Which headquarter's truck has the highest shipments in year 2016?
in 2016 refers to CAST(ship_date AS DATE) = 2016; make = 'Peterbilt' means headquarter is 'Texas (TX)', make = 'Mack' means headquarter is 'North Carolina (NC)', make = 'Kenworth' means headquarter is 'Washington (WA)'; highest shipment refers to MAX(COUNT(ship_id))
SELECT CASE WHEN T2.make = 'Peterbilt' THEN 'Texas (TX)' WHEN T2.make = 'Mack' THEN 'North Carolina (NC)' WHEN T2.make = 'Kenworth' THEN 'Washington (WA)' END AS "result" FROM shipment AS T1 INNER JOIN truck AS T2 ON T1.truck_id = T2.truck_id WHERE CAST(T1.ship_date AS DATE) = 2016 GROUP BY T2.make ORDER BY COUNT(T1.ship_id) DESC LIMIT 1