Hands On What You Will Need • ArcGIS Desktop (ArcView, ArcEditor, or ArcInfo license) • Sample dataset downloaded from ArcUser Online An Overview of the Exercise This exercise introduces a heads-up methodology for constructing and measuring line segments and calculating turn radii on a carefully digitized road centerline. In the next portion of the workflow, the road is broken into curves and straight lines. Once each curve contains its own radius, travel restrictions and impedance parameters may be developed and used for response modeling. This methodology consists of five tasks. Task 1: Identify and assign the start and endpoints of each curve—the point at which the road polyline transitions from straight to curved or tangent. Task 2: Construct a two-node polyline (the Chord) to connect the curve points. Calculate its length in project units and assign each chord a unique, sequential number. Task 3: Construct the Middle Ordinate, a two-node line perpendicular to the Chord, and intersecting the curve at its farthest point from the Chord. Assign a unique number for each curve in the Middle Ordinate table and calculate its length. Task 4: Break the road polyline into curves and noncurves. Calculate the lengths of all road segments and assign each curve a turn number matching its Chord and Middle Ordinate. Task 5: Join the Chord and Middle Ordinate tables to road segments. Populate the Chord and Middle Ordinate length fields for each curve. Finally, apply the curve radius formula to calculate the radius of all curves and make a map. The Study Area: Chuckanut Ridge Chuckanut Ridge is a private, gated community on Chuckanut Mountain in Bow, Washington, an unincorporated community in northwestern Skagit County. It is the second Firewise USA Community [Firewise Communities/USA, recognized by the National Fire Protection Association, are small, cohesive neighborhoods and towns within the Wildland/Urban Interface acknowledged for homeowner involvement and commitment to minimize home loss to wildfire.] organized in Washington state. Chuckanut Ridge Road, a single hardsurfaced 16-foot-wide road, accesses a handful of private homes scattered up the mountain. It starts at Chuckanut Drive and climbs from an elevation of 160 feet to nearly 1,600 feet in just 3.5 miles. Its average slope is nearly 11 percent, and its many twists and turns include at least 20 switchbacks or sharp S-turns. In addition, some curves actually tighten within a turn, creating an additional driving hazard. Skagit County Fire District 5 provides fire and emergency medical service to Chuckanut Continued on page 52 www.esri.com ArcUser Winter 2010 51