Bay Area Rapid Transit (BART) is a rapid transit public transportation system serving the San Francisco Bay Area in California. The heavy rail elevated and subway system connects San Francisco and Oakland with urban and suburban areas in Alameda, Contra Costa, and San Mateo counties. BART serves 48 stations along six routes on 112 miles (180 km) of rapid transit lines, including a ten-mile spur line in eastern Contra Costa County which utilizes diesel multiple-unit trains and a 3.2-mile (5.1 km) automated guideway transit line to the Oakland International Airport. With an average of 423,000 weekday passengers and 124.2 million annual passengers in fiscal year 2017, BART is the fifth-busiest heavy rail rapid transit system in the United States. Map of the system What Makes the BART Unique: The BART of course is a heavy rail rapid transit system, which I think would make an interesting addition to Train Sim World. Now this seems highly unheard of since there has never been a heavy rail route in Train Simulator before and seems very unlikely since when we think of heavy rail, we're likely to think mostly underground subway trains. However, a portion of the BART is over ground with only 15 underground stations out of 48 total stations. Another thing that makes the BART unique is that it serves 2 major cities; San Francisco and Oakland (there's also plans to extend down to San Jose). Now I understand that the system is huge and probably won't completely fit into one route, if I were to pick a line to use as a route I would choose the Antioch-SFO/Millbrae Line. The reason I choose this line in case DTG can't fit the whole system is because it goes through different kinds of scenery such as from an urban environment into a more suburban environment, not only that but the line also goes through the famous Transbay Tube which is a tunnel that goes under the San Francisco Bay connecting both San Francisco and Oakland. The BART does not use standard gauge tracks unlike most American rapid transit systems, instead they utilize in 5 ft 6 gauge tracks which are common in countries such as India, Pakistan, Sri Lanka and Argentina. Transbay Tube Operations: The BART consists of 5 main lines; Antioch-SFO/Millbrae Line (Yellow), Richmond–Warm Springs/South Fremont line (Orange), Warm Springs/South Fremont–Daly City line (Green), Richmond–Daly City/Millbrae line (Red), and Dublin/Pleasanton–Daly City line (Blue). On weekdays after 6 PM and on weekends, both the Warm Springs/South Fremont–Daly City line and Richmond–Daly City/Millbrae line are out of service leaving only the other 3 lines taking over. Rolling Stock: There are currently 4 main sets of rolling stock on the BART, Rohr Class A, Class C units which were manufactured by both Alstom and Morrison-Knudsen, and Bombardier Class D. The Class A units are the oldest sets dating back to the late 60s, the Class C1 units date back to the 80s, and the Class D units just recently entered service in January 2018. Rohr Class A Alstom / Morrison-Knudsen Class C Bombardier Class D Conclusion: In my opinion, I feel that a heavy rail system like the BART would be a nice twist for Train Sim World (or Train Simulator). I'll be glad to hear what others have to say about this idea.