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44 horsepower to approximately 100. This is enough power to Internal noise test data for 10 HC buses are given in Ta- operate the bus electrical loads and run in the tunnel using the ble 38. Data for the average of four 40-ft diesel buses are also battery. In the 1.3 miles inside the tunnel, the fuel consumed included for comparison purposes. is about 1.5 cups, and there are essentially no emissions and no odor (J. Boon, King County Metro Transit, personal com- As shown in the table, the passenger compartments of the munication, March 4, 2007). 45-ft intercity and the double-deck buses are considerably quieter than the other bus types. The elevation from the road- Internal Sound Levels for Higher Capacity Buses way and engine would tend to make the upper deck of the double-deck and the 45-ft intercity buses quieter. Internal sound levels are a growing concern for the transit in- dustry in general. Data from the noise tests conducted at A LOOK AT THE FUTURE ABTC were reviewed to obtain data on the performance of HC and 40-ft buses. All tests are conducted with the bus Some hints of changes in HC vehicle technologies are begin- ning to emerge. The change to a hybrid propulsion technology at seated load weight. Two internal sound level tests are appears to be increasingly accepted. The significant improve- conducted. ment in vehicle performance (acceleration and gradability), along with improved fuel economy make hybrid propulsion in- 1. With doors and windows closed and the engine and all creasingly attractive, in spite of the higher initial capital costs. accessories off, the external surface of the left side of Transit agencies in Europe are increasingly using 15-m buses the bus is exposed to a 80 decibel [dB(A)] uniform for their intercity and regional routes because of the higher seat pressure level using a white noise generator. The noise capacities and improved operator productivity. Figure 27 transmitted to the interior is measured at six locations, shows a low-floor 15-m bus operating in Zeven, Germany. five in the center aisle at 48 inches in height (nominal ear height of seated passenger) and one at the driver There are a few transit agencies in Europe and South Amer- seat at ear height. ica that are using double (or bi) articulated buses that provide 2. With all openings closed and all accessories on, the very high capacities. These 24-m vehicles usually operate in bus is accelerated at full throttle from zero to 35 mph. bus lanes or exclusive busways. Recent French INRETS (Insti- The internal sound levels are measured at four loca- tut National de Recherche sur les Transports et leur Scurit) tions in the center aisle at 48 inches in height. research on super-high capacity buses was presented at a 2006 BRT conference in France (30). Bordeaux, in France, operated The sound levels are measured on a logarithmic scale, and a line with 10 megabuses from 1988 to 2004, when they were some example perceptions of the change of sound levels are replaced by light-rail transit (LRT). There have been high-floor listed here: bi-articulated buses in operation in Curitiba and Sao Paolo since 1992, and there are bi-articulated buses either in opera- A 1-db(A) change is an imperceptible change, tion, or planned, in Utrecht (The Netherlands), Aachen, A 3-db(A) change is barely perceptible, and Wuppertal, Goteborg, and Hamburg (Germany). The Wupper- A 10-db(A) increase is perceived as twice as loud. tal bus is shown in Figure 28. To place a sound level in perspective, a 40 dB(A) sound level A recent U.S. innovation of attempting to produce lighter- would be similar to that of a quiet library or home (29). weight transit buses using composite technology was not a TABLE 38 INTERNAL AND EXTERNAL NOISE TEST DATA FOR HC BUSES Interior Sound Levels in dB(A) APTA Guidelines 80 dB(A) External Noise 80 dB(A) Source 0 to 35 Acceleration Test 035 Test Bus Type Average Peak Average Peak Less than Less Than Articulated--Diesela 57.0a 64.6 75.7a 86.6 65 83 Articulated--Hybrid D/E 54.2 58.7 79.2 82.2 65 83 Double-Deck--Diesel Lower Deck 44.6 45.5 76.4 77.5 65 83 Upper Deck 40.4 41.4 64.4 66.6 65 83 45-ft Intercity--Dieselb 39.0b 46.3 69.9b 79.6 65 83 45-ft Compo--CNG 50.8 55.9 76.6 79.9 65 83 40-ft--Dieselc 52.0c 63.2 77.1c 83.2 65 83 D/E = diesel/electric; CNG = compressed natural gas. Source: References 2427. a The average measurements are for the average of four articulated buses. b The average measurements are for the average of three 45-ft intercity coaches. c The average measurements are for the average of four 40-ft buses.