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When we build a bus driving simulator it is important to recreate a realistic virtual experience that incorporates the physics of the bus. New drivers are familiar with how a car works and behaves, yet are likely unfamiliar with the nuances of how a bus turns, accelerates, and brakes. Understanding these differences is important to create knowledgeable drivers and happy passengers. To highlight how we emulate real world physics to reflect real world vehicle physics, let’s consider stopping a bus in an emergency situation compared to a car.
What factors need to be taken into consideration?
There are several key differences between buses and cars, especially when it comes to emergency stopping scenarios. Here are the main factors we considered in our simulator software:
1. Mass and Inertia:
Mass: Buses are significantly heavier than cars, which means they have greater inertia. This requires more force to bring them to a stop.
Inertia: The higher mass of a bus results in greater momentum, making it harder to stop quickly.
2. Braking Systems:
Brake Design: Buses often use air brakes, which have a different feel and response time compared to the hydraulic brakes typically used in cars.
Brake Force Distribution: The braking force needs to be more evenly distributed in buses to avoid skidding or loss of control.
3. Friction and Tire Contact:
Tire Contact Area: Buses have larger tires with a greater contact area, which affects frictional force during braking.
Road Conditions: The interaction between the bus tires and the road surface can be more complex due to the bus's weight, affecting stopping distance on different surfaces (wet, dry, icy).
4. Center of Gravity:
Height: Buses have a higher center of gravity compared to cars, which can affect stability during emergency stops.
Load Distribution: How passengers and cargo are distributed can impact the bus's center of gravity and its braking performance.
5. Response Time and Distance:
Brake Lag: There is often a slight delay in air brake systems due to the time it takes for air pressure to build up and apply the brakes.
Stopping Distance: The stopping distance for a bus will be significantly longer than for a car due to the combined effects of mass, braking system, and tire-road interaction.
6. Driver Reaction Time:
Perception-Reaction Time: The time it takes for a driver to perceive a need to stop and begin braking should be accounted for. This can be influenced by the simulator's design to reflect realistic scenarios. In reality, this shouldn't be an actual difference, and instead more of a constant. However, some would say bus drivers are more road aware. For now, we'll keep this a constant, yet feel free to add your thoughts in the comments.
7. Deceleration Rates:
Deceleration: The rate at which a bus can decelerate is generally lower than that of a car. Simulating different deceleration rates based on the type of bus and load is important.
8. Suspension System:
Suspension Dynamics: The bus's suspension system affects how it handles during emergency braking. Suspension characteristics influence weight transfer and stability.
9. Passenger Dynamics:
Passenger Movement: In an emergency stop, passengers inside the bus will be subjected to forces that can affect the vehicle's dynamics and should be considered in the simulation.
10. Environmental and External Factors:
Weather Conditions: Simulating different weather conditions (rain, snow, fog) that impact stopping distances and traction.
Traffic Situations: Emergency stopping often involves interactions with other vehicles, pedestrians, and obstacles, requiring realistic traffic modeling.
By incorporating these factors into the simulator, we create a more accurate and realistic emergency stopping experience for bus drivers, helping drivers understand the unique challenges and dynamics involved in handling a larger vehicle compared to a car.
And as a quick guide to remember, the stopping distance of a bus is approximately 1.5x that of a car.
In the next blog post, we'll review the math behind this, and then follow-up with how we incorporate these learnings into the virtual experience.
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