HomeMy WebLinkAboutFairgrounds IntersectionsTECHNICAL MEMORANDUM - DRAFT
Alt. Traffic Control Analysis, Surfside Road and Old South Road at Fairgrounds Road – Nantucket, Massachusetts
GPI Greenman-Pedersen, Inc.
105 CENTRAL STREET ♦ SUITE 4100 ♦ STONEHAM, MA 02180 ♦ TELEPHONE: (781) 279-5500 ♦ FACSIMILE: (781) 279-5501
REF: MAX-2006064.00
DATE: September 12, 2006
TO: Mr. Mike Burns
Nantucket Planning & Economic Development Commission
16 Broad Street
Nantucket, Massachusetts 02554
FROM: Mr. John W. Diaz, P.E., P.T.O.E., Project Manager
Mr. Joseph Johnson, P.E., Project Engineer
RE: Technical Memorandum
Alternative Traffic Control Analysis
Surfside Road and Old South Road at Fairgrounds Road
Nantucket, Massachusetts
Greenman-Pedersen, Inc. (GPI) has conducted this study to evaluate alternative traffic control
operations at the following two intersections in Nantucket, Massachusetts:
• Surfside Road/S. Shore Road at Fairgrounds Road
• Old South Road at Fairgrounds Road
Surfside Road at Fairgrounds Road is a four way intersection that is currently stop controlled
along the Fairgrounds Road approaches. This study will evaluate the proposed operations
utilizing a four-way stop control configuration.
Old South Road at Fairgrounds Road is a T-type intersection with Fairgrounds Road being the
minor street approach under stop control. This study will evaluate the proposed operations
utilizing a roundabout configuration.
This study utilizes much of the data presented in the Traffic Study & Strategy for the Mid-Island
Area in order to evaluate existing and proposed operations. Refer to Figures 1 through 3
regarding 2004 and expected 2014 Design Year traffic volumes to be utilized in this study.
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Accidents
Accident data for the two intersections were taken from the Traffic Study & Strategy for the Mid-
Island Area for the period between 2000 and 2003. The intersection of Surfside Road at
Fairgrounds Road experienced a crash rate of 0.69 accidents per million entering vehicles
(acc/mev). This is higher than the district wide (0.59 acc/mev) and statewide (0.66 acc/mev)
averages for unsigalized intersections, and therefore may be indicative of a safety problem,
which may be attributed to existing sight distance deficiencies. There was an average of
approximately 4 accidents per year at this intersection between 2000 and 2003. One hundred
percent (14 of 14) of the accidents involved property damage only.
The intersection of Old South Road at Fairgrounds Road experienced a crash rate of 0.61
acc/mev. This is lower than the statewide average (0.66 acc/mev) and slightly higher than the
district wide (0.59 acc/mev) averages for unsignalized intersections. Crashes may be attributed
to the heavy turning volumes and poorly defined lane markings. This intersection has
experienced approximately 4 accidents per year between 2000 and 2003. Approximately 93
percent (13 of 14) of the accidents involved property damage with only 7 percent (1 of 14) of the
accidents involving a bicycle.
CAPACITY ANALYSIS METHODOLOGY
A primary result of capacity analysis is the assignment of levels of service to traffic facilities
under various traffic flow conditions. The capacity analysis methodology is based on the
concepts and procedures in the Highway Capacity Manual (HCM).1 The concept of level of
service (LOS) is defined as a qualitative measure describing operational conditions within a
traffic stream and their perception by motorists and/or passengers. A level-of-service definition
provides an index to quality of traffic flow in terms of such factors as speed, travel time, freedom
to maneuver, traffic interruptions, comfort, convenience, and safety.
Six levels of service are defined for each type of facility. They are given letter designations from
A to F, with LOS A representing the best operating conditions and LOS F the worst. Since the
level of service of a traffic facility is a function of the traffic flows placed upon it, such a facility
may operate at a wide range of levels of service, depending on the time of day, day of week, or
period of year. A description of the operating condition under each level of service is provided
below:
• LOS A describes conditions with little to no delay to motorists.
• LOS B represents a desirable level with relatively low delay to motorists.
1Highway Capacity Manual 2000, Transportation Research Board; Washington, D.C.; 2000.
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• LOS C describes conditions with average delays to motorists.
• LOS D describes operations where the influence of congestion becomes more noticeable.
Delays are still within an acceptable range.
• LOS E represents operating conditions with high delay values. This level is considered
by many agencies to be the limit of acceptable delay.
• LOS F is considered to be unacceptable to most drivers with high delay values that often
occur, when arrival flow rates exceed the capacity of the intersection.
Unsignalized Intersections
Levels of service for unsignalized intersections are calculated using the operational analysis
methodology of the HCM. The procedure accounts for lane configuration on both the minor and
major street approaches, conflicting traffic stream volumes, and the type of intersection control
(STOP, YIELD, or all-way STOP control). The definition of level of service for unsignalized
intersections is a function of average control delay. Control delay includes initial deceleration
delay, queue move-up time, stopped delay, and final acceleration delay. The level-of-service
criteria for unsignalized intersections are shown in Table 1.
Roundabout Configurations
Levels of service criteria for roundabouts are not provided in the HCM. However, aaSIDRA
(software package utilized in this study to analyze roundabouts) applies signalized intersection
LOS criteria to roundabouts. aaSIDRA uses its own procedure for estimating delay based on its
own methods and procedures. Table 1 summarizes the relationship between level of service and
average control delay.
Table 1
LEVEL-OF-SERVICE CRITERIA FOR INTERSECTIONS
Level of Service
Unsignalized Intersection Criteria
Average Control Delay
(Seconds per Vehicle)
Roundabout Criteria
Average Control Delay
(Seconds per Vehicle)
A
B
C
D
E
F
≤10
>10 and ≤15
>15 and ≤25
>25 and ≤35
>35 and ≤50
>50
≤10
>10 and ≤20
>20 and ≤35
>35 and ≤55
>55 and ≤80
>80
Source: Highway Capacity Manual 2000, Transportation Research Board; Washington, D.C.; 2000. Page 17-2.
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For roundabouts, this delay criterion may be applied in assigning level-of-service designations to
individual lane groups, to individual intersection approaches, or to the entire intersection. For
unsignalized intersections, this delay criterion may be applied in assigning level-of-service
designations to individual lane groups or to individual intersection approaches.
Capacity Analysis Results
Level-of-service analyses were conducted at the two study area locations under their Existing
and Proposed configurations while utilizing 2004 and projected 2014 traffic volumes. The
capacity analysis methodology is based on the concepts and procedures in the HCM or aaSIDRA
as previously described. Table 2 and Table 3 show the level-of-service results while the analysis
worksheets for all conditions are provided in the Appendix.
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Table 2
INTERSECTION LEVEL-OF-SERVICE ANALYSIS SUMMARY
Intersection/Peak Hour/Movement Del.a LOSb Queuec Del. LOS Queue
Surfside Rd @ Fairgrounds Rd 2004 Two-Way Stop Config. 2004 All-Way Config.
Weekday AM:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
Weekday PM:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
Saturday Midday:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
30.9
16.2
7.4
8.2
59.7
49.9
7.7
8.6
26.8
34.4
8.3
8.0
D
C
A
A
F
E
A
A
D
D
A
A
3
2
1
1
4
8
1
1
2
7
1
1
10.08
10.04
10.05
12.98
11.43
14.52
15.39
22.83
10.72
15.42
13.39
18.82
B
B
B
B
B
B
C
C
B
C
B
C
--
--
--
--
--
--
--
--
--
--
--
--
2014 Two-Way Stop Config. 2014 All-Way Config.
Weekday AM:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
Weekday PM:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
Saturday Midday:
S. Shore EB approach
Fairgrounds WB approach
Surfside NB approach
Surfside SB approach
150.1
42.4
7.5
8.7
688.1
612.0
7.9
9.4
110.1
289.9
8.6
8.4
F
E
A
A
F
F
A
A
F
F
A
A
8
6
1
1
13
31
1
2
6
27
1
1
12.56
13.36
13.68
23.67
15.94
32.56
44.28
142.47
14.62
44.45
23.50
88.07
B
B
B
C
C
D
E
F
B
E
C
F
--
--
--
--
--
--
--
--
--
--
--
--
aAverage control delay in seconds per vehicle. bLevel of service. c95th percentile queue length (vehicles).
Surfside Road at Fairground Road - Under the existing configuration, the S. Shore Road
eastbound approach has a LOS ‘F’ during the 2004 PM peak hour. The approach of Fairgrounds
Road and S. Shore Road also have excessive delay and a LOS ‘F’ during the 2014 weekday PM
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and Saturday midday peak hour. The eastbound approach of S. Shore Road also experiences a
LOS ‘F’ during the 2014 weekday AM peak hour. With the implementation of a four-way stop
controlled intersection at this location, delay is more uniformly distributed among the
approaches. The approaches of Surfside Road experience an increase in delay as would be
expected with the installation of stop signs. The worse LOS predicted under the four-way stop
scenario occurs along the Surfside Road southbound approach during the 2014 weekday PM and
Saturday midday peak hours. Overall the delay experienced at this intersection is greatly
reduced with the implementation of the all-way stop control.
Table 3
INTERSECTION LEVEL-OF-SERVICE ANALYSIS SUMMARY
Intersection/Peak Hour/Movement Del.a LOSb Queuec Del. LOS Queue
Old South Rd @ Fairgrounds Rd 2004 Two-Way Stop Config. 2004 Roundabout Config.
Weekday AM:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
Weekday PM:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
Saturday Midday:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
175.1
9.4
--
496.6
10.5
--
153.0
9.7
--
F
A
--
F
B
--
F
A
--
16
1
--
26
1
--
14
1
--
9.2
5.3
4.5
11.0
6.0
5.5
9.1
5.4
5.0
A
A
A
B
A
A
A
A
A
4
7
5
5
7
8
3
6
6
2014 Two-Way Stop Config. 2014 Roundabout Config.
Weekday AM:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
Weekday PM:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
Saturday Midday:
Fairgrounds EB approach
Old South NB approach
Old South SB approach
1030
10.7
--
2591
13.7
--
1035
11.7
--
F
B
--
F
B
--
F
B
--
42
1
--
52
3
--
38
2
--
14.5
6.9
5.3
32.7
8.5
19.5
14.0
6.1
8.4
B
A
A
C
A
B
B
A
A
8
14
9
16
16
29
8
10
14
aAverage control delay in seconds per vehicle. bLevel of service. c95th percentile queue length (vehicles).
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Old South Road at Fairground Road - Under the existing configuration, the approaches of
Fairgrounds Road have excessive delay and a LOS ‘F’ during all six peak hours analyzed (both
2004 and 2014). With the implementation of a roundabout at this location, delay is greatly
reduced along Fairgrounds Road and acceptable levels of service (i.e., ‘C’ or better) are expected
along all approaches.
PROPOSED IMPROVEMENTS
Based on the capacity analyses of the existing configuration of the two project intersections,
excessive delay is experienced along one or more of the approaches at each intersection. The
alternative configurations analyzed will provide decreased delay, better levels of service and
enhanced safety by reducing travel speeds. Conceptual improvements have been developed
based on the available GIS information provided by the Town. These improvements are shown
on Figures 4 and 5.
Surfside Road at Fairground Road – The Manual on Uniform Traffic Control Devices (MUTCD)
has certain criteria to justify the installation of a multiway stop condition. This is primarily
based on traffic volumes along each of the approaches. It is recommended that automatic traffic
recorders (ATR’s) be installed along each approach for a typical weekday for a 24 hour period.
Based on the peak hour data available, it is believed that the volume criteria will be met,
however, more complete data will provide concrete justification for the multiway stop condition
that is compliant with the MUTCD.
Should the MUTCD criteria be met, it is recommended that stop signs be installed along the
Surfside Road approaches to the intersection. The existing stop signs along Fairgrounds Road/S.
Shore Road should be replaced if they are missing or are in bad condition. Stop lines and double
yellow center lines should also be provided or repainted along each approach to the intersection.
It is recommended that W3-1 (stop sign ahead) warning signs be installed along both approaches
of Surfside Road. A W3-1 sign may also be installed along the eastbound approach of S. Shore
Road to compensate for sight distance deficiencies. Consideration should be given to the
temporary installation of a variable message signs (VMS) along Surfside Road. These signs
could be provided seven days in advance of the stop sign installation to alert motorists of the
forthcoming traffic control changes. The VMS may remain seven days after the stop sign
installation to further alert motorists to the intersection reconfiguration.
There are no anticipated impacts to abutting properties. It is estimated that the signing and
striping can be installed at this intersection for a cost of approximately $1,500 (including the cost
of replacing existing stop signs/posts). Should variable message signs be utilized along the
Surfside Road approaches, it is estimated that each VMS would cost approximately $50 a day
(approx. $1,400 for two signs for two weeks).
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Old South Road at Fairground Road – Based on the available GIS information for this
intersection, it appears that a 100’ diameter roundabout could be provided without major
encroachment on private property. GPI understands that the Town owns the parcel to the south
of the intersection. This is the only parcel with right-of-way impacts as shown on Figure 5. The
placement of the roundabout could be shifted to the south or east to provide additional buffer to
abutters. The concept developed shows a 40’ diameter raised inner landscaped island. A 12’
cobblestone apron is provided around the raised island as a mountable surface for truck traffic
movements through the intersection. An 18’ travel lane is provided outside the mountable apron
for passenger vehicles. The concept provides accommodation of a WB-50 design vehicle. Input
from the Town is required if a smaller design vehicle is more appropriate. The design vehicle
directly impacts the footprint of the roundabout. GPI understands that a driveway is located in
the southerly quadrant of the intersection that is not shown on the GIS mapping. This driveway
would require relocation so that it does not enter the roundabout directly. Ultimately, the
driveway should access Old South Road or Fairground Road in advance of the splitter islands so
that left turn movements into and out of the driveway could be accommodated. If sidewalks are
desired at this intersection, crosswalks would be provided at the appropriate approaches with
curb cuts through the splitter islands. The additional width of the sidewalks may encroach on
private property depending on the final tweaking of the roundabout location. It appears that this
roundabout could be built with ADA compliant sidewalks while only encroaching on the Town’s
property to the south. Overhead utilities within the vicinity of the intersection would require
relocation.
The estimated construction cost for this project is $500,000 not including engineering, utility
relocation or property takings. This cost would vary depending on the amount of earthwork, if
sidewalks are provided, the reconfiguration of the Town’s driveway and many other factors
determined during final design.
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CONCLUSIONS AND RECOMMENDATIONS
The following conclusions and recommendations for this project are presented below:
Intersection of Surfside Road at Fairgrounds Road:
• Under the existing two-way stop condition at the intersection of Surfside Road at
Fairgrounds Road, the Fairgrounds Road/S. Shore Road approaches experience
significant delay especially during the weekday PM peak hour while utilizing projected
2014 traffic volumes. The Surfside Road approaches have little delay since they are not
required to stop.
• Additional 24 hour traffic data is need for each of the approaches to the intersection.
This is required to satisfy the multiway stop condition criteria provided in the MUTCD.
Although there is significant delay along the side streets and the peak hour traffic
volumes seem to indicate that the MUTCD criteria will be satisfied, 24 hour data is
necessary.
• Under the proposed four-way stop condition at the intersection of Surfside Road at
Fairgrounds Road, the delay for the Fairgrounds Road is greatly reduced, while the delay
for Surfside Road is increased during all three peak hours analyzed. The worse case
delay expected for Surfside Road is during the 2014 weekday PM and Saturday midday
peak hours when the southbound approach has a LOS ‘F’. All movements have a LOS
‘C’ or better while utilizing 2004 volumes.
• Given the relatively low cost to implement, it is recommended that a four-way stop
configuration be provided on a trial basis (provided MUTCD criteria are satisfied). This
would reduce delay along the Fairgrounds Road approaches and reduce travel speeds
through the intersections lessening the potential for serious crashes. Once implemented,
the reconfiguration of the intersection should be observed to verify its effectiveness and
to determine if the delay created along Surfside Road is acceptable.
Intersection of Old South Road at Fairgrounds Road:
• Under the existing configuration of Old South Road at Fairgrounds Road, the
Fairgrounds Road approach experience significant delay during all six peak hours
analyzed while utilizing 2004 and projected 2014 traffic volumes. The Old South Road
approaches have little delay since they are not required to stop.
• Under the proposed roundabout configuration of Old South Road at Fairgrounds Road,
delay along Fairgrounds Road is significantly reduced while delay along Old South Road
is also reduced. All movements operate at a LOS ‘B’ or better during all three peak hours
analyzed while utilizing 2004 traffic volumes. All movements operate at a LOS ‘C’ or
better during all three peak hours analyzed while utilizing projected 2014 traffic volumes.
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• It appears that the construction of a roundabout at this intersection would have right-of-
way impacts to the Town’s property located to the south. The driveway for this property
would also require relocation. Shifting the roundabout towards the Town’s property
would increase the buffer from abutters to the west.
• The Town should provide input as to the appropriate design vehicle for this intersection.
Reducing the design vehicle to a bus would greatly reduce the footprint of the roundabout
and the associated impacts.
• It is recommended that project abutters be presented with the conceptual roundabout
design to solicit feedback. If feedback is favorable, it is recommended that field survey
be obtained and the project be advanced to final design.
• The estimated construction cost for the roundabout is $500,000 not including
engineering, utility relocation or property takings. This cost would vary depending on
the amount of earthwork, if sidewalks are provided, the reconfiguration of the Town’s
driveway and many other factors determined during final design. The cost of
construction is based on 2006 pricing.
TECHNICAL MEMORANDUM - DRAFT
Alt. Traffic Control Analysis, Surfside Road and Old South Road at Fairgrounds Road – Nantucket, Massachusetts
Nantucket TechMemo.doc
APPENDIX
CAPACITY ANALYSIS WORKSHEETS
TECHNICAL MEMORANDUM - DRAFT
Alt. Traffic Control Analysis, Surfside Road and Old South Road at Fairgrounds Road – Nantucket, Massachusetts
Nantucket TechMemo.doc
CAPACITY ANALYSIS WORKSHEETS