Retrieve trip metrics (speed, travel time, etc.) aggregated by line over a date range.

Parameters for the /api/tripmetrics endpoint.

Attributes: start_date: Start of date range (YYYY-MM-DD). end_date: End of date range (YYYY-MM-DD). agg: Aggregation level — daily, weekly, or monthly. line: Line identifier (e.g., Red, Green-B).

Response for /api/tripmetrics — trip count, time, and miles for a line.

Attributes: data: Trip metrics at the requested aggregation level.