It by no means certain that any reduction will be approved. The SNP is a minority government, dependent on Green party support, and they are obviously opposed to any reduction, never mind deciding what public service will be cut back to fund it.
Nearly ten years ago, the Scottish parliament committed the country to a halving of Transport-related CO2 emissions. So far it has done virtually nothing to deliver on this, and transport emissions have continued to rise. But to actively encourage their growth?