In posters highlighting key points in the Active Mobility Bill, the same limit of 20kg is imposed on personal mobility devices (PMDs) and conventional bicycles. This is supposedly to "reduce the risk of serious injuries in cases of collision". However, is it reasonable for PMDs and bicycles to share the same weight limit?
PMDs incorporate heavy components such as batteries and electric motors. Heavier e-scooters incorporate safety features, such as suspension systems and large pneumatic wheels, to absorb the shock from uneven terrain.
Good suspension and large wheels are important to navigate safely. Heavier e-scooters also have better brakes, such as hydraulic disc brakes on both wheels.
To save on weight, lighter e-scooters use "electronic brakes", where its electric motor generates a braking force. Electronic brakes are much less effective than disc brakes.
Although e-scooters also have foot brakes, these require the rider to balance on one leg, not optimal if a collision occurs. Furthermore, foot brakes quickly lose effectiveness in Singapore's damp weather.
Finally, would the 20kg limit on e-scooters reduce the impact in a collision?
Suppose a rider and his groceries weigh 120kg. On a 20kg scooter, he collides into an object at 10kmh, while on a 30kg scooter with better brakes, he collides at 9kmh. Based on my calculations, the force on impact is actually 3.6 per cent less for the heavier scooter.
Even if they collide at the same speed, the difference in force is only 7 per cent.
Heavier e-scooters with better braking systems will tend to collide at a lower speed than lighter ones, assuming the brakes are applied at the same time. Even if they collide at the same speed, the difference in force is only 7 per cent.
The Government says active mobility is a "key pillar" of its vision for transport in Singapore (Registration, plates for e-bikes to boost safety; Jan 11) . To support this, we must allow Singaporeans to choose PMDs suitable for the terrain and distances they commute. Also, a weight limit of, say, 35kg, would be more reasonable.
Keith Tang Tien Wei
A version of this article appeared in the print edition of The Straits Times on April 11, 2017, with the headline 'Relook weight limit for heavier, 'safer' e-scooters'.