ITE Journal - August 2020 - 49

of lanes and distance to cross. Needless to say, implementation of
a protected/permitted display such as the FYA not only has the
potential to improve capacity, but also reduces the temptation
of running the red light signal, especially during light traffic
conditions when there are adequate gaps available in opposing
through movement.
The efficiency factor should always be considered as it increases
utilization level of green interval(s) and eliminates mandatory
holding of a green phase. This holds true even when there is no
demand on that movement, and has direct impact on generating
unnecessary stops, delays, increased fuel consumption, and negative
impact on air quality.

Conclusion
As shown in Table 1, the calculation result indicates that the build
scenario will significantly improve the traffic operation at Loop 820
and Marine Creek Parkway. The interchange cycle length can be
reduced from 145 seconds to 110 seconds. Average traffic delay will
reduce from 84.8 seconds to 52.1 seconds-an almost 38 percent
reduction of average delay. Build scenario will improve the level of
service from LOS "F" to LOS "D.
This improvement is only accommodated by utilizing an
alternative and modified phasing sequence, which is made possible
by the geometric modification that allows concurrent serving of
both eastbound and westbound left turns together, rather than
serving each side at a time or in sequence.
Table 1. Level of Service (LOS) Calculation at Marine Creek Parkway at
Loop 820 LOS.
Before

After

Movement

Delay

LOS

Delay

LOS

NB

69

E

71

E

NBL

36

D

37

D

SB

124

F

64

E

SBL

10

A

54

D

EB

99

F

32

C

WB

93

F

55

D

Intersection
Delay

84.8

F

52.1

D

FLDI is a unique solution that, at a minimum, provides
operational flexibility and improved capacity without restricting
any movements or impacting accessibility to adjacent properties. In
summary, the followings are advantages of FLDI configuration:
ƒ	 Ability to use additional and alternative signal phasing
sequences that could be utilized for improved synchronization along arterial roadways.

ƒ	 Improved capacity due to the fact that arterial movements
become independent of each other, which allows for
termination of a companion movement in absence of
demand and instead allows serving of the next movement in
the signal phasing sequence which has demand.
ƒ	 Providing arterial left-turn movements with permissive
indications and permissive intervals would enhance
intersection capacity and LOS, reduce unnecessary stops
and delays, and reduce the potential of red-light violation,
specifically during light traffic demands.
It is worth noting that all modifications at this interchange
are being done utilizing the existing lanes. There is no need
to add lanes that requires additional ROW or modifying the
existing infrastructure.
Roadway designs and constructions are major tasks. They
have high design and construction costs; and long-term impacts
on those who use them. It is crucial that different alternatives
and solutions be evaluated and compared against each other, and
against short- and long-term impact to all stakeholders, before
the most appropriate solution is chosen. It is highly recommended
that besides concentrating on a solution that solely addresses the
most common short-term need of additional capacity, long-term
factors including operational flexibility, accessibility, and efficiency
be considered to ensure a longer lasting solution. It is crucial to
understand that solutions which only meet today's needs and
today's shortfalls might not have the sustainability factor that is
adequate to handle fluctuation and changes in traffic demand and
pattern. A sound and proper design alternative should be able to
withstand unexpected scenarios, as it would be less susceptible to
change in traffic volume or change in traffic pattern; and where
it would not require modifications that are both expensive and
disruptive to the traveling public in the long term. itej
Ali Mozdbar, P.E., PTOE (F) has more than 35 years of
experience in traffic engineering, signal design and
operations, signal systems timing development and
implementation, intelligent transportation systems
applications, communication network design and
implementation, development of technical specifications, PS&E
(plans, specs, and estimate) development, and bidding and construction phase services. Before joining LJA Engineering, Inc. as senior
project manager in Austin, TX, Ali worked for several major cities in
Texas as the city traffic signal engineer. He has a bachelor's degree in
Civil Engineering and a master's degree in Civil Engineering from
University of Texas at Arlington. He was the recipient of the ITE
Texas District Engineer of the Year Award in 2002, and the Wallace
Ewell Award from the Intelligent Transportation Society of
Texas in 2019.
w w w .i t e.or g

Augu st 2020

49


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