This week I pushed a couple of two foot gauge boxcars by hand around the yard. A little hard to start but once in motion easy to keep in motion. I have also had to move dead automobiles by hand and it seemed much harder. But with high presure rubber tires on a asphault road is there really a dircelable diffrence?
dircelable?
I bet he meant “discernible”.
direnable…yeah thats what I meant to say
Steel wheel on steel rail is very efficient. It is hard to get started because of static resistance is more significant then the dynamic resistance. With a rubber tired vehicle there is higher static resistance and dynamic resistance. You rare not just turning the wheel bearing but the rear end bearings and planetary and the driveline and a bunch of gears (or clutch packs and planetary gears in an automatic) in the transmission. But the biggest drag is the rubber tire on the pavement, not very efficient.
I wonder what the coefficient of friction is of one loaded boxcar and. one loaded 18 wheeler.
I heard someone say (don’t remember where, maybe here) that the coefficient of friction for one 18 wheeler was more than that of an entire train.
I remember talking to a guy that worked in a flour mill in Pendleton, OR back in the late 60s/early 70s. He said they used to pull the boxcars around with a rope.
I’ve heard a number of descriptions of the area of contact between a RR wheel and the rail, mostly coming in around the size of a quarter. That makes the total area of contact between a standard 4 axle freight car and the rail about that of a dollar bill. You could easily hide a couple of bucks under each of those 18 wheels on a semi.
And, while there is some flexing of both the rail and the wheel, it’s miniscule compared to the flexing in each of those 18 tires, even if the road hardly gives at all.
So, even using the extremely simplistic (and hardly scientific) comparison of two bucks under each wheel to one buck under all the wheels of a railroad car, you come up with one semi having the same rolling resistance as 36 freight cars.
The ease with which a rail car will roll gives credence to the railroader’s rule of always expecting a train (or in this case, car). It doesn’t take much to get them going, and once they are, they’re pretty quiet about it.
Yes but on a hundred car train there has to be at least 5 cars with flat wheels
So how would this rule apply to passenger trains? one automoble vs 1 passenger car that has 70 people on it?
I do not know if it is true, but, it is said that 2 men could push a N&W “J” on level track.
a J is a Locomotive?
A 4-8-4 Northern steam engine I believe.
Yes but the steel wheel cant go where the rubber tire can.
True enough. Each has its place in the overall scheme of things. We all just happen to prefer trains…
A modern tire may have a coefficient of resistance of between .005 and .01 (for a 4000 lb car and a .01 coefficient tire, you have to push the car with 4000X.01 for with 40 pounds of force to move it).
The steel wheel on steel rail coefficients I have seen quoted are on the .001 to .002 range – about 5 to 10 times improved over a rubber tire.
There is this thing called the Davis formula for train resistance, but it dates back to the journal (friction) bearing days – haven’t seen a roller-bearing version.
But trains can have a starting force that is large compared to the force to move at a slow steady speed. There is a journal bearing effect and roller bearings help. There is also a you-save-flanges-jammed-against-the-rails and perhaps some other starting force terms that you have even with roller bearings.
If you are moving heavy tonnage of a bulk commodity at slow speeds, the low resistance of the steel wheel on steel rail helps immensely. If you are talking about a high-speed passenger train, the effect is not so important because aerodynamic drag along with the energy required to accelerate to speed to maintain schedules will dominate. The train has an improved aerodynamic effect compared to a road vehicle because you have train cars in effect drafting each other. On the other hand, bus and more recently truck people are OK with streamlined shrouds while train people seem to have an aversion to streamlining – especially undercarriages and underbody accessories, and the drag on passenger trains from unstreamlined undersides can be considerable.
The other thing to consider is that in parts of the world trains are routinely and safely operated at speed in excess of 180 MPH, while I don’t know if a bus could go that fast even if you wanted to on account of the risk of blowing a tire. On the other hand, those 180 MPH trains take a lot of maintenance of track, wheels, and suspensions, and some people think that maglev is a magic soluti
Today I observed my local city bus parked at the the bus turn around (Formaly a trolley turn around)
I took 2 doller bills and laid them on there side. It took about 4 and half doller bills to mesure the surface area that the rubber tire covered.–Likewise later at the NFTA trolley stop I mesuered how much surface area does the trolley wheel cover. It was about the size of a nickle when I covered it.
No I remember back in Cleveland when they ran a steam engine don the line down my street and we would pennys on the track. The Pennys were crushed to the size of a quater to a half doller.
Likewise I mesured a car tire at the local Sunoco Gas Station. The Surface area was 2 Dollers worth.
My Bicycle was about a quarter surface area
Now how does this apply to passenger transportation?
Buses carry at the most 50 to 60 people. A Modern railroad car that is double decked can carry as many as 200 people in rush hour. The co-efficate of friction of 200 people in there automobile is about 400 car tires times 4 dollers or 1200 dollers of resitnce. The Bus is about 200 dollers of restance to carry the same people.
Busways have been toted as the wave of the future in that they are cheaper to build and run. The truth it seems that buses actualy consume more energy per passenger then trains do. The Contruction studys do not also take into account that in order to build any modern roadway you have to use reenforcment rods so for a Busway like the East Busway(Downtown to Swissvale) in Pittsburgh PA probaly used more steel then a two track railroad right of way to build it. Also the Cleveland Rapid Transit basicaly had been using the same rails for about 35 years till they had to update and replace the tracks. Replacement for highways is more like every 10-15 years. The only issue here is start and stop. The FRA needs to aprove lighter weight railroad passenger stock to improve effecinacy.