Article II Highway Design Specifications

Unless otherwise stated, this article is written for rural or suburban roads but shall be used as applicable for other classes of highways.

See Figure II-3 for a subdivision road typical cross section. Some modifications to the specifications in this article are shown on Figures II-1 and II-2 for other classes of highways.

Continuation of streets into adjacent property.

Streets shall be arranged to provide for the continuation of principal streets between adjacent properties where such continuation is necessary for convenient movement of traffic, effective fire protection, efficient provision for utilities and particularly where such continuation is in accordance with the Town plan.

If the adjacent property is undeveloped and a street must dead-end temporarily, the right-of-way and the improvements must run to the property line. A temporary circular turnaround shall be provided on all temporary dead-end streets.

Road names.

The developer shall receive prior approval for any proposed road name from the Town Clerk.

§ A197-21 Classes and right-of-way.

The Highway Superintendent shall determine and designate into which of the four following classifications each proposed street falls on the basis of one or more of the defining criteria. The Highway Superintendent may delegate to the Planning Board the authority to designate the class for any highway that is part of a subdivision or site plan also reviewed by the Planning Board.

[Amended 11-14-2002 by L.L. No. 5-2002]

Major or through highway.

Commercial or industrial highway.

Rural or suburban highway.

Minor local road.

Major or through highway.

The proposed highway is the direct and logical continuation of an existing highway that carried 500 or more heavy and light vehicles during a twelve-hour period as shown on the latest traffic count if heavy vehicles (trucks) are more than 10% of the design hour traffic volume. At least half of the trucks are anticipated to be at or near the legal maximum weight.

The proposed highway creates a shorter and more convenient through traffic artery so that it can be reasonably expected that traffic will be diverted from other major highways to such an extent that it will reach at least 500 cars in 12 hours within two years after opening.

The proposed highway could logically be expected to become a major highway because of future construction or other foreseeable circumstances.

Commercial or industrial highway.

The proposed highway is in an area zoned for commerce or industry.

The proposed highway is on or so close to the dividing line between a residential and a commercial or industrial area that it may reasonably be expected to carry a substantial volume of heavy vehicles.

The proposed highway creates a shorter and more convenient route between a commercial or industrial area and a major traffic artery.

The proposed highway for any other reason may be expected to carry a substantial volume of commercial or industrial traffic.

Rural or suburban highway (local road). (This classification is intended to cover the majority of subdivision streets.)

[Amended 11-14-2002 by L.L. No. 5-2002]

The proposed highway shall not be, or be reasonably expected to become, a major or commercial highway.

The proposed highway shall be a dead end, loop or other minor highway within a residential development.

The proposed highway is not, or cannot reasonably be expected to become, a continuation or extension of a major or commercial highway. Should such be the case, the proposed highway shall take the classification of the highway of which it is a continuation or extension.

The proposed highway does not, or cannot reasonably be expected to, carry a substantial volume of traffic.

Minor local road. (This classification is intended to cover only certain streets in cluster subdivisions or CRD Developments.)

[Added 11-14-2002 by L.L. No. 5-2002]

The proposed street shall not be, or be reasonably expected to become, a rural or suburban highway (local road).

The proposed street shall only serve residential properties in a cluster subdivision, or a CRD Development.

The proposed street shall be no longer than 2,500 lineal feet.

The proposed street shall not carry, nor be reasonably expected to carry, more than 1,000 cars or other vehicles per twenty-four-hour timeframe.

(5)

The proposed street shall be expected to accommodate pedestrian traffic in more densely settled areas, and must provide sidewalks, pathways or other off-road pedestrian accommodations, and street trees.

(6)

Within CRD Developments and cluster subdivisions, the Planning Board shall also have discretion to approve one or more private roads. Such roads may include those serving small groups of dwellings. Private roads providing primary access to dwelling units shall have a right-of-way width of not less than 42 feet, and shall meet the other standards of minor local roads. Private roads may also include rear service lanes, subject to the following: (1) pavement width shall be not less than 18 feet; (2) a rear service lane may not be a dead-end road; (3) a rear service lane may not provide the primary access to a dwelling; (4) any garages deriving access from the rear service lane shall be set back at least 25 feet from the edge of pavement. No private roads may be approved unless the Board is satisfied that the road will be permanently maintained by a homeowners' association or other similar entity.

The roadway right-of-way (ROW) width shall be a minimum of 50 feet for rural or suburban highways and minor local roads and a minimum of 60 feet for major or through highways and commercial or industrial highways.

[Amended 11-14-2002 by L.L. No. 5-2002]

Where regrading extends beyond the fifty-foot ROW, the developer shall include all regrading outside of the right-of-way in permanent grading easements.

Where there is no defined or dedicated ROW, the subdivider or developer shall deed to the Town, at minimum, all land within 25 feet of the mean center line of the existing "road by user" when so requested by the Highway Superintendent.

Where sidewalks are planned, the ROW width may be increased by five feet per side to provide a buffer strip.

Where a boulevard is proposed, the minimum right-of-way width shall be 60 feet, to consist of two eighteen-foot travel lanes and one eight-foot landscaped median, plus shoulders, plus additional width, as set forth in Subsection F(3), for sidewalks.

§ A197-22 Vertical alignment.

All highways other than minor local roads shall be designed so that finished tangent grades will not be less than 1% nor more than 10%. Minor local roads shall be designed so that finished tangent grades will not be less than 1% nor more than 12%.

[Amended 11-14-2002 by L.L. No. 5-2002]

Every change in grade shall be effected with a vertical curve of sufficient length to ensure adequate stopping sight distance and to provide for a smooth transition.

[Amended 11-14-2002 by L.L. No. 5-2002]

All streets other than minor local roads shall be designed so that the length of any crest vertical curve shall be a minimum 30 times the algebraic difference of the tangent grades, but not less than 100 feet.

For minor local roads, the length of any crest vertical curve shall be a minimum 15 times the algebraic difference of the tangent grades, but not less than 100 feet.

All streets other than minor local roads shall be designed so that the length of any sag vertical curve shall be a minimum 40 times the algebraic difference of the tangent grades, but not less than 100 feet.

For minor local roads, the length of any sag vertical curve shall be a minimum 30 times the algebraic difference of the tangent grades, but not less than 100 feet.

(5)

The maximum length of any vertical curve shall not exceed 143 times the algebraic difference of the tangent grades.

When an existing road is extended, the new road profile shall match the existing tangent slope or continue the existing vertical curve as applicable.

There is no minimum tangent length requirement between vertical curves, either successive or reverse.

§ A197-23 Horizontal alignment.

[Amended 11-14-2002 by L.L. No. 5-2002]

For all streets other than minor local roads, two tangent sections of a roadway shall be connected with a horizontal curve of at least three-hundred-foot radius, measured at the center line. The minimum curve length shall be 200 feet.

For minor local roads. two tangent sections of a roadway shall be connected with a horizontal curve of at least two-hundred-foot radius, measured at the center line. The minimum curve length shall be 100 feet.

For all classifications of highways:

Superelevation shall be used only when approved by the Highway Superintendent and the Town Engineer.

When an existing road is extended, the new road alignment shall match the existing tangent section or start or continue a horizontal curve.

There shall be a minimum one-hundred-foot tangent section between reverse curves. "Broken back" curves may be used only if the segments of the same hand are separated by a minimum two-hundred-foot tangent section.

§ A197-24 Combination alignment.

The recommendations of the AASHTO guidelines shall be followed as closely as practical.

Where a crest vertical curve and a horizontal curve occur together, there shall be greater than the minimum (300 feet) sight distance to ensure that the horizontal curve is visible to approaching drivers.

§ A197-25 Intersections.

At an intersection, the major road grade should normally be limited to 3%, but in special cases the Town Engineer or Highway Superintendent may authorize up to an eight-percent grade, with adjustments to design factors, particularly as affecting sight distance along the road and corner sight distance.

[Amended 11-14-2002 by L.L. No. 5-2002]

When a new roadway intersects another new roadway, the mainline roadway profile shall be designed in accordance with Figure II-4.

Normally, the grade-line of the major road should be carried through the intersection, and the grade-line of the minor road should be adjusted. Such a design requires a transition of the crown of the minor road to an inclined cross section at its junction with the major road. Drainage shall be carefully designed to prevent ponding and minimize sheet flow across the pavement.

Intersections of a major road by other roads shall be at least 800 feet apart, center to center. A distance of at least 150 feet, center to center, shall be maintained between offset intersections on all classes of streets. At-grade intersections shall have no more than four legs on all classes of streets.

[Amended 11-14-2002 by L.L. No. 5-2002]

Within 40 feet of an intersection, the minor road center line shall be approximately at right angles, but not less than 70°, to the major road. Where a minor road intersects a major road that is on a horizontal curve, the minor road center line shall be tangent and radial to the major road for a minimum of 40 feet.

The ROW lines at a road intersection shall be connected by a minimum twenty-five-foot radius curve, tangent to each leg.

For more complex intersections, such as those involving sidewalks, islands, curved alignment, etc., the AASHTO guidelines shall be followed to the greatest possible extent.

§ A197-26 Turning circles.

Wherever a temporary or permanent dead end is allowed on a subdivision road, a circular turnaround shall be constructed. There shall be a notation on the plat that the land outside the road right-of-way shall revert to abutters whenever the road is continued. See Figure II-5.

All turning circles shall have grades between 2% and 5%, unless otherwise approved by the Highway Superintendent or the Town Engineer, and shall assure properly directed drainage flow into the catch basin(s).

[Amended 11-14-2002 by L.L. No. 5-2002]

Surface treatment shall be of the same type as the road leading to the circle, as shown on Figures II-1, II-2, and II-3, and must be approved by the Highway Superintendent.

For major or through highways, and commercial or industrial highways, the radius of the cul-de-sac at the right-of-way line shall be 65 feet and the radius of the paved area shall be 50 feet.

[Added 11-14-2002 by L.L. No. 5-2002]

For rural or suburban highways (local roads) and minor local roads, the radius of the cul-de-sac at the right-of-way line shall be 50 feet and the radius of the paved area shall be 40 feet.

[Added 11-14-2002 by L.L. No. 5-2002]

§ A197-27 Sight distance.

Actual sight distance shall be determined by roadway speed limits, grades, pavement surface and related criteria. An adjustment shall be made for the effect of grades, per the AASHTO guidelines.

At intersections (including driveways) or along curves, where required by the Highway Superintendent or the Town Engineer, the developer shall provide the Town with a deeded sight easement which shall remain free of any plantings over one foot in height and free of any buildings, structures or other obstructions, in order to maintain clear, unobstructed sight distance. Tree overhang shall be trimmed and maintained to a line at least eight feet above the level of the roadway.

A minimum three-hundred-foot sight distance shall be provided along a curve for a 30 mph design speed, except for a minor local road.

[Amended 11-14-2002 by L.L. No. 5-2002]

Stopping sight distance shall be measured from a point on the center line of the approaching lane of the minor road or driveway 12 feet behind the projected edge of the roadway of the major road, to a point on the center line of the approaching lane of the major road, to a point on the center line of the approaching land of the major road. The height of eye and height of object shall both be assumed to be 44 inches above the road pavement.

Each approach to the intersection or driveway shall be considered separately.

For a driveway, or where the minor road is stop controlled, a minimum of 200 feet of unobstructed stopping sight distance shall be provided for both approaches along a level, 30 mph paved road.