Location and road geometry at weigh station

The WIM system should be installed away from acceleration or deceleration or gear change areas (traffic lights, toll stations or slope sections). This is to ensure weighing the vehicles travelling at uniform speed. 

It is also desirable to avoid areas where lane change is encouraged. 

With regard to the road geometry, the longitudinal and transverse slope and radius of curvature before and after the weigh station are vital. 

According to European specifications for WIM systems in COST 323 (1997) (Jacob et al. 2002), the longitudinal slope should be less than 1% for the class I site or less than 2% for other class sites in the road section between 50 m ahead of and 25 m beyond the system. Similarly, at all class sites, the transverse slope should be less than 3% and the radius of curvature should be greater than 1000 m. However, in all cases, it is preferable to place the system in a straight road segment. 

The requirements set by ASTM E 1318 (2009) are similar to these. The Australian WIM specifications (Austroads 2010) specify road geometry requirements per type of weighing system used. 

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