In a recent YouTube video post, retired Civil Engineer Ken Bowman speaks out about Highways England’s proposals for a new River Thames road crossing.

The satnav people TomTom found that the slowest running traffic in the whole national trunk road system is at the Dartford Crossing between Kent and Essex. The crossing is the most congested part of the UK’s strategic trunk road network. They found speeds down to 8mph. The Design speed for the M25 is 70mph so you can see that 8mph is only about 11% of this.

If other things ran at little more than 10% efficiency be it the car or central heating system, we’d all call that an emergency. It is not unreasonable therefore to consider the problems at Dartford a near emergency.

So the Government have asked Highways England to find a solution to this problem. Highways England have considered several alternatives and eventually decided upon what they consider to be the best; a second crossing of the River Thames about 10 miles downstream from Dartford.

This is NOT a solution to the Dartford problem. Highways England forecast that the flow of traffic across the Dartford Crossing will steadily escalate. The purpose of this proposed new crossing is to divert traffic that would otherwise cross the river at Dartford to this new crossing.

This new crossing is going to take some 10 years to create, and during this time traffic condition will of course get steadily worse.

The amount of traffic Highways England predict will divert from the existing crossing is actually quite small. In fact it is fairly similar to the increase in traffic which will have occurred over the 10 years.

So what is it they are offering us? They are offering:-

  • The existing emergency
  • 10 years of increasing emergency
  • Back to the original emergency
  • And then increasing emergency forever

Clearly this is not the solution to the Dartford Crossing problem.

So is there a solution? Yes there is! But it’s not easy. First we have to consider that the existing crossing is used not only by traffic on the national trunk road network, but also by local traffic moving between employment, retail and residential areas in Dartford, Thurrock and surrounding areas. Herein lies one of root causes of the congestion.

If we just increase the capacity of the Dartford Crossing itself we don’t achieve much because to the north and the south of the crossing lie major junctions providing local access to the crossing. Increasing capacity alone will simple clog up these junctions. No benefit is achieved.

So what is the answer? The answer is a bypass around the crossing and both these junctions. A conventional bypass isn’t a practical proposition due to the disruption it would cause to existing traffic.

An underground bypass however would provide the same benefit without the disruption. The tunnel required would be a long twin-bore tunnel about six and a half miles long which would start well back in Kent, south of junction 2 and go on well into Essex, north of junction 30 and would bypass all the congestion in between.

Highways England tell us that the proportion of traffic at Dartford that is classified as through traffic is about 40% – that’s traffic trying to use the M25 as a long-distance trunk route. The remainder is local traffic trying to get from Kent into Essex and from Essex into Kent. If we could separate these two components we’d be doing some good; congestion at the junction on the north and south sides of the crossing would be reduced because the tunnels would carry the through traffic and the existing crossing would carry the remainder- some 40% less in volume. So this looks like a very good solution to the problem.

Now in comparing these long tunnel proposals with Highway England’s down-stream proposals we must consider several other factors.

Ecologically the downstream proposal chew up large amounts of the Green Belt in Kent and Essex and disturbs several villages. The tunnel does none of these so the tunnel is clearly best.

If we consider disruption during construction the downstream proposal involves the modification of many existing road junctions and these works would all be likely to cause delay during construction. None of this applies to the tunnel because to a great degree no one would know the tunnel was being built.

When we consider the social implications, the downstream solution requires the compulsory purchase of a large amount of land and the demolition of a number of properties. The tunnel required very little of this because the two ends of the tunnel are more or less in rural areas alongside the M25 requiring relatively little land.

Now we come to the issue of pollution. According to a report published recently in The Times newspaper, it is estimated that 25,000 people in England each year die as a result of traffic pollution. If we considering this on a pro-rata basis, based on population then if Dartford was an average place then its share of this would be nearly 50 deaths a year. Actually because it has the Dartford Crossing on its doorstep, quite likely it is above this average figure. So you can see if the downstream solution is used this provides no benefit to Dartford which remains at best as it is now but increasingly worse as traffic increases over the next ten years. If the tunnel option was built the pollution that builds in the tunnel can be treated before it is discharged into the atmosphere. And the more free-flowing the existing crossing the more the pollution there will be reduced.

If the downstream solution is adopted it is impossible to say, we simply don’t know, how many more people in Dartford will die as a result. But surely there would be extra deaths. So you see on every count the long tunnels seem to be superior to the downstream solution.

But there remains one consideration and this is of cost. Highways England have not provide any details of the long tunnel solution that they apparently costed and rejected on the grounds of cost. They designated this Option A14 in their consultation documents and pre-emptily dismissed it.

Is the £6.5bn cost they are suggesting reasonable? We have no details of their scheme so it is impossible to know. So the best we could do is consider what information is available and make a best guess.

Ken Bowman, a retired Civil Engineer considered this using four different methods. He used two separate government publications to cost the long tunnel and the two other methods were to look at long tunnels that have been built in recent times and comparing costs on that basis. All four methods showed results much, much cheaper than the £6.5bn than Highways England suggest. However the precise cost is actually a secondary consideration because we can’t continue as we are, we need a solution to the Dartford Crossing problem as soon as possible.

The long tunnel appears to provide that solution, the downstream offer doesn’t. So whatever the cost we have just got to bite the bullet, pay up and get these tunnels built as soon as possible.

Highways England are recommending the downstream solution on the basis that it offers the most benefit at least cost. But to quote Mr Bowman, “Is there anything dearer than a bargain that doesn’t work?”