Why do US and UK trains use different types of couplers?

Question

I know the automatic knuckle coupler was adopted in the US for safety reasons. Why isn't a similar coupler used in the UK as well?

Answer 1

Prior to the adoption of the knuckle automatic coupler, which was actually more than a hundred years ago, most U.S. trains used a link and pin coupling method. This was dangerous to train crews and made uncoupling cars difficult and slower.

Trains in Japan use knuckle couplers very much like, if not identical, to U.S. knuckle couplers. These are handy for all trains, but especially for freight cars.

The UK does have a much higher percentage of passenger train traffic and has found the screw and buffer system to be very reliable and safe. There has been no reason to change and the security of this coupling system has been an advantage. There is also the matter of communications and other connections, which can also be managed with knuckle couplers, but are separate connections.

Answer 2

On some older UK passenger coaches a side operated version of the US knuckle coupler is used, called the buckeye. But the differences arise nowadays mainly because in the US the main rail traffic is freight, which doesn't usually need electrical connections in the coupler, only pneumatic and mechanical. Also heavy rakes of wagons can stay coupled for long periods. So safety and strength was the main concern, and the AAR (American Association of Railroads) coupler (an autocoupler) was proven to be very safe and reliable.

However in Europe, which has a high passenger traffic percentage, many more trains need to be able to 'talk' to each other both pneumatically and electrically when coupled, especially now with increasing use of onboard computerised Train Management Systems. Also with high frequencies of coupling and uncoupling of multiple units at stations, a fully automatic coupling to do all that was needed. So in the UK the older coupler is the BSI (Bergische Stahl Industrie), and newer trains normally have either the Dellner or the Scharfenberg, with a few notable exceptions. These coupling remove the need for any personnel to go between vehicles, at least when they work correctly.

Answer 3

I have no idea. It really limits the freight business over there, as they just can't run big trains for lack of strong couplers. I assume the issue is backwards compatability. Changing over Europe's entire freight car fleet at once isn't really practical.

Passenger cars separating in accidents and T-boning each other has been a serious issue in the UK. They're starting to redress that, here is a good old American type H Tightlock on some UK passenger equipment. Now you're talking!
http://en.wikipedia.org/wiki/Image:Northern-321901-coupling-02.jpg
The box below the coupler isn't part of a Type H... that contains contact fingers that connect the cars electrically for controls and brakes.

Answer 4

Tonnage. And lots of it.

The couplers used in the US today are improvement on the original, the Janey Automatic coupler, aka, the "knuckle coupler."

These devices have high tensile strength necessary for keeping the coupler or draw bar from failing under heavy load. The standard couplers are rated for 240,000 lbs psi. Heavy duty couplers are necessary for even heavier trains, such as found on coal and some grain cars. Here they jump to 300,000, allowing for very heavy (16,000 ton) unit trains of coal and grain to operate without ripping themselves apart.

Rarely mentioned are the "shelf" type automatic couplers. Here, the knuckle is the same (usually type "F" with conventional draft gear utilizing "E" type couplers), but the outside will have an interlocking, male/female type arrangement that will reduce the "jack-knifing" that can occur under heavy load when in "buff" (That is to say, slack bunched, such as when using dynamic brake). These are usually found in inter-modal cars which, being much longer, are more susceptible to this phenomena.

Then there are the "double shelf" coupler. Here, this arrangement is four quadrant; that is to say, both sides, top and bottom. These will prevent jack-knifing as well as keep the couplers from "slipping" by or experiencing "cradle effect". This four way protection is found primarily on passenger equipment or on cars designed for the transportation of hazardous materials. In the event of a collision or derailment, it keeps one car from riding up upon the car ahead, possibly puncturing the tank.

Answer 5

Money. And we don't interchange very often between the two countries. So, we don't need matching equipment.