330 strain criteria, established by the Shell Oil Company, ensures that per- manent deformation in the subgrade will not lead to excessive rutting at the pavement surface (133). The results summarized in Table 8.6 suggest that these pavements are not susceptible to functional deterioration, provided the desirable levels of moisture and loading conditions are maintained. 8.2.3 Summary The previous discussion has demonstrated that layer moduli from NDT tests can be valuable in predicting the response of a pavement to the combined effects of load and environment. Also, the use of the maximum deflections from NDT equipment as an indicator of structural adequacy may lead to erroneous interpretation. High deflections do not necessar- ily mean high stresses or a structurally deficient pavement. The computations for US 441 and SR 80 suggest that the performance and response characteristics of pavement materials are highly dependent upon the effects of moisture, temperature, and the properties of the asphalt binder. A pavement's resistance to load-induced cracking can be improved by either increasing the stiffness of support layers or using a lower viscosity asphalt to eliminate excessively high asphalt concrete moduli at the minimum pavement temperatures. In those environmental situations where rates of cooling and thermal stresses are very high, it is important that both factors, improved stiffness of underlying support layers, and softer asphalts, be incorporated in the pavement's struc- ture. Provision of proper drainage--adequate camber, side drains, free- draining materials, etc.--would help to ensure that the in-place materials would maintain desirable levels of strength.