Resolution 064-2021 s
2 MONROE COUNTY, FLORIDA
3 MONROE COUNTY BOARD OF COUNTY COMMISSIONERS
4 RESOLUTION NO. 064 -2021
5
6
7 A RESOLUTION BY THE MONROE COUNTY BOARD OF
8 COUNTY COMMISSIONERS APPROVING UPDATES TO
9 THE U.S. 1 LEVEL OF SERVICE ("L.O.S.")
10 METHODOLOGY BASED ON RECOMMENDATIONS
11 MADE BY THE U.S. 1 L.O.S. TASK FORCE WHICH
12 EVALUATED CONSIDERATIONS IDENTIFIED IN THE
13 DRAFT 2019 ARTERIAL TRAVEL TIME AND DELAY
14 STUDY ("ATTDS").
15
16 WHEREAS, in August, 1991, the BOCC adopted the U.S. 1 Level of Service ("L.O.S.")
17 C as measured by the U.S. 1 L.O.S. Methodology established by the U.S. 1 L.O.S. Task Force;
18 and
19 WHEREAS, on December 10, 1997, the BOCC approved an amendment to the U.S. 1
20 L.O.S. Methodology based on recommendations of the U.S. 1 L.O.S. Task Force; and
21 WHEREAS, on July 15, 2020,the BOCC considered the Draft 2019 Arterial Travel Time
22 & Delay Study ("ATTDS"), prepared by the County's traffic consultant, AECOM Technical
23 Services, Inc. ("AECOM"), which identified several considerations regarding methodology; and
24 WHEREAS, at the July 15, 2020, meeting,the BOCC directed staff to re-engage the U.S.
25 1 L.O.S. Task Force to evaluate the L.O.S. methodology and consider updates to it based on the
26 considerations identified in the Draft 2019 ATTDS; and
27 WHEREAS, on October 21, 2020, the BOCC adopted Resolution No. 355-2020,
28 reconvening the U.S. 1 L.O.S. Task Force and tasking the U.S. 1 L.O.S. Task Force with evaluating
29 the L.O.S. Methodology and potential updates to it based on the considerations identified in the
30 draft 2019 ATTDS; and
31 WHEREAS, U.S. 1 L.O.S. Task Force met on November 10, 2020, January 6, 2021, and
32 January 21, 2021, to evaluate the L.O.S. methodology and to consider updates to it based on the
33 considerations identified in the Draft 2019 ATTDS; and
1 of 3
I WHEREAS, U.S. 1 L.O.S. Task Force agreed to the following recommended items
2 through a roll call for vote for the update to the L.O.S. methodology at the January 21, 2021,
3 meeting:
4 1. Signal Delay: Increase to 35 seconds (to be consistent with the current Highway
5 Capacity Manual);
6
7 2. Signal Delay: Continue to apply to only uninterrupted segments (not overall U.S.-1
8 L.O.S. calculations);
9
10 3. Drawbridge Delay: Deduct delays due to drawbridge openings from the time run
11 calculations for both affected segments and overall U.S.-1, using a delay time of 6
12 minutes (average gate closure time based on FDOT data for drawbridge delays), and
13 applying to only those travel runs which were impacted by bridge openings;
14
15 4. Overall L.O.S. calculation methodology for segments versus overall U.S.-1 will stay
16 the same;
17
18 5. Travel Time Schedule: Conduct 2021 travel time runs based on current schedule. Also,
19 conduct supplemental runs in the southbound direction within Segments 1 to 4 during
20 AM peak (7-8 AM) on Wednesday, Thursday and Friday of the second week.
21 Additionally, conduct supplemental runs in the northbound direction within Segments
22 1 to 4 during the PM Peak(5-6 PM)on Wednesday, Thursday, and Friday of the second
23 week. The results of the supplemental runs will be included in the 2021 ATTDS Report
24 for informational purposes only and will not be used in overall L.O.S. calculations.
25 This information will be reviewed to decide if supplemental runs should be
26 incorporated into future ATTDS and L.O.S. calculations, as directed by the Monroe
27 County BOCC; and
28
29 6. Include by reference the Data Collection Methodology into the U.S. 1 L.O.S.
30 Methodology document.
31
32 NOW, THEREFORE, BE IT RESOLVED BY THE BOARD OF COUNTY
33 COMMISSIONERS OF MONROE COUNTY, FLORIDA, THAT:
34 Section 1. The recitals contained herein are true and correct and are hereby
35 incorporated as if fully set forth herein.
36 Section 2. The Board of County Commissioners does hereby adopt the
37 recommendations of the U.S. 1 L.O.S. Task Force and the 2021 Updated
38 methodology document, A Methodology To Assess Level-Of-Service On
39 US-1 In The Florida Keys, attached as Exhibit A, for County use.
40
41 PASSED AND ADOPTED by the Board of County Commissioners of Monroe County,
42 Florida, at a regular meeting of the Board held on the 17th day of February, 2021.
2of3
1
2 Mayor Michelle Coldiron Yes
3 Mayor Pro Tern David Rice Yes
4 Commissioner Craig Cates Yes
5 Commissioner Eddie Martinez Yes
6 Commissioner Mike Forster Yes
7
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�, ) r OF MONROE • : s
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/ MAYOR MICHELLE COLDIRON
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16 T: KEVIN MADOK, CLERK
17 MONR O tarry
18
19 By g _ -v PETER MORRIS
20 AS DE UTY CLERK ASSISTANT COUNTY ATTORNEY
Dale: 2/2/21221
21
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3 of 3
R.E. De Arazoza
D.S.Macleod
Exhibit A
A METHODOLOGY TO ASSESS LEVEL-OF-SERVICE
ON US-1 IN THE FLORIDA KEYS
By
Rafael E. De Arazoza
Florida Department of Transportation
District 6
602 South Miami Avenue
Miami, Florida 33130
(305) 377-5910
And
Douglas S. McLeod
Florida Department of Transportation
Mail Station 19
605 Suwannee Street
Tallahassee, Florida 32399-0450 (904) 922-0449
For Presentation at the
Transportation Research Board Annual Meeting
January 1993
UPDATE January 2021
Updated by AECOM Technical Services, Inc.
Based on input from the 2020/2021 US-1 LOS Task Force
Page 1 of 11
R.E. De Arazoza
D.S. Macleod
ABSTRACT
This paper presents the methodology developed to assess level-of-service (LOS) on US-1
in the Florida Keys. Although predominantly an uninterrupted flow two-lane roadway in the
Keys, US-1's uniqueness warrants all alternative LOS evaluation process to that found
in the 1985 Highway Capacity Manual.
U.S.-1 extends from the Key West to the Florida mainland with no major roads
intersecting it. Furthermore, no other principal arterial serves the Keys or the Keys' resident
and tourist population, over 100,000. Its unique geography, land use patterns, trip making
characteristics presented a challenge in developing and applying a reasonable and acceptable
method to assess its LOS.
A uniform method was developed to assess LOS on U.S.-1 to cover both its overall arterial
length from Key West to the Florida mainland, and 24 roadway segments delineated. The
methodology employs average travel speed as the main measure of effectiveness. It was
developed from basic criteria and principles contained in Chapters 7 (Rural Multilane
Highways), 8 (Rural Two-Lane Highways) and 11 (Urban and Suburban Arterials) of the 1985
Highway Capacity Manual.
The results of the study correlate well with perceived operating conditions on US-1 and over a
two- year period the methodology appears to have a good level of reliability. The authors
recommend that for uninterrupted flow conditions in developed areas, Chapters 7 and 8
of the Highway Capacity Manual incorporates average travel speed as the main measure of
effectiveness to determine LOS.
Page 2 of 11
R.E. De Arazoza
D.S. Macleod
A METHOD TO ASSESS LEVEL-OF-SERVICE
ON US-1 IN THE FLORIDA KEYS
INTRODUCTION
The purpose of this paper is to present the methodology developed by the Monroe County US-
1 level- of-service (LOS) Task Force to assess LOS on US-1 (the Overseas Highway) in the
Florida Keys (1). The authors are members of the referenced task force.
US-1 which is mostly two-lanes, has unique geographic and trip characteristics. It extends
through the Florida Keys covering approximately 180 kilometers (112 miles) from the City of
Key West to the Florida mainland (Figure 1). There are 48 bridges crossing water for a total
length of 35 km (22 mi), with the longest bridge approximately 11 km (7 mi) long. There is no
other road, to provide vehicular access to the Florida Keys from the rest of Florida or
anywhere else. Few local roads are 5 km(3 mi) in length. Consequently, US-1 serves not only
as a regional principal arterial which serves intra as well as interstate travel, but also serves
as the local road for most of the trips within the Keys. US-1 Annual average daily traffic
(AADT) volumes range from a low of 4700 to a high of 34200. The road serves a large tourist
demand and is one of the most scenic in the United States. The linear geography with the
narrow land width of most of the Florida Keys are further characteristics.
Most of the surrounding land use is rural developed and suburban in nature; however, some
areas are totally rural and others are urban, such as the Key West and its suburbs. With the
exception of the few completely rural segments and the bridges, strip commercial stores,
motels and restaurants are very common throughout the Keys along US-1. Numerous
driveways and intersecting local roads provide access to the surrounding residential areas.
The US-1 LOS study encompassed approximately 174 km(108 mi)of US-1 from Key
West/Stock Island to the Monroe/Dade County Line, broken down as follows:
0 129 km (80 mi) (74%) two-lane uninterrupted flow;
0 32 km (20 mi) (19 %) four-lane uninterrupted flow; and
0 13 km (8 mi) (7%) four-lane urban/suburban interrupted flow.
Page 3 of 11
R.E. De Arazoza
D.S. Macleod
Part of the growth management process in Florida is to assess roadway LOS to determine if
roadway facilities meet standards established by state regulations. The Transportation
Research Board Special Report 209 Highway Capacity Manual (HCM) (2) is extensively used
throughout Florida as the source document to determine highway capacities and LOS.
HCM Chapter 7 (Rural Multilane Highways), 8 (Rural Two-Lane Highways) and 11 (Urban and
Suburban Arterials) were consulted to determine applicability to the unique conditions and
vehicular traffic operations and characteristics of the Florida Keys. Only the 13 km (8
mi) of urban/suburban interrupted flow and the small percentage of the two-lane truly rural
portions correlate directly to the HCM Chapters 11 and 8.
Thus, the challenge was to develop a methodology to assess arterial LOS along US-1 without
deviating from the principles of the HCM. Towards that end a task force was created
consisting of representatives from State and local agencies and an engineering consulting
firm.
Page 4 of 11
R.E. De Arazoza
D.S. Macleod
THE NEED TO DEVELOP A LOS MEASUREMENT METHOD
From a state transportation perspective, the overall operating condition of US-1 is important,
not the condition of any smaller segment. With Key West as a major tourist destination at the
southern end of the Keys and no alternative routes, the logical analysis section of highway
extends from Key West to the mainland. From local transportation and development approval
perspectives,shorter segments for analysis are desirable.
Chapter 8 of the HCM presents a methodology which applies to typical rural two-lane highways
with basically long stretches of roads,and few side intersecting streets and driveways directly
connecting to the roads. Chapter 8 methodology relies mainly on "percent time delay" to
assess LOS. The HCM further states that "Percent time delay...is defined as the average
percent of time that all vehicles are delayed while traveling in platoons due to inability to pass.
Percent time delay is difficult to measure directly in the field. The percent of vehicles traveling
at headways less than 5 seconds can be used as a surrogate measure in field studies."
Chapter 8 of the HCM also uses average travel speed and capacity utilization as additional
measures of effectiveness to assess LOS. However, the HCM states clearly that percent time
delay is the primary measure of service quality. Further inspection of the average speeds
for level terrain depicted by Table 8-1 of the HCM do not correspond well with the typical
operating speeds of US-1 in the Florida Keys. For instance, Table 8-1 shows average speeds
ranging from 58 mph (93 kmh) (LOS A) to 45 mph (72 kmh) (LOS D).
The overall weighted posted speed limit for US-1 in the Florida Keys is 79.7 kmh (49.5 mph).
The overall median operating speeds along US-1 according to the 1991 and 1992 field studies
(3, 4) were 76.8 and 75.5 kmh (47.7 and 46.9 mph), respectively. The field studies showed, for
the most part, the survey vehicle(s) was traveling close to the posted speed limit.
It is believed the average motorist in the Florida Keys is mostly concerned with operating
at an acceptable average travel speed rather than being concerned about the ability to
pass. This is supported by the physical and traffic characteristics of the Keys (e.g.,
adjacent land development, sight-seeing tourists), local knowledge, and discussions with
motorists.
Page 5 of 11
R.E. De Arazoza
D.S. Macleod
From the above statements, it was clear to the task team that HCM Chapter 8 methodology
could not be applied to US-1 for analysis of its two-lane sections.
With regards to the four-lane uninterrupted flow portions of US-1, a similar dilemma occurred.
HCM Chapter 7 methodology applies to multi-lane highways with operating characteristics
generally unlike those of US-1 through the Florida Keys. For instance, average travel speeds
depicted by Table 7-1 of the HCM are also higher than those encountered in the Keys. Further,
the methodology inherent in equations (7-1), (7-2) and (7-3)are closely related to those of
freeways with their higher service flow rates, which again neither simulate nor resemble those
of US-1 in the Keys. The Four-lane portion is found mostly in Key Largo(the northeastern end
of the Keys) which has a weighted posted speed limit of 72.5 kmh (45 mph). Key largo is
developed with strip commercial and residential development. It has numerous driveway
connections and side streets directly accessing US-1.
The remaining 7% of the total US-1 mileage is four-lane interrupted flow. These are the
portions encompassing Marathon(in the middle of the Keys)and Stock Island(near Key West).
The operating characteristics here are truly urban/suburban and interrupted flow in nature
resembling those of HCM Chapter 11. Thus, the methodology of Chapter 11 was employed in
assessing LOS on these segments.
From the preceding discussion, it was evident that a distinct method to assess LOS on US-1
had to be developed. The task team's efforts concentrated on keeping consistency with the
basic philosophy of the HCM,and yet be sensitive to the Keys uniqueness. Thus,the proposed
methodology correlates measured travel speeds along US-1 with LOS speed thresholds
developed as part of this study. This is in line with the concept behind the HCM of average
travel speed being the main parameter to measure arterial LOS.
Page 6 of 11
R.E. De Arazoza
D.S. Macleod
METHODOLOGY
Considering the types of trips served by US-1, it was decided to conduct travel time and delay
runs to cover both the entire length of US-1 from Key West to the Monroe/Dade County Line
(mainland) and for each segment of the highway along the way. Twenty-four segments were
selected as depicted by Table 1. Each segment is fairly homogeneous in nature having a
uniform roadway cross section and traffic flow.
Travel speeds for the overall length (from Key West to the mainland) provide an indication of
the LOS for the regional trips. Travel speeds for each segment also provides an opportunity
to assess the impact of local trips. Establishing speed criteria for both the overall length
and for each roadway segment satisfies the requirements of the Florida growth management
process.
The next step in the process was to determine the number of travel time runs and how, when
and to/from where. Runs were started at both ends of US-1. For example, one run started on
Stock Island (Key West City limits) and proceeded to the mainland (Dade County). After
reaching this point, the vehicle turned back and proceeded to end the run where it started, on
Stock Island. On another day the reverse was true (i.e., the run started in Dade County instead
of Stock Island). It was decided to perform a total of fourteen two-way runs or twenty-eight in
each direction covering the 174 km (108 mi)study portion of US-1. Twenty-eight runs provide
enough data for statistical significance. Control points were established at each of the 24
segments to record travel time and speed data specific to each one of those segments. Seven
runs were started at Stock Island and seven in Dade County. Each began at staggered hours
to cover the varied trip purposes and time frames within the Keys. The surveys were conducted
during March, reflecting the area's peak traffic season.
The 2021 travel time runs shall be conducted based on the current schedule. In addition,
supplemental runs shall be conducted in the southbound direction within Segments 1 to 4
during AM peak (7-8 am) on Wednesday, Thursday and Friday of the second week. Also,
conduct supplemental runs in the northbound direction within Segments 1 to 4 during the PM
Peak (5-6pm) on Wednesday, Thursday, and Friday of the second week. The results of the
supplemental runs will be included in the 2021 ATTDS Report for informational purposes only
and will not be used in overall or segment LOS calculations. This information will be reviewed
to decide if supplemental runs should be incorporated into future ATTDS and LOS
calculations, as directed by the Monroe County BOCC.
Page 7 of 11
R.E. De Arazoza
D.S. Macleod
For each run the process provided data (see Exhibit 1, Data Collection Methodology), such as
running speed and travel speed, in each direction of US-1. Vehicular traffic counts were also
collected at three locations covering seven days.
The travel time runs yielded a total of 28 one-way travel speed values for the overall length of
US-1 and for each of the 24 segments. The value selected for analysis was the median speed
which would reflect a "typical peak period during the peak season." In other developed parts
of Florida the typical peak hour of the peak season approximates the 100th highest hour of
the year(5). The median value was also selected, instead of the average,to avoid the influence
of extremely high or low speed value at either end of the survey population. The process up
to this point provided median travel speeds. The question then became, what LOS do these
speeds represent.
The next step was to develop a set of LOS/Speed threshold values for both the overall length
of US-1 and the pertinent segments of the highway. Towards this end, the speed ratios
between LOS thresholds from Tables 7-1, 8-1 and 11-1 of the HCM were used in the analysis.
These ratios were weighted against actual mileage of US-1 in the Florida Keys to represent
the prevailing type of flow; two-lane uninterrupted flow, four-lane uninterrupted flow and four-
lane interrupted flow. For example, from the level terrain portion of HCM Table 8-1, the ratio
between LOS B speed and LOS A speed is 55/58 = 0.948. The ratio between LOS C/LOS A =
52/58 = 0.897; the ratio between LOS D/LOS A = 50/58 = 0.862 and so on. The same process
was applied to Tables 7-1 (96.6 kmh)(60 mph)and 11-1. Then each ratio was weighted to take
into account the length of the section of US-1 to which that type of traffic flow applied. Once
all the ratios were developed, the weight criteria was applied as in the following example:
TYPE OF FLOW LOS C/LOS A RATIO WEIGHT
Two-lane uninterrupted 52/58 = 0.897 74
Four-lane uninterrupted 44/50 = 0.880 19
Four-lane interrupted 22/35 = 0.629 07
Therefore, the overall speed ratio between LOS C and LOS A is:
[74(0.897)+19(0.880)+7(0.629)]+100=0.875
Page 8 of 11
R.E. De Arazoza
D.S. Macleod
The above process was applied to develop all the required ratios. Further observations with
reference to Tables 8-1, 7-1 and 11-1 yielded the following. From Table 8-1 the difference
between LOS A and LOS B speeds is 4.8 kmh (3 mph), or 4.8 kmh (3 mph)above an assumed
posted speed limit of 88 kmh (55 mph). From Tables 7-1 and 11-1 the differences are 3.2 kmh
and 11.3 kmh (2 mph and 7 mph), respectively, with LOS lower than assumed speed limits.
Therefore, from these observations plus local knowledge, it was determined that the overall
US-1 posted speed limit is 79.7 kmh (49.5 mph) reasonably fell between the LOS A and B
thresholds.
This assumption is not far away from the premise that if a vehicle is able to sustain a travel
speed equal to the posted speed limit, then it will correspond typically with the upper ranges
of LOS (i.e., LOS A or B).
With the above speed differentials and LOS range premise in mind, the US-1 overall speed
thresholds for LOS A and B became 82.1 kmh (51 mph) (2.4 kmh (1.5 mph) above 79.7 kmh
(49.5) and 77.3 kmh (48 mph), respectively. Applying the developed ratio between LOS
C/LOS A to the LOS A speed resulted in 72.5 kmh (45 mph), rounded off (i.e., 0.875 x 82.1
kmh (51 mph) = 71.8 kmh (44.6 mph)), which then became the threshold for LOS C. After
applying all the ratios the overall LOS criteria for US-1 became:
LOS Speed
A >_ 82 kmh (51 mph)
B >_ 77 kmh (48 mph)
C >_ 72 kmh (45 mph)
D >_ 68 kmh (42 mph)
E >_ 58 kmh (36 mph)
F < 58 kmh (36 mph)
Inspection of the criteria above indicates a close relationship with the speed differentials
of both Tables 8-1 and 7-1 of the HCM. Comparing the median speed data for US-1 from the
1991 and 1992 field studies to the above criteria resulted in an overall LOS of C for both years,
i.e., 76.8 kmh (47.7 mph)for 1991 and 75.5 kmh (46.9 mph)for 1992. These speeds are 2.9 kmh
(1.8 mph)and 4.2 kmh(2.6 mph) below the overall weighted 79.7 kmh (49.5 mph) speed limit,
which would correspond to the upper range of LOS C. The authors also believe that LOS C
is the appropriate LOS designation for the whole of US-1 from Key West to the mainland.
Page 9 of 11
R.E. De Arazoza
D.S. Macleod
A final step was still needed to complete the task of developing LOS/Speed threshold values
for the segments of US-1. No further work was needed to cover the 7% mileage of the
interrupted portions of US-1 found on Marathon and Stock Island, adjacent to Key West.
As discussed earlier, these segments correlate with Chapter 11 of the HCM. Therefore,direct
application of Table 11-1 LOS/speed criteria for a Class I arterial was made.
The remaining segments fell within the two-lane and four lane uninterrupted flow criteria.
It was decided to make LOS A speed criterion 2.4 kmh (1.5 mph) above the weighted posted
speed limit in order to keep consistency with the overall criteria. LOS C speed was set 9.7
kmh (6 mph) below LOS A speed consistent with Tables 7-1 and 8-1 of the HCM. LOS B and D
speed criteria were set to provide equal increments between LOS A and LOS D (i.e., LOS B 4.8
kmh (3 mph) below LOS A speed and LOS D 4.8 kmh (3 mph)below LOS C speed). LOS E was
set 9.7 kmh (6 mph) below the LOS D Speed. This makes the segmental speed differential
between LOS thresholds consistent with the differentials in the overall criteria, except for
one consideration. On any uninterrupted flow segment, signalized intersection delay would
be deducted from the segment's travel time to account for the influence of that signal ^" the
seg the traffic signals (i.e., signal delay = 1.0 x 4,&-35 seconds average stopped delay).
This corresponds to an LOS C delay due to isolated signals. LOS C delay was chosen because
LOS C is the state LOS standard for US-1 in the Florida Keys. The rationale behind deducting
signal delay from the segment analysis was to recognize the impact of signals in reducing travel
time. This provides the required sensitivity in the segment which is not only to assess the
impact of regional vehicular trips, but also those that are local in nature. The following
illustrates the concept plus one example for the US-1 Segmental LOS/speed relationship.
o The uninterrupted flow segment criteria are:
LOS SPEED
A >_ 2.4 kmh (1.5 mph) above the posted speed limit
B >_ 4.8 kmh (3.0 mph) below LOS A
C >_ 9.7 kmh (6.0 mph) below LOS A
D >_ 14.5 kmh (9.0 mph) below LOS A
E >_ 24 kmh (15.0 mph) below LOS A
F <24 kmh (15.0 mph) below LOS A
o A segment having a weighted posted speed limit of 72 kmh (45 mph)would then have
this criteria:
Page 10 of 11
R.E. De Arazoza
D.S. Macleod
LOS SPEED
A >_ 74.9 kmh (46.5 mph)
B >_ 70.0 kmh (43.5 mph)
C >_ 65.2 kmh (40.5 mph)
D >_ 60.4 kmh (37.5 mph)
E >_ 50.7 kmh (31.5 mph)
F < 50.7 kmh (31.5 mph)
o The LOS/Speed criteria for interrupted flow segments (marathon and Stock
Island)are based directly on a Class I arterial from Table 11-1 of the HCM.
LOS SPEED
A >_ 56.4 kmh (35 mph)
B >_ 45.1 kmh (28 mph)
C >_ 35.4 kmh (22 mph)
D >_ 27.4 kmh (17 mph)
E >_ 20.9 kmh (13 mph)
F < 20.9 kmh (13 mph)
Speed data from both the overall length of US-1 and the individual segments were compared
against the applicable LOS/speed thresholds. This provided for an assessment of the facility
LOS plus an indication of reserve speed, if any.
Under Florida's and Monroe County's growth management process if the overall LOS for
US-1 fell below the LOS C standard, then no additional land development would be allowed
to proceed in the Florida Keys. Unless the proposed new development traffic impact were
mitigated. If the overall LOS for US-1 was C or better, then additional development could take
place in those segments where there was reserve speed available (i.e., segment's speed was
higher than the standard threshold).
Besides meeting highway LOS standards there are numerous other considerations in Florida's
growth management process pertaining to the Florida Keys that are beyond the scope of
this paper. As mentioned in the introduction, the purpose of this study was to present the
methodology to assess-LOS on US-1.
Page 11 of 11
Exhibit 1
DATA COLLECTION METHODOLOGY
(Previously Approved by Task Force)
Calibration of the DMI
Prior to beginning the study, the DMI was calibrated over a half-mile course. The
calibration procedure set-up by the DMI manufacturer established a calibration factor
of 0.682 for the test vehicle, which resulted in measurements within 3 feet of the 5,280-
foot distance (0.057%). At this level of accuracy, the DMI would measure the 108 mile
distance of US 1 between Stock Island and the Dade County line to within 325 feet, or
to within 0.03 mile per hour(mph) of the 45 mph standard for LOS C.
loatin_ ar Method an assin_ Score
The study employed the floating car method, whereby under ideal conditions the test
vehicle passes and is passed by an equal number of vehicles (i.e. "goes with the flow").
A passing score was recorded for each segment to document the extent to which this
objective was accomplished. Positive scores indicate the number of excess vehicles
the test car passed; negative scores indicate the number of excess vehicles that passed
the test car; and zero indicates an even balance. The overall passing score consists of
the sum of the segment scores.
The passing score provided an objective measure of the traffic flow, allowing the driver
to adjust the test car speed accordingly. In the event that the traffic flow was higher
than the posted speed limit, as was frequently the case in the Dade County and Boca
Chica segments, the test car also traveled above the speed limit.Vehicles turning on or
off US 1 were omitted from the passing score.
Employing the floating car method in two-lane segments was fairly straightforward,
where the observers frequently encountered platoons of sufficient size to discourage
or prohibit passing. When positioned at the rear or in the middle of a platoon, the
observers simply traveled with the pack.When positioned as the lead car,the observers
avoided delaying the platoon yet kept the platoon within sight.
On two-lane segments the observers occasionally encountered stopped vehicles
waiting to turn left, raising the question of whether the test vehicle should leave the
lane or paved road surface and pass to the right of the stopped vehicle. When the
vehicles ahead of the observers passed to the right of the stopped vehicle, then the
observers did also. However, when the test car was the lead car in the platoon, the
observers only passed on the right if they could do so without leaving the paved
roadway.
Within four-lane segments with light congestion, the observers often encountered
traffic traveling in the right lane at or below the posted speed limit, while there was little
or no traffic in the left lane. Rather than "floating" below the speed limit in the right lane
or traveling at the maximum possible speed in the left lane, the observers traveled at
the posted speed limit, which resulted in passing score as high as +10. Thus, in these
cases,a passing score of zero is undesirable,since the corresponding speed would fail
to reflect the availability of the vacant passing lane.
Within four-lane segments with moderate or heavy congestion, the observers often
encountered separate platoons in the right and left lanes, with the left lane typically
Page 1 of 2
Exhibit 1
moving at a faster speed. Rather than continuously changing lanes to achieve a
passing score of zero, the test car"floated" in the faster of the two platoons,which also
yielded high passing scores.
Platoon Size
To provide a measure of roadway congestion within each segment,the average number
of vehicles traveling in the test car's platoon was recorded, including the test car itself.
Within four-lane segments,this number represents the average number of vehicles that
traveled in the test car's platoon within the test car's lane.
Treat men o slay
In accordance with the FDOT Manual on Uniform Traffic Studies, the observers began
recording delay when the test car's speed fell to 5 mph and terminated the delay event
when the test car's speed rose to 15 mph. Each delay entry was identified, in the DMI
memory by a sequential code number. The observers recorded the type and location
of the delay on a field data sheet.
When computing both segments and overall travel times, delays due to typical events
such as turning movements, traffic signals, and certain types of congestion were
included. Unusual or non-recurring delays, such as construction, accidents, school
bus, and emergency vehicles were excluded. Delays due to drawbridge openings were
should be deducted from the segment travel times(all affected segments), but inGlude
e and the overall travel times, to account for the influence of the drawbridge
openings. A delay of 6 minutes should be deducted from those travel time runs that
were impacted by bridge openings. -However, regardless of how a particular type of
delay was treated in the analysis, all delays of all types were identified and recorded on
the field data sheets.
Occasionally an external event slowed traffic speeds, but not enough to meet the 5 mph
criteria for a formal delay. Highway construction and maintenance activities were the
most common example of this borderline situation. The decision of whether to record
these events was made on a case-by-case basis in the field. As long as the observers
were traveling at speeds within 5 to 10 mph of the posted speed limit and the event
occurred over a distance of about a mile or less, the event was not recorded. However,
if the activity caused speeds slower than this or when the observers witnessed active
interference, such as bulldozers or flagman blocking the traffic, the event was recorded
and later excluded from the analysis.
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