Understanding the growth mechanisms of nanowires is essential for their successful implementation in advanced devices applications. In situ ultrahigh-vacuum transmission electron microscopy has been applied to elucidate the interaction mechanisms of titanium disilicide nanowires (TiSi2 NWs) on Si(111) substrate. Two phenomena were observed: merging of the two NWs in the same direction, and collapse of one NW on a competing NW in a different direction when they meet at the ends. On the other hand, as one NW encounters the midsection of the other NW in a different direction, it recedes in favor of bulging of the other NW at the midsection. Since crystallographically the nanowires are favored to grow on Si(110) only in the [1-10] direction, this crucial information has been fruitfully exploited to focus on the growth of a high density of long and high-aspect-ratio Ti suicide NWs parallel to the surface on Si(110) in a single direction. The achievement in growth of high-density NWs in a single direction represents a significant advance in realizing the vast potential for applications of suicide NWs in nanoelectronics devices.