<p>The <b>M25</b> or <b>London Orbital Motorway</b> is a 117-mile <a href="/pages/w/103128616394576">motorway</a> which almost encircles <a href="/pages/w/112173458800074">Greater London</a>, England, in the United Kingdom. A narrower concept was first mooted in the 1960s as part of the plan to build <a href="/pages/w/143847282297152">four ring roads</a> around London. A few sections, based on the abandoned <a href="/pages/w/143847282297152">London Ringways</a> plan, were constructed in the early 1970s and it was completed in 1986.</p><p>It is one of the busiest of the <a href="/pages/w/227253980647742">British motorway network</a>: 196,000 vehicles were recorded on a busy day near <a href="/pages/w/107786952577615">London Heathrow Airport</a> in 2003 and the western half experienced an average daily flow of 147,000 vehicles in 2007.</p><p>Although technically not an entire orbital motorway – a short non-motorway stretch forms the <a href="/pages/w/103186169737195">Dartford Crossing</a> of the <a href="/pages/w/107685822587432">River Thames</a> – the M25, at 117 miles is Europe's second longest orbital road after the <a href="/pages/w/113576148691097">Berliner Ring</a>, which is 122 miles .</p>