a-b-street/abstreet · error · anyhow::Error

biking to a different part of

Error message

biking to a different part of {} is silly, why not walk?

What it means

ped_ready_to_bike handles a cyclist at a car/bike handoff point. When the computed bike PathRequest starts and ends on the same lane, routing a bike trip would be a pointless ride within one lane, so the code deliberately returns this error instead of pathfinding. The TODO in source indicates the trip should have been converted to walking earlier.

Solutions

  1. Convert such trips to walking before scheduling (as schedule_trip does), per the TODO.
  2. Filter out bike trips whose start and end lane are identical during trip generation.
  3. Adjust trip origin/destination sampling so bike trips span meaningful distance.
  4. If hit interactively, treat it as a signal the trip should have been a walking trip.

Example fix

// before
let req = PathRequest::vehicle(driving_pos, end, PathConstraints::Bike);
// after: convert short trips to walking at scheduling time
if driving_pos.lane() == end.lane() {
    // schedule a walking TripSpec instead of a biking one
    return schedule_walking_trip(...);
}
Defensive patterns

Strategy: validation

Validate before calling

// Before scheduling a bike trip, ensure the lanes differ
if driving_pos.lane() == end.lane() {
    // schedule as walking instead of biking
    return schedule_walking_trip(origin, destination);
}

Try / catch

// Treat this error as a signal to convert to walking
match ped_ready_to_bike(...) {
    Err(e) if e.to_string().contains("why not walk?") => convert_to_walking(),
    other => other,
}

Prevention

When it happens

Trigger: A bike trip (via TripSpec / ped_ready_to_bike in trips.rs) whose driving_pos and end resolve to PathRequests with identical start.lane() and end.lane(), e.g., origin and destination buildings adjacent to the same lane.

Common situations: Very short bike trips between nearby buildings on the same street; synthetic trip generation that doesn't filter out sub-lane-length bike trips; maps with sparse building coverage along a single lane.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/3203b6ebd2f9d9f4. Report an issue: GitHub.

Appendix: source

Thrown at sim/src/trips.rs:613

        let end = if let Some(end) = drive_to.goal_pos(PathConstraints::Bike, ctx.map) {
            end
        } else {
            let trip = trip.id;
            self.cancel_trip(
                now,
                trip,
                format!("no bike connection at {:?}", drive_to),
                None,
                ctx,
            );
            return;
        };
        let req = PathRequest::vehicle(driving_pos, end, PathConstraints::Bike);
        let maybe_router = if req.start.lane() == req.end.lane() {
            // TODO Convert to a walking trip! Ideally, do this earlier and convert the trip to
            // walking, like schedule_trip does
            Err(anyhow!(
                "biking to a different part of {} is silly, why not walk?",
                req.start.lane()
            ))
        } else {
            ctx.map
                .pathfind(req)
                .map(|path| drive_to.make_router(bike, path, ctx.map))
        };
        match maybe_router {
            Ok(router) => {
                ctx.scheduler.push(
                    now,
                    Command::SpawnCar(
                        CreateCar::for_appearing(
                            self.people[trip.person.0].get_vehicle(bike),
                            router,
                            trip.id,
                            trip.person,

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