In determining the appropriate transportation mode by evaluating the trade-off between cost and service, both carrier rates and load size are crucial factors. Carrier rates directly impact the cost associated with transportation, while load size influences the efficiency and type of transportation method chosen. Larger loads may benefit from bulk shipping methods, which can be more cost-effective, while smaller loads might be more adequately served by less-than-truckload carriers. Thus, considering both carrier rates and load size together provides a comprehensive approach to modal determination.