Due to the large variations in urban and village settings, no table of values has been given; however, the following guidelines will apply. On urban and village Principal Arterials, lane widths may vary from 10 to 12 feet, and there should be appropriate offsets to curb. The 10-foot widths are appropriate in highly restricted areas having little or no truck traffic. The 11-foot lanes are used extensively for urban and village Principal Arterial street designs. The 12-foot lane widths are generally used on all higher speed, free-flowing Principal Arterials. Under interrupted-flow conditions at low speeds (up to 45 mph), the narrower lane widths are normally adequate and have some advantages. Reduced lane widths allow greater numbers of lanes in restricted right-of-way and facilitate pedestrian crossings because of reduced distance. They are also more economical to construct. An 11-foot lane width is adequate for through lanes, continuous two-way left-turn lanes and a lane adjacent to a painted median. A 10-foot left-turn lane, or a combination lane used for parking, with traffic during peak hours, is also acceptable.

Lane and shoulder widths within Historic Districts should be compatible with the historic character of the District.

Shoulders are desirable on urban and village Principal Arterials, and should be provided where feasible for maneuvering room, space for immobilized vehicles, safety for the pedestrian in areas where sidewalks are not provided, safe accommodation of bicycles, speed-change lanes for vehicles turning into driveways, and storage space for plowed snow. Despite these advantages, the width of shoulders in urban and village areas may be restricted because of available right-of-way, adjacent development and other constraints.

Where shoulders are provided to accommodate disabled vehicles, they must be at least 6 feet wide. Parking lanes require approximately 7 feet of actual street space. The desirable minimum width is 8 feet; however, to provide better clearance and the potential to use the parking lane as a travel lane during peak periods a parking lane width of 10 to 12 feet is desirable.

As an absolute minimum, on limited access principal arterials, where bicycles and pedestrians are prohibited, a 2-foot offset to vertical curb should be provided, and a 1-foot offset to sloped curb. In all cases, drainage grates and drop inlets should be designed so that they do not project into a travel lane. Drainage grates should always be designed bicycle-safe.

Lane and shoulder widths on rural Principal Arterials will adhere to values in Table 3.3. Note that shoulder widths in this table are considered necessary for adequate safety and service for this class of highway, and may exceed the minimum paved widths needed solely to provide bicycle safety. The required shoulder width beyond that needed to adequately accommodate bicycles as defined in Section 3.14 need not be paved.

The full width of approach roadways will (normally) be provided across all new bridges on rural Principal Arterials, and the same curb-to-curb width as the street across all new bridges on urban and village Principal Arterials. New bridges should be designed to HS-25 loading capacity.

Bridges to remain in place without treatment should have at least the width of the roadway approach travel way plus 2-foot clearance to face of rail on each side, and should be adequate for State legal loads without posted restrictions.

New or reconstructed structures should provide at least 16 feet of vertical clearance over the entire roadway width, including shoulders. Existing structures that provide 14 feet of clearance may be retained. In urban areas, a minimum clearance of 14 feet may be provided if there is an alternate route for trucks that provides a 16-foot clearance. Structures should also provide an additional clearance of 3 inches for future resurfacing of the underpassing road.

Structures over railroads should provide a minimum vertical clearance of 23 feet over both rails, unless otherwise provided in a variance agreement entered into by the VAOT, the railroad and any affected municipality, and approved by the Transportation Board in accordance with 5 VSA, Section 3670. Where "double-stacks" are to be accommodated on the railroad, an absolute minimum vertical clearance of 20.75 feet will be required.

Bridges over rivers and other bodies of water will, where practicable, be designed to pass the 50-year frequency flood with a minimum clearance of 1' between the water surface elevation and the low chord of the bridge. In addition, overtopping of the road should not be permitted during the 50-year flood. Consideration shall also be given to the potential effects of the 100-year flood on upstream and downstream property, the environment, hazards to human life and floodplain management criteria.

A clear unobstructed roadside is highly desirable for motorist safety along rural principal arterials. Clear zone distances for new construction and reconstruction projects on rural principal arterials will normally be based on the values shown in Table 3.4.

Despite the recommendations of Table 3.4, clear zones as narrow as 10 feet may be used on rural principal arterials, without design exception, where necessary to avoid or minimize disturbance of significant historic, archaeological, scenic, natural or other resources.

On uncurbed urban and village principal arterials, clear zones will be the same as for rural areas.

On curbed principal arterial urban and village streets, a 1.5 foot horizontal offset to obstructions from face of curb should be provided. This dimension should be increased to 3 feet near turning radii at intersections with side roads and driveways.

Horizontal curvature will normally be designed in accordance with recommended AASHTO values for the design speed. However, curves up to 10 mph below the stated design speed may be used, without design exception, where necessary to avoid and/or minimize disturbance of historic, archaeological, scenic, natural or other resources. In addition, horizontal curves within 750 feet of a stop sign may be designed up to 15 mph below the stated design speed without design exception. When curvature sharper than the AASHTO recommended values is used, a post-construction test of those curves will be conducted, and advisory speeds will be posted where appropriate.

Maximum grades on rural and urban Principal Arterials will adhere to the values shown in Tables 3.5 and 3.6. In curbed areas of village and urban streets and on all bridges, grades less than 1 percent should be avoided where possible to promote efficient runoff of storm water.

Two-lane pavements are normally designed with a centerline crown and a parabolic surface with an average cross slope of 2 percent. When drainage is carried across adjacent lanes, the cross slope may be increased from one lane to another. Refer to the VAOT design manual for cross-slope design in various situations.

When the use of curves is required on a rural Principal Arterial alignment, a superelevation rate compatible with the design speed must be used. Superelevation of curves on rural Principal Arterials should not exceed 8 percent. Where a side road intersects on the outside of a main road curve, superelevation of the main road curve should be limited to 6 percent or less to prevent operational difficulties for vehicles entering the main road under snowy or icy conditions.

Superelevation is generally not used on low-speed (45 mph or less) curbed urban and village streets. This is to avoid problems with such items as drainage, ice formation, driveways, pedestrian crossings and developed property (Refer to the 1990 AASHTO Policy, Chapter III, for a detailed discussion of design for low-speed urban streets).

Bicycle and pedestrian traffic may be expected along the sides of most Principal Arterial roads and streets, except those which are designed and posted as limited access facilities. Where bicycles and pedestrians are allowed by law, the roadway should be designed and constructed under the assumption that it will be used by bicyclists and pedestrians. Bicycles require a paved surface; pedestrians, however, may often be adequately accommodated on unpaved roadway shoulders.

In recent decades, highways were not always designed with bicycle and pedestrian travel in mind. There are many ways in which roadway corridors should be improved to more safely accommodate bicycle and pedestrian traffic. Bicycle accommodation within the highway corridor may take four forms: (1) shared use of the highway by bicycles and motor vehicles, (2) designated bicycle route, (3) designated bicycle lane, or (4) a separated bicycle path. Many of the tools listed in section 3.15.1 provide roadways which are safer for bicyclists and pedestrians.

Adequate accommodation of bicycles in rural areas is usually provided by paved shoulders designed to the widths shown in Section 3.6. However, where shoulder width is less than those values, where shoulder paving must be minimized, and in urban or village areas, Tables 3.7, 3.8, and 3.9 provide additional guidance in the selection of appropriate widths of paved areas to safely accommodate bicycles and motor vehicles on the same facility. Note that additional width may be desirable in very high traffic areas or where sight distance is restricted.

In lieu of a paved shoulder, it is permissible to use a shared-use curb lane of at least the width shown in Table 3.9. When a shared-use lane is employed, a white edge line should be placed within 1 foot of the face of curb to discourage parking. For all shared-use curb lanes, recessed drainage inlets or curb inlets should be used.

Wherever bicycles are to be accommodated on newly constructed bridges, shoulders with a minimum dimension as shown in Tables 3.7, 3.8 and 3.9 in this subsection should be provided between the parapet, rail or barrier and the edge of the nearest travel lane.

Designated bicycle routes or lanes may be appropriate along some principal arterial highways. Because designated routes and lanes will attract bicyclists encompassing a wide range of abilities, special care must be taken to ensure adequate width. Principal concerns for designated bicycle routes and lanes are rider safety and comfort. Because of these concerns, some high speed and/or high volume arterial routes may not be appropriate for designated routes and lanes. In such cases, alternate routes or separate paths for bicycles may be desirable.

Adequate accommodation of pedestrians must be designed for all roadway projects. Depending on the locality and expected frequency of pedestrians, adequate accommodation may range from a graded space alongside a rural road to a sidewalk in a village or city. Projects in urban or village areas shall include consideration of sidewalks and crossing locations. In addition, at the request of a municipality, sidewalks should be considered in other areas of expected pedestrian use such as near schools and recreation areas.

Where pedestrians are accommodated on sidewalks, the design must observe, to the extent possible, current Americans with Disabilities Act Accessibility Guidelines (ADAAG). These guidelines establish acceptable grades, cross-slopes, widths, ramps, surface textures and other facets of pedestrian facility design.

Pedestrian accommodation on combined bicycle/pedestrian paths must also respect the ADAAG to the extent feasible.

Pedestrian accommodation along the shoulders of roadways do not need to comply with ADAAG. However, to the extent that those guidelines can reasonably be achieved, the designer is urged to do so.

These Special Design Guidelines are presented to assist the designer in avoiding, minimizing, or mitigating negative impacts upon the environment and other sensitive resources as well as to enhance the design to fit the context of the project site. These Special Design Guidelines note the importance of the individual resources and suggest tools which may be used in the development of a design which recognizes the resource at the proper level of importance. Under this Functional Classification there are guidelines for:

> Scenic Resources

> Village or City Entrance Considerations

> Economic Vitality Considerations

When such resources are present within a project site and the use of the tools suggested do not provide an adequate protection of the resources then the design may be eligible for reductions in geometric values. The decision to pursue reductions in the standards is subject to approval in accordance with the "VAOT Design Exception Policy".

The primary strategy for Principal Arterial projects on new alignment should be to use alternative roadway alignments to avoid the impact on the resource. When the project must remain on existing alignment such as a major roadway reconstruction, "Preservation" or "3R" project, bridge repair or replacement, design solutions should be pursued that minimize the extent of the impact. Major tools to be used to avoid sensitive resources include: slope adjustments, clear zone reduction with installation of guard rail and other means which do not reduce the integrity and safety of the design. Reduction in the size/area of impact, and the utilization of creative design and engineering solutions should be pursued. These strategies are described as "common tools" in the following subsection.

> Reduction of Posted Speed.

> Reduction/minimization of lane and shoulder widths

> Reduction/minimization of clear zones

> Reduction of horizontal curves with advisory speed postings.

> Alterations to typical cross section including:

$ Sideslopes steeper than normal (in combination with additional guardrail)

$ Use of curb and closed drainage systems, elimination of roadside ditching

$ Retaining walls

> Wetland and wetland buffer restoration/creation

> Wildlife habitat restoration/creation

> Water quality/stream bank, stream buffer, lake buffer creation, restoration, and enhancement

> On and Off - site mitigation

> View/scenic enhancement through vegetation management and grading of sideslopes

> Use of guard rail to allow steeper than 1:4 graded slopes, retaining walls or cribbing

> Use of grade separation/bridging/elevated structures etc.

> Separation of vehicular/pedestrian facilities.

> Fencing or landscaping for screening or earth berm buffers.

> Retrofitting of historical bridges for alternative uses off-site.

> Integration of historical features in interpretive facilities, overlooks, etc.

> Light poles and fixtures with down shielded luminaires.

> Architectural/Landscape design:

$ street trees

$ use of native materials

$ use of architectural design details

$ pedestrian facilities

$ signage

$ historical design elements

Principal Arterial projects should be designed to avoid historic or archaeological resources wherever possible. This may be in the form of avoiding disturbance of specific sites and structures as well as historic districts or areas where the presence of the road is disturbing to the historic land use and development pattern. Many Principal Arterial roads pass directly through city, town, and village centers and designers must work within these constraints while fitting roadways close to community historic landmarks.

Where Principal Arterials pass through historic town centers an appropriate balance must be struck between the mobility of through traffic and the historic and community values. Since a roadway's design characteristics are a function of the design and posted speeds, consideration should be given to reducing these speed variables. An appropriate response would be to work with local officials in reviewing the tradeoffs between impacts to historic areas and the posted speed.

Providing curbs along Principal Arterials in historic centers will allow improved pedestrian safety as well as a reduction in clear zone requirements to allow preservation and enhancement of historic elements. Where avoidance of historic and community landmarks proves unfeasible, every effort should be made to minimize impacts including mitigation strategies and design enhancements to enable the maximum integration of the Principal Arterial with the historic area. The following additional design techniques address the potential tools available to designers for Principal Arterials:

Principal Arterial construction projects should be designed to avoid natural resources wherever possible. This may be in the form of avoiding the disturbance of specific sites or areas where the presence of the road conflicts with important natural resources. Where avoidance proves unfeasible, every effort should be made to minimize impacts or pursue mitigation strategies and design enhancements to enable the maximum integration of the Principal Arterial with the natural landscape.

All Principal Arterial projects should consider the presence of environmental resources in project planning, design and construction. The following resources are protected by State and Federal law:

> Wetlands, lakes, rivers, streams and their shorelines

> Water supplies

> Groundwater protection areas

> Watershed protection areas

> Agricultural districts and farmland

> Floodplains/ways

> Critical wildlife habitat and natural areas

> Rare and endangered species

> Designated "Wild and Scenic Rivers"

> Local Conservation districts or zones

> State and Federal forests and wildlife management areas

> Outstanding Resource Waters

Principal Arterial projects should be designed to avoid public recreational facilities wherever possible. Where avoidance proves unfeasible, every effort should be made to minimize impacts including mitigation strategies and design enhancements to enable the maximum integration of the Principal Arterials with the landscape. Examples of Recreational Resources are:

> Federally owned, funded, or managed property

> State owned, funded or managed property

> Locally owned parks and recreational areas

> Privately owned recreational facilities open to the public

> Trails and Greenways

All Principal Arterial projects should consider scenic and aesthetic issues for projects that possess scenic qualities. Assessment of scenic qualities should be completed in the Project Development Process. This includes, but is not limited to "Designated Scenic Roads" or "Scenic Byways" as well as other roads with scenic attributes. Techniques for preservation of scenic resources should be employed for scenic resources seen from the road, as well as views of the road from surrounding areas. The following techniques should be considered where scenic issues in a Principal Arterial project are identified:

> Extension of sideslope grading to round-out cut and fill slopes

> Scenic turnouts should be considered and provided, where demand is apparent.

> Treatment of bridges, abutments, retaining walls should de-emphasize structures where prominent long views and vistas are present.

Many of the Principal Arterials in Vermont enter and pass directly through towns, villages or cities. These Standards are specifically designed to allow greater flexibility and reduce the conflict with the small scale of many of the affected communities along Principal Arterials. The following additional guidelines may be appropriate at such locations:

Creative design should integrate economic issues where transportation needs of people, goods and services are significant, and where design of the roadway may affect the vitality of a downtown, commercial or industrial area. In these cases, the following additional guidelines may be appropriate:

> Use appropriate turning radii for large commercial vehicles at appropriate intersections.

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