Perry Barr was supposedly a planned service area between J6 and J7 on the M6, an elevated section of motorway running through a densely urban area, and part of a long section of motorway without any services.
The site is absolutely tiny - it's bordered by houses on three of the sides and immediately to the south is a canal. For this reason, it's not clear how serious the plans actually were. It wasn't original to the motorway as there are no hard shoulders through the junction.
Due to the heights involved and the lack of space, the sliproads would have been steep two-way roads with a sharp bend on each one, joining the motorway at a right angle with red and white paint in the middle, which leaves me to question just how serious the plans were.
Today it is used as a works unit, which heads round and under the motorway. It is officially known as the 'Perry Barr Motorway Facility', and it's also used by the police as a place to pull motorists over rather than stopping them on the busy and narrow M6.
When the site was first built in preparation for the services, some maps had it down as an open but unnumbered junction.
With thanks to Nic A47 for the information used on this page.