On 13 September 2021, five-year-old Allie Hart was doing something ordinary – riding her bike on a pedestrian crossing near her home in Washington, DC.

When the driver of a transit van hit her, she died instantly.

For Allie's mother, Jessica Hart, "My whole world was shattered." Yet, she says, nothing changed in the outside world to safeguard people like Allie.

The gap between business-as-usual and her grief prompted Ms Hart to become a crusader against traffic deaths. Now a member of the campaign group DC Families for Safe Streets, she advocates for better-designed streets, more attentive drivers, and safer vehicles.

She believes that the safety of people outside of cars is typically an afterthought when someone decides to buy a car. "For most people, it just comes down to price, preference, and then their perceived safety [for the driver and passengers]."

Technology abounds that can help keep vulnerable road users (VRUs) safer. VRUs include pedestrians, wheelchair users, cyclists, motorcyclists and scooter riders. Together they are the majority of people killed by cars globally.

Yet some well-established safety features are not always integrated into new vehicles, safety ratings and regulations.

One reason is cost. Drivers might, in theory, be keen on extra safety features, but if they make the car significantly more expensive, would they actually buy them?

Alex Thompson has given that question a lot of thought. He is the principal safety engineer for Thatcham Research, a nonprofit automotive risk intelligence company funded by insurers.

Much of Mr Thompson's job involves crash testing.

Mr Thompson says that, as the technology matures, costs tend to come down. "You don't want the most safe vehicle to always be the most expensive vehicle," he says.

A relatively simple design transition has been toward more flexible materials, including smoothing out areas of the bonnet where struck pedestrians are likely to hit their heads. "Anything stiff is bad for a pedestrian," Mr Thompson explains.

Along these lines, front bumpers need to be very rigid, but new models have foam padding or other materials under the bumpers to absorb some of the energy of impact.

Certain challenges remain in this regard. Windscreen pillars (A-pillars) are designed not to collapse on collision, and Mr Thompson says that vehicle manufacturers still find it challenging to integrate safety for VRUs.

"As a pedestrian, if you hit that, it's probably the worst place in the vehicle where you can hit." The top of the windscreen is a particular danger point for cyclists.

It's this zone that Volvo targeted back in 2012, when it introduced pedestrian airbags to its V40.

According to the company, "The purpose of these airbags was to help protect pedestrians in certain situations when they impact the bonnet, and the area around the windscreen wiper recess and A-pillar, where there may be a risk of serious head injuries."

However, rollout of this innovation has been slow across other models.

Another passive safety feature is a pop up bonnet, which uses sensors to detect when a person has been hit, then uses pyrotechnic charges to lift the bonnet. This reduces the impact of the collision. Mr Thompson says that this feature depends for instance on the size of the engine and amount of available space.

Passive safety is no substitute for active safety features. "You can make a vehicle as benign for pedestrians as possible. But it's better to prevent that crash in the first place," Mr Thompson points out.

For active safety, a key preventive technology is automatic/autonomous emergency braking (AEB). This system automatically applies the brakes when a vehicle's cameras and sensors detect a pedestrian at risk.

AEB has become common for new cars in Europe. It's not a perfect technology; it works best at low speeds, and performance can suffer at night or with darting movements of pedestrians. But it's becoming more sophisticated and varied.

Car manufacturers are increasingly using lidar (light detection and ranging) alongside radar as AEB sensors. They're also fitting a variety of AEB systems targeting not just pedestrians, but also other VRUs.

These include cyclists. Thatcham Research is a test facility for the European New Car Assessment Programme (Euro NCAP), which from 2023 has incorporated dooring into its safety assessments. Dooring refers to opening a car door onto an oncoming cyclist. Technology systems now exist to warn people inside a car of a cyclist near a door, or to prevent the door from being opened.

Speed is also a critical factor in the severity of impacts. The risk and extent of an injury go down with lower speeds, notes Mike McGinn, the executive director of the advocacy organisation America Walks. The EU has mandated intelligent speed assistance (ISA) systems, which warn of high speeds or automatically reduce speeds, on new cars.

As well as speed, the size of cars is an important factor.

The increasing popularity of larger passenger vehicles like SUVs, in the US and elsewhere, is worrying for the safety of people on the street.

"They're heavier, but there's also blunt force impact," Mr McGinn says.

In addition, "as the cars have gotten larger, their ability to see what is in front and behind has just gone down".

Certain cities have attempted to discourage SUVs by charging owners more to park or register them.

More broadly, vehicle regulation to improve safety for vulnerable road users has been varied.

In the US, the National Highway Traffic Safety Administration (NHTSA) is considering a change to its own New Car Assessment Programme (NCAP) to factor in pedestrian protection.

"This is the first time that vehicles in the US are potentially being rated or regulated with regard to their safety for pedestrians," says Mr McGinn.

The NHTSA is also mulling over a safety rule for pedestrian automatic emergency braking. According to the agency, this has "an estimated safety potential to save hundreds of lives annually".

More technology of business

Commercial vehicles are already subject to stricter regulation. For example, the EU and Japan require direct vision on heavy goods vehicles. In other words, lorry drivers need to be able to see vulnerable road users directly, without needing to depend on mirrors. London has also now made it mandatory for lorries to reduce blind spots.

Ultimately, Ms Hart points out, preventable tragedies from traffic violence don't just affect non-drivers. "Everyone gets out of their car, no matter where they live."

"Nobody is immune. So one thing we have to do is think about how we design vehicles, and one way to do that is through regulation."