Vehicle Design

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Low-Floor Vehicles

Low-floor bus technology has evolved substantially. European fleets adopted low-floor bus technology in the 1980s. Early models had only a partial section of low-floor access (with a sloped floor or steps to access the rear of the vehicle). Full section, low-floor vehicle designs are now available.

Low-floor buses comply with the requirements of the Americans with Disabilities Act (ADA) of 1990 and concurrently reduce time needed to service persons using mobility aids. Access to the vehicle can either be at raised platforms (providing level boarding) or using an on-vehicle ramp which flips down to bridge the gap between the step and the curb. In contrast, high-floor buses require lifts which are difficult to maintain under all operating conditions. A curb height of at least 150mm (5.85 in) is desirable to permit easy access from curb to the vehicle level.

Low-floor vehicles permit the possibility of level boarding, an effective way of reducing dwell time at stations. A high-level bus with internal steps cannot be docked with a raised station platform (see Stop Location, Design and Spacing).

With low floor buses, one concern is the ability to move the bus close enough to the raised station platform to permit level boarding without damaging the vehicle's tires or structure. One solution to this problem is automatic control of vehicles to provide precision docking. In August 1997, New York City Transit successfully demonstrated low-floor buses with full automatic control. The buses were equipped with vision and radar sensors to control the bus in both lateral and longitudinal directions. Such technology could also be used to steer a bus close to a raised platform (see TCRP Report 41). The use of mechanical systems to guide the vehicle, particularly at stations, is also an option.

Bus manufacturers offering low-floor bus designs for the North American market include: Gillig, Neoplan USA, New Flyer Industries, North American Bus Industries, Nova Bus, and Orion Bus Industries.

Number and Width of Doors

Adding additional and wider doorways facilitates the rapid entry and exit of passengers. A clear width of 32 in (820 mm) is desirable for easy access by persons in mobility aids (1).

Increasing the number of doors from two to three for a 40 foot conventional bus potentially increases the passenger handling capability at stops or stations by 50 percent. Combining additional doors with level boarding and off-vehicle fare collection can reduce dwell time to a minimum. The number and location of doors, however, needs to be carefully integrated with the vehicle's structural support systems to prevent any compromise of crashworthiness.

Location of the doors is also of concern. Some BRT systems may require left-sided doors to access bus lane or busway stations with central platforms without having to engage in complicated and time consuming crossing maneuvers. Two-sided BRT vehicle designs may also be desired to support double loading at side platform stations, emulating light or heavy rail operations.

Internal Circulation

A well-designed internal vehicle can reduce crowding, facilitate rapid passenger boarding and alighting, and can minimize the bypassing of waiting passengers because the bus is perceived by the operator to be at full capacity due to poor passenger distribution. Some general factors to consider are:

  • The role or function that the BRT system and service plays within the overall transit system (i.e., whether as an express, line-haul system connecting major subareas, or as a downtown distributor).
  • Policies on seating versus standing.
  • Average passenger trip length.
  • Specialized markets served, e.g., connection to the regional airport (where provision for luggage capacity is a requirement), or serving markets with a large modal share of bicycle access (where carrying capacity for bicycles, and rapid loading and off-loading of the bicycle is a requirement).

Passengers tend to congregate around doorways and often do not distribute themselves evenly throughout the vehicle. Increasing the number of doors to three for a standard size (40 foot) bus may help to achieve a better distribution of passengers and improve the flow in the. Off-vehicle fare collection (including proof-of-payment systems) can also help to alleviate any bottlenecks at the front entryway.

For an interesting case study of poor internal configuration giving rise to problems which stimulated a search for better alternative configurations, see TCRP Report 41, §2.3.3.2, highlighting the STCUM's deployment of low-floor buses in Montreal.

Wheelchair Loading

Wheelchair loading is best facilitated by level loading of the BRT vehicle. If this is not possible, a low-floor bus with ramp extension is the next best alternative. In the latter case, boarding and alighting times are roughly 25 percent of boarding and alighting times using lifts (Spiller and Labell, 1997, Operational Assessment of Paralympics Transit System: Low-Floor Buses, Lift-Equipped Buses, and Signage).

Vehicle Size

BRT vehicle design should permit procurement of alternative vehicle sizes and internal seating configurations to match transit supply parameters (i.e., frequency of service or headway, and vehicle size) to current and projected demands for service.

Noise and Emissions

A BRT vehicle should have very low noise and pollutant emissions. It is particularly important that acceleration noise and brake squeal be minimized or eliminated. This is consistent with establishing a new "image" for BRT in which a BRT vehicle does not sound and perform as a "bus."

Low-floor, compressed natural gas (CNG) bus operating on the Lymmo downtown circulator route in Orlando, Florida. This bus sports a Leonardo DaVinci design. Parked low-floor CNG bus.

On-Board Diagnostics

On-board diagnostics that contribute to early detection and correction of vehicular subsystem problems and reduced vehicle downtime, should be incorporated into the BRT vehicle design. The BRT vehicle design life should also exceed the 12 years for a conventional bus, possibly on the order of 20-25 years, depending on the optimal design life that minimizes life cycle costs.

Crashworthiness

The vehicle design needs to provide adequate passenger occupant protection given the higher operating speeds of BRT service. This also includes incorporation of ITS technologies that sense impending hazards and provide a warning to the driver to prevent certain types of crashes.

Propulsion

Recently compressed natural gas (CNG) and hybrid electic-diesel buses have emerged as viable alternatively fueled vehicles. These types of power produce very low emissions. At the same time, diesel engines have become much cleaner in response to EPA regulations. New diesels emit virtually none of the black smoke that has given buses a bad image in the past. Tighter regulations in place will force even greater reductions from bus emissions in future years.

Another option is the electric trolley bus, powered by catenary (overhead wires). The wires can be considered unsightly, although they are very similar to catenary for light rail. Electric trolley buses are proven technology, have no emissions from the tailpipe, and are the quietest transit mode of all.

Notes

1. There are no doorway clear width requirements set by ADA for buses, except by implication in that a clear space of 30 in (769 mm) by 48 in (1231 mm) needs to be provided for a securement location sited as close as possible to the entryway. There is, however, a clear width requirement of 32 in for passenger doorways on vehicle sides of rail cars (§1192.53 (a), FR Vol. 56, No. 173, Sept. 6, 1991). To the extent that BRT emulates an LRT operation, the use of a 32 in (820 mm) clear width requirement makes sense.

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