LARIMER COUNTY RURAL AREA ROAD STANDARDS

Chapter 4 – Road Design and Technical CriteriaSection 4.3 Road Design4.3 ROAD DESIGN4.3.1 ClassificationsAll roads are classified as Arterial, Collector or Local roads. These classifications relateto the function of the roads. Lower order roads function primarily as access to individuallots, and higher order roads function primarily for the purpose of mobility (expeditiousmovement of people and goods). Larimer County has adopted an expandedclassifications system that is to be used within the County except for areas withinrecognized GMA’s in which case the County may, at its discretion apply the City orTown’s functional classification of roadways.4.3.2 AlignmentHorizontal and vertical road alignments should conform to existing land layout plus thefollowing criteria:4.3.2.1 Horizontal AlignmentOn Arterial and Major Collector roadways, curve radii and tangents shall be as largeas possible using the minimums only where necessary. Angle point directionchanges are not allowed. All changes in direction shall be made using standardcurves.a. Horizontal Curve Radii. The minimum allowable centerline radii forhorizontal curves shall be as designated in Table 4-1. Reverse andcompound curves should be used only when a single radius curve will notwork. For driver safety, compound curves shall have a ratio no greater than1.5 where the value of the larger radius is divided by the smaller radius.b. Minimum Tangent Length. Requirements are as follows:1) Intersection. Whenever a minor road intersects a road of higherclassification, a tangent length (measured from the nearest edge ofpavement of the intersected road to the point of curvature in theintersecting road) shall be provided for a safe sight distance and safetraffic operation. The minimum required tangent lengths indicated in Table4-1 apply to the minor leg(s) only. The angle of departure shall notexceed 10 degrees for the length of tangent.2) Reverse Curves. The tangent between reverse curves shall be no lessthan the length shown in Table 4-1.3) Broken Back Curves. Two curves in the same direction (broken backcurves) shall be separated by a tangent with a length of at least 2 timesthe minimum length shown in Table 4-1.c. Curves with Small Deflection Angles (10° or less). To reduce theappearance of kinks in the road, minimum lengths of curve shall be designedwith minimum centerline arc lengths as shown in Table 4-1.d. Horizontal Curves on Vertical Curves. For driver safety, horizontal curvesshall not begin near the top of a crest vertical curve nor near the bottom of asag vertical curve.Larimer County Rural Area Road Standards Page 4-2October 22, 2007