Analysis of variance for the effects of independent variables on UPCI
Results indicated that UPCI was significantly different among semi-arid, sub-humid and Mediterranean climates (P < 0.01). Road maintenance strategy with varying levels of budget had a significant effect on UPCI values, as a lower UPCI was observed for low budget maintenance roads (P < 0.01). Results indicated that traffic levels or severity on forest roads could significantly change the UPCI (P < 0.01). There were no significant interaction effects from the mentioned independent parameters on UPCI (P > 0.05), except for climate and traffic (P < 0.05; Table 6).
Effect of maintenance strategies with different budget levels on UPCI
Figure 5 presents a comparison among the mean condition of roads in different road maintenance strategies in Mediterranean, semi-arid and sub-humid climates. In all studied climate zones, UPCI values for roads were maintained with a low budget standard was significantly lower than two other budget classes (P < 0.05). For roads were maintained with a high budget in Mediterranean climate, the road in initial condition presented a mean UPCI of 9.16 and after one year a mean UPCI of 7.74 (annual deterioration 15.5%). Annual deterioration rate of forest roads in semi-arid and sub-humid climates were 15.6% and 23.9%, respectively. For roads were maintained with a medium budget in Mediterranean climate, the road in initial condition presented a mean UPCI of 8.79 and after one year a mean UPCI of 6.91 (annual deterioration 21.4%). Deterioration rate of forest roads in semi-arid and sub-humid climates were 14.1% and 26.4%, respectively. For roads were maintained with a low budget in Mediterranean climate, the road in initial condition presented a mean UPCI of 8.32 and after one year a mean UPCI of 6.54 (annual deterioration 21.4%). Deterioration rate of roads in semi-arid and sub-humid climates were 29.7% and 24.8%, respectively.
Effect of traffic levels and climate on UPCI
Figure 6 presents a comparison among the mean condition of roads in different traffic levels in Mediterranean, semi-arid and sub-humid climates. In all studied climate zones, UPCI values for roads with a low traffic was significantly higher than two other traffic levels (P < 0.05). For forest roads with a high-traffic volume in Mediterranean climate, the road in initial condition presented a mean UPCI of 8.3 and after one year a mean UPCI of 5.9 (annual deterioration 29.3%). Annual deterioration rate of forest roads in semi-arid and sub-humid climates were 19.8% and 31.0%, respectively. For roads with a medium-traffic volume in Mediterranean climate, the road in initial condition presented a mean UPCI of 8.7 and after one year a mean UPCI of 7.1 (annual deterioration 16.0%). Deterioration rate of forest roads in semi-arid and sub-humid climates were 18.6% and 20.2%, respectively. For roads with a low-traffic volume in Mediterranean climate, the road in initial condition presented a mean UPCI of 9.2 and after one year a mean UPCI of 8.2 (annual deterioration 10.9%). Deterioration rate of roads in semi-arid and sub-humid climates were 20.2% and 21.0%, respectively (Fig. 6). From the analysis of mean data it is observed that important difference exists among climates. Sub-humid climate significantly presented lower UPCI (7.19) compared to the two other climates. UPCI values for Mediterranean and semi-arid climates were 7.81 and 8.82, respectively (Fig. 7).
Analysis road condition performance curves
The road surface performance curves obtained from the simulation of time series for roads with different maintenance strategy and traffic levels are presented in Figs. 8. Each graph includes three curves, representing the performance observed under semi-arid, Mediterranean and sub-humid climates. In high traffic roads in semi-arid climate the UPCI curves shows same trend for all maintenance strategy (Fig. 8a) It is observed that, the mean UPCI decreased rapidly during one year in semi-arid climate, especially in high-traffic roads maintained by low budget level. The UPCI performance of medium and low-budget strategy were same in medium (Fig. 8b) and low traffic roads (Fig. 8c). In Mediterranean climate, similar trend is observed for different maintenance strategy for roads in each traffic levels of high (Fig. 8d), medium (Fig. 8e) and low (Fig. 8f). As expected for sub-humid climate, the UPCI value drops significantly during the first year of service especially in high-traffic roads due to the appearance of distresses caused by traffic and climate (Fig. 8g). High budget maintenance strategy in medium traffic roads can increase the service life of the road (Fig. 8h), while the UPCI performance of different maintenance strategy in low-traffic roads is same (Fig. 8i). In the last three to five years of service, a wearing course of road presents severe access problems and is in poor and very poor condition, resulting in UPCI values less than 4.
Determining time to deterioration and maintenance cycle
In Mediterranean climate where high and medium-traffic roads were maintained by high-budget strategy, deterioration time was longer than other maintenance strategies and number of maintenance per decade was lower, while in low-traffic roads, number of maintenance per decade after low-budget maintenance activities was more than those of other strategies. In semi-arid climate where high traffic roads were maintained by low-budget strategy, deterioration time was longer than other maintenance strategies and number of maintenance per decade was lower. In low and medium-traffic roads, maintenance cycle after high-budget maintenance activities was longer compared to the other strategies. In sub-humid climate, where high, medium and low-traffic roads were maintained by high-budget strategy, deterioration time was longer than other maintenance strategies and number of maintenance per decade was lower (Table 6).
Determining the cost-effectiveness of different maintenance strategies
The cost-effectiveness analysis evaluates the effects of maintenance strategy during the whole life cycle of a road. From this analysis, optimal maintenance strategy was defined for each traffic levels in different climate zones. In Mediterranean climate zone it was observed that CE values of low-budget maintenance strategy was more than other strategies in all traffic levels. In semi-arid climate zone, CE values of low-budget maintenance strategy were more than those of other strategies only in high-traffic roads. In medium and low-traffic roads, medium-budget maintenance strategy was more efficient based on CE analysis. In, sub-humid climate, CE values severely vary depending on the level of traffic. Medium, high and low-budget maintenance strategies were respectively efficient in high, medium and low-traffic roads based on CE values (Table 7).