Ease of implementation.
The shoulder exists; no need to acquire and develop additional right of way
Low costs. The cost to
strengthen and modify an existing road shoulder is significantly less than
constructing a new busway.
bus-only shoulders follow existing routes, no changes to bus routes, bus
stops, or transit stations are needed to support bus-only shoulder
Transit customers who travel on buses which use a bus-only shoulder perceive
a travel time saving two to three times greater than actually realized.
Keeping the bus moving at all times offers a significant psychological
Increased ridership. A
1997 study of bus-only shoulders in the Twin Cities analyzed more than nine
BOS routes for a period of two years and found that overall there was a 9.2
percent increase in ridership along these routes. At the same time, total
ridership had decreased by 6.5 percent.
Despite these advantages,
the use of bus-only shoulders does impose additional stress and strain on a
driver. As shown in Figure 1, the narrow bus-only shoulder leaves a
driver very little margin of error. Operating with this small error margin is
difficult even during the best traffic and weather conditions, and degrades to
nearly impossible during heavy traffic and poor weather conditions
Driver Assist System (DAS)
Given the small margin for error with bus-only shoulder
operation, the MVTA has partnered with the University of Minnesota Intelligent
Vehicles Lab to develop a Driver Assist System (DAS) for these busses. The DAS
combines GPS (Global Positioning System) satellite tracking and on-board
technology to support the new challenges presented with this operation.
The system provides two
primary capabilities: lane keeping, and collision awareness. The system
provides assistance only; the driver is always responsible for vehicle control.
The DAS provides alerts and
warnings via a multi-modal human-machine interface (HMI) though three modes:
Graphically: through a
Head-up Display (HUD)
Haptically: through a
torque actuated steering wheel giving the steering wheel a restorative
torque in the event of lane drift.
Tactically: through a
seat equipped with actuators that vibrate on the side of the seat to which
the lane is being departed.
(“Elbow Room on The Shoulder," 2010)
The DAS enables lane keeping using dual frequency, carrier phase
Differential Global Positioning System (DGPS) as its primary positioning
technology. This DGPS system provides position estimates accurate to 5-8 cm at a
rate of 10 Hz. The DGPS system is used to determine vehicle position and
heading; an on-board map database is used to determine the position,
orientation, and trajectory of the vehicle relative to the roadway. The map
database describes the location and type of lane boundaries and other relevant
roadway elements to an accuracy of approximately 10 centimeters.
The DAS provides sensing for forward collision assistance using a front
bumper-mounted IBEO Lux multi-plane scanning LIDAR sensor. Forward collision
alert and warning information is provided in two stages to the driver through
the HUD. As presently configured for the Minnesota bus-only shoulder operation,
if the obstacle detected is in the present shoulder of travel, the obstacle is
represented as a red, open rectangle, with red indicating a warning status. If
an object is located in an adjacent lane, the obstacle is represented as a
white, open rectangle with white indicating an alert status.
Side Collision Awareness
The DAS provide side collision awareness through use of multi-plane Ibeo Lux
LIDAR scanners mounted on both the left and right sides of the bus. These
sensors are mounted on the front bumpers to a pneumatic actuator. When the
actuator is extended, the sensors scan a 100-degree arc on each side of the bus.
When retracted, the sensor points toward the ground, enabling the bus to use
curbs or roadway barriers to support driver assist functions in GPS-denied
environments (Driver Training, 2011).
Figure 2: Side Collision Sensors
Training to support bus-only shoulder operation is a
difficult challenge. However, the MVTA is also now faced with the challenge of
training operators on use of the DAS to support and enable shoulder operation.
Because of the limitations inherent with instructor-led
training in this type of situation, the MVTA commissioned Realtime Technologies,
Inc. to develop a specialized training simulator. This simulator places
the operator in a life-like environment, and integrates traditional bus-driver
training with DAS components, effectively overlaying the DAS virtual world, on
top of the simulator’s virtual world
Valley Transit Authority, 2010).