  The interlock drive system generates traction by penetrating narrow
articulated spikes into the ground and by using the strength of the deeper soil
layers to resist horizontal draft forces. The system promises good tractive
performance in low gravity environments where tires generate little traction
due to low vehicle weight. Possible applications include heavy-duty vehicles
for civil engineering tasks like earthmoving or mining excavation. Safe vehicle
operation in complex terrain geometry requires lateral vehicle stability to
prevent vehicle rollover. Good lateral stability is a particular requirement
for excavation and piling operations where the margins of safety define the
terrain geometry that can be worked in, and it is a major constraint in
operational planning. An earthmoving vehicle that can operate at a high roll
angle reduces the need to maintain ramps in pits and on piles and can shorten
and simplify the paths for individual maneuvers. Here we report on several
field trials on the lateral stability of an earthmoving vehicle that uses the
interlock drive systems. We find that the vehicle can work well at roll angles
of up to 20{\deg}, but that it needs further improvement if work at roll angles
of 30{\deg} or more is required.
