Banking on curves...

[Jacktal]

I know that prototype railroads use some degree of banking on curves to allow more stable running at higher speeds.I suppose that the banking varies whether the track is intended for slower freights or high speed passenger service,and is also dependent on the curve radius and possibly other geographical restraints.I'm also wondering if railroad builders do start the banking slightly ahead of the curves,sort of "banking easement",so that the trains kind of "flow into the curve" for maximum passenger comfort and reduced stress on rolling stock.

I'm planning a future layout and would like to add banking to the curves,and since I'd like to run a Bullet type train on one of the tracks,it would look much more realistic with proper banking.Could someone tell me more?Thanks.

[ericboone]

You are correct about the easements into super elevated curves. Just like the curves themselves should have easements, so should the super elevation. The transition from normal track and super elevated track should start and end just like easements for the curves themselves.

[DSchmitt]

The superelevation used is determined based on degree of curve (how sharp it is) and the speed of trains. Since most lines have trains running on them at different speeds the number picked is a compromise. Not enough and the fast train could derail. Too much could result in slow trains tipping over.

From the book - Railway Track and Maintenance - available from the NMRA
"Runout of Superelevation"
"........ the uaual practice on circular curves is to form the runout on tangents and give full superelevation for the entire length of curve.......... "When transition curves are used, the runouts should coinside with them." It also says that with some transition curves the runout may extend into the tangent so that the change in elevation of the rail is not too abrupt.

[Jacktal]

Thanks for the very nice answers.However,I don't have any specialized information (books,etc) nor any degree in engineering.Let's say I want to have an average slant for both passenger and freight trains on most of my tracks and possibly have a dedicated "Bullet" train track,what would then be reasonable banking angle(s)?
I will have radiuses between 18 and 22 in. (in "N" scale) on my main lines.Thanks.

[DSchmitt]

The general consensus is that superelevation is not necessary to good operation on a model railroad. Too much is definately detrimental just as it woud be on the prototype.

The purpose for superelevation on a model railroad is therefore scenic. It adds to the realism of a model scene.

The outside rail is raised enough to be visible, but not enough to cause operational problems. Lifting the ouside rail a distance equivilent to the thickness of a couple sheets of paper (perhaps the thickness of a single 3 x 5 card) will work. The rail is stiff enough that the runout should take care of its self.

[Leon Silverman]

One other caveat about curve banking: Curved turnouts are a no-no unless yopu are going to a lower level branchline. If you are running long wheel base steam engines or tenders with a centipede configuration or 8-wheel trucks, turnouts should be positioned beyond any banked portion of your track for reliable operation since the equalization (conformity to track irregularity) on these long wheel based trucks is non-existent in HO or smaller scales.