These are some engineering constraints to keep in mind when crayoning your own transit routes and proposals.
This page incorporates contributions from the following individuals: RailsRoadsRiverside; ArchBoston users JeffDowntown and The EGE; Reddit users r/Graflex01867 and r/CreatureXXII.
Light Rail
Maximum grade: 4% (unlimited length), 6% (up to 2500 feet), and 7% (up to 500 feet)
Minimum turning radius:
- The industry standard is 82 ft (25 m). This allows you to use most off-the-shelf Light Rail Vehicles (LRVs) without heavy customization.
- MBTA Green Line, however, has much tighter curves due to being a legacy system. This (and other info about Green Line) have been surveyed in this MIT Thesis in great detail, and other ArchBoston users have provided their digests.
- TL;DR: 45′ anywhere, 49′ non-revenue with simple yard modifications, 60′ revenue. (Note that Park St inner loop is 49′, and it’s very useful in Green Line Reconfiguration concepts.)
- The EGE mentioned that the smallest off-the-shelf LRVs have a turning radius of 66 ft.
Heavy Rail
I’m not sure if there exists an industry standard, but here’s some info from a few heavy rail systems:
Maximum grade:
- On the New York City subway system, the maximum grade is 5.5% (for 390′), and there’s a 5.4% grade for much longer distance (928′). (Source)
- MBTA’s Red Line has maximum grade of 4% (for 1200′). Orange Line has a very short segment with a 5.6% grade (for 60′); otherwise, the maximum grade is 4% (for 750′). (Source: MBTA vehicle procurement technical specifications)
Minimum turning radius:
- On the NYC subway, for routes that can operate 75′ cars, there’s a minimum radius of 145′. However, they’re hard to navigate for 75′ cars, so all new cars are now 60′. (Source, original discussion no longer accessible) (I think they also have tighter curves for routes that only use 60′ cars, but I’m not sure.)
- MBTA’s Red Line has a minimum radius of 250′, presumably the Harvard curve. (There’s a permanent speed restriction there because of the tight curve, which may potentially limit RL’s headways, so that’s not ideal.) Orange Line has a minimum radius of 440′. (Source: MBTA vehicle procurement technical specifications)
- Note that Red Line’s cars are 69′ long, and Orange Line’s cars are 65′ long.
- Toronto Rocket has a minimum turning radius of 75 m (246 ft), and their cars have length 75′. (Thanks to this Reddit comment)
Mainline Rail
Maximum grade: Most info I can find seem to suggest 4%. (citations TBA)
Bus
Maximum grade: 6% to 8% (Citation 1, Citation 2)