ITE Journal - January 2020 - 39

Conclusion
Either of the mistakes discussed can cause the analyst to
underestimate delay when conducting an intersection analysis.
When both mistakes are made (also a common occurrence), the
errors are exacerbated.
How does one know if a multiple period analysis is needed and
if actual demand is greater than stop line counts? A good rule-ofthumb is that a multiple-period analysis should be performed if any
one lane group approaches a volume-to-capacity ratio of 1.00. This
also would imply that stop line counts should be adjusted to reflect
demand, either by using the method illustrated in this article or by
collecting concurrent mid-block counts upstream of the stop line
(beyond the back of the queue) and adjusting the stop line counts
proportionally. itej

References
1. Transportation Research Board, Highway Capacity Manual, Special Report
209, Washington, DC, USA, 1985.
2. Transportation Research Board, Highway Capacity Manual, Special Report
209, Third Edition, Washington, DC, USA, 1998.

3. Transportation Research Board, Highway Capacity Manual, Washington,
DC, USA, 2000.
4. Transportation Research Board, Highway Capacity Manual, 6th Edition: A
Guide for Multimodal Mobility Analysis, Washington, DC, USA, 2016.

Tom Creasey, P.E., Ph.D. (M) is vice president of
Transportation Engineering for Caliper Corporation.
He is a longtime member of the TRB Highway Capacity
and Quality of Service Committee, which oversees the
Highway Capacity Manual, and currently serves as
chair of the committee. Tom received his bachelor's, master's, and
Ph.D. degrees in civil engineering from the University of Kentucky.
Bill Sampson, P.E. (F) is the director of the McTrans
Center at the University of Florida and is responsible
for technical assistance and ongoing development of the
Highway Capacity Software. He is a former member of
the TRB Highway Capacity and Quality of Service
Committee and has been continually active for more than 30 years.
Bill received his bachelor's and master's degrees in civil engineering
from the University of Kentucky.

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