Your arborvitae (Thuja occidentalis) are fairly tolerant of various soils and locations but need both consistent moisture at the roots and soil that drains well. Compacted soil that does not drain or inadequate irrigation during hot, dry periods would both result in this kind of damage.
There are also a few pests and diseases that could create this pattern of dieback and that can afflict arborvitae. Look closely at the needles, stems and trunk for further evidence.
Leaf blight would most commonly begin at the branch tips but is similar in appearance; look for any unusual growth on the leaves. Canker is caused by fungal spores entering wounds in the trunks or branches; look for sunken areas on the woody parts. More likely, given the appearance, is root rot. There are several types that attack arborvitae and result in plant starvation. They can stem from the irrigation issues discussed above. Some can be identified by evidence of disease at root line. Scale insects and spider mites can also be a problem and it would be worthwhile to examine the plants closely for any signs of these tiny insects.
You may want to consult with a certified arborist for help. You can find one in your area by referring to the International Society of Arboriculture (http://www.isa-arbor.com/).