Idaho Administrative Code
Title IDAPA 39 - Transportation, Department of
Rule 39.03.42 - RULES GOVERNING HIGHWAY RIGHT-OF-WAY ENCROACHMENTS ON STATE RIGHTS-OF-WAY
Section 39.03.42.400 - LOCATION AND DESIGN STANDARDS FOR APPROACHES

Universal Citation: ID Admin Code 39.03.42.400

Current through September 2, 2024

01. Required. Location, design, construction and operations of all approaches will comply with current Department geometric standards and design principles.

02. Guidelines. The following access management guidelines will be considered on all approach applications:

a. Design approaches for current and future property access requirements; and

b. Reduce conflicts associated access points through the application of channelization, auxiliary lanes, joint-use approaches, frontage and other local roads, restricted on-street parking and off-street traffic circulation.

03. Signal and Approach Spacing. In order to maintain system capacity, safety and efficiency, maximize signal progression and minimize delays to the traveling public, all approaches and signals will be spaced in accordance with the following standards:

a. All traffic signal locations will meet Department signal warrant requirements and a signal operational analysis;

b. Location preference will be given to State highways that meet or may be reasonably expected to meet signal warrants within five (5) years; and

c. Minimum recommended distances between approaches and signals are as follows:

TABLE 1 - ACCESS SPACING*

HIGHWAY TYPE

AREA TYPE

Signalized Road Spacing

Public Road Spacing (A)

Driveway Distance UpstreamFrom Public Road Intersection (B)

Driveway Distance Downstream From Unsignalized Public Road Intersection (C)

Distance Between Unsignalized Accesses Other Than Public Roads (D)

Interstate

All

Accessible only by interchanges (ramps) and requires approval by the Board and Federal Highway Administration.

Freeway

All

Accessible only by interchanges (ramps).

Expressway

All

Accessible only at locations specified by the Department.

Statewide Route

Rural

5,280 ft

5,280 ft

1,000 ft

650 ft

650 ft

Transitional

5,280 ft

2,640 ft

760 ft

500 ft

500 ft

Urban >35 mph

2,640 ft

1,320 ft

790 ft

500 ft

500 ft

Urban <35 mph

2,640 ft

1,320 ft

790 ft

250 ft**

250 ft**

Regional Route

Rural

5,280 ft

2,640 ft

1,000 ft

650 ft

650 ft

Transitional

2,640 ft

1,320 ft

690 ft

360 ft**

360 ft**

Urban >35 mph

2,640 ft

660 ft

660 ft

360 ft**

360 ft**

Urban <35 mph

2,640 ft

660 ft

660 ft

250 ft**

250 ft**

District Route

Rural

2,640 ft

1,320 ft

760 ft

500 ft

500 ft

Transitional

2,640 ft

660 ft

660 ft

360 ft**

360 ft**

Urban >35 mph

1,320 ft

660 ft

660 ft

360 ft**

360 ft**

Urban <35 mph

1,320 ft

660 ft

660 ft

250 ft**

250 ft**

*Distances in table are minimums based on optimal operational and safety conditions such as adequate sight dis-tance and level grade. Definitions of spacing designated by (A), (B), (C), and (D) are represented on Figure 1.

** Where the public road intersection or private access intersection is signalized, the distances in the table are for driveways restricted to right-in/right-out movements only. For unrestricted driveways the minimum distance will be 500 feet from a signalized intersection.

Click here to view image

d. The District Engineer will have the authority to deny an encroachment permit or require the applicant to provide a Traffic Impact Study when an on-site review indicates that the optimal conditions (such as sight distance and queue length) assumed in Table 1 do not exist, and that operational or safety problems may result from the encroachment spacing.

e. The District Engineer will have the authority to approve a decrease in the minimum access spacing distances set forth in Table 1, provided that the basis for any exception is justified and documented. The basis for the exception may include overriding economic opportunity considerations. For any exception that would result in a decrease in access spacing of more than ten percent (10%) of the distances set forth in Table 1, a Traffic Impact Study will be required in order to determine whether auxiliary lanes or other appropriate mitigation must be included in the permit's conditions.

f. Unless the requirement is waived by the District Engineer, a Traffic Impact Study will also be required when a new or expanded development seeks direct access to a state highway, and at full build out will generate one hundred (100) or more new trips during the peak hour, the new volume of trips will equal or exceed one thousand (1000) vehicles per day, or the new vehicle volume will result from development that equals or exceeds the threshold values in Table 2. If the District Engineer waives the requirement for a Traffic Impact Study, the basis for such waiver will be justified and documented.

g. When required, the Traffic Impact Study will document access needs and impacts and whether any highway modifications are necessary to accommodate the new traffic volumes generated by the development. Such modifications could include, for example, turn lanes, additional through lanes, acceleration or deceleration lanes, medians, traffic signals, removal and/or consolidation of existing approaches, approaches limited to right-in/right-out access only, etc.

h. If a District Engineer denies an encroachment permit application and the denial is appealed to the board, the board or its delegate will have the authority to approve exceptions to the access and signal spacing distances in Table 1 if, in the judgment of the board, overriding economic considerations cause the exceptions to be in the best interests of the public.

Table 2

LAND USE TYPE

THRESHOLD VALUE

Residential

100 Dwelling Units

Retail

35,000 square feet

Office

50,000 square feet

Industrial

70,000 square feet

Lodging

100 rooms

School (K-12)

All (Sections 67-6508 & 67-6519, Idaho Code)

04. Corner Clearance.

a. Approaches should be located as far as practical from intersections: to preserve visibility at the intersection, to permit safe vehicle movement, and to accommodate the installation of traffic signs, signals and lighting where required.

b. Approach transitions or flares will not encroach upon curbs or pavement edges forming the corner radii of the intersection.

c. Minimum corner clearances between signalized and unsignalized urban and rural intersections will comply with current Department standards.

05. Approach Alignment. Whenever possible, all new or relocated approaches will intersect the state highway at right angles and will be aligned on centerline with existing approaches to facilitate highway safety and the development and use of turn lanes and/or signals. Approach skew angles will be in conformance with current Department standards.

06. Width and Radius.

a. An approach will be wide enough to properly serve the anticipated type and volume of traffic. Minimum widths should be used only when space limitations apply.

b. An approach that is adjacent to a public alley may include the alley as part of the approach if approved by the local jurisdiction, however, the width of the combined approach will not exceed forty (40) feet.

c. Commercial approaches with volumes exceeding fifty (50) vehicles per hour during a total of any four (4) hours per day should be designed to public road standards.

d. A Boulevard Approach may be required to improve operation and/or aesthetics of commercial approaches and some public highways, when warranted, by a combination of vehicle length and higher traffic volumes. The approach will be designed to serve the traffic with a right-turn lane, a left-turn lane, a median, and one (1) or more entrance lanes.

e. Minimum and maximum recommended approach widths and radii are as follows:

APPROACH USE

< 35 MPH

> 35 MPH

RADII

Minimum

Maximum

Minimum

Maximum

Minimum

Maximum

Single Residential, Farmyard, Field

12ft

40ft

20ft

40ft

20ft

30ft

Multiple Residential

28ft

40ft

28ft

40ft

20ft

30ft

Commercial (One-Way)

15ft

30ft

20ft

30ft

30ft

40ft

Commercial (Two-Way)

25ft

40ft

25ft

40ft

30ft

40ft

Boulevard Approach

84ft

84ft

84ft

84ft

Contact Department

Joint-Use Residential/Farm

25ft

40ft

25ft

40ft

20ft

30ft

Joint-Use Commercial

12ft

40ft

20ft

40ft

30ft

40ft

Public Highways

28ft

N/A

28ft

N/A

30ft

50ft

07. Property Line Clearance.

a. In curbed sections, there will be a minimum property line clearance of six (6) feet to accommodate approach transitions. Approaches will be constructed so that all approach flares and any extensions of the approach remain within applicant's property.

b. In rural or uncurbed sections, property line clearances will be equal to approach radius. Approaches will be constructed so that all approach radii remain within applicant's property.

c. Approach transitions or radii may be allowed to abut the adjacent property line when required for proper utilization of property. Joint-use approaches will be required whenever property frontage is insufficient to include full width of the approach, including both radii.

08. Setback.

a. Improvements intended to serve patrons on private property adjacent to state highway right-of-way will be setback from the highway right-of-way line so that stopping, standing, parking or maneuvering of vehicles on the right-of-way is not necessary. A minimum setback of fourteen (14) feet from state highway right-of-way line is recommended, unless a greater minimum is established by an engineering study. When an ordinance requires a certain number of parking spaces per square footage of building, the parking spaces will not be included within state highway right-of-way.

b. Traffic movements into and out of a business will be designed, whenever possible, to utilize existing local roads. Existing approaches along traveled way should serve as exits only from the business onto the state highway. Entrance to the property should be made from a local road.

09. Sight Distance. Any encroachment, including but not limited to hedges, shrubbery, fences, walls, or other sight obstructions of any nature, that constitutes a traffic hazard within the "vision triangle" of vehicle operators at the intersection of roads with other roads, private approaches, alleys, bike or pedestrian paths, or railroad crossings will be removed.

10. Transitions and Flares.

a. In curb and gutter sections, the transition connecting the edge of the approach to the curb will meet minimum Department standards.

b. In sections not having a curb and gutter, approach flares should connect the outside edge of the approach to the outside edge of the roadway shoulders and will meet minimum Department standards. The approach flare tangent distance should not exceed twenty (20) feet unless a larger radius is warranted by an engineering study.

c. The distance between approaches will be such that the curb approach transition or radii of the one (1) approach does not encroach upon the transition or radii of the adjacent approach.

11. Grade.

a. If the maximum allowable slope is not great enough to bring the approach to the level of the sidewalk or back of curb, a depressed sidewalk should be installed, when required. If sidewalks exist, the connection between the original sidewalk and the depressed sidewalk will be made through a transition area with a slope no steeper than twelve horizontal to one vertical (12:1) from the longitudinal grade of the original sidewalk. All new curbs or sidewalks should be constructed to the line and grade of the existing curb or sidewalk with every effort to construct a sidewalk that is uniformly graded and free of dips.

b. To accommodate emergency service vehicles, the Department recommends a maximum approach grade of plus or minus ten percent (± 10%).

12. Border Area.

a. Border area work (including grading, seeding and landscaping) will insure that adequate sight distance, proper drainage, desirable slopes for maintenance operations, and a pleasing appearance are provided. The border area will be free of encroachments and designed as needed to prevent vehicular use through the incorporation of appropriate methods such as ditching, special grading, use of concrete or bituminous curbs, fencing, guard rail, and guide posts. The design or devices should not impair adequate sight distance or constitute a hazard to pedestrians, bicycles, or vehicles.

b. The maximum slope beyond the outside edge of shoulder, back of curb, or back of sidewalk to the right-of-way line will meet minimum Department standards. The creation of ponds, pools, or drainage/evaporation swales within the highway right-of-way will be prohibited.

13. Drainage.

a. All approaches will be graded so that private properties abutting the highway right-of-way do not drain onto the traveled way, do not impair the drainage within the right-of-way, alter the stability of the roadway subgrade or materially alter the drainage of areas adjacent to the right-of-way. Post-development drainage flows will not exceed predevelopment drainage flows.

b. Culverts and drop inlets will be installed where required and will be the type and size specified by the Department. Where the border area is regraded, landscaped or reclaimed (seeded), it will have sufficient slope, ditches, culverts, and drop inlets for adequate drainage. Slopes, where practical, should be a six-horizontal-to-one vertical (6:1) maximum.

14. Base and Surfacing.

a. It will be the responsibility of the permittee to supply, place and properly compact the approach fill and base material. All base and surfacing materials and compaction requirements will meet minimum Department design and construction standards.

b. All rural private, commercial and public approaches will be paved to the right-of-way line or to the back of the approach radius. Farmyard and field gravel approaches that are occasionally used will be paved a minimum of five (5) feet from the edge of pavement.

c. In curb and gutter areas, approaches will be paved to the right-of-way line.

Effective July 1, 2024

Disclaimer: These regulations may not be the most recent version. Idaho may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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