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INTRODUCTION---------------------------------- 1 TRAFFIC VOLUME COMPARISON--------------------- 3 SPEED PROFILE COMPARISON---------------------- 5 LICENSE TAG ORIGIN-DESTINATION SURVEY--------- 8 OTHER OBSERVATIONS----------------------------10 CONCLUSIONS-----------------------------------17 Figure 1 Study Area Map--------------------------------- 2 2 Speed Profile by Time Period------------------- 12 3 Proposed Conceptual Improvement Diagram-------- 14 Table 1 Peak Hour Traffic Volume Counts---------------- 3 2 85th Percentile Speed Comparison--------------- 6 3 License Tag Origin-Destination Survey---------- 9 4 85th Percentile Speed Comparison by Time Period 11 5 Speed Comparison At and Near Device #3--------- 15 6 Speed Comparison At and Near Device#5--------- 16 Seminole County Public Works commissioned GMB Engineers & Planners, Inc. to perform a comparison of the "before" and "after" traffic flow characteristics to evaluate the effectiveness of traffic calming devices that were recently implemented along the Kewannee Trail/Derbyshire Road/Cedarwood Drive/Birchwood Drive/Cherrywood Drive/Spartan Drive residential neighborhood corridor. Figure 1 illustrates the general location of the study area. The “before” study was performed in September 2001 as part of the Kewannee Trail Traffic Calming Study completed by Kittelson & Associates, Inc. consisting of: • Traffic volume data collected at the east end (Kewannee Trail) and west end (Spartan Drive) of the residential neighborhood corridor, • Speed studies along various segments of the corridor, and • A license tag survey to quantify cut-through traffic passing through the corridor. Seminole County recently completed the installation of traffic calming devices placed at strategic locations and intervals that were recommended as part of the Kewannee Trail Traffic Calming Study. In December 2002, GMB Engineers & Planners, Inc. performed the "after” traffic flow characteristics study consisting of traffic volume counts, a license tag survey and speed studies along the corridor. Consistency between the "before” and "after" study methodologies was maintained in order to make a meaningful comparison of the traffic data. This report provides a comparison of the traffic flow characteristics in the "before" and "after" condition associated with the implementation of traffic calming measures along the Kewannee Trail/Derbyshire Road/Cedarwood Drive/Birchwood Drive/Cherry Wood Drive/Spartan Drive residential neighborhood corridor.   Table 1 provides a comparison of the “before” and “after” traffic volumes at Kewannee Trail, south of SR 436 and at Spartan Drive, east of US 17-92. The count comparison provides the following indications: • In the peak traffic flow direction, the “after” condition registered a significant reduction in traffic volume at Spartan Drive during the morning (17.08% less) while Kewannee Trail registered a 7.27 percent decrease. During the evening peak hour, both Kewannee Trail (19.0% increase) and Spartan Drive (11.4% increase) experienced higher traffic flows in the “after”. • In the off-peak traffic flow direction, Kewannee Trail registered an increase of 25.45 percent during the morning peak hour and 37.86 percent during the evening peak hour. Spartan Drive registered an increase of 80.0 percent during the morning peak hour, while showing a decrease of 40.0 percent during the evening peak hour. • Using the total daily traffic count data, the “after” condition at Kewannee Trail experienced an increase of 15 percent in the northbound direction and 19 percent southbound. Spartan Drive showed a slight decrease in the eastbound direction of 4.9 percent, and a significant decrease (29.9%) in the westbound direction. The results of this comparison indicate that the implementation of traffic calming measures was effective in reducing the magnitude of travel entering Kewannee Trail and exiting Spartan Drive during the a.m. peak hour period. On the other hand, these devices had no effect in deterring traffic demand through the residential neighborhood during the evening peak hour. In the off peak direction, the traffic calming devices were only effective in reducing traffic flow at Spartan Drive during the evening peak hour; all the other conditions experienced an increase in traffic flow. Daily traffic flow conditions revealed a reduction in vehicular traffic flowing at Spartan Drive; however, Kewanne Trail registered an overall increase in traffic volume of 16.9 percent.  GMB Project No. 02-112.01 4/23/2003 This section presents a comparison of the speed profile characteristics measured in terms of the 85th percentile speed recorded at various locations along the corridor for the “before” and “after” conditions. It should be noted that traffic engineers typically use the 85th percentile speed (i.e., the highest speed that 85 percent of the surveyed vehicles did not exceed) as a guide for speed limit posting. Since majority of the motorists drive at speeds they consider safe, the 85th percentile speed is a valid indicator of the speed profile characteristic. The “before” speed profiles were obtained by Seminole County Public Works staff between 1999 and 2001, as part of the response to public complaints about cut-through traffic flow along the corridor. The “after” speed profiles were obtained in December 2002 at approximately the same locations where the “before” speed profiles were taken. In addition to the use of the 85th percentile speed, we also compared the percentage of vehicles in the “before” and “after” conditions that traveled in excess of 30 miles per hour. We selected 30 mph because the speed study indicated that motorists appear to be comfortable driving along at or near this speed in the “before” and “after” conditions. Table 2 provides a summary of the speed profile comparison in the “before” and “after” condition using the 85th percentile speed and the percentage of vehicles moving in excess of 30 mph as the performance indicators. Along Kewannee Trail (north and south of Talbot Road), the speed profiles recorded a reduction in the “after” condition ranging from 4.7 percent to 9 percent. The northbound direction, north of Talbot Road registered a 3.86 percent increase in speed. Overall, the 85th percentile speed profile along Kewannee Trail ranged between 29.60 mph to 31.94 mph in the “after” condition compared to a range between 28.5 to 33.5 mph in the “before” condition. The narrower spread in the speed profile in the “after” condition indicates that the traffic calming measures were effective in inducing a more uniform speed profile along Kewannee Trail. Speed profiles were obtained at three locations along Derbyshire Road: east of Winston Road, east of Oxford Road, and east of Glastonberry Road. The “before” condition registered speed profiles ranging from 28 to 40.5 mph. The “after” condition revealed a speed profile range of 25.35 to 29.4 mph. The highest speed reduction was recorded in the eastbound direction east of Oxford Road when the speed decreased from 36.80 mph in the “before” to 25.40 mph in the “after”. Another significant reduction in speed was recorded on eastbound Derbyshire Road, east of Glastonberry Road when the “before” speed of 40.5 mph was reduced to 29.30 mph in the “after”. Another point of observation is that the speed characteristics by direction are more uniform in the “after” condition. East of Oxford Road, the eastbound speed is 25.4 mph, while the westbound speed is 25.35 mph. East of Glastonberry Road, the eastbound speed is 29.3 mph compared to 29.4 mph in the westbound direction. East of Winston Road, the eastbound speed of 28.7 mph is slightly higher than the 25.7 mph recorded in the westbound direction. In summary, the speed profiles obtained along Derbyshire Road indicated that the traffic calming  GMB Project No. 02-112.01 4/23/2003 measures reduced the speed differences by direction and also created a more uniform speed profile along the length of Derbyshire Road.
Along the west end of the corridor, there appeared to be no significant
change in the speed profiles resulting from the implementation of the traffic
calming measures along CedarwoodDrive, Birchwood Drive, and Cherrywood Drive.
At Cedarwood Drive, the northbound speed decreased 5.93 percent from 27 mph
in the “before” to 25.4 mph in the “after”; however, the southbound speed
recorded a 9 percent increase from 23.4 mph in the “before” to 25.5 mph in
the “after”. At Birchwood Drive, the eastbound speed increased almost 10
percent from 30.7 mph in the “before” to 33.7 mph in the “after”; while the
westbound speed decreased 2.8% from
31.8 mph in the “before” to 30.9 mph in the “after”. At
Cherrywood Drive, the “before” and
“after” speed profiles registered a less than 3 percent
increase.
Another performance indicator to determine the effectiveness of
traffic calming devices was to
compare the proportion of vehicles traveling in excess of 30 mph
in the “before” and “after”.
This measure proved that traffic calming devices had a
significant effect in reducing speeding
over 30 mph. Along Kewannee Trail, the percentage of speeding in
excess of 30 mph dropped
37 to 41 percent in the “after”. Along Derbyshire Road, the
reduction is even more dramatic,
with 55 to 96 percent fewer speeding vehicles over 30 mph
(except for eastbound, east of
Winston Road where the percentage increased almost 11 percent).
Cedarwood Drive,
Birchwood Drive, and Cherrywood Drive experienced a lower
proportion of vehicles (ranging
from 30 to 94 percent decrease) speeding over 30 mph in the
“after” condition (except for
eastbound Birchwood Drive where the percentage rose 63 percent).
In summary, the traffic calming devices placed along Kewannee Trail and Derbyshire Road has
proven to be effective in managing to keep a more uniform speed profile along the length of the
corridor. This conclusion is supported by the comparison of the 85th percentile speed and also by
comparing the proportion of vehicles moving in excess of 30 mph. Speed flow characteristics
taken at various segments indicated that motorists are maintaining the speed profile around the
25-30 mph range, well within the 25 mph posted speed limit. Toward the west end of the
corridor, the traffic control devices had little effect in reducing the 85th percentile speed.
Birchwood Drive and Cherrywood Drive maintain speeds near the 30-35 mph range, which is
well above the posted speed limit of 20 mph. However, the most significant benefit derived from
these devices resulted in reducing the proportion of vehicles traveling in
excess of 30 mph.
In order to quantify the cut-through traffic using Kewannee Trail/Derbyshire Road/Cedarwood Drive/Birchwood Drive/Cherrywood Drive/Spartan Drive as an alternative corridor connection between SR 436 and US 17-92, GMB Engineers & Planners, Inc. conducted a license tag survey of inbound and outbound vehicles passing through Kewannee Trail, south of SR 436, Spartan Drive, east of US 17-92 and Temple Trail, north of Howell Branch Road. The survey recorded the last three digits of each vehicle’s license plate during the 7-9 a.m. and 4-6 p.m. weekday peak hour periods. Using a matching algorithm, license tags that entered one end of the corridor and exited at the other end during the same peak hour period constituted cut-through trips. The methodology adopted in this survey is consistent with the “before” study documented in the Kewannee Trail Traffic Calming Study completed in 2001. The results of the license tag survey are documented in Table 3. The following observations are noted from the survey: • During the 7-9 a.m. period, the “before” study determined that 227 vehicles or 56.75 percent of the total vehicles entering Kewannee Trail were classified to be cut-through trips, with 209 vehicles (52.25%) exiting at Spartan Drive and 18 vehicles (4.5%) exiting at Temple Trail. The “after” study determined that 134 vehicles or 46.53 percent of the entering vehicles were cut-through trips, with 116 vehicles (40.28%) exiting at Spartan Drive and 18 vehicles (6.25%) exiting at Temple Trail. This comparison showed that the traffic calming devices were effective in reducing the magnitude and percentage of cutthrough trips entering Kewannee Trail during the a.m. peak hour. • During the 4-6 p.m. period, the “before” study indicated that 301 vehicles or 36 percent of the total vehicles entering Spartan Drive were classified as cut-through trips, with 281 vehicles (33.6%) exiting at Kewannee Trail and 20 vehicles (2.4%) exiting at Temple Trail. In the “after” study, 304 vehicles or 35.23 percent were classified as cut-through trips, with 279 vehicles (32.3%) exiting at Kewannee Trail and 25 vehicles (2.9%) exiting at Temple Trail. The close comparison measured in terms of magnitude and percentage between the “before” and “after” conditions indicates that the traffic calming measures have no significant effect on discouraging cut-through trips through the residential neighborhood corridor during the p.m. peak hour.
• The survey also
indicates that the magnitude of cut-through trips entering at Temple Drive
during the morning and evening peak hours has not significantly changed in the
“before” and “after” conditions. In the 7-9 a.m. period, there were 24
cut-through trips recorded in the “before” and 33 cut-through trips in the
“after”, representing 13.6% and 17.9% of all trips that entered at Temple
Trail, respectively. In the 4-6 p.m. period, there were 42 (9.4% of total)
cut-through trips in the “before” compared to 47 (14.6% of total) cut-through
trips in the “after”.
 GMB Project No. 02-112.01 4/23/2003 Speed Profiles by Time of Day In addition to the direct comparison of traffic flow characteristics between the “before” and “after” scenarios, we also performed a quantitative analysis of the speed profile by time of day in the “after” condition. The premise used in these observations was that travel speeds tend to move at a higher rate when traffic densities go down. For example, during peak hours, high traffic volume conditions represent high traffic flow densities and as such, speeds tend to flow slower. Conversely during non-peak hours, traffic volumes and densities are lower and as a result, motorists are not constrained by how fast other vehicles are moving and are free to travel at a rate they feel comfortable given the prevailing conditions of the road. This section evaluates whether or not the traffic control devices affected travel speeds during peak and non-peak hour conditions. As such, we developed the 85th percentile speeds at various locations for four time periods:
• 7-9 a.m. peak hour period The results are summarized on Table 4 and graphically illustrated in Figure 2. The temporal distribution of travel speeds indicates that for the most part along the corridor, motorists move at similar speeds throughout the day. At Derbyshire Road between Glastonberry Road (i.e., 27.85 mph to 28.95 mph) and east of Oxford Road (i.e., 24.30 mph to 24.69 mph), vehicles were observed maintaining the same speed profile during the four time periods. The maximum spread between the lowest speed and highest speed by location was recorded at Birchwood Drive with a low speed of 29.27 mph during the a.m. peak hour and a high speed of 33.26 mph during the 10 a.m.-2 p.m. off peak period. All other locations recorded a spread of less than 3 mph between the lowest and highest speeds by time period. These observations support our conclusion about the effectiveness of the traffic control devices in inducing a more uniform speed profile regardless of traffic densities that prevail during peak and non-peak hours.
It should be noted that one traffic calming device proposed at Derbyshire Road
east of Wellington Terrace was not implemented as part of the traffic calming
construction program proposed in the “before” study. The speed data shown in
Table 4 and in Figure 2 reveal that the 85th percentile speeds range between
31 mph during the a.m. and p.m. peak hours to 33 mph during the midday and
evening periods at this location. This speed range is certainly the highest
recorded throughout the study corridor and as such, we recommend that Seminole
County proceed with implementing the raised choker island recommended at this
location. In addition to
 GMB Project No. 02-112.01 4/23/2003  the choker island, Seminole County should construct a concrete separator between the through lane and the right-turn lane in the westbound approach. The combination choker island and concrete separator would convey a narrow lane effect in the wide pavement area of westbound Derbyshire Road east of Wellington Terrace. The proposed conceptual design is shown in Figure 3. Speed Profiles At or Near Traffic Calming Devices This section describes whether or not motorists drive slower while negotiating through traffic calming devices but drive faster after passing through them. This hypothesis was tested on the section of Kewannee Trail between SR 436 and Derbyshire Road. Traffic calming devices placed within this study segment consist of a raised choker island with curb extension at Device #3, and a raised choker island used at Device #5. Table 5 presents the speed characteristics at or near Device #3 (north of Talbot Road). The 85th percentile and median speeds of vehicles negotiating through Device #3 are slower than corresponding speeds at a station taken 200-ft. to the north (except during the 4-6 p.m. in the departing direction where the 85th percentile speed recorded at the device is higher than the 85th percentile speed recorded 200-ft. away). The difference in the 85th percentile speed is only in the order of 1-2 mph slower recorded through the device. The difference is more pronounced (i.e., 2-4 mph) using the median speed as an indicator Table 6 provides the speed characteristics at or near Device #5 (north of Falmouth Road). Device #5 happens to be located north of a horizontal curve, and the results of the speed comparison reveal that the horizontal curve had a speed calming effect relative to the traffic control device itself. The 85th percentile speeds recorded near the horizontal curve are predominantly lower by 1-3 mph than the speeds recorded near Device #5, except during the 4-6 p.m. when the speed is slower at the device than at the curve. Using median speed, the horizontal curve registered slower speeds in the order of 1-4 mph than those recorded at the device.
The 85th percentile speed profiles presented in this section support the
premise that there is a slight speed difference between vehicles negotiating
through traffic calming devices and those traveling in between them. The
differences are only in the order of 1-2 mph. The close speed comparisons
indicate that these traffic calming devices are quite effective in maintaining
uniform speeds through the neighborhood corridor and that the spacing between
devices is adequate to minimize speeding at non-calmed segments of the
corridor.   GMB Project No. 02-112.01 4/23/2003  GMB Project No. 02-112.01 4/23/2003 The results of the comparison of traffic flow characteristics between the “before” and “after” conditions associated with evaluating the effectiveness of traffic calming measures implemented along the Kewannee Trail/Derbyshire Road/Cedarwood Drive/Birchwood Drive/Cherrywood Drive/Spartan Drive corridor revealed the following observations: • During the a.m. peak hour, the entering movement (southbound) at Kewannee Trail and the exiting movement (westbound) at Spartan Drive experienced significant reductions in traffic volume after the traffic calming devices were installed. However, the traffic calming devices had little effect in reducing traffic volumes entering at Spartan Drive and exiting at Kewannee Trail during the p.m. peak hour. The number of vehicles passing through Spartan Drive on a daily basis has also decreased after the traffic calming devices were implemented. • The traffic calming devices proved effective in inducing a more uniform speed profile along Kewannee Trail and Derbyshire Road. The speed profile range in the “after” condition narrowed down to between 25 to 30 mph in both directions of travel, as opposed to a speed range of 28 to 40 mph in the “before” condition. The traffic calming devices placed along Cedarwood Drive, Birchwood Drive, and Cherrywood Drive have little effect on the speed profile characteristics. Additional analysis also proved that the proportion of vehicles traveling in excess of 30 mph has significantly decreased throughout the corridor. • The traffic calming devices have reduced the magnitude and percentage of cut-through traffic during the a.m. peak hour period. During the p.m. peak hour period, the magnitude and percentage of cut-through traffic has remained unchanged even after implementation of the traffic calming devices along the corridor. In conclusion, the results of the “before” and “after” comparison reveal that the traffic calming devices implemented by Seminole County proved effective in controlling the speed flow profiles to a more uniform pattern. Speed data and field observations have shown that differences in speed are less pronounced, and that motorists maintain virtually the same speeds whether they are negotiating through or away from traffic calming devices.
The volume of traffic using the corridor and the level of cut-through trips
have not experienced an across the board decrease after the traffic calming
devices were installed. While there was a benefit detected during the a.m.
peak hour in the way of lower traffic volumes on Kewannee Trail and Spartan
Drive as well as reduced cut-through trips, these devices have not deterred
motorists to use this corridor as a cut-through route during the p.m. peak
hour. We hypothesize that as long as US 17-92 and SR 436 operate at congested
levels, motorists are likely to find an alternative path of least resistance
and that the Kewannee Trail/Spartan Drive connection provides this alternative
path. In conclusion, the traffic calming devices constructed along Kewannee Trail, Derbyshire Road, Cedarwood Drive, Birchwood Drive, and Cherrywood Drive are effectively proving their worth in “calming” traffic flow through the corridor. These devices were not intended to physically restrict or deter motorists from using this corridor as a commuter route. Rather, these devices proved their worth in reducing the percentage of vehicles traveling at a high rate of speed, and in inducing a more uniform speed flow by time of day and by location along the corridor.
Finally, this study supports the need to install
Device #10, at Derbyshire Road east of Wellington Terrace. Existing speed data
taken at this location revealed speeds that are higher than any recorded along
the corridor. In order to maintain the narrow lane effect, a concrete
separator between the through lane and the right-turn lane in the westbound
approach is also recommended. |