Alleys
Alleys provide both unique benefits and challenges to the mapping community. They are exist extensively in urban and suburban road networks, but aren't intended for widespread use. Ideally, an alley should only be available to those who live or work adjacent to the alley, those who service those addresses, and as a last resort in case of closures of the nearby standard roads.
Historically, alleys have had disprite treatments across various map editing regions and states, with some communities choosing to map them as Parking Lot Roads while other communities may have chosen to use the Private Road road type, and still other communities have chosen not to map unless absolutely necessary . At one point, there were even experiments to alternate between PLR and PR block to block, in an effort to prevent through routes.
In recent years, the routing behavior of the Parking Lot Road and Private Road road types has diverged slightly and as of April 2023[update], the recommendation is to use Private Road for alleys. This has several benefits:
- Most through routes are prevented, due to the inherent transition penalty for Private Road segments on the routing server.
- Routes crossing standard drivable segments may be discouraged because of slower real-time and average segments speeds due to turn delays at junctions.
- In case of a closure applied to nearby standard drivable road segments, PR alleys could be used as a last resort detour, due to the high, but surmountable transition penalty. An alley mapped with PLR segments would never be offered as a detour, and routing could fail altogether if there are no other options.
There are some precautions that should be taken when adding PR alleys to the map:
- Be sure to follow local guidance. Segment naming, speed limits, and other measures may vary depending on region/region/locality. Some areas may require additional routing measures to ensure compliance with laws and regulations or in response to routing issues. These measures may include adding prohibited turns or difficult turns to continue straight when crossing standard drivable segments.
- Check nearby destinations. When adding alleys to the map, ensure all nearby House Numbers are nudged and the entry point for Residential Point Places, and standard Places are accurately placed. If nearby destination stop points are not checked, routing errors can occur, sending users to the back of businesses or residences.
- Watch for existing PRs. If there are existing PRs used as gates of a private installation or as a driveway, double check that you aren't creating a routing issue bypassing the gate or creating a preferential pathway.