Don't eliminate the solid axle!

The solid axle is critical to proper shunting of track circuits, permitting reliable and safe operation of nearly all grade crossing signals, automatic block signals, CTC systems and interlockings in the United States; and most of the rest of the world as well (although other methods are somewhat more common elsewhere).

No other method of detecting the presence of a rail vehicle has ever proved more reliable than the track circuit - not even close. But it has its limits. Each galvanic joint (metal to metal contact point) limits the wheelset's ability to electrically shunt the track, making the track circuit less reliable. To shunt the track, an electrical path must be established from rail to rail through the axle. With only four galvanic joints, (two very solid connections between wheel and axle and two relatively poor ones between wheel and rail), the solid axle tapered wheel set is still a stellar performer at electrically shunting the track.

But without the solid axle, there are several very poor galvanic joints and no good ones, thus presenting a much poorer electrical path, making these vehicles harder to detect and therefore less safe to operate. The worst example of such a vehicle being the hi-rail vehicle; it's pointless to even try to detect it for block signaling purposes. So most railroads don't even try. Instead they use human procedural methods to provide protection. Accidents are thus more common. If memory serves me correctly, the Budd RDC was also a poor shunter, which caused some railroads much consternation (the WP for example). I seem to remember that not all of its axles were solid either - not sure.

Not only that, but the solid axle is also critical to proper tracking of the wheel set; wherein flange to rail contact is minimized by the natural tendency of a solid axle tapered wheel set to self track. Rolling resistance and noise are also minimized. This even works while going around a curve - as long as you're at equilibrium speed for the degree of curvature and cant.

Without a solid axle and tread tapering, no self tracking is possible. Therefore, we must then depend solely upon the flange to stay on the track, causing excessive wheel and rail wear; plus sharply increased rolling resistance. Even worse (in a passenger car), as the wheel flanges rapidly wear, the ride gets rougher and rougher - necessitating much higher maintenance costs in wheel grinding and replacement.

Most squealing noise is caused by flanges scraping against the side of the rail. When you hear a regular railroad wheel squealing, it is mostly because of plain old deferred maintenance (poorly maintained taper). As the resultant flange wear gets worse, the squealing get louder. When properly tracking, wheels are fairly quiet. But without the solid axle, or the tapering, the flanges are always scraping and thus always squealing. That is why BART has become so noisy. It has the solid axles, but no tapering on the treads and a lot of worn flanges.

Any deferred maintenance while depending solely upon the flange (missing axle or taper) can get very serious. The flange will eventually wear to the point that it is so sharp that it can dig into the rail and climb right up and over. I have actually witnessed that happening - first hand! And the gouges in the rail made by the flanges at the point of derailment were plain to see, as I pointed them out to our safety investigators.

Again, the hi-rail vehicle, with its independent wheels, is the worst example of poor tracking. They love to bite the ballast! So much so that their speed must be severely restricted. Even a mere 40mph is too fast, as a friend and I personally found out the hard way.

About thirty years ago, I found myself in the way of the next scheduled train and it was a long way to get into the clear (several miles); so I hi-tailed it hard (above 40mph) to get to the nearest set off point as soon as possible. But as soon as I attempted to lift the front wheel set - lo and behold, the whole assembly just fell to a dozen pieces right there in the middle of the track. It was very sobering! (Too much lateral stress and no solid axle to transfer it off the bearings).

A few weeks later, a friend who worked at BART bounced over a frog at less than 20mph, only to derail, hitting the hot third rail. The resultant flash-over destroyed the hi-rail truck and put the track out of service for most of the day. He was lucky, with only minor electrical burns. But he himself was put out of service for more than two weeks!

Thus, solid axle tapered wheel sets are critical to efficient and safe railroading. A lot is lost when they are not used - it ain't worth it; even for low floors.

OPB