def all_ped_combos_lsts(num_locs=4, val_set=("0", "1")):
    """Return a list of all pedestrian observation combinations (in list format) for a vehicle under the 4 location scheme"""
    res = []
    if num_locs == 0:
        return []
    if num_locs == 1:
        return [[flag] for flag in val_set]

    for comb in all_ped_combos_lsts(num_locs - 1, val_set):
        # append a flag for all possible flags
        for flag in val_set:
            appended = comb + [flag]
            res.append(appended)
            
    return res