By Daniel Mwamba

Studies show that while rollover crashes are very rare, they occur in 2 percent of all crashes, they account for about one-third of passenger vehicle occupant deaths. This was true with the Kapena Transport Bus Crash horror which happened on Tuesday, 23rd May, 2017 killing 19 people, after the driver failed to negotiate a curve making the bus to rollover.

Similarly in February 2014, over 58 people were killed when a Post Bus rollover as it was travelling from Ndola to Lusaka, as the driver tried to avoid a head-on collision with another vehicle. Over the years, many Zambian lives have been lost in crashes that have involved rollovers. This article I intend to look at how and why this happen, how risk it is, and also recommending ways to help save lives on Zambian roads.

Indeed in Zambian studies, the death rate for all occupants, not just drivers, has been higher in heavy passenger’s vehicles than in the other kinds of vehicles. This can be attributable to the number of passengers, the higher occupancy rate. So the fact of high occupancy is the problem. The purpose of the buses, more passengers, also is the source of their risk, when they crash, more people risk dying.

The National Highway Traffic Safety Administration (NHTSA), in the USA, studies defined a vehicle is classified as rolling over if it tips onto its side or roof at any time during a crash.

Rollovers also can occur when a driver attempts to turn a vehicle too aggressively — at a high speed or with a tight turning radius. In such conditions, the frictional force between the tires and road surface can cause the vehicle to tip up and then roll over. The forces in a multiple-vehicle crash may also cause a vehicle to roll. Similar to what happened in the Post Bus crash that killed 58 people.

Most rollovers studied, have happen when a driver loses control of a vehicle, and it begins to slide sideways. When this happens, something can “trip” the vehicle and cause it to roll over. This tripping object could be a curb, guardrail, tree stump or soft or uneven ground on the side of the roadway. Many rollovers crashes lead to partial or full ejection of occupants from the vehicle, increasing the likelihood of injury or death.

For example, a vehicle struck in the side may be pushed over by the striking vehicle. NHTSA studies, however, show about three quarters of rollover deaths occur in single-vehicle crashes, again similar to the Kapena Transport Bus that left 19 dead.

Buses and other larger vehicles tend to be involved in rollovers more frequently than cars largely due to the physical differences of these vehicles. They are taller than cars and have greater ground clearance, causing their mass to be distributed higher off the road relative to the width of the vehicle. Additional passengers and cargo can increase the centre of gravity even more. Other things being equal, a vehicle with a higher centre of gravity is more prone to roll over than a lower-riding vehicle.

Electronic stability control (ESC) helps prevent the sideways skidding and loss of control that can lead to rollovers. ESC is a vehicle control system comprised of sensors, brakes, engine control modules and a microcomputer that continuously monitors how well a vehicle responds to a driver’s steering input. The computer compares a driver’s commands to the actual travel of the vehicle. In general, when the sensors indicate the vehicle is leaving the intended line of travel, ESC applies the brake pressure needed at each wheel to bring the vehicle back on track. In some cases, ESC also reduces engine speed. ESC has been found to reduce single-vehicle fatal crash risk by 49 percent.

Safety belt use is one of the most effective ways to reduce the risk of injury or death in a rollover. A 2015 survey undertaken by the Zambia Road Safety at the Lusaka Inter City bus station revealed that, while most of the passenger big buses in Zambia are equipped with seatbelts, few passengers burgle up. It’s not known yet, whether the Kapena Bus had seatbelts. But without safety belts, occupants in vehicles that roll over can be thrown from the vehicle, greatly increasing the risk of serious injury or death.

When occupants are contained in the vehicle during a rollover, the performance of restraint systems and structural components is crucial to preventing injury. Head-protecting side curtain airbags triggered by rollover sensors can prevent the upper body from contacting the ground and also prevent occupants from being ejected from the vehicle. Good safety belt designs are important to hold occupants in their seats and away from the roof as much as possible. Finally, the roof and other vehicle structures must be strong enough to resist occupant compartment intrusion that can increase the risk of head and neck injury.

During the past 30 years, there has been much debate about the association between roof crush in rollovers and serious head and neck injuries. Some studies have reported that roof strength and injury are not causally related but that occupants are injured as they “dive” into the roof before it crushes. Other researchers maintain that injuries occur when the roof buckles into the occupant compartment and contacts the people inside.

The perspective we need to keep is that buses aren’t menaces on Zambian roads. They aren’t accounting for a big proportion of road deaths in this country. Vulnerable road users – pedestrian and cyclists account for huge number of fatalities, at least 60 percent, according to Zambia Police figures. However, buses when they’re loaded they do pose a risk to their occupants.

This problem should lessen, if government monitors that all newer buses are equipped with ESC, though still we need to pay attention to who is driving the bus and whether their occupants are doing what all vehicle occupants should do, like buckle up. Maintenance is another issue, and tire pressure might be affecting bus stability.

RTSA can encourage or give incentives to bus operators to buy vehicles equipped with ESC— important because studies show that drivers of big vehicles with ESC are less likely to lose control of their vehicles in the kinds of high-speed maneuvers that can result in rollovers. The real-world experience of vehicles with and without ESC also demonstrates the benefits of this technology in reducing single-vehicle rollovers.

The Ministry of Transport and Communications Statutory Instrument (SI) 79 of 2016, which prohibits importation of a vehicle not equipped with seatbelts, should be speedup, not wait for 2018. The usual safety measures like education and enforcement of buckling up can significantly reduce rollover deaths.

The other SI 90 of 2016, that restricts the speed of public passenger vehicle to the maximum of 100km per hour on highways, is also a welcome measure made by government. Another important factor, the Zambia police should improve data collection and analysis, detail crash data, highlight crash data involving rollovers so that we can more evidence on this topic.