Let’s face it, you can’t imagine Next Generation Mobility without public transport. Cities grow, their layout changes, more people commute from farther away. So what needs to be done to reduce gridlock, achieve emission targets while at the same time offering people a flexible and affordable way to get from A to B? The answer is buses. When it comes to mass transit, they are the most versatile tool – especially in cities where building or expanding subway and rail systems is not feasible.
But just as with cars, passengers demand a certain level of comfort and, above all, safety from their buses. This is especially critical when driving through urban traffic. Here, unexpected situations are par for the course: cyclists merging into lanes, pedestrians darting across streets, cars pulling out of parking spots, the list goes on.
Enter ZF. As a market-leading systems integrator for the commercial vehicle sector, the company is uniquely positioned to fulfill these requirements. “Our extensive portfolio already covers a broad range of integrated safety solutions,” says Philipp Helmich, Head of ZF’s CVS Product Line Vehicle Dynamics. “For example, ZF already offers advanced emergency braking systems for trucks and coaches. Now we are bringing this additional layer of advanced safety to urban traffic. That’s why we designed the City Bus Collision Mitigation System. It’s a smart approach to supporting bus drivers in situations where it counts the most.”
The best way to greater traffic safety is avoiding crashes altogether. That’s why one aspect of the City Bus Collision Mitigation (short: City Bus CMS) concept is a forward collision warning feature (FCW). ZF’s state-of-the-art camera and radar continuously monitor traffic. If they detect an obstacle in the path of the bus, City Bus CMS issues a warning – both as an acoustic signal and a visual display on the driver’s dashboard.
At the same time, the active braking assistant – another crucial component of ZF’s City Bus CMS – initiates in order to reduce speed as much as possible. However, calibrating the braking force for a bus is a lot trickier than a conventional car.
Everybody who ever had to suddenly hit the brakes while driving will remember the forces acting upon the body, accelarating both themselves and unsecured bags towards the dashboard. While passengers in a car can rely on seatbelts to break this motion, the situation looks different in a bus packed full of people: no seatbelts, many passengers standing, unaware of the impending collision ahead. “Coming to a sudden full stop might avoid a crash, but passengers can still get injured from falling over and bumping into each other,” explains Helmich. Therefore, balancing these safety requirements was crucial to the development of City Bus CMS. The key question: how much braking force is necessary to maximize the chance of avoiding a crash while still keeping occupants inside the bus safe?
To figure this out, Advanced Driver Assistance Systems (ADAS) experts from ZF’s Commercial Vehicle Solutions (CVS) division went above and beyond the usual testing protocol. At the company’s test track in Jeversen, Germany, the team strapped on safety harnesses and helmets, then picked up a questionnaire and boarded a city bus.
Testing, documenting and evaluating the experience at different speeds and braking forces from a passenger perspective helped to determine how much deceleration intensity is acceptable at which speed. “After that, we had to transfer these findings into algorithms for the system’s control software,” says Jakob Schmidt, Customer Requirements Engineer at ZF. “What we did was integrate the data with ZF’s advanced braking capabilities that are precisely calibrated to the vehicle’s speed and weight. That way, we achieve a seamless interaction between the ADAS and braking system. Braking pressure is carefully applied across the braking profile, making passengers far less likely to be jolted and put off-balance,” Schmidt explains. “Designing the breaking profile like that minimizes the adverse effect on the passengers while still providing the best possible support for the bus driver in these challenging situations.”
Smart braking is the way forward
City Bus CMS is independent of both manufacturer and platform. This means that it can be applied to buses from any OEM, both with conventional engines and electric drives. “As more and more public transit authorities and OEMs switch to sustainable drivetrains, we planned for a system that can be easily integrated into a broad range of vehicle models. Mastering the braking maneuver is also important for autonomous driving, where city bus applications are a remarkably interesting use case,” says Philipp Helmich. “So, with this project we are not only entering a new market segment for our Advanced Driver Assistance Systems technology. We are also developing a critical building block for higher automation levels – in line with our company’s goal of mobilizing commercial vehicle intelligence.”