Autostrada A51

{{Short description|Controlled-access highway in Italy}}

{{Use dmy dates|date=June 2024}}

{{Infobox road

| country = ITA

| type = A

| route = 51

| alternate_name = Tangenziale Est di Milano
Milan east ring road

| established = 1973

| beltway_city = Milan

| direction_a = South

| terminus_a = Milan

| junction = 23px A1 in Milan
23px A52 in Cologno Monzese
23px A4 in Agrate Brianza

| direction_b = North

| terminus_b = Usmate Velate

| length_km = 29.4

| regions = Lombardy

| map = Italia - mappa autostrada A51.svg

| map_notes = The motorway A51 and the connecting motorways

| previous_type = A

| previous_route = 50

| next_type = A

| next_route = 52

| maint = Milano Serravalle - Milano Tangenziali

}}

File:Mappa autostrada A51.svg

Autostrada A51 or Tangenziale Est di Milano ("Milan east ring road"){{Cite web |url=http://www.aiscat.it/pubblicazioni/downloads/mensile-dic-09.pdf |title=A pag. 8 |access-date=2020-04-01 |archive-date=2013-10-16 |archive-url=https://web.archive.org/web/20131016102523/http://www.aiscat.it/pubblicazioni/downloads/mensile-dic-09.pdf |url-status=dead }} is an autostrada (Italian for "motorway") {{convert|29.3|km}} long in Italy located in the region of Lombardy and tangent to the city and suburban area of Milan in its eastern part, managed by Milano Serravalle – Milano Tangenziali.

Together with the Autostrada A50 (Milan west ring road), the Autostrada A52 (Milan north ring road) and the Autostrada A58 (Milan external east ring road), it is the largest system of ring roads around a city in Italy, for a total length greater than {{convert|100|km}}.{{cite web|url=https://www.milanocittastato.it/evergreen/forse-non-sapevi-che/7-curiosita-sulla-tangenziali-di-milano/|title=7 cose che forse non sapevi delle TANGENZIALI di Milano|access-date=13 June 2024|language=it}} By adding the urban sections of Autostrada A1 and Autostrada A4, which runs parallel to the Milan north ring road by connecting Autostrada A51, Autostrada A50 and Autostrada A58, to the four ring roads, a system of urban highways that totally surrounds the city. The traffic flow that affects this stretch of motorway is over 170,000 daily transits.{{cite web|url=http://www.serravalle.it/doc/47testi_2Bilancio_07.pdf|title=Bilancio 2007 della Milano Serravalle Milano Tangenziali Spa|access-date=19 May 2019|language=it}}