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ion.
• Left-Turn Volume (VL) – the portion of the advancing volume that turn left at theintersection.
• Percent Left Turns (PL) – the percentage of the advancing volume that turn left; equal to theleft-turn volume divided by the advancing volume (PL = VL ÷ VA).
• Straight Through Volume (VS) – the portion of the advancing volume that travel straight
through the intersection (VL + VS = VA).
• Opposing Volume (VO) – the total peak hourly volume of vehicles opposing the advancing
volume.
Figure 1. Volumes for Use in Left-Turn Lane Warrant Methods.
Advancing Volume
(VA)
Left-Turning Volume
(VL)
Straight Through
Volume (VS)
Opposing Volume
(VO)
Fitzpatrick and Wolff 3
2nd Urban Street Symposium (Anaheim, California) — July 28-30, 2003
GUIDELINES REVIEWED

CONCLUSIONS
Several methods are available for determining when to include a left turn lane in the design at an
intersection. Methods based on delay typically do not recommend a left-turn lane at lower left or
through volumes when compared to methods based on conflict avoidance or safety. Because of
the high benefits for crash reductions provided by left-turn lanes, a method that results in a
recommendation at lower volumes would be preferred. The Harmelink model is a widely
accepted approach that is based on conflict avoidance. The procedure first proposed by
Harmelink in 1967 includes assumptions that may need to be revised. Findings from current
research on the time to clear an intersection and on critical gaps suggest that Harmelink
guidelines should be modified. Table 5 lists suggested guidelines for installing left-turn lanes for
operating speeds of 30, 50, and 70 mph (50, 80, and 110 km/h).
If the Harmelink approach is preferred and the operating speed of interest (or number of lanes) is
not provided in Table 5, the reader can use the interactive spreadsheet included as part of
NCHRP 457 (https://trb.org/trb/publications/nchrp/esg.pdf). The assumptions need to be changed
to match those at the intersection of interest or to reflect more recent research findings such as
using a critical gap of 5.5 sec, a time to make left turn of 4.3 sec, and a time to clear of 3.2 sec.
Fitzpatrick and Wolff 20
2nd Urban Street Symposium (Anaheim, California) — July 28-30, 2003
Table 5. Guidelines for Installing Left-Turn Lanes on Two-Lane Highways.
Vo Percent Left Turns
10 20 40
30 mph (50 km/h)
800 197 148 121
700 217 162 133
600 238 178 146
500 261 196 160
400 286 215 175
300 314 236 193
200 345 259 211
100 380 285 232
0 418 313 256
50 mph (80 km/h)
800 153 115 94
700 168 126 103
600 184 138 113
500 202 152 124
400 222 166 136
300 244 183 149
200 268 201 164
100 294 221 180
0 323 243 198
70 mph (110 km/h)
800 88 66 54
700 97 73 59
600 106 80 65
500 117 88 71
400 128 96 78
300 141 105 86
200 154 116 95
100 170 127 104
0 187 140 114
ACKNOWLEDGMENTS
This paper is from research conducted as part of a project sponsored by the Texas Department of
Transportation and performed by the Texas Transportation Institute of the Texas A&M
University System. The contents of this paper reflect the views of the authors, who are
responsible for the facts and the accuracy of the data presented herein. The contents do not
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