Transit Source Reference SEL Calculator

Introduction

This calculator converts a close-by noise measurement of a transit vehicle passby or a stationary source into the source reference SEL, normalized to a distance of 50 ft and a speed of 50 mph. Every additive term of the conversion is listed, so each step can be checked against your own working.

Five measurement types are supported: the SEL of a vehicle passby (locomotive, rail car, bus or automobile), the Lmax of a rail passby with locomotives, the Lmax of a rail passby with rail cars, the Lmax of a highway vehicle passby (bus or automobile), and the SEL of a stationary source. Depending on the type, the conversion uses the speed, the closest distance, the group length, the event duration, the number of locomotives or rail cars and the average locomotive throttle setting.

The equations follow Appendix F of the FTA Transit Noise and Vibration Impact Assessment Manual (2018). The result is given to 1 decimal, the angle θ to 4 decimals and all other terms to 2 decimals.

How to use the calculator

1. Choose the measurement type that matches your measurement.
2. For type 1 or type 4, choose the vehicle class.
3. Enter the measured SEL or Lmax in dBA and the closest distance D in ft.
4. Enter the remaining fields that are shown: speed S in mph, group length L in ft, event duration E in s, the number N of locomotives or rail cars, and the average throttle setting T for locomotives.
5. Read SELref at 50 ft and 50 mph and the table of terms. The result updates as you type; the Calculate button runs the same calculation.
6. Check any warning (D above 100 ft or S below 30 mph for types 1 to 4) and correct any field named in an error message.

Frequently asked questions

Which equation does each measurement type use?

Type 1, SEL of a vehicle passby: SELref = SEL + 10 log(S/50) + 10 log(D/50) + Cconsist + Cemissions. Type 2, Lmax of a rail passby with locomotives: SELref = Lmax + 10 log(L/50) + 10 log(D/50) - 10 log(2θ) + Cconsist + Cemissions + 3.3. Type 3, Lmax of a rail passby with rail cars: the same as type 2 but with - 10 log(2θ + sin(2θ)) in place of - 10 log(2θ). Type 4, Lmax of a highway vehicle passby: SELref = Lmax + 20 log(D/50) + Cemissions + 3.3. Type 5, SEL of a stationary source: SELref = SEL - 10 log(E/3600) + 20 log(D/50). All logarithms are base 10.

How are θ, Cconsist and Cemissions calculated?

θ = atan(L/(2D)) in radians, where L is the group length in ft and D the closest distance in ft; θ is carried unrounded. Cconsist = -10 log(N) for locomotives and rail cars, where N is their number, and 0 for buses and automobiles. Cemissions is 0 for locomotives when the average throttle setting T is below 6 and -2(T - 5) otherwise, -30 log(S/50) for rail cars, -25 log(S/50) for buses and -38.1 log(S/50) for automobiles, where S is the speed in mph.

When does the calculator show a warning instead of an error?

For types 1 to 4 a warning appears when the closest distance D is above 100 ft or the speed S is below 30 mph; the result is still calculated. An error, with no result, appears when a field is empty or invalid: speed, distance, group length and duration must be above 0, N must be a whole number of 1 or more, and T must be above 0.

What is the source of the formulas and what is left out?

The formulas are Tables F-1 and F-2 (Eq. F-1 to F-5) of Appendix F, FTA Report 0123, Transit Noise and Vibration Impact Assessment Manual, 2018, pp. 231-234, with examples F-1 to F-4. No shielding is included and no impact criterion is evaluated.