There is nothing at all complicated about low traffic neighbourhoods, even if urban planners turn them into acronyms ("LTNs") and introduce jargon such as "modal filter". A low traffic neighbourhood is simply an area of residential streets in which motor traffic is restricted to access — to households and businesses, for deliveries and services — and the streets are designed for people rather than motor vehicles.
The amount of motor traffic in Oxford has steadily increased over the last few decades. One result of this is that some neighbourhoods that were low traffic are now used by large numbers of vehicles rat-running around traffic lights or avoiding sections of main roads. The hostile environment this has created pushes residents to make even short trips by car, creating still more traffic; there has been a steady decrease in the fraction of children walking or cycling, to school or elsewhere.
Retrofitting low traffic neighbourhoods attempts to reverse some of these changes, which have been stealthily imposed on communities over decades. This doesn't ban cars from anywhere, but blocks through routes for motor traffic while preserving access to households and business. That can be done with bollards, gates that allow emergency access, planter boxes, or parklets. And it can be combined with traffic calming, junction tightening, and other measures such as School Streets schemes to reduce school-run traffic.
The obvious gains are in reducing road danger and air and noise pollution, but less motor traffic also creates opportunities for broader healthy streets and public realm improvements.
Not everyone has an alternative to driving, but some people do and some residents will switch to other modes for some trips: perhaps to public transport or ride-sharing, perhaps to walking or cycling. With lower traffic volumes, some people may let their children walk or cycle themselves to school.
The evidence from places where low traffic neighbourhoods have been implemented is that overall traffic volumes decrease. One way to measure what happens on main roads is the impact on bus timetables: in the schemes that have been in place longest in London, there were no adverse effects on bus times on the surrounding roads. And Oxford needs better management of traffic at larger scales than the neighbourhood, but a key requirement for this is first restricting that traffic to main roads.
It's also worth noting that low traffic neighbourhood schemes have already been implemented in a variety of locations across Oxford. In Iffley Fields, when Meadow Lane and Addison Crescent were blocked to motor traffic. In the area between Barns Rd and the B480, when Phipps Rd was blocked to motor traffic. North of Jericho, when Hayfield Rd was bollarded. And so forth. Once these are in place, residents and businesses and services adjust to slightly different routes and largely forget they exist.
There's nothing at all novel about low traffic neighbourhoods and they shouldn't be at all controversial. They are what planners design for in areas of new housing — and they are what pretty much all residential neighbourhoods were fifty years ago.