Western Railroad Discussion > turnout speeds

I have always wondered what is the maximum speed a turnout could be constructed for assuming the best conditions. I have looked at a numberof BNSF timetables and don't see anything above 40 MPH. Is that the MAX?

I believe that the NEC may have some super turnouts that allow speeds
in excess of 75MPH. They may be as long as 1/4 mile, maybe more.

Marty Harrison
MP208.1 on the UP's Sedalia Sub

In Europe there are some very high speed turnouts. For example in Britain, Colton Junction has a 125mph turnout.

Its all a matter of geometry...a shorter, higher degree of curvature turnout will always be a slower speed turnout than a longer, flatter curvature turnout. As example, a No. 9 turnout is around 75 feet in length (if I remember from a long time ago), and generally has a 10 mph turnout speed. A No. 24, on the other hand, is around 250 feet long, and is generally accepted as a 50 mph turnout (or has BNSF downgraded that to 40 mph?). That 125 mph turnout spoken about above I'm sure must be close to 800 to 1000 feet in length - almost like tangent track.

I should point out that length is generally measured from the point of switch to the location where the turnout track no longer fouls the straight rail track...roughly 14' center to center.

As you can see, a highspeed turnout is going to cost considerably more than a lower speed turnout, so you try to match the utility of the switch to the speed required. A yard track rarely needs anything greater than a No. 15 (usually 15 to 20 mph), while a highspeed Amtrak route would favor a No. 24. If the speed of track, however, is limited by curvature (or grade or a bridge or whatever) to 30 mph, then a No. 24 is a waste...just use a No. 20 and the trains won't know the difference!

We have 50 mph turnouts on the Clovis Sub. So that 40 mph restriction is probably for whichever sub you were looking at.
Chris S.

There are a couple of equlateral turnouts on Metrolink's San Diego Sub. (in Southern California) that are rated at 90 mph for passenger.

most high speed turnouts have a moveable frog to allow for higher speeds. most on UP are 40mph turnouts.
JC

Maximum Speed through a turnout is controlled by two factors, the mimimum radius of curvature occuring anywhere in the turnout and the allowable "underbalance".

Underbalance is the absense of super elevation since turnouts are typically flat. General FRA and AREMA limitations for maximum underbalance is 3" for freight and 4" for passenger. Typical turnouts in North America range from #4's in transit to the #30 UP Freight Turnouts and the #32.7775 Amtrack Passenger Turnouts used in the northeast. In Europe turnouts range up to #62's.

Turnout speed is usually calculated using the FRA/AREMA VMAX formula. A close approximation of the max speed may be had by multiplying the turnout frog number by two and adding two to five miles per hour.

nitewatchman

Railfool03 Wrote:
-------------------------------------------------------
> Its all a matter of geometry...a shorter, higher
> degree of curvature turnout will always be a
> slower speed turnout than a longer, flatter
> curvature turnout. As example, a No. 9 turnout is
> around 75 feet in length (if I remember from a
> long time ago), and generally has a 10 mph turnout
> speed. A No. 24, on the other hand, is around 250
> feet long, and is generally accepted as a 50 mph
> turnout (or has BNSF downgraded that to 40 mph?).
> That 125 mph turnout spoken about above I'm sure
> must be close to 800 to 1000 feet in length -
> almost like tangent track.
>
> I should point out that length is generally
> measured from the point of switch to the location
> where the turnout track no longer fouls the
> straight rail track...roughly 14' center to
> center.

I think mostly the length referred to on a turnout is the "lead", which is the distance from the tip of the switchpoints where you enter the turnout to the 1/2 inch point of the frog. The 1/2" point of the frog is where the two crossing rails diverge 1/2", and on the No. 9 turnout in your example would be 4 1/2 inches beyond the theoretical point of the frog.

AREA standards for a No 9 turnout call for a lead of 72 feet 10 1/2 inches, but this can vary a few feet on different railroads, or using different components, such as frog length, length switch points, heel spread, and point angle.

MTMEng,

You're absolutely right...its been a long time since I last laid out a turnout and had forgotten the measurement is generally to the frog. Thanks for the correction...