IEffectof TruckWeight

Transcription

1 IEffectof TruckWeight Enforcement in the Kingdom of Saudi Arabia BY HAMAD 1.AL-ABDULWAHHAB r e government of Saudi Arabia has built an impressive modern highway system composed of more than 38,000 kilometers (km) of expressways and 8,00 km of two-lane, two-way roadways during the past two decades. The rapid development of Saudi Arabia s highway system, in less than 15 years, has accompanied a rapid growth of urbanization and industrialization. The road freight industry which provides basic goods, construction materials and fuel transportation services has developed rapidly both in volume and in weight. Truck fleet owners, in an attempt to maximize their profits, have often loaded their vehicles to maximum capacity. These heavily loaded vehicles have resulted in significant road and bridge damage. Many of these trucks exceed the safety margins of their designs, which might result in serious accidents and frequent breakdown of the trucks. This has led to premature rutting problems and bridge deck cracking shortly after opening pavement to traffic. The Ministry of Communications (MOC) realized the extent of the problem early in 1985 and moved quickly to protect the national highway network by enforcing legal truck weights. Weight Control Royal Decree Number M/9, issued in 1970, regulated the traffic system in general and permissible truck weights in particular. The part of this decree concerning weights was not implemented because of the small road network and the limited movement of goods at that Conversion Factors To convert multiulv by km mi time.1 However, because of the vast development in the past decade, the problems associated with truck overloading grew in magnitude, and the need to enforce truck weight limits became more and more urgent. Early in 1983, a number of field studies conducted by several agencies2, 3 indicated that 90 percent of all trucks weighed during the studies were in violation of the weight limits (Figure 1), carrying from 30 percent to as much as 300 percent more than the permissible loads. Figure 1 shows the legal truck weights, dimensions and penalties of overloaded trucks. Trucks are classified into eight classes. Classes 1 and 2 represent rigid-bodied trucks with two or three axles (RB2 and RB3). Classes 3 to 8 represent semitrailer trucks with towing tractor having two or three axles and single trailer having single, tandem or triple axle. Type, 6 and 8 are the only types operating on local roads. Table 1. Comparison of Vehicle Masses, In Tons Average Mass, Maximum Permitted Mass Saudi Arabia Average Vehicle M<O.C. in Traffic Saudi Type Class Streamr (%) Arabia USA, U.K. RB ,5 19! RB ,0 2,0 2s , S , s , Source: Cited reference 2,3 38 ITE JOURNAL NOVEMBER 1993

2 Type consists of two axle tractor and tandem axle tractor, commonly abbreviated as 2S2. Type 6 is a three axle tractor and tandem axle trailer (3S2) andtype 8 is a three axle tractor and triple axle trailer (3S3). Table 1 presents a comparison between average loaded truck masses operating on Saudi highways in the early 1980s and maximum permissible truck mass in the United States and United Kingdom. It also presents the legal maximum permitted mass in Saudi Arabia as regulated by the royal decree. Five truck types (RB2, RB3, 2S2, 2S3 and 3S3) are included, with RB3 and 3S2 representing 71 percent of all operating trucks. It also is clear that the majority of trucks were violating international and local weight limits. Before 198, 2S2 and 3S3 classes were violating weight limit by up to 50 percent and 100 percent, while in 1986 both classes were in violation of weight limit by 25 percent and 50 percent, respectively. Comparison of permitted axle groups loading for the same countries is shown in Table 2. The average loading of axle groups operating on Saudi highways for the same period is also presented. The multiaxle groups (TD and TR) are grossly overloaded when compared to local and international standards. In 1985, the MOC started to build 11 weigh stations on some of the busy highways to control the weight of trucks. At the same time, an information campaign about the need to control truck weights was carried out in the media. Although weigh stations were operational early in 1986, overweight penalties were not collected; rather, a grace period was granted to truck owners to convert their fleets to the national truck standards (Figure 1). The grace period ended in mid-1986, and the MOC started to enforce weight limits and collect overweight penalties. Currently, there are 28 weigh stations in operation locally (see Figure 2). 1 M.O.C* TRIJCK class TRUCKTYPE 1 MAX AXLE WEIGHT ( TONS) SR,300 PfNA-TY DIMENSIONS NAx. AXLE SR.300 INCREMENT. Wss PENALTY WElOl+_r ATWEICI Al WEI13HT, INCREMEI mns) ]5]6 TONS OFTON ~[~ LENGTH WIDTH HEIGHT [m) (m) m g : I I IGW 26 3 Q&q 32 6, m %EH I I! I ,,Jk+=# L-L c o o L!@%l _ o o I I I I I ++ M O,C - M,n,stry of Commumc.t, cos $1 = SR 3.75 Figure 1. Saudi Arabia s national truck standards. Y\ -%. 18 2, SAUDI - 7?% /71? Study Approach This study was conducted shortly after the enforcement of truck weight limits began. The main objectives were to evaluate the effect of the weight enforcement program on loaded trucks characteristics. The study covered three major Figure 2. Weigh station locations currently in operation. \ 0 ITE JOURNAL NOVEMBER 1993

3 provinces in the Kingdom of Saudi Arabia: the Eastern, Central and Western provinces. Two major six-lane divided highways were selected in each province. Truck weights were monitored by the existing weighing stations on each highway, and traffic volumes were recorded using classified traffic counters to recognize vehicle type and speed on each lane of the highway. Tire pressures of weighed trucks also were measured for one side of the truck and recorded. Data were analyzed statistically, and the general findings are summarized in this article. Traffic Characteristics The characteristics of truck traffic operating in the three major provinces of Saudi Arabia are presented in Table 3. The table indicates higher percentages of trucks in the coastal provinces (Eastern and Western) than in the Central region. Moreover, 60 percent to 70 percent of trucks use the outer-right lane of the highway. The size distribution of the truck fleet has shifted. Before the implementation of weight limits, the major types of trucks operating were RB3 and 3S2 (Table 1). However, after the implementation of weight limits, the major truck type became 2S2. This indicates a major reduction in the percentages of RB3, 3S2 and 3S3 trucks operating in Saudi Arabia. The 3S3 truck type has been reduced to less than one percent in all three provinces. The truck owners feel that more net load can be transported by the 2S2 truck under the current load regulations than by the other trucks and on fewer tires. 100 c 90- g c ; 60- $. al 50- : % E 20-2 loo I Psi ~-- ~ ~- ~ kpo Tire Pressure Figure 3. Cumulative tire pressure distribution. Table 2. Comparison of Axle Group Loadings, in Tons Axle Saudi Arabia Saudi Maximum Permitted Group (Average) Arabia U.S.A. U.K SD ,0 TD ,0 TR Notes: SS = single axle, single tire SD= single axle, dual tires TD = tandem axle TR = triple axle Truck Loading Rational evaluation of the impact of increasing truck loads on life of high- Table 3. Characteristics of Truck Traftic Operating on Saudi Roads Trucks on Each Lane (%) Trucks According to Type (??) Trucks in Traffic Outer Province Streamr (%) Right Central Left RB2 RB3 2s2 3S2 3s3 Eastern 5, Central 28, ,3 0.7 Western , ITE JOURNAL NOVEMBER

4 way pavements is necessary to obtain realistic input data for design of new pavements and rehabilitation of existing pavements. Spectrum of axle loads operating on the highway system are converted into equivalent number of applications of 8.2 ton standard single axle load with dual tires on either side (EAL). This is accomplished through the use of the concept of load equivalency factor. The load equivalency factor of a given axle loading is defined as the number of applications of 8.2 ton standard axle, that is equivalent, in terms of pavement damage, to one application of the axle load under consideration. The concept of load equivalency factor was developed from the American Association of State Highway and Transportation Officials (AASHTO) Road Testb based on the criterion of present serviceability index (PSI). Despite several limitations and criticism, the results of the AASHTO Road Tests are most widely used for pavement damage analysis. The socalled fourth power law, which states that the pavement damage is proportional to the fourth power of the axle load, has been one of the most significant contributions of the AASHTO Road Tests. This means if axle load is increased to twice the EAL, one application of this axle will cause the same amount of damage to the pavement as 16 applications of the EAL. As a result of the AASHTO Road Test and subsequent extension studies, the following relationship has been developed to obtain equivalences of other axle configurations relative to the standard axle. EAL = ; [1] [1 where, P = axle load (ton) s = 5. ton for single axle with single tires; 8.2 ton for single axle with dual tires; 13.6 ton for tandem axle with dual tires; and 18.5 ton for triple axle with dual tires. The above equations were used to determine EALs for each individual truck that was weighed. EALs of various trucks belonging to a particular type were then grouped together and their mean value was determined. The results are summarized in Tables, 5 and 6 for the Eastern, Central and Western provinces, respectively. The tables show maximum, minimum and average axles and truck weights recorded, percentages of violations of MOC weight limits and percentages of fined trucks. Overloaded trucks are fined only if the overloading exceeds 10 percent of Table, Truck Loading Summary, Eastern Province Minimum Maximum Average Gross Gross Gross MO, C. Truck M, O.C. Axle Axle Average Weight Weight Weight Limits % Type Class # Type EAL Ton Ton Ton Ton Violation Fined RB SD 1, Gross , RB3 2 2 TD 1, } Gross , s2 2 SD TD , } } Gross , , S2 6 2 TD , } TD 1, , } } Gross , s3 8 2 TD 1, , } TR } } Gross 11, O* A Penalties are based on gross weight, Table 1 2 ITE JOURNAL NOVEMBER 1993

5 the truck s weight limit. In such cases, a penalty of SR 300 ($80US) is collected. The penalty is increased by equal increments of SR 300 when the overloading is increased as shown in Figure 1. Tables to 6 indicate that the most damaging truck in terms of equivalent axle load is 3S3, followed by 2S2 for all provinces. Also, there are trucks carrying loads up to 60 tons to 68 tons still on the roads. The number of trucks violating weight limits is still high, while many fewer are penalized. This is attributed to the fact that more and more truck owners try to take advantage of the failure to penalize 10 percent overweight. For example, in the Eastern Province 60 percent of the 2S2 and 80 percent of 3S2 trucks violate the weight limits, while just 6 percent and 35 percent, respectively, are fined. Moreover, if a vehicle violates axle load limits while the gross vehicle load is less than the penalty limit, the vehicle will not be penalized although damage to the pavement will take place. In the Central and Western provinces, 38 percent and 2 percent of the 2S2 trucks violate axle load limits while 19 percent and 15 percent of those trucks violate the gross weight limits and only 5 percent and 6 percent are fined. Tire Pressures High tire pressure is known to be one of the major causes of pavement rutting, especially in surface layers, regardless of tire load magnitude., 5 The tire pressures on the American Association of State Highway Transportation Officials test road in 1959 were typically 75 PSI. The development of radial plytires, which reduce fuel consumption and operating costs, has attracted the attention of truck owners. The manufacturers recommended tire pressures for such tires range between 100 PSI and 120 PSI. The cumulative tire pressure distribution for all surveyed trucks is shown in Figure 3. The figure clearly shows that 50 percent of all trucks operate at tire pressures higher than 125 PSI. On the other hand, the lowest tire pressure recorded was 30 PSI with a tire pressure difference, between dual tires, of 60 PSI. This large difference means that only one tire is transferring a concentrated load to the pavement. The maximum tire pressure measured was 170 PSI. Conclusions Based on the comprehensive amount of data collected in this study, the fol- Table 5. Truck Loading Summary, Central Province Minimum Maximum Average Gross Gross Gross M.0, C, Truck M,0, C, Axle Axle Average Weight Weight Weight Limits % % Type Class # Type EAL Ton Ton Ton Ton Violation Fined RB2 1 1 Ss 1, SD 1, Gross Ss ,50 5, RB TD , } Gross , , Ss 1, s2 2 SD ! TD , } 0, } Gross , Ss L81O , S TD } 1 TD 0, Gross s3 8 1 Ss.320 6, TD, } , TR , } } 6 2,270 11!710 6,893 7 Gross , Penalties are based on gross weight, Table 1. ITE JOURNAL NOVEMBER

6 lowing points can be stated: Current weight limit enforcement is not enough; a more rigorous enforcement program is needed. The weight limit and penalty schedule should be revised to prevent a shift of overloading from one truck type to another and also to prevent taking advantage of the 10 percent overweight with no penalties. Tire pressure must be checked as part of the enforcement program. High tire pressure will eliminate the benefits of weight control. Trucks must be penalized for violating the axle load limits as well as truck weight limits. Acknowledgment The author would like to thank King Fahd University of Petroleum and Minerals and the Ministry of Communications for their valuable support throughout this study. References 1 Mufti, Rasin and Khalid A1-Rashid. Monitoring Truck Weights, The Experience. Proceedings of the Third [RF Middle East Regional Meeting. Vol. 6 (February 1988): Pearson-Kirk, Donald, and Saleh A1-Idi. Traffic Loadings on Road and Bridge Structures. Proceedings of the First Saudi Engineering Conference. Vol. 2 (May 1983): Pearson-Kirk, Donald, Abul Azad, Mohammed Baluch, Mustafa A1-Mandil and Alfarabi Sharif. Vehicular Loading on Highway Structures. Proceedings of the Second Saudi Engineers Conference. Dhahran, Vol. 1 (November 1985): Phang, Willam A. Rutting-The Contribution of High Tire Pressure and Remedial Measures. Proceedings of the Third IRF Middle East Regional Meeting. Vol. 6 (February 1988): A1-Abdul Wahhab, Hamad and Rezgallah Ramadhan. Prediction of Pavement Rutting in Eastern Province of Saudi Arabia. The Arabian Journal for Science and Engineering. Vol. 15, No. 3 (holy 1990): B Hamad I. Al- Abdul Wahhab, Ph. D., is an associate professor in civil engineering at the King Fahd University of Petro - leum and Minerals, Dhahran, Saudi Arabia. He received his doctorate in transportation engineering from Oregon State University. He has participated in a number of funded projects dealing with programming pavement maintenance and the evaluation of highway and airport pavements. Table 6. Truck Loading Summary, Western Province Minimum Maximum Average Gross Gross Gross MO. C, Truck MO, C. Axle Axle Average Weight Weight Weight Limits % %* Type Class # Type EAL Ton Ton Ton Ton Violation Fined RB2 1 1 Ss ,890 5, SD Gross , Ss , RB3 2 2 TD ,10 9, } Gross , ,5 1 Ss s2 2 SD 1,00 19,600 9, TD 1, } 1, } Gross 5,761 10, , Ss , S2 6 2 TD 1, , } TD 1,210 1, } 1,090 16, } Gross , Ss s3 8 2 TD 1, o } TR , } ,12 7 } Penalties are based on gross weight, Table 1 Gross , ITE JOURNAL NOVEMBER 1993