This is the exact opposite of what every modern three-phase locomotive operator's manual says, and what test run measurements confirm. Modern traction control systems can and will use slip to condition the wheels and rails very precisely, resulting in a significantly higher usable tractive effort. The difference between conditioned and unconditioned rails is particularly noticeable in places where trains frequently accelerate or brake. The friction coefficients there are significantly higher than in other places. When passing through stations, our measurements have shown an increase in traction force of around 150% (65 kN to 160 kN) under otherwise identical conditions. Wheel slip for conditioning rails is therefore desirable. The optimum slip value depends on the track conditions and the speed. The main limiting factors are comfort values and impermissible torsional vibrations, which the traction control must also manage. At high speeds and low friction coefficients, high slip has little effect on the overall tractive force; however, at low and medium speeds, it does.
Manually driving the train without any slip on the "weakest" axle usually results in the other axles remaining significantly below the otherwise achievable tractive effort.
The route between Brugg and Frick is a great “test track” for us, as it carries a lot of heavy freight traffic and double heading would be incredibly inefficient and expensive due to the relatively short length of the route. As a result, many trains there run with a single four-axle locomotive close to the maximum load (which is set by the TOC, by the way). Are there any traction problems under certain circumstances? Yes, but very rarely. However, these are accepted because adding a second locomotive or reducing the load would result in disproportionately large productivity losses.
Possible due to poor language choice on my part and widespread general lack of understanding of Class 88 operation there has been some misinterpretation of what I meant.
1. In order not to exceed the maximum permitted power draw per train, pairs of Class 88 are power limited so on the curved part of the TE curve they are automatically limited to circa 80% of max traction power of a single locomotive
2. In order not to exceed the maximum coupler rating, pairs of Class 88 are automatically TE limited on the flat low speed part of the TE curve, they are automatically limited to 75 - 80% of max traction effort of a single locomotive at low speeds
3. This effectively means a pair of Class 88 is only asking for ~80% of the performance per axle of a single Class 88. And they seem to be able to operate successfully like this. The derating is fully automated with no driver interaction, the driver can still put the power lever to max but the computer will cap the requested power.
4. The leading axle of Class 88s does lots of software controller rail head conditioning work thus leaving 3axles (single 88) or 7 axles (double 88) to deliver a full performance and reduced performance from the leading axle. I wasn't suggesting turning this or any of the slip management systems off.
My Quote:
There may also be an element of the drivers leaving the computer to try to work miracles when they might get better outcomes using traditional drivers common sense... (e.g. backing off the power to stay with adhesion limits rather than asking for too much power resulting in letting the computer try to recover from uncontrolled slip lots of the time)
5. Single Class 88 operation on intermodal requires full power on meaningful hills to keep to time hence drivers have a tendency to apply full power by default which some times appears to be a bad idea. In adverse conditions they might be far better applying 80% of the power in similar manner to the automated double headed power /TE caps thus allowing the slip management systems to work rather than asking the impossible of them. E.g replicate what works with double heading as closely as possible
6. There are multiple reasons that pairs of Class 88s work better in poor conditions than a single Class 88 (ignoring driver inputs)
- More axles
- Lower maximum TE per axle at any speed
- less need to apply the (lower) maximum TE or close to lower maximum TE per axle to run train to time
- proportionately fewer axles applying reduced TE while engaged in rail head conditioning (if needed)
Unfortunately all the commentary so far has just focused on the first point!
