Road Safety Audit

Pelham, New Hampshire

Mammoth Road (NH 128)/Sherburne Road

October 19, 2011

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Project Title: Pelham, NH – Mammoth Road (NH 128)/Sherburne Road Intersection

Date Audit Conducted: October 19, 2011

RSA Team and Participants:

Town of Hudson John Cashell Town Planner Gary Webster Town Engineer Town of Pelham Edmund Gleason Selectmen Jeff Gowan Town Planner William McDevitt Selectmen James Midgley Fire Chief Joseph Roark Chief of Police Nashua RPC Julie Chizmas Transportation Planner Matt Waitkins Transportation Planner FHWA Martin Calawa Safety & Traffic Operations Engineer NHDOT Stuart Thompson Safety Engineer Bill Oldenburg Administrator Highway Design Mike Dugas Highway Design Bill Lambert Traffic Engineer Dave Rodrigue District 5 Engineer CHA Robert Pinckney Project Manager Nicolas Bosonetto Project Engineer

Project Characteristics:

Audit type: Existing Road

Units of Measure: US

Adjacent Land Use: Residential

Posted Speed Limits: Mammoth Road - 40 mph, Sherburne Road – 40 mph

Functional Classification: Mammoth Road – Urban Collector, Sherburne Road – Urban Local Road

Terrain: Flat, wooded

Climatic Conditions: Cold winters with snow – icing possible

Location: Town of Pelham, NH

NHDOT Project Number: 21645

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Background:

The intersection studied is located 1,500 feet north of the New Hampshire/Massachusetts state line.

The area is urbanized and lies in the Town of Pelham which is between the City of Nashua, NH and the

City of Lowell, MA. Both Mammoth Road and Sherburne Road are maintained by the New Hampshire

Department of Transportation (NHDOT). The intersection is stop-controlled for Sherburne Road traffic

only.

Mammoth Road runs north to south, has a functional classification of urban collector, and had an ADT of

9,580 at the state line during a 2009 traffic count. Mammoth Road is posted at 40 mph in the vicinity of

the intersection with Sherburne Road. The roadways are relatively level and straight in the immediate

project area. There are large trees and woods and either side of the road which make for shaded areas

in the roadway.

Figure 1 - Project Location Map

Sherburne Road is an east-west local road that connects Dracut Road in Hudson to NH 128 in Pelham.

Sherburne Road is classified as a local road, and it is posted at 40 mph. There are various residential

subdivisions on Sherburne Road. Due to geographic attributes of the area, Sherburne Road is one of the

few east-west connections in the general area.

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NHDOT selects projects for safety analysis using three methodologies:

1. Network Analysis – Using GIS and accident analysis software, NHDOT selects the 50 highest

accident locations throughout the state for improvements.

2. Systematic Improvements – Projects such as rumble strips, improved signs, and guardrails are

done on an area-wide basis to improve overall safety.

3. Special Projects – Projects which are submitted to NHDOT for analysis by concerned citizens,

public officials, or other interested parties.

This intersection does not appear on the top 50 accident locations for the state but has been of concern

to local officials for several years. The Town of Pelham has contacted NHDOT to express their concerns

and to request safety improvements. As such, this project is categorized as a Special Project.

On September 28, 2011 Nashua Regional Planning Commission (NRPC) conducted traffic turning

movement counts at the intersection from 7:00 – 9:00 AM and 4:00 – 6:00 PM. Both morning and

afternoon counts show a very similar traffic pattern (see Figure 2). There is heavy volume of left-hand

turns from Sherburne Road to northbound Mammoth Road and right-hand turns of southbound

Mammoth Road traffic onto Sherburne Road.

The traffic turning movements clearly show that traffic uses Sherburne Road as a major east-west route

in the general area. It is important to note that during the AM peak hour there is more traffic turning

left out of Sherburne Road than there is northbound through traffic on Mammoth Road.

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Figure 2 – Turning Movement Counts

Data Collected 9/28/11

Peak Morning Hour

7:00 – 8:00 AM

Data Collected 9/28/11

Peak Afternoon Hour

4:45 – 5:45 PM

Southbound Mammoth Road

339

(47%)

381

(53%)

Northbound Mammoth

Road

75

(30%)

176

(70%)

Southbound Mammoth Road

292

(50%)

289

(50%)

Northbound Mammoth

Road

80

(17%)

400

(83%)

STOP

Sherburne Road

49

(17%)

235

(83%)

STOP

Sherburne Road

75

(18%)

339

(82%)

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Accident data compiled by the Nashua Regional Planning Commission (NRPC), from Pelham Police

records, show 12 accidents at this intersection over the last three years. Only one of these was an injury

accident. Five accidents occurred between vehicles traveling on Mammoth Road and vehicles turning

left out of Sherburne Road. Two accidents were run-off-the-road during snow/slush conditions, and

three were rear end collisions.

Figure 3 - Accident History

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Road Safety Audit Process:

The Road Safety Audit (RSA) is an eight step process. Step 1 and Step 2 were completed by NHDOT and

NRPC. Together they selected the intersection for study and identified the key stakeholders, owners,

and consultants necessary to conduct the RSA. This RSA Team was involved in Steps 3 through 6, and

NHDOT will be responsible for Steps 7 and 8.

The RSA Team met on October 19, 2011 at the Town of Pelham Police Department. The agenda was as

follows:

1. Presentation of the RSA process, scope, and objectives to the RSA Team;

2. Present background information on project area;

3. Group discussion on safety issues and concerns;

4. Field review at project site;

5. Discussion of site observations, risk assessment, and possible solutions;

6. Discussion of next steps.

This audit was conducted in conjunction with a road safety audit for the intersection of Sherburne Road

and Dracut Road in the Town of Hudson. While a separate audit report has been prepared for that

intersection, some of the comments and information are relevant to this audit. Also, since both of these

intersections share the similar traffic patterns and are in close proximity of each other, the stakeholders

from both towns were encouraged to participate in both audits.

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Stakeholder Concerns:

A field visit was conducted between 10:00 and 11:30 AM on October 19, 2011. The weather was cool

and rainy. The RSA Team was provided with a list of possible safety issues to consider during their

inspection. As a result of this site visit and other discussions during the RSA Team meeting, the

following concerns and comments were raised:

There is heavy traffic using Sherburne Road as an east-west connection.

Most of the traffic is familiar with the road.

The area is primarily residential in nature.

The intersection has good line of sight for both roads.

There is currently overhead lighting at this location; however, NHDOT may potentially turn off

the street light as part of a statewide cost saving measure.

The Planning Boards in both the Town of Pelham and the Town of Hudson have approved

various large subdivisions and a 40 unit senior housing development on Sherburne Road. Some

of the subdivisions may not be constructed, but this demonstrates that development in this area

has the potential to continue increasing the traffic at the study intersection.

The Town of Pelham reported that they collect impact fees from developers in the amount of

$2,200 per new subdivided building lot. Per state statutes, a town must expend this revenue

within six years or return the money to the builder.

There is a small amount of pedestrian activity on Sherburne Road consisting mostly joggers and

dog walkers.

NHDOT District 5 recently paved Sherburne Road. At the time of the Audit, the pavement

markings had not been applied yet.

Rear end collisions on Mammoth Road are primarily due to vehicles waiting to turn left onto

Sherburne Road.

There is a substantial amount of pavement area at this intersection. Right turning vehicles from

Sherburne Road tend to bypass other vehicles waiting to turn left which blocks the sight

distance for those turning left thus causing further delay. The Police Chief reported that the

police tried to eliminate the dual lane turning movement and this caused an even longer delay

on Sherburne Road.

There is a congestion issue at this intersection. On Fridays, the traffic backs up on Sherburne

Road for a long distance. This causes drivers to get impatient and take greater risks turning left

onto Mammoth Road.

It was reported that there are numerous rear end collisions on Sherburne Road that are not

reported because they are under $1,000 in damage.

The Town of Pelham has drafted preliminary plans for a roundabout at this location.

There is ample right-of-way at this intersection.

There are numerous bicycle users on Mammoth Road.

The ability of vehicles travelling northbound on Mammoth Road to bypass other vehicles waiting

to turn right onto Sherburne Road is good.

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Risk Analysis:

Based on the data presented, stakeholder discussion, and site evaluation, the RSA Team identified and

prioritized safety issues and concerns. Safety issues were prioritized based on their perceived

contribution to accident risk. The rankings were: High, Medium, and Low Risk.

Next the RSA Team brainstormed ideas on how these safety issues could be corrected. All suggestions

were welcomed and considered. Each possible risk-mitigation solution was categorized as a long,

medium, or short term solution based on when they could be implemented. Short term solutions could

feasibly be accomplished within six months, medium term within six months to two years, and long term

solutions would be those that would take more than two years to implement.

The following chart summarizes the risk analysis and mitigation strategies that were discussed. A more

detailed review of these strategies is presented in the summary section of the report.

Safety Issue Risk Level Suggested Strategy Mitigation Timeframe

Responsible Stakeholder

1 Intersection is not readily apparent to northbound Mammoth Road traffic

Medium a) Improved / relocated intersection ahead signs b) Median Island

a) Short b) Long

a) NHDOT b) NHDOT

2 Excessive speed of NH 128 traffic

High a) Roundabout b) Shorten taper on NH 128 NB bypass shoulder

a) Long b) Long

a) NHDOT b) NHDOT

3 SB NH 128 traffic can turn right at high speeds

High Narrow intersection by removing pavement

Medium NHDOT

4 Right turning vehicles on Sherburne Road block sight for left turning vehicles

High a) Paint turning lane with pork chop island b) Build median island

a) Medium b) Medium

a) NHDOT b) NHDOT

5 High volume of turning traffic

High Build roundabout Long NHDOT

6 Pavement markings faded or missing

Medium Apply pavement markings

Short NHDOT

7 Inadequate signs and visibility of signs

Medium a) New retro-reflective signs b) Move stop sign closer to intersection

a) Short b) Short

a) NHDOT b) NHDOT

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Summary:

High Risk Safety Issues

The RSA Team identified four high risk safety issues that make this intersection dangerous. Foremost,

traffic on Mammoth Road (NH 128) travels very quickly and southbound traffic can turn right onto

Sherburne Road at a high rate of speed (issue #2 and #3). There is a large volume of traffic turning into

and out of Sherburne Road and they have difficulty seeing the traffic traveling northbound on

Mammoth Road because vehicles turning right block the sight lines (issues #4 and #5). To address these

high risk safety issues, five possible solutions were offered.

Medium Term Solutions:

1. Cut and remove the pavement in the northwest corner of the intersection to decrease the

radius of the curve for Mammoth Road (NH 128) southbound traffic turning right onto

Sherburne Road. The intent of this solution is slow the right turning vehicles and thereby

creating larger gaps in traffic to allow for left turns from Sherburne Road.

2. Build or paint an island or slip lane for Sherburne Road traffic turning onto Mammoth Road. The

purpose would be to separate left turning and right turning vehicles so that they don’t block

each other’s sight lines on Mammoth Road.

Long Term Solutions:

1. Build a roundabout at this intersection. A roundabout would resolve many of the issues at this

intersection by reducing speeds and accommodating the high volume of turning traffic.

2. Shorten the taper of the bypass shoulder on Mammoth Road that vehicles use to bypass

northbound vehicles turning left. The intent of this solution is slow the bypassing vehicles and

thereby creating larger gaps in traffic to allow for left turns from Sherburne Road.

Medium Risk Safety Issues

The RSA Team identified three medium risk safety issues that contribute to making this intersection

dangerous. The first issue is that the intersection is not readily apparent to traffic traveling north on

Mammoth Road (issue #1). The other medium risk issues identified were that of worn out or missing

pavement markings and old/misplaced signs (issues #6 and #7).

Short Term Solutions:

1. NHDOT should re-stripe the pavement markings, especially the stop bar, in the vicinity of the

intersection.

2. Place new retro-reflective signs on all approaches to the intersection. Signs should include stop

ahead and stop signs on Sherburne Road, and intersection ahead signs on Mammoth Road. The

intersection ahead signs on Mammoth Road should be relocated to give adequate notice to

northbound traffic. The stop sign on Sherburne Road should be moved to coincide with the stop

bars.

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3. Relocate the Turn Ahead sign for southbound Mammoth Road Traffic to a location closer to the

point of curvature of the horizontal curve south of the intersection. In its current location the

sign appears to be too far in advance of the curve and distracts the driver from the intersection.

Medium Term Solutions:

1. The feasibility of installing a median island on Mammoth Road should be investigated by

NHDOT. The purpose of this island would be give northbound traffic a visual cue of where the

intersection is located.

Low Risk Safety Issues

The RSA Team didn’t identify any low risk safety issues at this intersection. As such there are no

solutions or recommendations for low risk issues

Conclusions and Recommendations:

The main factors making this intersection dangerous are the high volume of vehicles turning combined

with high speed of Mammoth Road traffic. Secondary factors include worn out or missing signs and

pavement markings.

It is suggested that the short term solutions be implemented while investigating the feasibility of

medium and long term solutions. The Town of Pelham and NHDOT should also continue to monitor the

accident rates at this intersection. In summary the suggested recommendations are as follows:

A. NHDOT should apply new pavement markings at the intersection;

B. NHDOT should install new retro-reflective signs for all legs of the intersection and relocate

existing ones as necessary;

C. NHDOT should investigate all possibilities for reconfiguring the intersection, including:

a. Adding median islands/slip ramps on Sherburne Road and/or Mammoth Road;

b. Removal of pavement to decrease the SB right turn radius;

c. Construction of a roundabout.

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Figure 4 – Sherburne Road looking east

Figure 5- Traffic turning onto Mammoth Road

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.

Audit Response:

Submission of this report represents completion of Steps 1 through 6 of the RSA process. NHDOT, as the

project owner, will prepare a formal response addressing the audit findings. The responses should

outline what actions the owner will take related to each safety concern listed in the report. NHDOT may

either:

Agree with the suggestion described by the audit team and commit to its implementation

outlining a schedule for the completion of the suggestion;

Disagree with the suggestion described by the audit team and commit to an alternative,

outlining a schedule for the completion of the alternative. In doing so, the owner should

provide a valid reason as to why they choose not to adopt the audit team’s suggestions;

Choose not to implement certain improvements at all due to constraint or disagreement

regarding the safety issue, believing that there is no increased risk associated with the concern

raised by the audit team. In doing so, the owner should document the reasoning behind their

decision.