In terms of length and surface surrounded, it may be compared to London's North and South circular roads, or Paris' A86 super-périphérique.

The actual distance is much closer in the southern and eastern spans, which have been engulfed by the city in some points; than in the west, where the Casa de Campo and the projection towards Pozuelo brings it further from Madrid itself.

Furthermore, it is the only one of the several ring roads serving Madrid that runs as a full-fledged motorway for all its length: a span about 2 kilometres (1.2 mi) long at the northern arc of the inner M-30 are not freeway-grade, having level crossings and traffic lights; while the outermost M-50 is not a full ring road due to the interruption caused by the Mount of El Pardo protected natural zone.

The Madrid regional government, which built the M-45 motorway external to the M-40 specifically to decongest the southern and eastern spans of the older beltway, has recently aired plans to address the northern jams by effectively "closing" the M-50 ring with a tunnel under the protected area.

Instead, both the M-40 and the M-50 are state-owned freeways, as shown by the white text on blue background of their signals, whereas Madrid regional motorways like the M-45 use black text on an orange background that identify them as pertaining to the "regional first order roads" category of the Spanish Traffic Code.