COMPARISON OF LIGHT RAIL AND BUS TRANSIT NOISE IMPACT ESTIMATES PER FEDERAL AND INDUSTRY CRITERIA

Design work for a transitway proposed in suburban Maryland near Washington, D.C., using an abandoned railroad right-of-way was begun, then halted, then resumed over a period of time. An initial environmental noise evaluation was performed using the American Public Transit Association (APTA) guidelines. When work resumed, the Federal Transit Administration (FTA) guidance manual was available. Consequently, noise impacts were assessed via methods from both documents. Three alternative vehicle types to serve the transitway were considered: light rail vehicles, conventional articulated diesel buses, or dual-propulsion (electric motor/diesel engine) articulated buses. Passby noise measurements were performed to quantify or verify the noise emissions of each of the vehicle types, and measurements were compared to other available data. At 15 m (50 ft) and 56 km/h (35 mph), the diesel bus is noisiest; the light rail vehicle is slightly quieter. The electric bus is significantly quieter although its emissions are known with the least confidence. Line operation sound levels were predicted for each of the vehicle types for the entire length of the proposed project. The predictions were in terms of both maximum passby sound levels for comparison to the APTA criteria and day-night average sound levels for comparison to the FTA criteria. For the local land uses and ambient noise conditions, the distances for the unmitigated passby noise exposures to attenuate to the APTA and FTA criteria limits were estimated and the number of included dwellings counted. For the transitway project with 16% nighttime operations and proposed vehicle alternatives, the FTA impact-onset (i.e., some impact ) criterion curve yielded significantly greater noise-exposed areas; the APTA criteria yielded results intermediate to those from the FTA some and severe impact curves