Ringway 3 Eastern Section

But in the context of the Ringways - the wider network of motorways planned across the whole of London - it looked a bit odd. Around the north, west and south of London, Ringway 3 was only the second ring road from the edge. But here, in the east, Ringway 4 gives up, and Ringway 3 provides a crossing of the Thames for both ring roads. Why would that be the case? Certainly, we now know that the demand for the river crossing at Dartford is enormous, so it seems odd that on this side of the city the plan was for fewer rings than everywhere else.

What's more, Ringway 3 was planned to make its crossing of the Thames using just the twin-bore Dartford Tunnels. The present bridge, which doubled capacity at the crossing from four to eight lanes in total, was only opened in 1991 and nothing of its kind was thought to be needed when Ringway 3 was in planning.

So, while this whole section of Ringway exists on the ground, the inevitable question is: was that it?

Route description

This description begins at the northern end of the route and travels south.

Navestock to Dartford

All of this section of Ringway 3 exists as the modern M25, and can be driven today. Continuing from the Ringway 3 Northern Section, an interchange would be formed with the Ringway 4 North Orbital Road near Navestock, effectively marking the end of Ringway 4, and from there the motorway runs south-east to Brentwood.

Where the M25 meets the A12 at junction 28, a much more complex interchange would have been formed, with links not just to the A12 and a local road to Brentwood, but also free-flowing connections to the M12, which would approach from the west. The junction layout was plotted out by engineers working on the M12 project in the late 1960s, but no diagrams have yet come to light. Written descriptions suggest a three-level stacked roundabout junction would have been provided, with some free-flowing links.

Continuing south, the next interchange is with the A127. Between there and the A13, the Greater London Council wanted an additional local junction with the B1421 at North Ockendon, but Whitehall disagreed, and it wasn't built.

The modern M25 junction 30 is much bigger than that planned in the late 1960s; the A13 then followed what is now the A1306 and was a much smaller affair requiring a simpler interchange. The motorway ends at this point, and Ringway 3 follows the A282 in order to pass beneath the river at Dartford. In 1973, there was only one Dartford Tunnel, carrying two way traffic; the second was planned as part of Ringway 3 but did not open until 1980. Its approach road, southwards from the A13, would be a simple two-lane dual carriageway.

Dartford to Swanley

Emerging into the daylight on the south side of the Thames, the A282 would pass through the Dartford Tunnel toll plaza before resuming its run south as a two-lane dual carriageway. The local interchange with the A205 Bob Dunn Way is a later addition; the route of Ringway 3 would carry it straight to the junction with the A225 Princes Road instead.

A junction with the A2 would follow, and at this point the motorway resumes - though Ringway 3 would have carried the number M16, not M25. Turning to the south-west, the motorway would then run through the north Kent countryside to reach the A20 and M20 at Swanley, as it does today, with links to the local road network and a free-flowing connection between the north and east arms of the junction.

Turning further south-west as it crossed the M20, the road would become the Ringway 3 Southern Section.

Under the Thames

Today the Dartford Crossing is the busiest river crossing in the UK and a daily cause of congestion. Its two tunnels provide four lanes northbound beneath the Thames, while the Queen Elizabeth II Bridge carries four lanes southbound over the top of it. Highways England plan to provide another six lanes across the Thames further east to relieve it within the next decade. It's hard to imagine, then, that as recently as 1981 it was controversial to even suggest that two tunnels alone might prove inadequate.

Ringway 3 was planned in an era when the Dartford Tunnel was a single two-lane tube, and a second to duplicate it was in planning. The second bore opened in 1980, seven years after the abandonment of Ringway 3, as part of its successor, the M25 (or, pedantically, a section of A282 linking the ends of the M25). The orbital road may have changed, but the thinking had not: the pair of two-lane tunnels at Dartford would carry the M25's full load, plus local traffic, under the river.

The thinking went like this. The motorway would have three lanes of traffic moving at 70mph, which meant long headways between vehicles. If you slowed that traffic to 50mph or even 30mph, the vehicles would travel closer together, reducing the amount of road space needed for each vehicle. The same volume of traffic could, therefore, fit into fewer lanes if it moved more slowly. Exactly this idea was also used to justify the two-lane section on the M4 approaching London.

What happens in practice, of course, is that slowing traffic down and pushing it through something unusual like a tunnel will disrupt the flow, causing waves of brake lights and phantom traffic jams. You will not fit the traffic load of a three-lane motorway through a two-lane tunnel without congestion. If you wish to see this for yourself, simply drive through the Dartford Tunnels, where four lanes of motorway entering four lanes of tunnel will still somehow cause daily jams.

This was not lost on Desmond Jago, manager of the Dartford Tunnels, who wrote to his superiors at the Department of Transport in 1981 to recommend building a second pair of tunnels to prepare for the arrival of the M25. A total of eight lanes would be needed, he said.

The idea was considered utterly remarkable. His letter was discussed in an internal memo:

"We shall need to be able to deal with criticisms of this kind, which will no doubt be referred to us for comment… if there is a serious possibility that Dartford will become a bottleneck, we shall need to consider what to do about it."

Not to worry, another civil servant replied:

"In normal circumstances the twin bores ought to be able to carry, although admittedly with considerable stress, the 1998 high growth forecast for the tunnel."

In other words, the two tunnels would be adequate for decades ahead. In reality, the "high growth forecast" for 1998 roughly matched actual traffic levels, which seriously taxed even the present eight-lane setup.

In fairness to the road's planners, nobody could really have foreseen just how much an orbital motorway might become a victim of its own success, as it has done. Besides, there was one other assumption that fuelled their thinking: it was fully expected that a high-capacity river crossing would exist near Thamesmead, taking much of the local traffic away from Dartford. In the era of Ringway 3, that crossing would be the enormous Ringway 2 Eastern Section. By the time the M25 was being built, it had become the East London River Crossing, an extension of the North Circular over the Thames. The demise of the ELRC was the catalyst for the Department to finally admit that two tunnels were not enough and to commission the new bridge at Dartford, which opened in 1991.

The bridge to nowhere

If you need any further evidence that the east side of Ringway 3 was not particularly ambitious - beyond the lack of capacity at Dartford and the entirely absent east side of Ringway 4 - look no further than the interchange with the M20 at Swanley.

Laid out between 1975 and 1977, while the section of M25 to the north was being built, Swanley Interchange was all set for the motorway to continue south-west. Its layout was unchanged from the plans for Ringway 3 that would have seen the motorway continue onto the never-built Southern Section. The next length of M25 to the south, though, wouldn't open until 1986 and would take an entirely different route down to junction 5.

Standing in the middle of Swanley Interchange, and entirely unused for the intervening nine years, was the bridge that was meant to carry the M16 over the M20. It was provided as part of the junction works but, of course, couldn't be used until the next section of motorway was built. It too was a leftover from the Ringway 3 plans and locals nicknamed it the "bridge to nowhere".

If you drive that way today, you might notice the hard shoulder vanishing briefly as you follow the M25 through Swanley Interchange. That's because the bridge to nowhere was designed to carry just two lanes and a hard shoulder in each direction.

Narrowing the road down to two lanes on the way through a junction is hardly a bold statement of ambition for Ringway 3's Eastern Section - but then this might be the one component of the Ringways where bold ambition is not much in evidence. And the inadequate bridge is, at least, absolutely in keeping with the very modest ambition for Ringway 3 at Dartford.