The Long Haul Trucking Company is developing metrics for its drivers. The company computes variable costs of each load based upon miles driven and allocates fixed costs based upon time consumed. Load costing standards consider safe driving speeds and Department of Transportation regulations on hours of service (the amount of time the driver can be on duty or drive). The most effective metric for driver performance would likely be
a. Contribution per mile driven.
b. Gross margin per mile driven.
c. Achievement of delivered loads in allowed times.
d. Percentage increase in delivered loads below standard.