Inputs
Example Data
| Mode | Cruise speed | Control distance | Dwell | Block | Overlap | Train length | Decel | Buffer | Headway (approx.) |
|---|---|---|---|---|---|---|---|---|---|
| Fixed block | 60 km/h | 1200 m | 30 s | 300 m | 50 m | 120 m | 1.00 m/s² | 16 s | ~1.45 min |
| Moving block | 50 km/h | 900 m | 25 s | — | — | 110 m | 0.90 m/s² | 18 s | ~1.60 min |
| Manual | 40 km/h | 800 m | 20 s | — | — | 100 m | 0.80 m/s² | 10 s | ~2.50 min |
Formula Used
This calculator uses planning-level relationships to estimate minimum time spacing between successive trains. It is intended for early design, construction staging, and scenario comparison.
- Run time: t_run = control_distance / speed
- Braking distance: d_brake = v² / (2·a) × grade_factor
- Fixed block separation: blocks = ceil((d_brake + overlap)/block_length), d_sep = blocks·block_length + train_length
- Moving block separation: d_sep = d_brake + safety_margin + train_length
- Clearance time: t_clear = d_sep / speed
- Headway: H = max(t_clear, t_run) + dwell + reaction + buffer
- Trains per hour: TPH = 3600 / H
How to Use This Calculator
- Choose the unit system, then select a separation mode.
- Enter cruise speed and the control distance you are scheduling.
- Add dwell time for stations, work zones, or platform operations.
- Set reaction and buffer times to reflect construction constraints.
- For fixed block, enter block length and overlap distance.
- For moving block, enter your safety margin distance.
- Click Calculate to see headway and trains per hour.
- Use Download CSV or Download PDF for sharing.
Headway for construction work windows
Headway is the minimum planned time between successive trains through a controlled segment. On construction sites, it converts directly into safe access time for crews, plant movement, and track possession planning. Many programs target 3–6 minute gaps; heavy lifts need longer. For example, a 90 s headway allows about 40 trains per hour, leaving limited continuous working gaps unless the line is temporarily blocked.
Key inputs that drive capacity
Speed and braking performance shape clearance time because braking distance rises with the square of speed. If speed increases from 50 to 70 km/h, braking distance increases by roughly (70/50)² ≈ 1.96× for the same deceleration. Dwell, reaction, and buffer are additive, so a combined 45 s of operational time raises headway by 45 s regardless of signaling model. Adding 15 s buffer to a 150 s headway reduces capacity by 9%.
Fixed block versus moving block planning
Fixed-block estimates use discrete blocks, so separation increases in steps as braking plus overlap crosses each block boundary. Moving-block estimates use continuous distance, often reducing separation for the same safety target. In both cases, the calculator converts separation distance to clearance time as distance divided by cruise speed.
Grade allowance and conservative braking
Grades affect stopping distance and should be reflected during temporary speed restrictions and work staging. The planning factor here is limited to ±6% grade to avoid extreme outputs. A -4% downgrade applies about a 24% increase to braking distance, which can noticeably increase clearance time and headway.
Turning results into field decisions
Use trains per hour to translate the output into practical windows: TPH = 3600/H. A 180 s headway equals 20 trains per hour, while a 120 s headway equals 30. Add buffer when crews must clear equipment, protect crossings, or coordinate with dispatch. If you must clear a work zone in 60 s, choose headways that repeatedly exceed that threshold. Export the CSV/PDF to share assumptions, inputs, and calculated spacing with planners and supervisors.
FAQs
1) What does “headway” mean in this tool?
It is the planned minimum time between trains through the same controlled segment, including clearance, run time, dwell, reaction time, and an added buffer for construction constraints.
2) Which mode should I choose?
Use fixed block for traditional signal blocks, moving block for CBTC-style continuous separation, and manual dispatch when separation is enforced by time instructions rather than distance control.
3) Why does speed change the result so much?
Braking distance increases with the square of speed. Higher speeds therefore increase the separation distance and clearance time quickly, raising the headway even if dwell and buffer stay the same.
4) How should I set deceleration?
Use a realistic service-braking value for your fleet and conditions. Conservative values are safer for planning. If the line is wet, leaf-fall, or heavily loaded, reduce deceleration accordingly.
5) What is overlap and when is it used?
Overlap is an extra distance beyond braking used in fixed-block planning to reflect signal overlap, safety margins, or approach control. It increases the number of required blocks and the separation distance.
6) Can I use the output as an operational rule?
No. Treat it as a planning estimate for staging and scheduling. Final operating headways must follow your railway’s signaling design, rulebook, and safety verification for the specific corridor.