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Schedule speed for a 1.5 km run (trapezoidal)

Short answer

Using the trapezoidal relation 3600D=VmT-(Vm^2/2)K with K=1/0.8+1/3.2=1.5625 and Vm/Va=1.3, solve Vm=45.54 km/h, running time 154.16 s. Total time with 26 s stop is 180.16 s, schedule speed=(1.5×3600)/180.16=29.97 km/h (≈30 km/h).

An electric train is to have acceleration and braking retardation of 0.8 km/h/s and 3.2 km/h/s respectively. If the ratio of maximum to average speed is 1.3 and time for stops 26 seconds, find the schedule speed for a run of 1.5 km. Assume simplified trapezoidal speed-time curve.

Data: α=0.8\alpha = 0.8 km/h/s, β=3.2\beta = 3.2 km/h/s, Vm/Va=1.3V_m/V_a = 1.3, D=1.5D = 1.5 km, stop =26= 26 s.

Trapezoidal relation (speeds in km/h, time in s)

3600D=VmT−Vm22(1α+1β)3600D = V_m T - \frac{V_m^2}{2}\left(\frac1\alpha + \frac1\beta\right) K=10.8+13.2=1.5625K = \frac1{0.8} + \frac1{3.2} = 1.5625

Since Va=3600D/TV_a = 3600D/T and Vm=1.3VaV_m = 1.3V_a: VmT=1.3×3600×1.5=7020V_m T = 1.3\times3600\times1.5 = 7020.

5400=7020−Vm22×1.5625Vm2=2×16201.5625=2073.6Vm=45.54 km/h\begin{aligned} 5400 &= 7020 - \frac{V_m^2}{2}\times1.5625 \\ V_m^2 &= \frac{2\times1620}{1.5625} = 2073.6 \\ V_m &= 45.54\ \text{km/h} \end{aligned}

Running time and schedule speed

T=702045.54=154.16 sVa=5400154.16=35.03 km/hTs=154.16+26=180.16 sVs=1.5×3600180.16=29.97 km/h\begin{aligned} T &= \frac{7020}{45.54} = 154.16\ \text{s} \\ V_a &= \frac{5400}{154.16} = 35.03\ \text{km/h} \\ T_s &= 154.16 + 26 = 180.16\ \text{s} \\ V_s &= \frac{1.5\times3600}{180.16} = 29.97\ \text{km/h} \end{aligned}

Check: t1=45.54/0.8=56.9t_1 = 45.54/0.8 = 56.9 s, t3=45.54/3.2=14.2t_3 = 45.54/3.2 = 14.2 s, free running =154.16−71.1=83.0= 154.16 - 71.1 = 83.0 s.

Answer: Schedule speed ≈ 29.97 km/h (≈ 30 km/h); maximum speed 45.5 km/h.

✓ Answer checked by Claude Opus 5.5 (high effort)

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