Editing Altamont Corridor Express (section)

{{Short description|Commuter rail service in Northern California}}
{{Use American English|date=April 2024}}
{{Use mdy dates|date=April 2024}}
{{Infobox public transit
| name = Altamont Corridor Express
| image = Altamont Corridor Express logo.svg
| imagesize = 200px
| image2 = ACE Altamont Pass.jpg
| imagesize2 = 300px
| caption2 = Altamont Corridor Express train climbing its namesake [[Altamont Pass]]
| owner = San Joaquin Regional Rail Commission
| area served = [[San Joaquin Valley]], [[Tri-Valley]] and [[Silicon Valley]]
| transit_type = [[Commuter rail]]
| stations = 10
| daily_ridership = {{American transit ridership|CA Stockton ACE total daily}} ({{American transit ridership|dailydate}}){{American transit ridership|dailycitation}}
| annual_ridership = {{American transit ridership|CA Stockton ACE total annual}} ({{American transit ridership|annualdate}}){{American transit ridership|annualcitation}}
| headquarters = [[Robert J. Cabral Station]]<br />[[Stockton, California]]
| website = {{URL|acerail.com}}
| began_operation = {{start date and age|1998|10|19}}<ref name=acehistory />
| operator = Herzog Transit Services
| marks = ACEX<ref name="RailServe">{{cite web |title=AAR Railroad Reporting Marks (2015) |url=http://www.railserve.com/aar_railroad_reporting_marks.html |website=Railserve |access-date=June 28, 2016}}</ref>
| host = [[Union Pacific Railroad|Union Pacific]] (Stockton–Santa Clara)<br />[[Caltrain]] (Santa Clara–San Jose)
| vehicles = 10 locomotives, 30 passenger cars
| train_length = 1–2 locomotives, 4–8 passenger cars
| system_length = {{convert|85|mi|km|abbr=on}}
| track_gauge = {{Track gauge|ussg|allk=on}}
| average_speed = {{convert|39|mph|km/h|abbr=on}}
| top_speed = {{convert|79|mph|km/h|abbr=on}}
| map = {{switcher
|{{maplink-road|from=Altamont Corridor Express.map}} Altamont Corridor Express highlighted in purple <hr />
|Show interactive map
|{{Altamont Corridor Express|inline=yes}}
|Show route diagram
}}
}}

The '''Altamont Corridor Express''' (also known as  '''ACE''', formerly '''Altamont Commuter Express''') is a [[commuter rail]] service in [[California]], connecting [[Stockton, California|Stockton]] and [[San Jose, California|San Jose]] during peak hours only. ACE is named for the [[Altamont Pass]], through which it runs.<ref name="Solomon_2013">{{cite book|last1=Solomon|first1=Brian|title=North American Railroad Family Trees : An Infographic History of the Industry's Mergers and Evolution|date=2013|publisher=Voyageur Press|location=Minneapolis, MN|isbn=978-0-7603-4488-0|page=127}}</ref> Service is managed by the '''San Joaquin Regional Rail Commission''', and operations are contracted to Herzog Transit Services.<ref name="Solomon_2013" /> The {{convert|86|mi|adj=on}} route includes ten stops, with travel time about 2 hours and 12 minutes end-to-end. In {{American transit ridership|annualdate}}, the line had a ridership of {{American transit ridership|CA Stockton ACE total annual}}, or about {{American transit ridership|CA Stockton ACE total daily}} per weekday as of {{American transit ridership|dailydateasof}}. ACE uses [[Bombardier BiLevel Coach]]es, [[EMD F40PH|MPI F40PH-3C]] locomotives, and [[Siemens Charger]] locomotives.

Service began on October 19, 1998, with two weekday round trips. A third round trip was added in May 2001, followed by a fourth round trip in October 2012. Saturday service commenced in September 2019. {{As of|2018}}, average weekday ridership was 5,900.<ref name=apta>{{cite web |url=http://www.apta.com/resources/statistics/Documents/Ridership/2018-q2-ridership-APTA.pdf |title=Transit Ridership Report: Second Quarter 2018 |date=August 24, 2018 |publisher=American Public Transportation Association |access-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181004062506/https://www.apta.com/resources/statistics/Documents/Ridership/2018-Q2-Ridership-APTA.pdf |archive-date=October 4, 2018 |url-status=dead }}</ref>

The tracks are owned by [[Union Pacific Railroad]], previously built along the [[Western Pacific Railroad]] main line. Under the ACE''forward'' program, a number of improvements to the service are being considered. These include a rerouted line through Tracy, an extension to [[Modesto]] and [[Merced]], and connections to BART at Union City and Tri-Valley.