Roadway Standards Section 240 - Sight Distance

240.1 General

Sight distance shall be determined and approved in accordance with the procedures as stated in the current AASHTO "A Policy on Geometric Design of Highways and Streets" or AASHTO's "Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT ≤ 400)". 

240.2 Sight Distance – Standard

1. Comply with the requirements of County Code Section 7.03 which requires that no person shall place objects in the right-of-way or private property in such a way that they limit ISD or SSD per Table 2-6 to 2-10.
2. Adequate intersection sight distance ("ISD") and adequate stopping sight distance ("SSD"), per Tables 2-6, 2-7, and 2-8, should be provided at all existing intersections and shall be provided at all new intersections.
3. Adequate intersection sight distance ("ISD") and adequate stopping sight distance ("SSD"), per Tables 2-6, 2-7, and 2-8, should be provided at all proposed accesses and existing accesses that are subject to land use approval that increase in ADT by 21 or more.
4. Sight distance at intersections and accesses to very low volume local, connector and collector roadways with a 20 year entering volume of less than or equal to 400 ADT and meeting the eligibility requirements of Table 2-9 may be based upon Table 2-9.
5. Existing access subject to land use approval where ADT is increased by 20 or fewer trips shall provide adequate SSD per Table 2-10.
6. Existing access not subject to land use approval but subject to a permit shall maximize ISD and SSD by removing visual obstructions located on the applicant's property or located in the road right-of-way.
7. Proposed access to parcels or contiguous parcels with no other access and not subject to land use approval but subject to a permit shall maximize ISD and SSD by removing visual obstructions located on the applicant's property or located in the road right-of-way.
8. Adequate SSD should be provided along all roadways per Table 2-10 except very low volume local roads, which may be based upon Table 2-9.
9. Adjustments to the sight distance tables of these Standards for street grade, design vehicle, or other factors, with regard to ISD and SSD requirements, shall be made per AASHTO guidelines.
10. If required ISD or SSD cannot feasibly be achieved, lesser sight distance may be acceptable per Section 170.

 An applicant may be required to provide evidence that proposed improvements will not create situations where sight distance is made inadequate for other driveways, intersections, or other sections of roadway.  If sight distance for existing driveways, intersections or sections of roadway is already inadequate, the applicant shall provide evidence that sight distance is not worsened by the applicant's improvements.

Access that doesn't comply with the above criteria are subject to denial, removal or modification.

40.3 Existing Offsite Public Roadway Intersections

Proposed developments subject to adequate safety requirements of the ZDO that impact off-site public roadway intersections (public road intersecting another public road) may be subject to ISD and SSD adequacy requirements at those off-site intersections if safety issues may result from the proposed development in the judgment of the Road Official.  A development may be found to impact off-site intersection(s) if the development's only access or all directions of access to the nearest collector or arterial road is/are via intersection(s) turning movement(s) with inadequate ISD or SSD per Section 240.2.  The applicant may be responsible for submitting data that substantiates trip movements.  The following criteria apply:

1. Developments that add a minimum of 15 daily trips to the inadequate movement(s) at the off-site intersection(s) may be required to mitigate that/those intersection(s) along at least one route from the site access to the nearest collector or arterial roadway per the standards of Section 240.2 or be denied access; or
2. Developments that add between five and 14 daily trips to the inadequate movement(s) at the off-site intersection(s) may be required to mitigate that/those intersection(s) along at least one route from the site access to the nearest collector or arterial roadway per the standards of Table 2-10 and measured per Section 240.4 or be denied access; or
3. Developments that add less than five daily trips to the inadequate movement(s) at the off-site intersection(s) will only be required to mitigate that/those intersection(s) along at least one route from the site access to the nearest collector or arterial roadway per the standards of Table 2-10 and measured per Section 240.4 if any of the off-site intersections are experiencing a crash history related to the inadequate ISD, inadequate SSD or if the development is anticipated to create a significant safety issue.

240.4 Intersection Sight Distance Measurement

ISD shall be measured from a driver's eye height of 3.5 feet and 14.5 feet from the edge of the nearest travel lane (edge line, bike lane line or if neither exits, edge of pavement) to an object height of 3.5 feet above the roadway surface and measured along the center of a travel lane.  Sight distance measurements shall be modified under the following conditions:

1. Where a significant percentage of trucks will intersect a roadway, sight distance measurements may also dictate compliance with the truck sight distance measurements of AASHTO.
2. At the intersection of a local roadway and a private driveway serving up to two single family residential homes, sight distance may be measured 10 feet from the edge of the nearest travel lane except where backing maneuvers are likely to occur.

240.5 Stopping Sight Distance Measurement

SSD shall be measured from a driver's eye height of 3.5 feet to an object height of 2.0 feet above the roadway surface and measured along the center of a travel lane.

240.6 Sight Distance Design Speed

Design speed, for the purpose of determining sight distance, shall be based upon the guidance of Section 250.1.2.  If desired or required, a speed study shall be completed by the applicant in conjunction with County staff direction.   

Table 2-6
Table 2-7
Table 2-8
Table 2-9
Table 2-10