Yes, 40 km/h is a residential street speed limit, of about 25 MPH; this would not be a highway (Interstate or otherwise) limit, and it is in metric because this is the 21st century. Here, we see 40 km/h speed limit signs; that is in fact the default speed limit for all streets in Edmonton (Alberta) that are not otherwise posted, which in 2021 replaced the traditional 50 km/h (which was 30 MPH half a century ago).Plus when was the last time you saw speed limits posted for 40 km/h --was that in your residential area or on the interstate?
The 1.6 km is an obvious rounded conversion from the somewhat arbitrary one mile, just as the 4,536 kg is a conversion from the similarly arbitrary 10,000 pounds. It would make sense to round them to less precise values, but depending on the rounding direction that could incidentally render previously legal vehicles illegal.
Whether expressed as 40 km/h or as 25 MPH, this is a perfectly rational speed choice, distinguishing between vehicles to which the standard applies, and low-speed vehicles (such as neighborhood electric vehicles) which are exempt.
