(a) Clear width between curbs or rails, whichever is the lesser, is considered to be at least the same as the roadway

New or reconstructed structures should provide at least 14 feet of vertical clearance over the entire roadway width, including shoulders plus an additional clearance of 3 inches for future resurfacing of the under passing roadway.

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 Agency of Transportation, 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.

On state highways and their connecting links on Class I town highways, bridges over rivers and other bodies of water should be designed to pass a 50-year frequency flood with a minimum clearance of 1 foot between the water surface elevation and the low chord of the bridge. In addition overtopping of the roadway must not be permitted during the 50-year flood. Consideration shall also be given to the potential effects of the 100-year flood on upstream property, the environment, hazards to human life and floodplain management criteria.

Other town highway bridges over rivers and other bodies of water will, where practicable, be designed to pass the 25-year frequency flood with a minimum clearance of 1 foot between the water surface elevation and the low chord of the bridge. In addition, overtopping of the road should not be permitted during the 25-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 collectors. Clear zone distances for new construction and reconstruction projects on rural principal arterials will normally be based on the values shown in Table 5.5.

Despite the recommendations of Table 5.5, 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. In addition, on low speed (45 mph or less) rural collectors, clear zones may be limited to 10 feet, irrespective of the recommendations of Table 5.5.

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

On curbed collector 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 15 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 value 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 Collectors will adhere to the values shown in Tables 5.6 and 5.7. 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 Collector alignment, a superelevation rate compatible with the design speed must be used. Superelevation of curves on rural Collectors 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.

Bicycles and pedestrian traffic may be expected along the sides of most Collector roads and streets. 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 5.15.1 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 5.6 above. However, where shoulders width is less than those values, and where shoulder paving must be minimized and in urban or village areas, Tables 5.8, 5.9 and 5.10 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 a least the width shown in Table 5.10. 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 5.8, 5.9 and 5.10 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 Collector roads and streets. Because designated routes and lanes will attract bicyclists encompassing a wide range of abilities, special care must be taken to ensure adequate widths. Principal concerns for designated bicycle routes and lanes are rider safety and comfort. Because of these concerns, some high speed and/or high volume collector 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 Collector road and street projects on new alignment should be to avoid or minimize 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. Collector roads and streets should be designed to allow both local access and mobility and as such should make the most use of tools to avoid impact to sensitive resources. Reduction in the size/area of impact, and the utilization of creative design and engineering solutions should be pursued. The following strategies are described as "common tools" in the following subsection to avoid impact to the resources.

> Reduction in Posted Speed

> Reduction/minimization of lane and shoulder widths

> Reduction/minimization clear zones

> Sharpening of horizontal curves with advisory speed postings

> Alterations to typical cross sections including:

$ Roadside ditches shallower than normal

$ 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

Collector road and street 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. Designers must contend with environmental constraints to fit new and renovated roadways within historic environments.

Where Collector roads and streets pass through historic town centers, an appropriate response is to work with local officials to reconcile posted speed and historic property conflicts and to apply that resolution to the specific community context. Reduction in lane and shoulder widths may be considered as appropriate to avoid the imposition of wider road sections through historically sensitive areas. Additionally, decisions regarding measures to accomplish speed management should be considered.

Providing curbs along Collector roads and streets in historic areas will allow both improved pedestrian safety as well as reduce in clear zone requirements. Street trees and other urban streetscape elements are essential parts of these roads. Every effort should be made to design enhancements which maximum integration of the Collector road and streets with the historic area.

The following additional design techniques are suggested to designers for Collector roads and streets:

> Alterations to typical cross sections including:

$ Roadside ditches shallower than normal

$ Sideslopes steeper than normal

$ Use of curb, and elimination of the roadside ditch

$ Retaining walls

> Landscaping for screening

> Retrofitting of historical bridges should be considered.

Collector roads and street construction projects should be designed to avoid natural resources wherever possible. This may be in the form of avoiding disturbance of specific sites or areas where the presence of the road conflicts with 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 Collector Roads and Streets with the resource. Examples of resources included:

> Wetland, lakes, rivers, and 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

Collector road and street projects should be designed to avoid public recreational facilities and protect and enhance their use 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 Collector road and streets with the resource. Examples of resources include:

> 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

> Federal and State forest and wildlife management areas

All Collector road and street projects should consider scenic and aesthetic issues for projects that are either designated Scenic Roads or other roads or areas with scenic attributes. Techniques for preservation of scenic resources should be employed for both scenic resources seen from the road, as well as views of the road from surrounding areas. Some of these roads travel through the State's most dramatic landscapes where dominance of the road could negatively impact scenic values. The following additional techniques should be considered where scenic views from the roadway are identified:

> Tree removal or trimming to preserve or enhance views.

Many of the Collector roads and streets in Vermont enter and pass through towns, villages or cities. These standards are specifically designed to allow greater flexibility to reduce the conflicts with the small scale of many of the affected communities along Collector roads and streets. 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.