This effect can be reduced somewhat by installing a capacitor in the right place. This form of detection is still adequate, but it is no longer cost effective to use such high current transistors to carry the train running current. The next form of current detector uses diodes in the common rail path to the block. Very low cost diodes, capable of handling 3 amps or more continuously, while giving a voltage drop of less than 1 volt, are readily available. This has the same effect as the power transistors used in the Twin-T circuit, at a much reduced cost.
Sensitivity can be just as high or even higher.
The only thing remaining is to sense the voltage drop across the diode using an operational amplifier or comparator of some kind. Today, such integrated circuits are readily available at low cost. Techniques of this type result in reduced costs when compared to Twin-T and similar transistor based circuits. They also operate very quickly, and will respond to breaks in current flow due to dirty rail or wheels. As with Twin-T circuits, this can be controlled with a capacitor or other filtering in the right place.