SUMMARY: To address the problem of rear underride crashes@ Federal safety standards require heavy trailers and semitrailers to be equipped with underride guards. Compliance with these requirements is not practicable for vehicles featuring work-performing equipment mounted in the area where an underride guard would normally be located. These trailers and semitrailers are designated as ????special purpose vehicles???? and are excluded from the standard. On November 5@ 2004@ we published a final rule amending the definition of ????special purpose vehicles???? in order to clarify the exclusion by specifying the dimensions of the area where the work-performing equipment must reside or pass through in order for the exclusion to apply. On December 14@ 2004@ we were petitioned by the National Truck Equipment Association to reconsider the final rule because the amendment has had an unintended effect of narrowing the exclusion applicable to ????special purpose vehicles.????In response to that petition for reconsideration@ this document further amends the definition of a ????special purpose vehicle???? to exclude a specific group of vehicles that cannot comply with the underride guard requirements in a practicable manner.