Being visible to other drivers has always been the first step toward motorcycles staying safe in traffic, but as the world’s carmakers race to develop semi-autonomous vehicles, riders are starting to face a new challenge: Being noticed by the electronic eyes of modern vehicles rather than the biological ones of their drivers.
While the vast arrays of electronic assistance systems proliferating on modern cars are made with the intention of increasing safety by reducing opportunities for driver error, motorcycles have the potential to slip through the gaps in these digital safety nets. Radar in particular is an issue. It’s fast becoming normal for modern cars to have radar systems. Front-mounted radars enable adaptive cruise control and automatic emergency braking systems by monitoring distance to vehicles ahead, while rear-mounted radars create blind spot monitoring systems. But bikes are small and often contain plastic or composite bodywork that’s relatively hard for radar to see, and that means automotive radar might not pick them up as early as it would a large, metal car. As we move toward a future where cars are increasingly semi-autonomous, with fully autonomous vehicles already under development, being seen by their radars will be as essential to safety as being seen by drivers is today.
As a maker of both high-tech cars and bikes, including the 2021 R 1250 RT that’s among the first two-wheelers with a radar safety system of its own, BMW is in a good position to understand the problem, and a newly published patent application shows that the company is already working on simple solutions to the issue. The firm has looked to the sea for inspiration—another place where radar has become ubiquitous and small fiberglass-clad vehicles share space with much larger metal ones—and borrowed the idea of passive radar reflectors.
Radar reflectors are already commonplace on small boats, either in passive or active form. The passive ones are simply made of sheets of metal attached at right angles to form sets of corner reflectors that are able to bounce radar waves directly back at their source, and it’s these that BMW has adapted for use on bikes.
While seagoing passive radar reflectors are a foot or more in diameter, their bike-mounted equivalents can be far smaller and still reflect the millimeter wave radar used in cars. BMW’s patent application shows a bike fitted with golf ball-sized reflectors that are simply miniaturized versions of their marine equivalents. By mounting them on the ends of the bars and on the bike’s axles front and rear, there’s no angle at which a radar can be pointed at a bike without hitting at least one of the reflectors, bouncing a strong signal back to the radar sensor.
BMW’s patent suggests the reflectors could be made of plastic to keep weight down, with a metalized coating to ensure they’re still radar-reflective, and that their mounting positions mean they serve a secondary purpose as sacrificial crash protectors; if you drop the bike, they’ll be the first parts to hit the ground. This secondary purpose helps separate the BMW design from an earlier patent from Suzuki which also describes passive radar reflectors fitted to bikes.
Given that we’re all going to have to learn to share the roads with increasingly automated cars, it’s reassuring that manufacturers are considering bikes and that their solutions, while perhaps not pretty, are simple and low-cost. There’s no reason to believe that radar reflectors like these couldn’t be retrofitted to older bikes once they’re available, and even if BMW doesn’t go ahead and turn this patent application into a production system, no doubt aftermarket parts makers will soon be looking at similar ideas.
