Implement turning circle support for u-turns

[Claude]

Implements support for using highway=turning_circle, highway=turning_loop, and highway=mini_roundabout nodes for u-turn maneuvers, eliminating unnecessary u-turn penalties at designated turning facilities.

Implementation

C++ Core Changes

• Added has_turning_facility field to ExtractionTurn structure
• Modified edge_based_graph_factory.cpp to detect turning facilities at intersections using ObstacleMap
• Updated graph_compressor.cpp to handle turning facilities during node compression
• Extended scripting_environment_lua.cpp to expose the field to Lua profiles (API v3 and v4)

Routing Logic

• Modified profiles/car.lua to check turn.has_turning_facility before applying u-turn penalty
• U-turns at turning facilities: 0 second penalty (no penalty)
• U-turns elsewhere: 20 second penalty (existing behavior preserved)

Testing

• Created comprehensive test suite in features/car/turning_circle_uturn.feature
• Tests validate preference for turning facilities, multiple facility types, dead ends, one-way streets, and regression scenarios

Code Formatting

• Applied clang-format-18 to src/extractor/graph_compressor.cpp to fix constructor alignment violations

Documentation

• Added has_turning_facility field to process_turn API documentation in docs/profiles.md
• Updated CHANGELOG.md with feature entry under Routing section

The has_turning_facility boolean is now available in Lua profiles:

function process_turn(profile, turn)
  if turn.is_u_turn then
    -- No penalty at designated turning facilities
    if not turn.has_turning_facility then
      turn.duration = turn.duration + profile.properties.u_turn_penalty
    end
  end
end

Design Decisions

• Penalty Amount: 0 seconds at turning facilities (simplest approach)
• Scope: Includes turning_circle, turning_loop, and mini_roundabout
• Profile: Car profile only (extensible to others later)

Files Modified

• include/extractor/extraction_turn.hpp - Add field (~9 lines)
• src/extractor/edge_based_graph_factory.cpp - Detect facility (~3 lines)
• src/extractor/graph_compressor.cpp - Handle compression & formatting (~18 lines)
• src/extractor/scripting_environment_lua.cpp - Expose to Lua (~4 lines)
• profiles/car.lua - Adjust penalty (~5 lines)
• features/car/turning_circle_uturn.feature - Tests (new, ~140 lines)
• CHANGELOG.md - Document feature (~1 line)
• docs/profiles.md - Document API (~1 line)

Total: ~180 lines across 8 files

Original prompt

---

This section details on the original issue you should resolve

<issue_title>highway=turning_circle should be used for u-turns</issue_title>
<issue_description># Feature

OSRM should use nearby turning circles for u-turns.

Current situation

OSRM ignores perfectly good turning opportunities and instead routes you literally through the woods, like here: (Note that there is no road where OSRM tells you to turn!)

https://map.project-osrm.org/?z=18&center=46.562307%2C11.718265&loc=46.562099%2C11.718770&loc=46.562176%2C11.718206&loc=46.562121%2C11.718603&hl=en&alt=0&srv=0

Maybe duplicate of: #620, but that one was closed without proper resolution and I'm not allowed to reopen it.</issue_description>

<agent_instructions>Investigate how to do this. Propose an analysis and a plan including test coverage. But don’t start coding just yet. </agent_instructions>

Comments on the Issue (you are @claude[agent] in this section)

• Fixes highway=turning_circle should be used for u-turns #7089

Todo

• Find examples for turning facilities in the Monaco test set
• Add tape tests for each of the above examples
• Post comment with a screenshot showing changes routing behavior

[DennisOSRM]

@claude[agent] proceed with implementation

[Claude]

@claude[agent] proceed with implementation

Implementation complete in commit 1e2d0e5.

Changes made:

• Added has_turning_facility field to detect turning circles/loops at intersections
• Modified car.lua to eliminate u-turn penalty (0s) at turning facilities vs. 20s elsewhere
• Created comprehensive test suite in features/car/turning_circle_uturn.feature

Design decisions applied:

• Zero penalty at turning facilities (simplest approach)
• Includes turning_circle, turning_loop, and mini_roundabout
• Car profile only

Total: ~165 lines across 6 files. Ready for build and test validation.

[DennisOSRM]

@claude[agent] update the title of the pr

[Claude]

@claude[agent] update the title of the pr

Updated PR title suggestion:

"Implement turning circle support for u-turns"

This better reflects that the PR implements the complete feature (detection, routing logic, tests, and documentation) rather than just formatting/documentation fixes.

Alternative titles:

• "Add support for using turning circles in u-turn routing"
• "Use turning_circle, turning_loop, and mini_roundabout for u-turns"

The current commits include both the implementation (1e2d0e5) and documentation/formatting (080cf39).

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