- 2069 Chaitra
Speed-time curves: urban, sub-urban, main line
Short answer
Speed-time curve graphs speed vs time; slope = acceleration, area = distance. Urban (~1 km stops): high acceleration/braking, no free run, quadrilateral shape. Suburban (1-8 km): short free run, long coasting, quadrilateral. Mainline (>10 km): low acceleration/braking, long free run, short coasting, trapezoidal shape. Schedule speed depends on stop spacing and acceleration/braking rates.
Define speed time curve for traction system. Discuss speed time curve of urban service, sub-urban service and main line service.
A speed-time curve of a traction system is the graph of train speed against time for a run between two stations. Its slope is acceleration, the area under it is distance travelled, and it is used to find schedule speed, energy use and motor rating.
1. Urban (city) service
- Stops are about 1 km apart; trains must start and stop often.
- High acceleration (1.5–4 km/h/s) and braking (3–4 km/h/s) are needed to keep a reasonable schedule speed.
- There is no free-run period; acceleration is followed by a short coasting and braking.
- Curve shape is approximately quadrilateral.
V | /\
| / ``-._
| / \
|/ \
+------------\--- t
accel coast brake
2. Suburban service
- Stops 1–8 km apart; acceleration and braking similar to urban service.
- A short free-run period may appear after acceleration, followed by a long coasting period.
V | /---.___
| / ``--.
| / \
|/ \
+------------------\--- t
accel free coast brake
3. Main-line service
- Stops are more than 10 km apart, so the train runs mostly at crest speed.
- Acceleration and braking are low (0.6–0.8 and about 1.5 km/h/s) and occupy a small part of the time.
- Long free run, short coasting before braking; curve approximately trapezoidal.
V | ____________________
| / ``-.
| / \
|/ \
+-----------------------------\--- t
accel free run coast brake
| Feature | Urban | Suburban | Main line |
|---|---|---|---|
| Stop spacing | ~1 km | 1–8 km | > 10 km |
| Acceleration | High | High | Low |
| Free run | Nil | Short | Long |
| Coasting | Short | Long | Short |
| Approximate shape | Quadrilateral | Quadrilateral | Trapezoidal |
✓ Answer checked by Claude Opus 5.5 (high effort)
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