# User:CBenson/tunnel

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Tunnels are drawn and modified the same way as any other road using geometry nodes to shape the roadway through the tunnel, but with a negative elevation.

## Theory of operation

The complication with navigation through tunnels is that generally they obscure GPS communication and cell phone data connections. The Waze servers track each mobile device (driver) as they enter and exit each segment along their route. With the start and end times of each segment, the Waze server can calculate the average speed of drivers through that segment. This is how the Waze server can determine if the tunnel traffic is flowing normally, or if there is a slowdown of the vehicles in the tunnel even without the GPS tracking information while inside the tunnel. Waze recognizes that GPS should be absent in tunnels.

## Definition of a tunnel

A tunnel is any road segment that is underground and thus the GPS reception is inconsistent. Very short tunnels need not be mapped as tunnels where the gap in GPS reception is not significant. Tunnels shorter than about 200 meters on divided highways typically do not need to be indicated as tunnels. Tunnels on other roads shorter than about 100 meters typically do not need to be indicated as tunnels.

## Elevation of tunnel segments

To indicate to the waze servers that a segment is a tunnel in which GPS reception will be absent, tunnel segment are marked with an elevation lower than 0. No segments other than tunnels should have an elevation lower than 0.

Roads passing into or out of tunnels should be split into multiple segments at the point where GPS reception is lost or acquired (that is the entrance or exit of the tunnel) such that the segment in the tunnel has a negative elevation and the segments with GPS reception have positive or ground elevation. If a tunnel segment would otherwise end at a junction node within 200 meters of the point where GPS reception is lost the segment need not be split to indicate the entrance or exit precisely.

Tunnels can be topographically on the same level or higher than other segments and still be considered tunnels (and assigned a negative elevation) as long as they are underground.

Designating tunnels with a negative elevation allows the waze servers to better capture speed measurements through tunnels. This improves ETA accuracy and provides better detection of real time traffic jams. Proper indication of tunnels also allows for improved map problem analysis and display of tunnel segments.

## Creating a tunnel

Due to the GPS and mobile device data communication problems inside tunnels, the mapping process of the tunnel is difficult if it does not follow a straight path from the entrance to the exit. The important point of any tunnel mapping is to at least connect the two entrances to enable the routing engine to use the roadway through the tunnel as appropriate for destinations on the other side of the tunnel.

Find on the visual map the locations of the two entrances of the tunnel. If you know the tunnel is a straight path through the tunnel you can simply draw a new straight road between the two entrances and name the segment appropriately. If you don't know the path of the tunnel personally, check to see what is shown with the GPS tracks through that area. If it shows a consistent path of curves, then the active mobile devices are able to track and communicate the data back to the Waze server and you should lay out the road following that path by altering the geometry nodes to match it.