I don't understand the distinction. If the UK is allowing tests of driverless cars, it must be allowing them on the roads, and of course "in January" means "starts in January", what else would it mean
Driverless cars are a risky unproven technology, and done wrong could easily kill people.
It'd be like taking "FDA approves new drug for human testing" and making the headline "FDA to allow human use of new untested drug."
Both are technically true, but the latter makes it sound like a widespread thing being done regardless of poorly understood risks. And that's misleading, since it's being done in very limited scope to help us understand and reduce those risks.
While the title is technically true, it could easily be interpreted to mean anyone could buy or build a driverless car and drive it on UK roads starting in January.