They may be progressing, but there is simply no way LEDs could be economically viable for this operation with any current technology, and even combining multiple sources, would fail to provide sufficient illumination over the required area.
We had this before
http://www.hiddenglasgow.com/forums/vie ... treetlight
Monochromatic yellow lamps are Low Pressure sodium (SOX), used for their low running cost vs high light output. Reckoned to be the most efficient light source available, these cost the least to run for our tax pennies. They have another advantage in that they don't contain mercury.
High Pressure sodium lamps (SON) produce a wider spread of emissions, but are still more like peach than white. This wider spread allows the eye to perceive a range of colours, so does the equivalent of a white-balance to compensate, much like a digital camera. Compared to SOX, they are more expensive to make, using more exotic and hazardous materials, and consuming more power for a given illumination.
Monochromatic SOX light cannot be split and dispersed like SON light, so is safer for driving illumination in rain/mist/fog situations. SON is favoured in and around city areas to keep designers happy, so that their creations can be seen in colour, even at night.
Hopefully the council are just replacing old and knackered installations with new, and not chucking council tax away replacing servicable lighting for fashion.