T-shaped and crossed junctions based on graphene nanoribbons (GNRs) were designed and studied in this paper. These junctions were made of shoulders (ZGNRs) joined with stems (AGNRs). We demonstrated the intrinsic transport properties and effective boron (or nitrogen) doping of the junctions by using first-principles quantum transport simulation. Several interesting results were found. (i) The I-V characteristics of the pure-carbon T-shaped junctions were shown to have metallic behavior, and the current of the junction strongly depends on the height of the stem. (ii) The conductances of the devices are found to depend sensitively on their geometric structures and be controlled by selective doping. This feature could make such a quasi-2D carbon-based junction a possible candidate for nanoelectronic devices.