True Elevation
Wisconsin uses the concept of True Elevation on segments within the State. The use of True Elevation (TE) is to better represent segments in relationship with its surroundings/ground level. Most segments should have an elevation of Ground unless they pass over another segment, waterway, or natural feature. Drivable and non-drivable segments are handled the same way with elevation.
The practice of True Elevation is NOT observed on Freeway or Ramp segments.
Definitions
Bridge
- Segment travels over another segment (also known as Overpass)
- Segment travels over a river or body of water
- Segment artificially elevated to pass over ground level objects and natural features.
Tunnel
A tunnel is any road segment that is underground and thus the GPS reception is inconsistent.
Implementation
- Elevation of overlapping segments should be set relative to each other, with the lowest segment as Ground (unless that segment is a tunnel).
- Only elevate/lower the actual bridge/tunnel section of the road.
- Bridges should be cut at the start/end of the bridge where the land falls away. You can usually see guardrail at the start/end of the bridge section. Also the pavement type may change (Asphalt to Concrete for example).
- Do not cut segments for elevation purposes if the bridge starts/stops within 500ft(150m) of an existing junction.
- Do not create a segment less than 200 feet(60m) in length
- No need to elevate segments over every small creek or box culvert. Only elevate over significant waterways or natural features.
- Only set elevation as low/high as necessary. For example, no segment should be Elevation +2 unless it passes over another segment with Elevation +1.
- Tunneled segments shall have lower elevation, relative to ground and Tunnel should be checked.
- Only segments that are actually underground should have the negative elevation.
- Tunnels should be cut at least 15m/50ft before and after the tunnel, to allow time for the GPS to regain signal.
- The use of common sense is paramount in using True Elevation.
NOTE: If you use the Bridge tool to join segments, be aware that it raises the elevation of the joined segment. Lower the joined segment as appropriate.