Character of development
C,B,I,M,R,X    
33. Level of pedestrian activity
L,M,H    
  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Right shoulder type:

    P = Paved.

    G = Gravel.

    T = Turf.

    C = Curb.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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).

  15. 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).

  16. 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.

  17. 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.

  18. 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.

  19. 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).

  20. 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.

  21. Traffic control:

    N = None.

    ST = STOP controlled.

    SG = Signalized.

  22. 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).

  23. Pedestrian signals:

    Y = Pedestrian signals (WALK/DON'T WALK) present for crossing the approach in question.

    N = No pedestrian signals for crossing the approach.

  24. 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.

  25. 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.

  26. 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.

  27. 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.

  28. 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).

  29. 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).

  30. 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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