Sand barrels in work zones

Iowa uses a standard barrel array for all work zone situations – 15 barrels total, laid out as follows, starting from the rear:
(2) 2100 lbs.
(2) 1400
(2) 1400
(2) 700
(2) 400
(1) 700
(1) 400
(1) 200
(1) 200
(1) 200