Three Intersections Projects

The purpose of these projects is to utilize Town of Nantucket’s Complete Streets Policy and the 2006 Massachusetts Highway Department’s Project Development and Design Guide and other Highway Division standards and criteria to design and construct a modern roundabout at the following three (3) intersections, as recommended in the Nantucket Master Plan and the NP&EDC’s Regional Transportation Plan (click links below for additional information on each location):

  • Surfside Road at Bartlett Road 
  • Four Corners (Sparks Ave, Surfside Rd, Atlantic Ave, and Prospect St) 
  • Old South Road at Fairgrounds Road 

WHY ROUNDABOUTS?

  • “A primary benefit is the reduction of vehicle speeds in and around the roundabout. Roundabouts improve pedestrian crossing opportunities, providing mid-block refuge and the ability for pedestrians to focus on one traffic stream at a time while crossing with or without crossing guards.” – Federal Highway Administration, Safe Roads for a Safer Future
  • “In settings with large numbers of children, lowering vehicle speed has great potential for injury prevention. Pedestrian crashes involving a child most often result from the child’s error, thus slower speeds give motorists more time to react and can lessen injuries when crashes do occur.” [Retting, Ferguson, & McCartt, 2003] – National Center for Safe Routes to School, Safe Routes to Schools Guide
  • General benefits according to the National Center for Safe Routes to Schools:
    • Lower motor vehicle speeds and increased yielding behavior
    • Fewer conflict points
    • Higher visibility of pedestrians in the crosswalk
    • Lower exposure to motor vehicles because of the shortened crossing distance
    • Simpler crossing due to the splitter islands, which provide mid-crossing refuge and allow the pedestrian to focus on traffic from one direction at a time3 Intersections Nantucket

PUBLIC MEETINGS

Surfside Road at Bartlett's Road

The purpose of this project is to utilize Town of Nantucket’s Complete Streets Policy and the 2006 Massachusetts Highway Department’s Project Development and Design Guide and other Highway Division standards and criteria to design and construct a modern roundabout at this location, as recommended in the Nantucket Master Plan and the NP&EDC’s Regional Transportation

This intersection is currently an unsignalized ‘T’ intersection with three single lane approaches. It is located in a densely settled part of the island populated with large portion of year round residents. Congestion is experienced throughout the peak summer season, but also during morning commuting hours in the shoulder season due to the close proximately to the Nantucket Elementary School. The primary activity of concern that must be considered is during morning commute times during the school year when children walk or bike to school and require the assistance of a crossing guard at the crosswalk on Bartlett Road at the intersection, and at the crosswalk on Surfside Road just north of the intersection.

The intersection was originally reviewed as part of the 2005 Traffic Study and Strategy for the Mid-Island Area, which was completed by Greenman-Pedersen, Inc. using data collecting in the summer of 2004. The study showed that under the 2004 traffic conditions the Bartlett Road approach to the intersection was experiencing an acceptable level of congestion (LOS D) in weekday morning and evening hours, but experienced unacceptable congestion level during mid-day Saturday hours (LOS F). Under modest growth conditions, congestion at the intersection was projected to be unacceptable at all peak times by 2014.

Crash statistics included in the study (from 2000 to 2003) showed that the intersection had a crash rate that was less than the state-wide and district-wide averages for unsignalized intersection. However, from 2004 to 2006 the number and severity of crashes were higher than any other intersection on the island. As this intersection is adjacent to the Nantucket Public Schools, and used by children walking or biking to school, improving the safety condition for all users is vital.

Building on the data and recommendations of the 2005 study, two subsequent studies were completed in 2010 and 2013 by Greenman-Pedersen, Inc. These studies were to further evaluate traffic control options and refine the conceptual design and understand right of way impacts for the preferred option of a modern roundabout. Based on these updated reports verifying a modern roundabout configuration would provide a reduction is safety conflicts and added capacity the Town has acquired property abutting the intersection to facilitate the construction of a roundabout, and approved funding to develop a MassDOT approved plan for construction.

CONCEPTUAL PLANS

DESIGN STUDIES

 MASSDOT PROJECT FORMS


Four Corners Intersection

The purpose of this project is to utilize Town of Nantucket’s Complete Streets Policy and the 2006 Massachusetts Highway Department’s Project Development and Design Guide and other Highway Division standards and criteria to design and construct a modern roundabout at this location, as recommended in the Nantucket Master Plan and the NP&EDC’s Regional Transportation

The existing intersection (also known as the “Four Corners” intersection) consists of an awkward configuration consisting of an approximately 75 foot offset alignment of the Sparks Avenue and Prospect Street approaches, which creates a double turning movement responsible for considerable confusion, congestion / delays, and accidents. The four single lane approaches are under an all-way stop control with Surfside Road, Sparks Avenue and Prospect Street approaches providing 11-foot travel lanes and Atlantic Avenue only providing 10-foot lanes. Sidewalks are provided along both sides of Surfside Road and Sparks Avenue, along the east side of Atlantic Avenue and along the south side of Prospect Street. A marked crosswalk is provided on the east leg of the intersection across Sparks Avenue with school-crossing signs. Utility poles are located close to the exiting roadway edges and there a utility control cabinet located on the High/Middle School property at the southeast comer of the intersection. Also located in front of the High/Middle School property on Surfside Road is a significantly sized elm tree. This tree is located directly behind the existing curb line, approximately 100 feet south of Sparks Avenue.

 The intersection is primarily surrounded by single family residential structures, with the exception being the Nantucket High School and Middle School located in the southeast area of the intersection. Recent analysis shows there have been a total of 6 crashes from 2009 through 2013. These crashes generally consisted of angle and rear-end type collisions. These types of crashes can be attributed to the offset intersection geometry, sight distance constraints, and minimal roadway widths. The intersection was found to have averaged less than two (2) reported motor vehicle crashes per year over the five-year review period with no fatalities. This crash rate is below the MassDOT statewide and Highway Division District 5 averages for an unsignalized intersection.

Improvements to this intersection were originally recommended in the Mid-Island Area Plan by the Nantucket Planning and Economic Development Commission (NP&EDC) in June 2003, and later further studied as part of the Traffic Study and Strategy for the Mid-Island Area in July 2005. A roundabout alternative was ultimately supported by the NP&EDC and included in the Regional Transportation Plan following an analysis completed by Vanasse Hangen Brustlin, Inc (VHB) in March 2010.

Since a modern roundabout alternative would have significant right of way impacts to abutting property owners, primarily the Nantucket Cottage Hospital, an additional alternative was explored by Vanasse & Associate, Inc. in June 2016 as part of the improvements to the Hospital. This alternative reconfigures the intersection to function as a single-lane "mini" modern roundabout with improved pedestrian and bicycle access. This alternative also provides a right-turn slip lane to accommodate Atlantic Avenue right turns to South Prospect Street for passenger cars and buses. This slip lane is necessary to accommodate right turns from Atlantic Avenue to South Prospect Street due to the restricted existing roadway configuration approaching the intersection. The size of this roundabout is significantly smaller than a single lane modem roundabout, with a 38-foot diameter center island and a 16-foot travel lane for a total inscribed circle diameter of 70 feet. To accommodate larger design vehicles, the center island and median delta islands at the approaches to the roundabout would be constructed of mountable materials (i.e., cobblestone or belgium block) and pavement markings to allow trucks and buses to maneuver through the roundabout. Trucks (WB-50) could be accommodated on all movements except right turns from Surfside Road to Sparks Avenue and from Atlantic Avenue to Prospect Street; and left turns from Prospect Street to Atlantic Avenue. It is expected that trucks could avoid these movements via alternative travel routes through the implementation of appropriately placed signage. Large vehicles would occupy most of the circle when turning, limiting access to the roundabout to other entering vehicles and significantly reduce the capacity of the mini roundabout.

 This Option would advance the latest “mini-roundabout” alternative as it would have reduced property impacts to both the School and Hospital properties.

CONCEPTUAL PLANS

DESIGN STUDIES


Old South Road/Fairgrounds Road Intersection

The purpose of this project is to utilize Town of Nantucket’s Complete Streets Policy and the 2006 Massachusetts Highway Department’s Project Development and Design Guide and other Highway Division standards and criteria to design and construct a modern roundabout at this location, as recommended in the Nantucket Master Plan and the NP&EDC’s Regional Transportation

This is an unsignalized 'T' intersection with three single lane approaches with the Fairgrounds northbound approach operating under a stop sign control. It should be noted that a short (approximately 60 feet in length) and unmarked portion of the Fairgrounds single lane approach is very wide and functions as a right turn lane. This intersection is also located in a densely settled part of the island, the Town Overlay District, populated mostly by year round residents. Congestion is experienced throughout the peak summer season, and during the morning and evening commuting times of the shoulder season due to the year round population in the vicinity of the intersection. 

The intersection was originally reviewed as part of the 2005 Traffic Study and Strategy for the Mid-Island Area, which was completed by Greenman-Pedersen, Inc. (GPI) using data collecting in the summer of 2004. The study showed that under the 2004 traffic conditions the left turns from Old South Road onto Fairgrounds Road operated at an acceptable LOS B or better during peak times. Left and right turning movements from Fairgrounds Road onto Old South Road operated at LOS F during all peak times. Although the recommended improvement of this study was to expand the right turn lane for the Fairgrounds Road approach, the analysis showed this approach would still operate at LOS F with insufficient capacity.

In 2006, a supplemental study was completed by GPI to evaluate the intersection under a modern roundabout configuration. This study concluded that the implementation of a roundabout at this location would greatly reduce delays and would operate at an acceptable LOS C or better. This evaluation used single lane approaches to a 100 foot diameter roundabout with a 40 foot inner landscaped island with a 12 foot cobblestone apron, which could be provided without any major right of way impact on private property, but would require overhead utility pole relocation.

 In 2016, a Traffic Impact and Access Study (TIAS) completed by Ron Muller & Associates as part of an Old South Road Mixed-Use Development proposal evaluated the development’s potential impact to this intersection using data collected in August 2015. This study described the intersection as continuing to operate at LOS F during all peak times with very long delays and queues on the Fairgrounds Road approach, particularly for left turn movements. Although the TIAS confirmed the roundabout would have acceptable operations with or without the development, the report recommended considering a right turn lane on the Fairgrounds Road approach to the intersection to improve capacity and operations.

Crash data in all the recent studies show that the intersection has had a crash rate that was less than the state-wide and district-wide averages for unsignalized intersection. However, this intersection is included in MassDOT’s 2012-2014 Highway Safety Improvement Program (HSIP) eligible crash clusters, which indicates it is in the top 5 percent of intersections in the Nantucket region for crash incidences and severity. 

Based on the reports and studies completed to date verifying a modern roundabout configuration would add capacity and reduce unsafe conflicts, the Town has approved funding to design and permit a MassDOT approved project for construction.

CONCEPTUAL PLANS

DESIGN STUDIES