The device that measures jerks on public buses

A jerking, lurching bus ride can be enough to put someone off their lunch – or even dissuade them from using public transport.

But just how much do public buses jostle passengers?

Measuring this, according to one team of researchers, might help to make the vehicles more comfortable.

The researchers, from University of Technology Sydney, have published a recent study in Scientific Reports.

According to co-author Dr Anna Lidfors Lindqvist, bumpy bus rides aren’t just annoying. They can carry health risks.

“Passengers, especially if they’re a little bit elderly or if have a pre-existing injury, those sorts of sudden changes can actually make it worse,” she tells Cosmos.

“If that’s a blocker for elderly people to take public transport, that’s a great area to further look at.”

In addition, studies on frequent or professional drivers and passengers have suggested that long-term exposure to engine vibrations could be linked to chronic pain conditions like lower back pain.

The team set out to measure the speed and direction of vibrations and sudden movements on public buses, to give them a baseline for improving bus bumpiness.

One of the researchers – Md Imam Hossain – took rides on 30 public buses driving different routes around Sydney, carrying an inertial measurement unit (IMU).

“An IMU can gather the acceleration in vertical and longitudinal as they’re ported backwards, side to side, and up and down, as well as then being able to measure the rate of change in those directions,” says Lidfors Lindqvist.

They were particularly keen to measure “jerks” – jolts caused by sudden acceleration or braking – which are a strong indicator of bus ride discomfort.

They found that, on average, passengers experience 0.12 times the force of gravity in acceleration, with peaks at 0.44 times.

They’ve got several different ideas for reducing jerks.

“There’s a lot of different sorts of suspension – like where they use air pipe suspension, rather than pneumatic suspension, that’s usually a softer ride,” says Lidfors Lindqvist.

Softer seats – like those used in coach buses or for truck and bus drivers – are also more comfortable.

“Cushioning a seat is enough for it to be a softer ride in terms of the overall vibration from the seat. Whereas, the jerk itself is a little bit more difficult to have a mechanical solution because your body will still move the same.”

Lidfors Lidqvist says that the transition to electric buses is a mixed bag – they don’t vibrate like diesel engines, but they can accelerate much faster.

“This is really another open question: does that then introduce another sort of jerk?”

But buses don’t need to be wholly redesigned for more comfort. The team thinks that driver training can also help.

“Bus driver behaviour is also a factor, and so is the traffic environment that they’re exposed to. Peak hour traffic looks very different than if it’s off peak,” says Lidfors Lindqvist.

In this study, Hossain sat at the same seat on the bus each time for consistency. But there are more and less comfortable zones on a bus, according to Lidfors Lindqvist.

“Other research, will tell you that you’ll find that the ride is often a little bit softer if you sit on top of the wheel axis, for example,” she says.

“But that jerk movement, when you move back and forth when the bus takes off or stops – that will remain pretty much the same, because it’s just your body in relation to the vehicle itself.”

The team is now interested in looking at the connection between buses and human injuries, as well as optimising bus comfort with efficiency of the ride, and greenhouse gas emissions.