Hardware-in-the-Loop (HIL) Simulations Supports Vehicle Design and Driver Training

Minnesota Valley Transit Authority (MVTA)

Over the past several years, the Minnesota Valley Transit Authority (MVTA) has begun implementation of bus-only shoulder operation.   Bus-only shoulders allow a bus to use typically unused road right-of-way to bypass congestion during morning and afternoon rush hours (See Figure 1).

The use of the shoulder as a busway offers a number of construction and operational advantages:

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Figure 1: Bus-Only Shoulder Lane

  • Ease of implementation. The shoulder exists; no need to acquire and develop additional right of way exists

  • Low costs. The cost to strengthen and modify an existing road shoulder is significantly less than constructing a new busway.

  • Routing. Because bus-only shoulders follow existing routes, no changes to bus routes, bus stops, or transit stations are needed to support bus-only shoulder operations.

  • Customer Satisfaction. 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 advantage.

  • 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 Training, 2011).

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)

Lane Keeping
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.

Forward Collision Assistance
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).

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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 (Minnesota Valley Transit Authority, 2010).

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Figure 3: Simulator Interior

The MVTA simulator combines Hardware in the Loop (HIL) and Human in the Loop (HITL) concepts to integrate hardware, software and operator elements into an effective simulated experience.

The simulator itself (See Figure 3) consists of:

  • Driver cab appointed with the same equipment designed for the actual vehicle

  • Visual system field of view

  • 3 DOF motion base

  • Torque feedback steering

  • All appropriate software to simulate the roadway environment, feedback information to the operator, and reporting following completion of the simulation

Because the simulator replicates the hardware used in real buses, it can be used for training, software development, as well as Human Machine Interface (HMI) testing.  Working in a simulator allows for a safe, controlled, repeatable and observable environment which can be difficult to replicate in the real world.

         From a training perspective, the simulator allows operators to train in optimal and sub-optimal conditions prior to on-road DAS training.  It can also introduce on-demand scenarios to maximize training effectiveness and driver preparation for real-world DAS usage and eventual shoulder driving.

         As a development tool,  RTI's Simcreator software provides the ability to emulate sensor functionality, and interface with existing software using TCP/IP or UDP communications.  This capability enables  development and testing of hardware/software in a safe and controlled system.  

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Figure 4: MVTA Simulator

The simulator, as installed at the Burnsville, MN, MVTA bus garage, is shown in Figure 4. The simulator uses a seat-based motion platform to achieve realistic vehicle dynamics. The DAS is installed in the simulator, and allows a driver to train in all weather and traffic conditions on a geospecific roadway before transitioning to a DAS-equipped bus.  Geospecificity is achieved through the creation of virtual worlds based on the roadway data collected by mapping vehicles, then managed and manipulated by Realtime Technologies software application(s).

To enable the simulation, RTI has correlated the DAS GPS data with the roads developed in RTI’s OpenFlight visual database.

During the simulation:

  • The system sends vehicle positions in real-time to the University of Minnesota’s DAS system over Ethernet.

  • The vehicle positions are provided in the DAS GPS coordinate system and simulate the real DAS peripherals.

  • The DAS software draws the head up display and this correlates with the out-the-window view drawn by the simulator.

  • The DAS software also draws the heads down vehicle information displays.

  • Torque is played back on the steering wheel based on DAS warnings commands that are sent back from the DAS system.

  • This system provides immediate, geospecific feedback to participants, and closely emulates the system and equipment used on a real-world bus.

Following simulator training, drivers begin training with the actual system in real-time on an actual road. The perspective a driver brings is generally different than that of the developer, and the insights the end-user provides typically produces a better system.   In this case, driver experience with the system during the initial training period resulted in a staged approach to lane departure alerts which were not initially included as part of the DAS design.  The staged warning was easy to implement, and in hindsight, offers improved driver acceptance when compared to simultaneous warnings. Honest driver feedback, possible through use of the simulator training scenarios, resulted in a system which better met the needs of the driver (Driver Training, 2011).


Elbow Room on The Shoulder. (2010, July 1010). Retrieved from GPS World: http://www.nxtbook.com/ygsreprints/ygs/1-27910831nxtbook/index.php#/4

Minnesota Valley Transit Authority. (2010, April 13). Retrieved from MVTA Cedar Avenue Bus Rapid Transit Newsletter: http://www.mvta.com/sites/d82719c7-9b33-46b8-a7af-e5577d7145af/uploads/mvta_cedar_avenue_w_captions_for_web_3.pdf

Driver Training. (2011, September 30). Retrieved from University of Minnesota – Bus 2.0: http://www.bus2.me.umn.edu/background.html

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Realtime Technologies Inc. (RTI) specializes in real time multibody vehicle dynamics, and graphical simulation and modeling.  We offer simulation software applications, consulting, custom engineering, software, and hardware development.  Realtime Technologies’ customer base includes international, government and private entities.  RTI was founded in 1998.