Just use the speed of light as base and measure the distance in time units (implying *c). 100 psc (lightpicoseconds) are a bit more than 1⅛ inch, 4 ~ 1 mm, 1 nsc (lightnanosecond) is 1 foot or 29.9 cm, 1 μsc (lightmicrosecond) ~ 299 m. Would be totally possible. Within city boundaries we should introduce a speedlimit of 1 pc (picolightspeed), pretty easy to implement.