a-b-street/abstreet · error

causes illegal entrance into a zone at

Error message

{} causes illegal entrance into a zone at {}

What it means

validate_zones enforces access-restriction zones: a path may not cut through a road that allows through traffic for the request's mode and then enter a restricted zone that is neither the origin's nor destination's zone. When a turn in the produced path crosses into such a zone, Path::new panics. The source notes known false positives when part of the graph is separated from the rest by access-restricted roads.

Solutions

1. Check whether the path legitimately must enter the restricted zone because the graph is disconnected otherwise — if so, it's a known false positive; extend the zone at map construction/edit time instead
2. Adjust the access restrictions on the edited roads so the zone partition matches reality
3. Fix the pathfind cost function to properly penalize/forbid restricted-zone crossings for the mode
4. Report upstream if it reproduces on stock maps, including the PathRequest and turn ID

Example fix

// before
panic!("{} causes illegal entrance into a zone at {}", req, t);
// after
warn!("{} crosses into restricted zone at {}; allowing (known false positive)", req, t);
return Ok(path); // or extend the zone during map construction

fn enters_foreign_restricted_zone(map: &Map, steps: &[PathStep], req: &PathRequest) -> bool {
    let z1 = map.get_parent(req.start.lane()).get_zone(map);
    let z2 = map.get_parent(req.end.lane()).get_zone(map);
    steps.iter().any(|s| match s {
        PathStep::Turn(t) | PathStep::ContraflowTurn(t) => {
            let z = map.get_parent(t.dst).get_zone(map);
            z != z1 && z != z2
        }
        _ => false,
    })
}

When it happens

Trigger: Path::new called on a path whose turn enters a zone with access restrictions after leaving an unrestricted road, where the entered zone differs from both the start and end zones — common after map edits that add access restrictions (e.g. private roads, gates).

Common situations: Hit when editing access restrictions in the map editor or importing OSM access tags; the code comment acknowledges false positives when a graph region is only reachable through restricted roads.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• PathConstraints::from_lt
• Negative dist_ahead?!
• expected turn, but found
• modify_step broke total_length, it's now
• Empty path

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/4acafde29ebf4aeb. Report an issue: GitHub.

Appendix: source

Thrown at map_model/src/pathfind/v1.rs:837

            if map
                .get_parent(t.src)
                .access_restrictions
                .allow_through_traffic
                .contains(req.constraints)
                && !map
                    .get_parent(t.dst)
                    .access_restrictions
                    .allow_through_traffic
                    .contains(req.constraints)
            {
                // Entering our destination zone is fine
                let into_zone = map.get_parent(t.dst).get_zone(map);
                if into_zone != z1 && into_zone != z2 {
                    // TODO There are lots of false positive here that occur when part of the graph
                    // is separated from the rest by access-restricted roads. Could maybe detect
                    // that here, or ideally even extend the zone at map construction time (or edit
                    // time) when that happens.
                    panic!("{} causes illegal entrance into a zone at {}", req, t);
                }
            }
        }
    }
}

View on GitHub (pinned to 0964f29315)