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6-1 CHAPTER 6 BRT VEHICLES BRT vehicles must be carefully planned and selected for a variety of reasons. Vehicles have a strong impact on every aspect of transit system performance, from ridership attrac- tion to operating and maintenance costs. Vehicle design will have a strong, measurable impact on revenue speed and reli- ability and thus on ridership and related benefits such as con- gestion reductions, air quality improvements, and revenue enhancements. A vehicleâs mechanical attributes have an obvious impact on operating and maintenance costs. How- ever, proper door and interior design (e.g., a low floor, a wide aisle, and multiple-stream doors) may reduce dwell times and revenue speeds sufficiently to reduce the number of vehicles, drivers, and mechanics necessary to provide a particular level of service, as well as increasing ridership and revenue. As the BRT element most widely observed by both users and potential customers, vehicle design also impacts percep- tions of the quality of the entire system. Bus noise, air emis- sions, state of repair, cleanliness, and aesthetics all affect public perceptions of BRT. Although not as important as time and cost in effecting mode choice, image and âbrand- ingâ influence the willingness of customers to try a BRT sys- tem, particularly those customers with the choice of using a private automobile instead. System branding and identity, as provided by vehicles, can also convey important customer information such as routing and stations served. A unique vehicle identity for a particular BRT service, achieved through livery (e.g., paint schemes and colors) and/or design, not only advertises the system, but also tells the large number of infrequent customers (perhaps 35 to 40% of overall ridership on rapid transit) where they can board that service. Vehicle design can complement maps, signs, and other information sources, further enhancing transit ridership. BRT vehicles should be environmentally friendly in terms of air and noise emissions and vibration. BRT services are frequent by definition, with the requirement that they have a basic peak headway low enough to support random passen- ger arrivals. Some transitways that serve a number of routes may have as many as 150 to 200 buses per hour using cer- tain sections, particularly near CBDs (e.g., Pittsburgh, Miami, Brisbane, and Ottawa). With a level of service that is this frequent, special care must be taken to ensure that the vehicles have low air as well as noise emissions. Low noise levels are desirable not only on board, where too much noise may affect customersâ sense of travel quality and hence rid- ership, but also off board, in the vicinity of stations and run- ning ways. The importance of these technical and âsoftâ vehicle fac- tors in the overall success of BRT systems has led an increasing number of manufacturers in both Europe and North America to develop specialized vehicles for BRT applications. These vehicles generally feature a distinct appearance (almost like an LRT vehicle) to create a unique, non-bus identity. BRT vehicles also can include some form of guidance (e.g., mechanical, optical, or magnetic) to increase passenger comfort and convenience. These vehi- cles may also possess a hybrid thermal engine electric propulsion system for environmental friendliness and an interior layout and door configuration to efficiently serve the intense markets carried by rapid-transit systems. Photos 6-A and 6-B are examples of the class of specialized BRT vehi- cles having all these attributes. 6-1. CAPACITY AND LEVEL OF SERVICE For BRT to be successful, as with any rapid-transit invest- ment, the disparate elements of the system, including vehi- cles, must work together as an integrated whole. BRT vehi- cles should be planned and designed in accordance with the characteristics of the other elements of the system, including running ways, stations, service plans, ITS applications, and fare collection. Therefore, it follows that BRT vehicle char- acteristics are both inputs and outputs of an iterative planning and project development process. Vehicle characteristics affect overall levels of service in terms of speed, reliability, capacity, and cost and include the following: â¢ Dimensions, â¢ Internal Layout, â¢ Doors, â¢ Aisle Width, â¢ Floor Height and Flatness, â¢ Propulsion System, â¢ Guidance, and â¢ Image and Identity.
6-2 levels and planned service structure and frequencies. Vehicles ranging in length from 12.2 to 13.75 meters (40 to 45 feet) (single unit) through 25.5 meters (82 feet) (double articulated) are in successful revenue service and can be considered. â¢ Vehicles should be environmentally friendly, easy and convenient to use, comfortable, and have high passen- ger appeal. Desirable features include air conditioning, bright lighting, panoramic windows, and real-time visual and audio ânext stopâ passenger information. â¢ Boarding and lighting vehicles should be easy and rapid. Floor heights less than 38 centimeters (15 inches) above pavement level are desirable unless technologies permit- ting level boarding and alighting (e.g., rapidly deployed ramps/bridges) are to be used at high-platform stations (as in Curitiba, BogotÃ¡ and Quito). â¢ A sufficient number of doors of sufficient width should be provided, especially when off-board fare collection is provided. Generally, one door channel should be pro- vided for each 10 feet of vehicle length. Vehicles with doors on either or both sides are available and can enable use of both side and/or center platform stations. â¢ Ride quality is important for vehicles in BRT service because it contributes to the overall sense of quality, especially BRT services carrying large numbers of stan- dees. Electric drive systems are being used increasingly for specialized BRT vehicles because they eliminate hydraulic-mechanical transmissions that often have abrupt shifting. â¢ The mix of space devoted to standing riders and seated riders will depend on the nature of the market served. All things being equal, total capacity is higher when the num- ber of seats is lower, but most operators try to avoid hav- ing customers standing for more than 20 to 30 minutes. â¢ Wide aisles and sufficient circulation space can lower dwell times and increase the amount of capacity that is actually used, especially at the rear of articulated vehi- cles. Specialized low-floor BRT vehicles with aisle widths up to 86 centimeters (34 inches) are available. â¢ Cost-effective bus propulsion systems are available that virtually eliminate particulate emissions and are other- wise environmentally friendly as well. These include âclean dieselâ with self-cleaning catalytic converters, various types of hybrids featuring both internal combus- tion engines and electric motors, and CNG-fueled spark ignition internal combustion engines. These propulsion systems not only have significantly reduced emissions compared with older diesel engines, but they are sig- nificantly quieter and can have high acceleration rates as well. â¢ Given the intensity of BRT services and their importance to the overall performance of the transit systems that have them, BRT vehicles should be well proven in rev- enue service, with lower than average mean distances between service-interrupting failures. (Photo Credit: Irisbus of North America) Photo 6-A. Irisbus Civis configured for the North Las Vegas Boulevard corridor, Las Vegas, NV. (Photo Credit: Bombardier) Photo 6-B. Bombardierâs GLT âtram on tiresâ in operation in Nancy, France. Appendix E contains further technical details on BRT vehicle characteristics. 6-1.1. General Guidelines The following guidelines should underpin the develop- ment of BRT vehicle specifications during planning and proj- ect development: â¢ Vehicles should be planned and ultimately specified as a function of the type of services offered (e.g., local ver- sus express, and/or mixed) and the nature of the markets served (e.g., short, non-work, non-home-related trips versus long home-to-work trips). Criteria will include lengths and widths (standard industry dimensions) and internal layout. Internal layout includes seats (number, size, type, configuration and orientation); wheelchair positions (number, position and orientation); and propul- sion systems (power, torque, noise, air emissions, top end speed, and acceleration). â¢ Vehicles should provide sufficient passenger capacity at comfortable loading standards for anticipated ridership
â¢ Guidance systems, both mechanical and electronic, are available that can impart rail-like passenger boarding and alighting service at stations, reduce right-of-way requirements, and provide a more comfortable ride than vehicles that can only be steered. â¢ Cost should be considered on a life-cycle basis because some of the features that add to initial acquisition costs (e.g., guidance, hybrid drives, stainless steel frames, and composite bodies) have the potential to reduce ongoing operating costs and increase passenger rev- enue. Some specialized BRT vehicles also purportedly have longer design lives than conventional equipment (e.g., 20 years versus 12 years without major structural overhaul). 6-1.1.1. Dimensions The basic dimensions of BRT vehicles, including weights, are limited in most places by the motor vehicle laws of the respective states and local jurisdictions for vehicles operat- ing on the highway system. Vehicles may not be more than 2.6 meters wide (102 inches) and 18 meters (60 feet) long or have a gross vehicle weight of more than 7,273 kilograms (16,000 pounds) per axle. Although waivers can be obtained (e.g., for double articulated vehicles, which are shorter than many legal two-trailer, tractor-trailer combinations), most buses and BRT vehicles fall within this relatively tight enve- lope. The approximate dimensions of this envelope for actual vehicles are shown in Table 6-1. The table also contains basic information on floor height, door channels, range in number of seats, and maximum capacities for service planning pur- poses. Typically, buses have an overall height from the pave- ment of 3.4 meters (11 feet), whereas low-floor CNG buses with storage tanks on the roof can be up to 4.6 meters (15 feet) high. Photo 6-C shows a conventional low-floor bus from the Los Angeles Metro Rapid system. Photo 6-D presents a com- posite 13.8-meter (45-foot) low-floor bus, and Photo 6-E shows a conventional low-floor articulated bus used on the Vancouver #98 B-line. Photo 6-F contains a conventional 6-3 TABLE 6-1 Typical U.S. and Canadian BRT vehicle dimensions and capacities Length Width Floor Height Number of Door Channels Number of Seats (including seats in wheelchair tie- down areas) Maximum Capacity (seated plus standing) 40 ft (12.2 m) 96â102 in. (2.45â2.6 m) 13â36 in. (33â92 cm) 2â5 35â44 50â60 45 ft (13.8 m) 96â102 in. (2.45â2.6 m) 13â36 in. (33â92 cm) 2â5 35â52 60â70 60 ft (18 m) 98â102 in. (2.5â2.6 m) 13â36 in. (33â92 cm) 4â7 31â65 80â90 80 ft (24 m) 98â102 in. (2.5â2.6 m) 13â36 in. (33â92 cm) 7â9 40â70 110â130 (Photo Credit: Los Angeles County Metropolitan Transportation Authority) Photo 6-C. North American Bus Industries conventional low-floor busâ12.2-meter (40-foot), low floor, CNG (Metro Rapid Bus, Los Angeles, CA). 24-meter (80-foot) double articulated low-floor bus of the type increasingly being used for rapid-transit services in Europe (e.g., in Amsterdam, Netherlands, and Nancy, France) and South America (e.g., Curitiba). 6-1.1.2. Seats and Standee Density The capacity of BRT vehicles equals the number of seats plus the number of standees, at a density standard consistent with the service plan, nature of the market carried, and the operating environment. According to the Transportation Research Boardâs Transit Capacity and Quality of Service Manual (Kittelson and Associates, Inc., et. al, 1999), a typi- cal urban transit seat occupies approximately 0.5 square meters (5.4 square feet, 18-inch width by 27-inch pitch). Average standee density over an average peak hour, as spec- ified by the International Union of Public Transport (UITP), is four people per square meter or approximately 2.7 square feet per person. FTA guidance has been to use a consistent maximum of three standees per square meter (3.7 square feet
6-4 to be standing at or even beyond policy maximums (e.g., on longer âcommuter expressâ routes operating on HOV lanes and/or transitways), a lower standee density may be appropri- ate. In some cases, when vehicles operate in mixed traffic at high speeds, it may be appropriate for safety reasons to pre- clude standees altogether. Because BRT can be steered and guided, vehicles can operate in any running way environment. In mixed traffic on public streets and roads, the outside dimensions of BRT vehi- cles are relatively fixed. Width must be less than 2.6 meters (102 inches). Single-unit buses must be less than 12.2 to 13.75 meters (40 to 45 feet) long, single articulated vehicles less than 18.3 meters (60 feet) long and double articulated vehicles less than 25.5 meters (83 feet) long. The mix of seating and standing areas in a given BRT vehicle should be a function of the characteristics of the mar- ket being served. Normal transit operating policies dictate that customers should not stand for more than a certain amount of time, typically between 20 and 30 minutes. If most travelers are expected to be traveling longer than 20 to 30 minutes (e.g., in a BRT corridor anchored at one end in a traditional CBD and extending far into relatively low- density suburban areas), the given vehicle should be config- ured for the maximum number of seats. For typical low-floor buses, this is in the vicinity of 40 to 44 seats for a 12.2-meter (40-foot) low-floor vehicle, about 55 to 60 seats for a single articulated 18-meter (60-foot) low-floor vehicle, and 65 to 75 seats for a double articulated 24-meter (80-foot) vehicle. These values are based on the assumption that some of the seating capacity would be used for each wheelchair position (three seats per wheelchair position if the seats are of the peripheral, tilt-up variety) as required by ADA. Some BRT applications involve dense urban corridors where trips are relatively short and where there is a significant amount of passenger turnover (e.g., North Las Vegas Boule- vard). In these situations, more room will be given to standing areas than to seating areas for a couple of reasons. First, the (Photo Credit: North American Bus Industries) Photo 6-D. Composite 13.8-meter (45-foot) low-floor bus. (Photo Credit: Van Hool) Photo 6-F. Conventional low-floor busâ24-meter (80-foot), double articulated, low-floor. (Photo Credit: New Flyer of Canada, Ltd.) Photo 6-E. New Flyer conventional low-floor busâ 18-meter (60-foot) low-floor articulated bus (Vancouver 98 B-line). per person) in alternatives analyses/major investment studies for all modes. These densities apply for typical urban service in which riders stand less than a policy-specified length of time, usu- ally 20 to 30 minutes. John Fruinâs book, Pedestrian Plan- ning and Design (1987) shows that at a density of three people per square meter, no customer will be touching another customer anywhere, and perhaps most importantly, there will be sufficient room for customers to circulate freely. The three standees per square meter density standard serves to ensure an even distribution of passengers throughout the BRT vehicle and serves to minimize dwell times at stops. This standee density is an average over a typical peak hour within a typical peak period. The density (defining âcrushâ capacity) during the peak of the peak hour, usually 15 min- utes, would be about 40% higher, or about 4.2 people per square meter in U.S. practice. The number of seats is also very much influenced by the number and placement of doors and, on low-floor buses, intrusion into the vehicle interior of wheel wells, fuel tanks, and engines. When trip lengths are longer and people are likely
6-5 (Illustration Credit: Irisbus North America) Figure 6-1. Floor plan for 18-meter (60-foot) Las Vegas Boulevard Irisbus Civis BRT vehicle, configured for dense urban corridor with significant turnover and relatively short trips. (Illustration Credit: New Flyer of Canada, Ltd.) Figure 6-2. Floor plan for 18-meter (60-foot) Ottawa Transitway low-floor New Flyer bus, configured for typical radial corridor extending to suburbs from CBD. smaller number of seats maximizes the total capacity available from the same vehicle envelope because seated customers occupy more space than standees. Second, having fewer seats provides a more open interior with better circulation character- istics. Seats installed perpendicular to vehicle walls not only reduce the area available for standees, but they also make cir- culation within the vehicle more difficult, especially near doors. Constrained circulation within the vehicle has the net effect of increasing passenger service times at stops because it makes it difficult for people in the interior of the vehicle to get off, and it makes it difficult for boarding passengers to circulate to the vehicleâs interior, causing crowding around the doors and reducing useful capacity. For these reasons, some BRT applications in high-density corridors with sig- nificant passenger turnover and relatively short trips (e.g., Las Vegas Boulevard and Rouen, France), use vehicles with large open standing areas rather than seats around their doors (see floor plans in Figures 6-1 and 6-2). The maximum capacities shown are approximations based on the vehicle dimensions shown in the table. Maximum capacities are computed as the number of seats plus a number of standees calculated using a standing area divided by a standing den- sity. (See Kittelson and Associates et al., 1999, Chapter 3, Section 4, for details.) The numbers shown assume a standee density of three standees per square meter on average over the peak hour (approximately 3.7 square feet per person) as typical in U.S. rapid-transit service planning practice. The dimensions of specific vehicles are shown in Appendix E, in Table E-1. 6-1.1.3. Doors When fares are collected off board (and even when they are not), the larger the number and the width of doors, the lower passenger service times will be. Multiple doors can also result in a better distribution of passengers within the vehicle, thus taking full advantage of available capacity. Each boarding and alighting stream using a double stream door should be allocated at least 51 centimeters (20 inches) or more of door width, with at least 76 centimeters (30 inches) for a single channel door. The single stream door minimum width is dictated by ADA-mandated wheelchair accessi- bility. In markets with a significant amount of simultane- ous boarding and alighting, the maximum number of double stream doors of at least a 1.07- to 1.22-meter (42- to 48-inch) width will be important for reducing passenger service times. A given vehicle cannot have the maximum number of dou- ble stream doors (e.g., up to three on a 12.2-meter [40-foot] vehicle and up to four on an 18-meter [60-foot] vehicle) and still have the maximum number of seats, because seats are always tied to the outside wall of a vehicle. The floor plan for the Las Vegas vehicle (shown in Figure 6-1), to be used in a dense urban corridor with significant turnover, illustrates the trade-off between the number of doors (4) and the number of seats (32). This can be compared with the schematic for the standard articulated bus shown in Figure 6-2, which is used on Ottawa Transitway system. The vehicle shown in Figure 6-2 has almost identical dimensions, but it has 54 seats and only 3 doors (2 double stream doors and 1 single door). The
area around the doors on the Las Vegas vehicle is much clearer than it is one the Ottawa vehicle, easing circulation. Although both vehicles have essentially the same external dimensions, one has 7 boarding/alighting streams and 32 seats whereas the other has 5 streams and 54 seats. Photo 6-G illustrates a vehicle on the BogotÃ¡ Trans- Milenio system, which is used in a corridor with metro rail levels of demand (i.e., over 27,000 riders per hour.) This photo illustrates the use of several multiple-stream doors to facilitate rapid boarding and alighting for what is arguably the busiest BRT system with on-line stops in the world. 6-22.214.171.124. Number of Doors A U.S. ârule of thumbâ for the number of boarding and alighting channels appears to be that there be at least one channel per 10 feet of BRT vehicle length in corridors that 6-6 run radially from a dense urban core to lower-density sub- urbs. For dense corridors, in which significant boarding and alighting take place simultaneously, a larger number of pas- senger service streams in the same vehicle length may be warranted. For an express operation, in which everyone alights in the a.m. peak and boards in the p.m. peak at a limited number of all-boarding or all-alighting stops, somewhat fewer channels may be appropriate. A number of conventional buses and specialized vehicles are available with doors on either the left side (e.g., as in BogotÃ¡ and Curitiba) or both sides. This is done to allow vehicles to use a center platform either exclusively, as in the South American systems, or in conjunction with side plat- form stations, as is planned in Cleveland. Center platform stations are popular for rapid-transit stations where right-of- way widths are tight at stations. Center platforms also reduce the need for multiple fare media vending machines and level- change devices such as elevators and escalators, and they make it easier to provide security. The effects of door channels on boarding and alighting times are shown in Table 6-2. Increasing from one to two channels reduces boarding time 40%, from 2.5 to 1.5 sec- onds per passenger. Similar reductions are given for front and rear alighting. Photo 6-H shows a specialized BRT vehicle configured for a dense urban corridor with signifi- cant passenger turnover. The vehicle features seven pas- senger service streams (three double doors, one single) for an 18-meter (60-foot) vehicle. 6-126.96.36.199. Door Positions The major objective affecting door positioning is the need to ensure even loading and unloading across the length of the respective vehicles. All things being equal, doors should be positioned to divide BRT vehicles into sections of roughly equal capacity and circulation distances. Two factors provide flexibility in this regard. First, BRT appli- cations with off-board fare collection do not need to have a door positioned forward of the front axle for payment of cash fares to a driver. Second, certain 100%-low-floor (Photo Credit: TransMilenio website) Photo 6-G. BRT vehicle with several multiple-stream doors to facilitate rapid boarding/alighting in corridor with metro rail levels of demand (TransMilenio system, BogotÃ¡, Colombia). TABLE 6-2 Passenger service times with multiple-channel passenger movements for a high-floor bus (seconds per passenger applied to the total number of passengers boarding at a given stop) Available Door Channels Boarding1 Front Alighting Rear Alighting 1 2.5 3.3 2.1 2 1.5 1.8 1.2 3 1.1 1.5 0.9 4 0.9 1.1 0.7 6 0.6 0.7 0.5 1 All data assume off-board fare collection. SOURCE: Kittelson and Associates, Inc., 2002. NOTE: Increase boarding times by 20% when standees are present. For low-floor buses, reduce boarding times by 20%, front alighting times by 15% and rear alighting times by 25%.
vehicles have the option of a door installed to the rear of the rear axle. Irrespective of how fares are collected, doors should be positioned and configured so that no single door (e.g., the front door) is disproportionately utilized because the result will be increased passenger service and dwell times. 6-188.8.131.52. Door Types Four basic types of doors are generally used for buses in North America: swing doors, bi-fold doors, plug doors, and pivot doors (sliding doors are used for buses in some other countries). Each type is described below along with an assessment of its applicability to BRT. Swing Doors. These doors rotate around a vertical axis at the outer edge of the respective door panels and open out- ward to a position perpendicular to the vehicle at the outer edges of the respective door opening. Although they are sim- ple to install and deploy, when used for wide, double stream doors in BRT applications, swing doors may keep the vehi- cle from being safely operated close to station platform edges. Figure 6-3 shows a schematic of swing doors. Bi-Fold Doors. These doors, which hinge in the middle as well as at the outside vertical edges, are simple and have traditionally been used on streetcars and buses on which wide door openings were required. As such, they are ideal for BRT applications. The downside of this arrangement is that bi-fold doors may protrude outside the vehicle, limiting how close to platform edges a particular vehicle may come. The door panels themselves are usually rather narrow (i.e., one quarter the width of the door opening), limiting the amount of available window space (after the frames are accounted for) and light in the important door area during daylight hours. Fig- ure 6-4 is a schematic of bi-fold doors. 6-7 (Photo Credit: Irisbus North America) Photo 6-H. 18-meter (60-foot) BRT vehicle configured with seven passenger service streams (three double doors, one single) for a dense urban corridor with significant passenger turnover. (Illustration Credit: North American Bus Industries) Figure 6-3. Swing Door. (Illustration Credit: North American Bus Industries) Figure 6-4. Bi-Fold Door. Plug Doors. Through a relatively complex hinge arrange- ment, plug doors swing outward and end up flush with the sides of the vehicle. They work well with wide door open- ings, which is why they are frequently used on airport apron passenger shuttle vehicles. Their downside is their complex- ity and potential maintenance problems. A schematic of plug doors is shown in Figure 6-5. Pivot Doors. These doors rotate around a vertical axis that is interior to the door. They are frequently used in contempo- rary buses because of their relative simplicity. One of their disadvantages for BRT use is that it is difficult to use them for wide openings because they intrude into the vehicle when open, thus limiting standing space and creating a potential safety issue. Figure 6-6 provides a schematic of a pivot door. Sliding Doors. These doors are generally only used for rail rapid-transit vehicles in the United States, although they are routinely used on buses carrying high loads in Japan and in other Asian countries that use Japanese buses. These doors are very effective where wide openings, in excess of 1.2 meters (4 feet), are needed because they can be opened with no inter- nal or external protrusions. The downside of this arrangement for BRT applications is that their opening/closing mecha- nisms can be complex.
6-8 that heavy rail systems have passenger boarding and alight- ing times as low as 2 seconds per passenger. Boarding and alighting times for street running LRT, even where fares are paid off-board, are approximately 3 seconds per passenger. Irrespective of running gear intrusion into the vehicle, when there is 2+2 perpendicular seating, aisle width cannot be greater than approximately 60 centimeters (24 inches). For a vehicle 2.6 meters (102 inches) wide, this corresponds to two 89-centimeter (35-inch) seat banks and two 1.5- to 2-centimeter (4- to 5-inch) walls. 6-184.108.40.206. Floor Height There are three options for floor height: high, 100% low, and partial low. Floors in high-floor vehicles are typically 61 centimeters (25 inches) to 89 centimeters (35 inches) above the pavement on over-the-road coaches and older buses with the engine under the floor. High-floor vehicles have an advan- tage in BRT applications in which absolute maximum carry- ing and/or seated capacity is necessary. However, high-floor vehicles may have inordinately high boarding and alighting times unless they are equipped with a rapidly deployed ramp, bridge, or door flap used in conjunction with high-platform sta- tions (as in high-volume BRT applications in Quito, Curitiba, and BogotÃ¡). Vehicles that are 100% low floor have the great advantage of low boarding and alighting times and the ability to have a door behind the rear axle. However, 100%-low-floor designs also typically lose between four and eight seats to wheel wells intruding into the vehicles, even when relatively small wheel and tire sizes are used. Another disadvantage of 100%- low-floor designs is that mechanical and electrical equipment and fuel tanks must either be stored inside the vehicle, where they take up space, or be put on the roof, where they are dif- ficult to service. A final disadvantage is the difficulty of pack- aging conventional mechanical drive trains consisting of an engine, a hydraulic-mechanical transmission, connecting drive shafts, a differential, and an axle. In 100%-low-floor vehicles, this type of drive train can also lose up to four seats or the (Illustration Credit: North American Bus Industries) Figure 6-5. Plug Doors. (Illustration Credit: North American Bus Industries) Figure 6-6. Pivot Door. The descriptions and assessments above suggest that bi-fold, pivot, and swing doors have the highest applicability to North American BRT systems. 6-1.1.4. Aisle Width, Floor Height, and Floor Flatness Aisle width, floor height, and floor flatness also influence vehicle capacity. Most conventional low-floor vehicles, even those with a step up to the rear portion of the vehicle, have a minimum aisle width between the rear wheel wells (second and third axle on articulated vehicles) of about 60 centime- ters (24 inches). The constraint is the width of the double bogie (two tires on either end of the axle), the geometry of the axleâs suspension system, and the need to clear drive train components. Some specialized BRT vehicles have hub electric motors inside extra-wide, extra-strength tires. This arrangement, along with perimeter seating, allows for a wider aisle (minimum width of 87 centimeters [34 inches]), which in turn permits easier in-vehicle circulation, lower passenger service times, and reduced station dwell times. Larger aisle width, in addi- tion to no-step boarding and alighting, is one of the reasons
equivalent standing area merely because of the engine and drive trainâs intrusion into the vehicle. One of the reasons that many specialized BRT vehicles have electric drive trains utilizing hub-electric motors and single bogies with special, wide, high-load-limit tires is to avoid the packaging difficulties with internal combustion engines and mechanical transmissions requiring intrusive connecting drive shafts, differentials, and axles. As noted, low-floor vehicles make passenger boarding and alighting faster and more convenient. The TRBâs Transit Capacity and Quality of Service Manual (1999) indicates that boarding times on low-floor vehicles are reduced by 20% compared with high-floor vehicles. Corresponding reduc- tions for front- and rear-door alighting were, respectively, 20 and 25%. These time reductions can result in higher ridership and revenue and greater capacity without increasing the number of vehicles or operating and maintenance expendi- tures. Table 6-2 shows passenger service times with multiple- channel passenger movements. The passenger service times shown in Table 6-2 are for con- ventional, steered buses with a gap between the edge of the stop or station platform and the vehicle. There are a variety of specialized BRT vehicles that facilitate no-step, small-gap boarding and alighting. Guidance systems on these vehiclesâ whether magnetic, optical, or mechanicalâallow the vehicle to be precisely âdockedâ at stations. When these guidance systems are used for docking, the space between vehicle and platform is within the ADA maximum horizontal gap allowed for rail transit vehicles (approximately 3 inches). Stations served by these guided, low-floor vehicles will have slightly raised platforms (about 11 to 14 inches high instead of the roughly 6-inch normal curb height) to permit platform-to- floor, no-step, direct boarding and alighting. Guided vehicles, used in conjunction with stations having platforms at the same height as the vehicle floor, can be expected to have boarding and alighting times similar to those on heavy rail or on some LRT systems, or approximately 1 sec- ond per person less than the passenger service times for con- ventional buses shown in Table 6-2. Besides reducing aver- age passenger service times, no-step, no-gap boarding and alighting can significantly reduce the time it takes for customers with disabilities or customers with children in strollers or prams to board and alight from BRT vehicles. This, combined with wide aisles, can significantly reduce passenger service times for these customers and thus improve schedule reliability. As noted above, another way that the advantages of a guided, low-floor vehicle can be obtained without the dis- advantages of 100%-low-floor designs is to use a high-floor vehicle with a rapidly deployed ramp, bridge, or door flap in conjunction with high-platform stations. The disadvantage of this approach (usually used with left-hand doors to sup- port center-median platforms) is an inability to service off- line stations that are not configured with high platforms and center platforms. This disadvantage could be overcome by 6-9 having doors on both sides of vehicles and steps feeding some of them, but this would reduce seating capacity, and the sys- tem would suffer from increased dwell times at the off-line stations. 6-220.127.116.11. Floor Flatness There are two types of low-floor vehicles potentially applicable to BRT: 100%-low-floor and mixed low-floor/ high-floor (usually 65 to 70% low-floor) designs. The advan- tages of 100%-low-floor vehicles are the following: â¢ No standing capacity is lost to the step up; â¢ Having no step up lowers the probability of acciden- tal falls; â¢ Better mobility within the rear portion of vehicles leads to higher utilization of this area, which is especially important with large articulated buses; â¢ Easier internal passenger circulation, which leads to lower dwell times and better capacity utilization; and â¢ The ability to put an additional door in the rear of the rear axle, which leads to lower dwell times in certain situations. The major disadvantage of 100%-low-floor vehicles when compared with partially low-floor vehicles is the loss of space caused by the intrusion of wheel wells and the drive train and the use of internal space for fuel tanks, batteries, and other devices that otherwise would be under the floor. Some of those devices can be placed in the vehicleâs âatticâ or on the roof; however, this creates access problems and increased maintenance difficulties and costs. Photo 6-I shows an inte- rior view of a 100%-low-floor vehicle. Photo 6-J shows the 12.2-meter (40-foot) partial-low-floor, step-up vehicle used by the Los Angeles Metro Rapid system. (Photo Credit: Irisbus North America) Photo 6-I. Interior view to rear of 100%-low-floor BRT vehicle.
As shown in Photo 6-K, a wide, no-step aisle supports cir- culation and makes it easier to access the rear of long, artic- ulated vehicles. Photo 6-L illustrates no-step boarding and alighting, as enabled by precision docking through an optical guidance system. Another class of specialized BRT vehicles has door flap plates or âbridgesâ that rapidly deploy from the vehicle when it pulls into a high-platform BRT station. The bridges allow no-step, no-gap boarding and alighting, yielding the extremely low passenger service times char- acteristic of high-platform metro rail and some LRT sys- tems. To date, these vehicles have been used only in South America, on 18-meter single and 24-meter (80-foot) dou- ble articulated buses in Curitiba and SÃ£o Paulo, Brazil, and on 18-meter (60-foot) vehicles in Quito, Ecuador. The vehicles used in Curitiba, as shown in Photo 6-M, use boarding/alighting âbridgesâ in the lower part of each door opening. The vehicles used in these applications combine the boarding and alighting ease and speed of low-floor, guided vehicles with the interior room and capacity of high-floor vehicles. The downside of this arrangement is that the vehicles can only operate to/from high-platform 6-10 (Photo Credit: Los Angeles County Transit Authority) Photo 6-J. 12.2 meter (40-foot), CNG, North American Bus Industries bus with partial (70%) low floor and step up to rear sectionâLos Angeles Metro Rapid bus. (Photo Credit: Translohr, France) Photo 6-K. Wide, no-step aisle supports circulation and makes it easier to access rear of long, articulated vehicles. (Photo Credit: Sam Zimmerman and Irisbus North America) Photo 6-L. No-step boarding and alighting enabled by optical guidance system.
stations that match the vehiclesâ high floors unless a combi- nation of doors is provided. 6-1.2. Key Physical Features 6-1.2.1. BRT Propulsion Systems BRT vehicle propulsion systems affect system perfor- mance, ride quality, environmental impacts (including noise and air pollutant emissions), attractiveness to customers and non-customers, service reliability, overall costs, and finan- cial feasibility. An increasing variety of propulsion systems is in use or under development, particularly for use in BRT vehicles, but there are four basic types of systems. The most prevalent propulsion system is the thermal or internal com- bustion engine, usually diesel cycle (compression ignition) driving a hydraulic-mechanical transmission. The second com- monly used propulsion system is the electric vehicle or trolley bus. Trolley buses normally use electric power collected from an overhead contact system (trolley wires) to power an on- board electric motor or motors. However, a number of other power distribution/collection systems have been developed and tried. The third type of system has âdual modeâ capabilities. These are typified by the 18-meter (60-foot) articulated dual mode vehicles used in Seattleâs CBD bus tunnel and the vehi- cles that will be used on the South Boston Transitway. These vehicles have full service capabilities when powered either by an independent thermal engine (e.g., diesel, CNG, or gas turbine) or by electric motors that receive their energy from overhead contact wires. The fourth and arguably most complex type of vehicle propulsion is the hybrid thermal-electric (the thermal part can be diesel, CNG, or gas turbine). By definition, hybrid vehi- cles have both thermal and electric propulsion capabilities, but they also have on-board energy storage capabilities. The on-board energy storage is usually electric (either a battery or ultra-capacitor), although mechanical systems using flywheels and hydraulic systems with compressed gas tanks have been tried with mixed success in the past. This on-board energy storage allows the thermal engine to be operated within its maximum fuel efficiency and mini- 6-11 mum emissions range and also provides the highly peaked energy and power needed for acceleration away from stops. This reduces the stress on the engine and allows it to be smaller and lighter, significantly reducing air and noise emissions and fuel consumption. The on-board energy storage takes advantage of regenerative braking to reduce fuel consump- tion and brake wear and tear. 6-1.2.2. Internal Combustion Engines The most common propulsion plant, and the one that would be likely if a conventional bus is selected for a BRT application, is the internal combustion (e.g., clean diesel and CNG spark ignition) engine driving a torque converter connected to an automatic four-, five- or six-speed trans- mission (gearbox) that is then connected to a driveshaft. Power output is typically in the range of 250 to 350 gross horsepower; however, for articulated vehicles operating on hilly terrain, engines up to 450 gross horsepower have been used. After deductions for driving auxiliaries such as an alterna- tor and air-conditioning compressor and after friction losses through the drive train, the net horsepower delivered to the wheels can be substantially less than the gross horsepower output. The trend is for vehicles to require more withdrawal of power for the alternator as the quantity of electrical equip- ment (e.g., electric rather than direct-driven air conditioning) on board increases. CNG-fuelled internal combustion engines are used by many operators to reduce emissions. CNG engines have significantly higher fuel consumption and costs and generally higher main- tenance costs because to date they feature spark ignition and are throttled (as opposed to unthrottled) compression ignition diesels. They also require costly special garaging, servicing, and fuelling facilities. There have been significant improvements in diesel engines over the last two decades in response to the need to reduce emissions. Electronically controlled, âdrive-by- wireâ clean diesel engines with exhaust gas recirculation have significantly reduced particulate, hydrocarbon, nitrous oxide (NOx) and carbon monoxide emissions from pre- emissions control level by orders of magnitude. Todayâs electronically controlled clean diesel enginesâ using low-sulphur fuel combined with electronically con- trolled hydraulic-mechanical transmissions with self-cleaning catalytic convertersâcan have lower particulate and hydro- carbon emissions than CNG spark ignition engines, although they can have slightly higher NOx emissions. These are de- scribed in more detail in Section 6-2. Contemporary spark ignition CNG engines have low par- ticulate emissions and can be somewhat quieter than diesels, but have higher total weight. (High-pressure fuel tanks have relatively high operating and maintenance costs and higher initial capital costs of about $50,000 per vehicle). They also Photo 6-M. Bi-articulated Volvo of Brazil (Marco Polo) high-floor BRT vehicle with boarding/alighting âbridgesâ in lower part of each door opening (Curitiba, Brazil).
have additional fuelling infrastructure costs compared with clean diesel vehicles. In the future, clean diesel engines using catalytic convert- ers enabled by low-sulphur fuels and either CNG spark igni- tion or diesel hybrids promise an almost complete elimination of emissions as a planning and project development issue. At the same time, advances in CNG engines (e.g., unthrottled diesel fuel compression ignition of unthrottled gas-air mix- tures) will significantly lower CNG operating costs, although additional infrastructure costs will remain. 6-1.2.3. All-Electric Trolley Buses The other common propulsion system that has been proven over many decades of operation is the fully electric trolley bus. It uses an electric power usually provided from overhead contact (trolley) wires to drive motors that can be reversed to brake the vehicle (saving brake wear and tear) and to regen- erate power for other vehicles that may be simultaneously accelerating. Unlike rail vehicles that have only one contact wire because the rails provide the ground, trolley buses col- lect power from two wires, one hot, one ground. Trolley buses sometimes carry on-board energy storage or power produc- tion mechanisms, usually batteries or a small âdonkeyâ engine plus generator, to enable them to operate for short distances away from overhead contact wires, in order to get around obstructions or to get to maintenance facilities if there are central power system problems. Over the years, a number of attempts have been made to distribute/collect electric power for streetcars, light rail vehi- cles, and trolley buses using different technologies than the visually intrusive overhead contact wires. These nonstandard distribution/collection techniques included underground con- duits and contact âthirdâ rails that were contacted by âploughsâ that extended below the streetcar through a narrow continu- ous slot in the street. Although this approach was aestheti- cally superior to overhead cables, it was expensive to build and maintain, had safety problems, and created difficulties for other city functions, such as firefighting and utility maintenance. A new approach for BRT vehicles is called the âstream system,â developed in Italy. It consists of underground con- duits with insulated contact plates on top at the street surface. These plates are safely energized only when the contact shoe mounted under a BRT vehicle is directly overhead. This ener- gization occurs when a powerful on-board magnet lifts up a continuous flexible power cable in a prefabricated, water- proof, and insulated box structure placed in a trench. This, in turn, energizes the contact plate at the street surface from underneath. Although this technology is not yet proven in extended revenue service, it has been successfully tested in Trieste, Italy. To date, speeds are limited to under about 33 kilometers (20 miles) per hour. The strongest advantages of an all-electric vehicle using an external power source for BRT applications are environ- 6-12 mental friendliness in terms of both noise and air (at least in the vicinity of the line) emissions and very high power and torque output, leading to high acceleration rates. Modern elec- tric vehicles also feature much smoother acceleration and deceleration than conventional internal combustion vehicles with multi-shift point hydraulic-mechanical transmissions. Trolley buses generally also have the highest power-to- weight ratio of any transit vehicle, power that can be effec- tively transmitted to the pavement through high-traction rubber tires. Photo 6-N shows the Quito, Ecuador, Trolebus, which is an all-electric BRT vehicle. A vehicle with electric propulsion will always have the potential for higher starting torque and higher horsepower at any given revolutions per minute (RPMs) than a thermal engine of equivalent physical size and weight. An electric vehicle has excellent acceleration and hill climb ability because the maximum tractive effort (the force applied at the wheel) of a direct current motor occurs at 0 RPMs. By contrast, a diesel engine must spin to about 2,000 RPMs to produce maximum torque, and a clutch must be used to allow the engine to be engaged with the wheels at a standing start, at considerably lower RPMs and less starting torque. Another advantage of electric traction is being able to power more than one set of wheels, which provides better traction in slippery conditions. As a practical matter, the greater torque at lower RPMs that is available with electric motors compared with thermal engines is a benefit with limited application. Normal acceler- ation rates generally will not exceed approximately 1.3 meters per second per second if the vehicle is to have standing pas- sengers. Otherwise, there will be excessive grip strength required of passengers, and they will be uncomfortable. Emergency braking rates as high as 5 meters per second per (Photo Credit: John Cracknell) Photo 6-N. Trolebus, an all-electric BRT vehicle (Quito, Ecuador).
second can be obtained with any type of vehicle, regardless of motive power. Electric traction allows high acceleration from a standing start, which is useful when there is frequent starting and stop- ping. However, this advantage fades as starting and stopping are less frequent and high speed is desired. When higher RPMs are maintained, either electric propulsion or internal combustion propulsion can achieve practical, maximum accel- eration rates. A final advantage of electric vehicles is that because of their lower vibration, all systems (including the electric motors, the air conditioning system, all electronics, and the body) tend to have a longer service life than their thermal equivalents. The disadvantages of trolley buses are the expense of build- ing and maintaining them, visually intrusive infrastructure, and service inflexibility (made necessary by the need to access power provided via costly and thus limited-extent fixed infra- structure such as overhead contact wires). This inflexibility can be overcome in two ways. One way to overcome the service inflexibility of trolley buses is to use an all-electric vehicle for the all-stop service and LRT-like service in places where acceleration rate and environmental friendliness (especially low noise) are most important. Express or skip-stop services would be provided by vehicles with thermal engines that do not require access to overhead contact wires or another external energy source. The other way to overcome the service inflexibility of trolley buses is to utilize âdual modeâ vehicles that have full service capabilities both on and off wire. 6-1.2.4. Dual Mode (Dual Power) Thermal-Electric Drives Dual mode vehicles combine an electric trolley bus with an internal combustion engine (e.g., diesel, CNG, or gas tur- bine) capable of providing full, stand-alone performance. Dual mode vehicles therefore have the advantages of both trolleys and normal buses with internal combustion engines. Electricity is obtained from overhead contact wires for part of a given routeâs trajectory, typically in the center of the city. The vehicles used in the Seattle CBD bus tunnel have this capacity. There can be two configurations for dual mode articu- lated vehicles. In the first, one axle is driven by the electric motor, the other by the internal combustion engine/trans- mission (as in Seattle). This is the most straightforward configuration, but it has drawbacks. It must carry two com- plete propulsion plants, making for a heavy vehicle. It also precludes the possibility of powering more than one axle simultaneously. The second dual mode configuration uses an internal combustion engine and a generator/alternator (in lieu of overhead contact wires) to provide electric power to the motor or motors that actually turn the wheels, thus avoiding 6-13 the need for both an electric motor and a mechanical trans- mission. This type of vehicle can also operate as either a trolley bus or a diesel-electric vehicle. With this approach, the ride quality of the vehicle is significantly advanced because the all-electric drive eliminates the often harsh shift points associated with hydraulic-mechanical transmissions, but this type of vehicle tends to have lower fuel economy than other configurations. Having internally generated or externally provided (via trol- ley wires) electricity allows powering of multiple wheels in the same way as a light rail vehicle, an approach used for vehi- cles in Las Vegas; Nancy, France; and Boston (as shown in Photo 6-O) and currently in service in Lausanne, Switzerland. Drive motors can also be mounted on a single axle to power the axleâs two wheel sets, the typical solution for trolley buses, or there can be no axles at all, only motors directly within the hub of the wheel. When the motors are in the wheel, tires and wheels must be of a wide design. Putting the motors in the wheel hub is the approach taken in all of the specialized BRT vehicles and accounts for a sig- nificant portion of their much higher cost. The use of hub motors means that the floor can be very low in the center of the vehicle, making for a very wide aisle, a 100% low floor, and the ability to have a door to the rear of the rear axle. One disadvantage is that these motors are very expensive, and the resulting system is heavy. Photo 6-P shows the drive axles with hub motors used on a BRT vehicle. Dual mode vehicles are attractive for transit operations because they can combine the performance and other environ- mental advantages of a trolley bus when they are needed with the freedom of movement of a conventional bus using an on-board prime mover. The main disadvantages of dual mode vehicles are their weight and cost. The Neoplan vehicles that will be used on the South Boston Transitway have an esti- mated cost of well over $1 million each, compared with about $500,000 for a standard, diesel, 70%-low-floor, articulated (Photo Credit: MBTA) Photo 6-O. Neoplan AN 460 LF18-meter (60-foot) dual mode, diesel-electric BRT vehicle proposed for South Boston Transitway.
bus. Dual mode vehicles are also more complex than con- ventional buses. Whereas a conventional bus requires mainte- nance of a single thermal engine and a tried and true hydraulic- mechanical transmission, dual mode vehicles require more maintenance effort and cost because they have more compo- nents. The trade-offs that must be considered in specifying the type of dual mode vehicle to use for a particular BRT operation involve cost, complexity/reliability/maintainability, weight, fuel consumption, and acceleration. 6-1.2.5. Hybrid Electric Drives with Energy Storage Hybrid drives combine a dual power vehicle (e.g., diesel, CNG spark ignition, or gas turbine driving a generator/ alternator) with an on-board energy storage medium such as a battery pack or an ultra-capacitor. True hybrid drive BRT vehicles perform even better than vehicles with a simple thermal-electric drive (in which the thermal power is provided by diesel, liquid petroleum gas [LPG], or CNG) without energy storage. Photo 6-Q shows a hybrid drive BRT vehicle. A hybrid vehicle with energy storage allows an engine with less horsepower to be used because the engine can be run at a much more constant load. When high power is needed, the additional power is drawn from storage. Con- versely, the engine can recharge the energy storage medium while cruising or coasting. Regeneration during braking also recharges the storage medium and reduces brake wear and tear. There are noise and air pollution advantages to hybrid drive vehicles. Peak noise levels are reduced since high engine RPMs are not required to achieve adequate acceleration or to climb hills. The air pollution (and fuel consumption) advan- tages stem from the more constant load on the engine. It is much easier to optimally tune an engine to reduce emissions 6-14 and fuel consumption within a narrow range of operations than in a wide range of applications. This is one of the spe- cial benefits of hybrid propulsion systems, even when diesel engines are part of the mix. Hybrid vehicles can use either of the two propulsion sys- tem configurations noted above under dual mode vehicles, but they may not need trolley wires. The third type of dual power configuration available for hybrids involves a thermal engine, a motor/generator, and a mechanical transmission, all mounted on one drive shaft. This approach, similar to the approach used by the Honda Insight and hybrid Honda Civic automobiles, is being tested in revenue service in Seattle as a replacement for its Breda dual mode vehicles. This third type of dual power configuration has the weight penalty of a transmission motor/generator or alternator and the stepped shifting of a hydraulic-mechanical transmission; however, it tends to have better fuel efficiency and acceleration than alternative configurations. 6-1.2.6. Fuel Cells Fuel cells, which are now in demonstration operation throughout the world, will mark a clear breakthrough in tech- nology for buses when commercialized, especially for BRT vehicles. Fuel cells utilize hydrogen and oxygen to directly produce electricity in the presence of a catalyst, without engines and generators/alternators of any kind. There are two basic fuel cell approaches for vehicles, one involving the use of hydro- gen gas carried in high-pressure cylinders (up to 350 bar pressure), and another in which the hydrogen is chemically separated from a liquid hydrocarbon fuel, such as methanol, in a reformer onboard the bus. Water vapor is the only exhaust product from a vehicle using pure hydrogen as a fuel, an improvement over the imperfectly combusted hydrocarbons, nitrous oxides, carbon monoxide and carbon dioxide that make up the potent greenhouse gas (Photo Credit: Irisbus North America) Photo 6-P. Drive axle with hub motor that permits a wide aisle and 100% low floor. (Photo Credit: Berkhof Jonckheere) Photo 6-Q. Hybrid BRT vehicle.
mix emitted by internal combustion engines. Fuel cell tech- nology promises to be an environmental boon for the transit industry as well as the entire large-vehicle industry because it can run on hydrogen created from a variety of renewable sources. Other than fan noise, fuel cell buses are remarkably quiet, quieter than most cars. Obstacles still to be overcome with fuel cell vehicles include the following: â¢ The need for hydrogen extraction (which can be an expensive, environmentally dirty operation if done centrally); â¢ The need for more efficient, less expensive, lighter, and more durable reformers if on-board liquid hydrocarbon fuels (e.g., methanol) are to be used; â¢ The need for a new hydrogen or methanol supply infra- structure throughout North America; â¢ The need for enough on-board fuel storage capacity to provide adequate operating range regardless of fuel; and â¢ The need to reduce the initial capital and ongoing oper- ating and maintenance costs of all the above. This technology is still some years away from commer- cialization and competitive purchase price, but the special- ized vehicles have been designed for eventual conversion to fuel cell technology. 6-2. EMISSIONS Given the service levels entailed in BRT applications (200 or more vehicles passing by a single point in a single peak hour), air and noise emissions are critical vehicle plan- ning and design parameters. Both are frequently cited as reasons that BRT systems are often passed over in favor of LRT, and they are thus important vehicle planning and selection criteria. 6-2.1. Air Emissions Great progress has been made in reducing air pollu- tion emissions from rubber-tired transit vehicles. The base diesel is significantly improved from previous generations of mechanically governed diesel engines. According to A Study of Bus Propulsion Technologies Applicable in Con- necticut (Werle, 2001), contemporary four-cycle, electron- ically controlled diesel engines have less than one-third (as low as 15% of earlier two cycle engines) of the particulate emissions of pre-1994 engines and significantly lower NOx, carbon monoxide, and hydrocarbon emissions. Figures 6-7 through 6-10 illustrate that the propulsion technologies increasingly being found on specialized BRT vehicles and high-end conventional buses (e.g., CNG and clean diesel hybrids) have lowered emissions for all pollutant types dramatically over the last 10 years. Diesel hybrids 6-15 using low-sulphur fuels and continuously regenerating tech- nologies (i.e., catalytic converters) reduce particulate emis- sions to virtually undetectable levels and hydrocarbon ozone precursors by 70%; they also provide significant improve- ment in fuel economy, upwards of a 30% increase. Clean diesels using low-sulphur fuel and catalytic convert- ers are not expected to cost significantly more to purchase when they go into more widespread use. They will likely only cost a few cents more per mile to operate (slightly higher fuel costs) than current conventional diesel engines and have sim- ilar reliability levels. The low-sulphur diesel fuel needed for the cleanest clean diesel busesâthose with after-burning, self- cleaning catalytic convertersâis currently available only in some U.S. locations today, but the U.S. EPA has mandated that it be available everywhere by January 2006. Diesel hybrids currently have somewhat lower levels of reli- ability than conventional hybrids and initial purchase prices of at least $150,000. As more and more of these vehicles go into general use, reliability can be expected to improve to straight diesel levels, and the initial purchase price can be expected to be reduced to that of CNG vehicles, about $50,000. 6-2.2. Noise A study done in late 1970s by Saab-Scania on bus noise determined that most bus noise was due to peculiarities asso- ciated with diesel engines that could be easily overcome. The major sources of bus noise were the following: â¢ Mechanical noise (e.g., high compression ratios causing pistons to move around in their respective cylinders, known as âpiston slapâ); â¢ Diesel knock from high-pressure fuel injection; â¢ Fan noise; â¢ Air intake noise; â¢ Exhaust noise (limited issue); and â¢ Tire noise. Saab was able to reduce bus noise to levels that were the same or less than those of contemporary cars (78 decibels under full acceleration 10 meters from the vehicle on the curb-side). They were able to achieve this with several rela- tively minor changes such as using a larger, slower-turning fan pointing backward into the vehicleâs back-wash; using a larger intake muffler; using electronically controlled âmulti- squirtâ fuel injection; and encapsulating the engine with sound insulation, particularly underneath, to reduce mechan- ical noise bouncing off the pavement. An independent FTA vehicle research project came to the same conclusion and designed a noise reduction kit that cost only about $10,000 to reduce noise by 5 to 10 decibels. This was the situation over 20 years ago for previous- generation propulsion technology buses. Todayâs BRT vehi- cles with four-cycle, clean diesels; low-compression CNG
6-16 Nova-Allison RTS Hybrid LS Diesel Orion-LMCS VI Hybrid Moss Gas New Flyer C4OLF CNG Series 50G Orion VCNG Series 50G Neoplan AN440T CNG L10280G NovaBUS RTS Moss Gas Series 50 Orion-LMCS VI Hybrid Diesel NovaBUS RTS Diesel Series 50 0.05 0.10 0.15 0.20 0.25 gram/mile (Chart Courtesy of Northeast Advanced Vehicle Coalition) Figure 6-7. Particulate emissions for various propulsion system types. Nova-Allison RTS Hybrid LS Diesel Orion-LMCS VI Hybrid Moss Gas New Flyer C4OLF CNG Series 50G Orion VCNG Series 50G Neoplan AN440T CNG L10280G NovaBUS RTS Moss Gas Series 50 Orion-LMCS VI Hybrid Diesel NovaBUS RTS Diesel Series 50 5.0 10.0 15.0 20.0 25.0 gram/minute (Chart Courtesy of Northeast Advanced Vehicle Coalition) 30.0 35.0 40.0 Figure 6-8. Carbon monoxide emissions for various propulsion system types. spark ignition engines; and/or gas turbines (either alone or combined with electric motors or hybrid drives with energy storage load levelling) should make noise control even easier because the basic engine noise emissions are even lower to start with. The major conclusion here is that noise emissions can be reduced to levels that are, for all practical purposes, insignificant in most BRT applications, and planners and implementers should elect to put a noise emissions specifica- tion in their plans and procurement documents. 6-3. GUIDANCE SYSTEMS One important new development in rubber-tired transit vehi- cles, particularly those used for rapid transit, is the use of advanced ITS technologies to provide lateral and even lon- gitudinal vehicle guidance. These systems, as distinct from the mechanical bus guidance technologies of the past (e.g., OâBahn), eliminate the need for expensive physical infra- structure because the guidance system is based on the elec- tronic detection of either magnetic or painted markers. The implications of such systems on right-of-way requirements, customer comfort, speeds, dwell times, and reliability can be profound. Rubber-tired, steered BRT vehicles can operate in any run- ning way environment, from running ways where they are mixed in with general traffic, to completely grade-separated, specialized busways like metro rail lines. This significant flexibility advantage allows a minimum of specialized guide- way to be built without forcing an undue amount of transfer-
6-17 Nova-Allison RTS Hybrid LS Diesel Orion-LMCS VI Hybrid Moss Gas New Flyer C4OLF CNG Series 50G Orion VCNG Series 50G Neoplan AN440T CNG L10 280G NovaBUS RTS Moss Gas Series 50 Orion-LMCS VI Hybrid Diesel NovaBUS RTS Diesel Series 50 20.0 40.0 60.0 80.0 100.0 gram/mile (Chart Courtesy of Northeast Advanced Vehicle Coalition) 120.0 NOx NMOC (non-methane organic compounds) Figure 6-9. Ozone precursor emissions (hydrocarbons, NOx) for various propulsion system types. 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 NY Bus Cycle Manhattan Cycle CBD Cycle (Chart Courtesy of Northeast Advanced Vehicle Coalition) Average Speed (mph) Fu el E co no m y (m pg ) Nova-Allison RTS HybridOrion-LMCS VI HybridNew Flyer C4OLF CNG Orion VCNGNeoplan AN440T CNG NovaBUS RTS Diesel Figure 6-10. Fuel economy for various propulsion system types. ring; however, this feature presents some disadvantages as well. These include the potential for passenger discomfort, the need for extra right-of-way with driven vehicles, and the difficulty drivers have in getting close enough to a station platform to permit no-step boarding and alighting. Perhaps the most significant disadvantage is the inability of conventional, steered-only vehicles (buses) to support rapid, no-step, station-platform-to-vehicle-floor boarding and alight- ing at low-platform stations that are easy and inexpensive to construct. The Transit Capacity and Quality of Service Manual (Kittelson and Associates, Inc., 1999) shows no- step, no-fare-payment-per-passenger service times from 1.1 to 2.6 seconds for mostly boarding situations, 1.4 to 2.0 seconds for mostly alighting situations, and 2 to 3 seconds for mixed boarding and alighting situations. Although part of the difference between these numbers and those shown in Table 6-2 is due to door width and internal vehicle configuration, a high proportion is due to the fact that people have to step up/down to board or alight from most buses. In fact, the high-floor LRT vehicles shown in the Tran- sit Capacity and Quality of Service Manual (Kittelson and Associates, Inc., 1999) have significantly higher boarding and
alighting times (up to 3.4 seconds per passenger) compared with no-step heavy rail systems (as low as 2.0 seconds). In response to these disadvantages, a number of technolo- gies have emerged in recent years that impart to BRT vehi- cles the kind of tracking precision normally associated with rail-based rapid-transit modes. Even low-floor buses may require stepping up and down if a vehicle is stopped far enough from the curb to require a step off the curb to the pavement level and then a step up into the vehicle. Therefore, one impor- tant new development in rubber-tired transit vehicles, partic- ularly those used for rapid transit, is the use of advanced ITS technologies to provide lateral vehicle guidance and thus support âprecision dockingâ as well as provide longitudinal control (e.g., starting and stopping and maintaining a safe distance from vehicles ahead). These systems can provide the more comfortable tracking and minimum right-of-way require- ments of rail vehicles, but perhaps even more importantly, they allow no-step boarding and alighting, which reduces dwell time. 6-3.1. Mechanical Guidance The first recent mechanical guidance system for buses was originally developed as the âO-Bahnâ system. This guidance approach, similar to that utilized on the rubber- tired, automated people mover systems often found at air- ports, has been proven in service for many years in Essen, Germany, and Adelaide, Australia, with newer, similar non-O-Bahn applications in a number of British cites (e.g., Leeds). These systems can utilize a pre-cast, concrete âtrackâ with low vertical side rails or curbs that are contacted by laterally mounted guide wheels that, in turn, are connected to the vehi- cle steering systemâs idler arm. The guideway tapers where the vehicle enters the guided section to allow easy entrance. Once on the guideway, the operator does not steer, but applies only power and braking. After leaving the guideway, driver steering is reactivated. In Essen, the vehicles shared a tunnel with light rail vehicles. Both Essen and Adelaide applications operated successfully for years (Essen has now ceased oper- ation) with enviable safety records, few safety problems, and excellent customer satisfaction. A more recent lateral mechanical guidance technique is to use one central guide rail or central metal guide groove in the roadway. In the guide rail approach, the rail is contacted by a guide wheel, or sheave. There is one sheave mounted between each set of wheels. In the guide groove approach, the guide is contacted by a wheeled arm mounted on the center- line of the bus. In either case, the contacting mechanism can be retracted when the bus is not operated on a guided section. There are some differences in how this guidance approach has been utilized in specialized BRT vehicles. For example, on several vehicles, all axles swivel to provide all-wheel steering to simplify precision docking and reduce the turning radius. Another vehicle has rigid axles directly under the 6-18 articulation joint, also permitting all wheels to swivel and fol- low the same track. Tracked systems can require complex locking/unlocking mechanisms to enable and disable axle movement relative to the vehicle chassis depending on whether the vehicle is traveling along a guideway. Both types of vehicles were tested extensively in revenue service on the Trans Val de Marne site in suburban Paris (Ventejol, 2001). The advantages of mechanical guidance systems are their tight running trajectory; precision docking; and high degree of safety, simplicity, and robustness under severe operating conditions. Disadvantages include vehicle weight and the additional infrastructure necessary for them to work (e.g., the vertical guiding surfaces or the track embedded in the pavement). It also may be difficult for vehicles to leave and enter guided track sections, precluding complex routing patterns. Guided vehicles often need a right-of-way that is physi- cally separate from other traffic because with some systems (e.g., O-Bahn) other vehicles cannot cross the right-of-way except at predetermined locations. Photo 6-R shows the guid- ance mechanism on the Translohr BRT vehicle. Photo 6-S illustrates a running way with guidance track used by mechan- ically guided vehicles in Nancy, France. Photo 6-T shows a running way used by the mechanically guided O-Bahn sys- tem in Adelaide, Australia. This photo illustrates the use of vertical curbs against which the guidance wheels play. 6-3.2. Optical Guidance Another lateral guidance technique uses a video camera mounted on the dashboard of the vehicle for position data acquisition. It views the position of two parallel stripes (Photo Credit: Translohr, France) Photo 6-R. Guidance mechanism on BRT vehicle and trackway.
6-19 The system facilitates very tight trajectories (approximately 5 centimeters), allowing close passing in the opposite direc- tion and error-free steering along narrow streets. It also allows vehicles to stop at stations within tight lateral tolerances. This allows high-speed vehicle entry into and exit out of sta- tions without tire scrubbing and obviates the need for time- consuming ramp and/or lift deployment for access/egress by passengers who have disabilities. This latter feature can result in significant savings in station service/dwell times over steering-only vehicles. Optical guidance systems avoid the vehicle weight asso- ciated with mechanical systems, and infrastructure costs are modest because no physical guide is installed in the road beyond painted stripes. With optical guidance sys- tems, the operator can take over at any time. Further, these systems are compatible with operating plans that feature mixed local and express operations on a single guideway because of their ease of driver-steered vehicle entry and exit. Optical guidance systems are used on some specialized BRT vehicles. As shown in Photo 6-U, the video camera on the dashboard and the painted dashed lines on the pave- ment are key components of the optical guidance system. Photo 6-V illustrates the BRT running way in Rouen, France, which has dashed lines for the optical guidance system. This system been thoroughly tested in service on the Trans Val de Marne in Paris and has been used in Rouen and Clermont Ferrand, France, since 2001. Las Vegasâs BRT system, which will utilize the Irisbus Civis vehicles, is scheduled to go into operation in the fall of 2003. One disadvantage of the optical guidance system used on the Irisbus Civis system is that because it turns like a conventional articulated bus with only one guided/steered axle, it must have a wider turning area than a vehicle on (Photo Credit: Bombardier) Photo 6-S. Running way incorporating guidance track used by Bombardier GLT vehicles (Nancy, France). Photo 6-T. Running way with vertical guidance walls used by mechanically guided O-Bahn system (Adelaide, Australia). (Photo Credit: Irisbus North America) Photo 6-U. BRT vehicle with a video camera on the vehicle dashboard and painted, dashed lines on the pavement as key components of the optical guidance system. painted on the roadway in relation to the lateral position of the vehicle and translates the relative position data to a com- puter that actually steers the vehicle with a servo motor when the system is activated. The video systems work even if the painted guide lines are partially obscured by another vehicle, leaves, or snow.
which all wheels follow the same track. This is the case with most tracked BRT vehicle systems. Optical guidance also lacks the safety of positive physical guidance. At high speeds, it is recommended that security curbs about 20 centimeters (8 inches) high be used that backup guide wheels can follow in case of system failure. There also may be issues at intersections where a dedicated transit- wayâs guidance lines may cross other traffic markings and confuse the system. Other safety issues include snow obscuring the guidance lines and vandals painting errant ones. 6-3.3. Magnetic and Other Electronic Guidance Systems Several organizations have developed magnetic guidance systems for BRT. These systems use data about a vehicleâs position relative to a magnetic field created by magnets or wires with electric current running through them embedded in the pavementâs surface for guidance. The advantage of these systems is their lower cost and vehicle weight in comparison with mechanical systems and the fact that data can be acquired from the magnetic field with regard to snow cover or other pavement surface conditions. However, these systems cost more to install and maintain than optical systems. All guidance systems utilized for BRT, to date, provide lat- eral guidance that can always be overridden by the driver. A driver must be present on every vehicle to start, accelerate, and stop it. Systems that provide longitudinal control (e.g., starting from and stopping at stations) are under development and in experimental use in Eindhoven, Netherlands. Adaptive cruise control systems that automatically apply the brakes and release the accelerator if an obstruction (a stopped vehicle) is 6-20 detected in front of the vehicle are already in use in trucks and will be adapted for BRT vehicle use. 6-4. IMAGE It is not only operating characteristics that define a BRT system. The matched characteristics of the vehicle and phys- ical infrastructure also project a physical image. This image is further enhanced by any particular features and amenities unique to the service, such as precision docking and real-time information at stations. As described more fully in Chapter 8, the image of a BRT system should be carefully cultivated in the initial conceptual planning and design stages. This image may be necessary to the ultimate success of the sys- tem for a variety of reasons. One is to attract choice riders by providing them with a transit choice that they perceive as more closely resembling the âquality experienceâ of driving than the background local bus system. The other reason for cultivating a distinct image and identity is to use the system itself for advertising and conveying information about rout- ing and schedules. Seeing distinct vehicles on certain routes serving certain stops and stations conveys information about where and when the system goes. It is not always necessary to have a rail-like appearance to be successful, as some successful applications have shown. The MBTAâs Silver Line in Boston, Los Angelesâs Metro Rapid bus, and Brisbaneâs highly successful South East Busway all successfully use late-model conventional articu- lated and single-unit buses that are attractive but do not look like railcars. These systems use a distinct livery to define the respective systemsâ image and identity. Such a âbrandedâ appearance can distinguish a bus in BRT operation from a regular one. The livery can be different from other buses, but match the livery at BRT stops, stations, and terminals, as well as on information signs, graphics, and all printed matter. In this way, the branded appearance of BRT vehicles stresses the systemic nature of BRT services. Photo 6-W shows the 12.2-meter (40-foot) bus used on Brisbaneâs South East Busway. As of 2003, at least five European bus manufacturers (Irisbus Civis, Bombardier, Neoplan, APTS, and Translohr) have designed and built specialized BRT vehicles that are similar to light rail vehicles in appearance, interior, and other features (such as guidance). In Europe and South America, Volvo has BRT vehicle projects under way, while in North America, both New Flyer and North American Bus Industries have BRT vehicle projects close to the production of prototypes. Examples of the features of BRT vehicles include their large sizes and distinct shapes (lengths from 13.75 to 25 meters [45 to 80 feet]); large, panoramic passenger windows; dra- matically curved front windscreens; several multiple-steam doors; lateral guidance/precision docking; quiet, thermal- electric hybrid propulsion; and the option for the driver posi- tion to be in the center of the vehicle. By comparison, the (Photo Credit: Sam Zimmerman) Photo 6-V. BRT running way with dashed lines for optical guidance system (Rouen, France).
6-21 (Photo Credit: Barry Gyte, Brisbane, Australia) Photo 6-W. Saab Omni âCity Busâ on Brisbaneâs South East Busway. (Photo Credit: Berkhof Jonckheere) Photo 6-Y. 24-meter (80-foot) hybrid, magnetically guided, modular BRT vehicle. (Photo Credit: Translohr, France) Photo 6-X. 18-meter (60-foot), dual mode, track-guided, modular BRT vehicle. (Photo Credit: North American Bus Industries) Photo 6-Z. 13.8-meter (45-foot) composite BRT vehicle. South American specialized vehicles resemble conventional buses much more in appearance, although there are significant functional differences (e.g., vehicle floor-to-station-platform bridges rapidly deployed at stops). In South America, the emphasis is more on acquisition cost and functionality than on image. Examples of BRT vehicles with distinct, modern images are shown in Photos 6-X through 6-Z. Photo 6-X shows an 18-meter (60-foot) dual mode track-guided modular BRT vehicle. Photo 6-Y shows a 24-meter (80-foot) hybrid, which is a magnetically guided, modular BRT vehicle. Photo 6-Z shows a 13.8-meter (45-foot) composite BRT vehicle. The interior appearance of a vehicle should also be stylish, in keeping with the exterior appearance. Panoramic and curv- ing windows make the task of designing well-lit and attrac- tive interiors easier. Comfortable, upholstered seats with a generous pitch also contribute to a positive image. However, functionality cannot take second place to appearance, even if specialized vehicles are selected. Easy and rapid passenger boarding, alighting, and circu- lation are still basic BRT vehicle requirements to minimize dwell times. Distinct BRT vehicle interior layouts usually involve large standing/circulation areas around doors. These aid boarding, alighting, and circulation and also function as storage areas for baby carriages, strollers, shop- ping carts, and wheelchairs and, in the process, support the image of a quality system that meets the needs of the entire community. Photo 6-AA and Photo 6-AB show the interi- ors of two BRT vehicles. All transit buses in the United States are being delivered with features to comply with the letter and spirit of the ADA. Thus, as with all buses, they will be equipped with automatic signage and audio annunciation systems for announcing stops. Because vehicles specially designed for BRT service operations will support easy and rapid board- ing and alighting to accommodate significant passenger flows, they are inherently more accessible for passengers who have disabilities. Given the special status of BRT vehicles operating in high-profile trunk lines, they are also likely to have a large number of connecting routes and/or branches off the trunk route. Thus, by maintaining a high-profile image, they are likely to provide additional information to the public on board. This can include visual and audio annunciation of real-time information about the next stop or stops and the availability of connecting routes.
6-22 example, the plushest interior with the largest seats available might be required. Because specialized BRT vehicles are currently produced only in Europe and South America, they do not comply with Buy America requirements for 60% U.S.-produced content. However, at least one transit agency, Citizens Area Transit in Las Vegas, Nevada, has obtained a waiver for the pur- pose of providing a demonstration site. Order quantities influence the price and willingness to locate manufacturing. As the volume of purchases increases, it may well become practical for vendors to meet Buy America requirements. There are differences in philosophy between European and U.S. procurement practices that also lead to large dif- ferences in purchase prices. These differences must be taken into account when comparing prices between European vehicles intended for Europe and European vehicles intended for export to the United States. European manufacturers tend to sell more standardized models (excluding the special- ized vehicles). The buses are specified by selecting amongst some standardized modules. Differences among operatorsâ purchases are confined to a few choices in power output and transmissions, air-conditioning output, minor interior details, and other limited changes. By comparison, U.S. procurements tend to vary a great deal from one agency to the next, includ- ing engines from more than one manufacturer, different axles, different door layouts, and different destination signs and other electronics. Variety in procurement raises cost because of the require- ment of procuring supplies in small quantities and preparing different production runs. Table 6-3 shows typical purchase prices for BRT vehicles. U.S. procurements, per FTA man- date, often include 12-year warranties on bodies and chassis and other shorter or longer warranties on drive train compo- nents. Warranty costs are almost always considered operat- ing costs in European practice, but in the United States, up to a point, these costs may be capitalized. Life-cycle costs should also be a prime selection factor in any vehicle procurement, and life-cycle costs are profoundly affected by design life and projected duty cycle. For exam- ple, stainless steel vehicle bodies are typically designed for a life of 20 years, whereas conventional mild steelâframed transit buses have a 12-year warranted life. Electric propul- sion systems should last longer than mechanical ones, often as long as 30 years. Vehicles in BRT service on dedicated rights-of-way should last longer than vehicles carrying the same number of customers in stop and go traffic with much more frequent local stops. A careful comparison would dictate reviewing the differ- ence in warranty terms and subtracting the warranty costs from U.S. prices. A rule of thumb is to allow $50,000 extra for CNG propulsion, whereas a premium of at least $200,000 appears to be the minimum add-on for hybrid vehicles once they are in general production. One of FTAâs procurement issues relating to specialized BRT vehicles is whether they should be treated as buses, with Altoona testing requirements and mandated 12-year life, or rail (Photo Credit: Translohr, France) Photo 6-AA. Translohr BRT vehicle interior. (Photo Courtesy of Bombardier) Photo 6-AB. âTram on tiresâ interior. 6-5. PROCUREMENT ISSUES AND COSTS Buses made in the United States that might be suitable for BRT service will generally be articulated, low-floor buses. However, single-unit 12.2-meter (40-foot) vehicles are also being used, such as those used to begin service on the Metro Rapid system in Los Angeles and the Silver Line in Boston. Irrespective of size, the vehicles to be used in BRT service will most likely be similar to those currently in production. Thus, current prices might be a good guideline. When conducting an actual procurement, more detailed specifications might result in having slightly higher prices. For example, BRT operations might dictate the highest horse- power engine and gearing for acceleration, or three or four sets of double-channel doors might be required. As yet another
vehicles with a different warranted life. As of this writing, this issue has not yet been fully resolved, but a change in overall investment policy to treat all BRT expenditures the same as expenditures for rail-based modes (as capacity and ridership- attracting enhancements eligible for âNew Startâ assistance) should go far in clearing up these differences. Issues related to federal funding are addressed more fully in Chapter 9. 6-6. CHAPTER 6 REFERENCES Fruin, J. J. Pedestrian Planning and Design. Elevator World, Mobile, AL (1987). 6-23 Kittelson and Associates, Inc., Texas Transportation Institute, and Transport Consulting Limited. TCRP Web Document 6: Transit Capacity and Quality of Service Manual. Transportation Research Board, National Research Council, Washington, DC (January 1999). Kittelson and Associates, Inc. âUpdate of the First Edition, Transit Capacity and Quality of Service Manualâ (TCRP Project A-15A). Unpublished Draft (October 2002). Ventejol, P. âTrams and Rubber-Tyred Guided Vehicles,â Savior Faire, 37 (April 2001) pp. 14â19. Werle, M. J. A Study of Bus Propulsion Technologies Applicable in Connecticut. Connecticut Academy of Science and Engineering, Hartford, CT (2001). TABLE 6-3 Typical purchase prices for BRT vehicles in 2002 U.S. dollars Vehicle Type / Feature Cost 60-foot Conventional Diesel Low-Floor Articulated Bus $500,000â600,000 60-foot Articulated Trolley Bus $900,000â950,000 60-foot (18-meter) BRT Vehicle with guidance, internal combustionâelectric or hybrid drive $1,000,000â1,600,000 40-foot Conventional Low-Floor Bus $300,000â350,000 Hybrid Premium $100,000â200,000 CNG Premium (Vehicle Only) $50,000â100,000 Electronic (Optical, Magnetic) Guidance $100,000