長豊橋, Steel bridge in Chiba Prefecture, Japan

The Nagatoyobashi is a 509.6 m steel bridge on National Route 408 over the Tone River, linking Tagawa in Kawachi, Ibaraki Prefecture, with Ryūdai in Narita, Chiba Prefecture. Its deck is 7.0 m wide and has no sidewalk, and the road shoulders are extremely narrow. The superstructure combines three-span and two-span continuous plate girders with three simple through Langer arches of 80.16 m each.

Residents of Nagao and Kanetsu villages in Ibaraki and Toyosumi and Namekawa villages in Chiba campaigned for a Tone River crossing, led by the Nagao village mayor. The bridge opened on 15 February 1968, completing the Narita-Edosaki route, now National Route 408. Its name joins the first characters of Nagao and Toyosumi.

The name Nagatoyobashi combines the first characters of Nagasao (長竿) and Toyosumi (豊住), the villages on the Ibaraki and Chiba sides that campaigned for the crossing. The bridge is managed by the Ibaraki governor, with upkeep costs split evenly between the two prefectures.

The bridge has no sidewalk and the roadway shoulders are extremely narrow, so walking across is not provided for. It carries one lane in each direction; the Nagatoyo-bashi intersection with National Route 356 on the Chiba side suffers chronic congestion from right-turning vehicles, eased after a right-turn lane was added in July 2007.

The name combines the first characters of Nagao village (長竿) in Ibaraki and Toyosumi village (豊住) in Chiba, the two communities whose residents campaigned for the crossing. The bridge has no sidewalk and very narrow road shoulders, so pedestrians cannot cross it.