The tunnel's long story began in 18th century

Tilbury Fort had been sited at the ancient ferry crossing point of the main highway from Essex to Kent and it was here that three phases of crossings were tried.

On August 3, 1780, a grand review of troops took place on Dartford Heath, after which the troops were marched to Gravesend and were taken over in barges to make a sham attack on Tilbury Fort, it is thought some 500 troops were involved.

This was undertaking using hawsers anchored on each shore and stretched across the river and the barges were ‘warped’ by the soldiers.

In 1798 and attempt was made to construct a tunnel under the Thames between Tilbury and Gravesend, this was promoted by Ralph Dodd through a share issue.

Two vertical shafts were constructed on either side of the river but despite the use of an early steam engine to pump water out of the shafts the force of water penetration was to much and the scheme failed. Ralph Dodd’s business plan relied on tolls being paid to offset the cost of construction and maintainace. The cost of digging two ‘wells’ came to £15,242 10/4d.

In 1914 a floating pontoon was constructed between Tilbury Fort and Gravesend for military transport purpose and was kept in place for some time, controlled by guards, the middle section was removable, using tugs, to allow shipping to pass in to Tilbury and the London docks.

Finally in 1929, Kent and Essex County Councils promoted a Bill for the construction of a tunnel and a pilot ‘Purfleet – Dartford’ tunnel was started in 1936 and completed in 1938. However the war started and budgets were diverted to the war effort so the tunnel was flooded.

Dartforf Tunnel cycle bus service in 1963

In 1955 the scheme was revived and re-started in 1959. The civil engineering utilized compressed air to keep the tunnel from flooding as the mines excavated through the chalk some 38 feet below the bed of the Thames, some the miners suffered from the ‘bends’ a decompression sickness caused by the change of pressure as they left the mine shaft.

On November 18, 1963, the Dartford Tunnel was opened at a cost of £13 million, the tunnel is 1,430 metres (4,690 ft) long, with the toll booths on the Kent side, cars were charged 25p and heavy goods vehicle 30p, a bus cycle service was introduced as it was to dangerous to ride through the two-war restricted carriage way.

The collected revenue helped to pay for the construction of the scheme. The Thurrock Gazette had a headline “It will be a toll free tunnel by 1976!”.

Early estimates of 2 million vehicles a year more than doubled in the first year of operation. Very quickly it was realised that a second tunnel was needed.

In between time the Tilbury – Gravesend car and lorry ferry closed, however a new bus route was formed the 300 and the Green Line Coach route 372 was extended, encouraging tourism to sites of interest in Essex and Kent!

By 1972 work on second tunnel started and was opened in May 1980, linked to the new M25 going north at an estimated cost of £37 million for the tunnel and short road extension on to the motorway. By 1986 the M25 was completed on the south side, the tunnels provided a vital link in the national road network.

Very soon the daily average volume of traffic regularly exceeded the maximum designed capacity of 65,000 vehicles and forecasts predicted annual throughput in excess of 40 million vehicles. Now a bridge was proposed to deal with the predicated capacity.

Pilot tunnel breakthrough 1938

The operation of the Dartford Tunnel was controlled by an Act of Parliament, new legislation was necessary to allow transfer of the crossing from Kent and Essex County Councils to Dartford River Crossing Limited. In July 1988 this process was completed on and construction of the bridge began just a few days later.

In an early example of a Private Finance Initiative, under the Dartford – Thurrock Crossing Act 1988 control of the crossing passed from Kent and Essex county councils to Dartford River Crossing Limited, who would now fund the construction of the QEII bridge and take on the remaining debt from construction of the tunnels.

In 1989 work started on the new cable-stayed bridge construction and the official opening was undertaken by the Queen in October 1991. The PFI scheme allowed Dartford River Crossing Ltd a 20 year concession to collect revenue, although this could be ended early once debts were repaid.

Under the scheme, some parties had expected that the government of the time would scrap the toll once the debt had been repaid and a suitable maintenance fund had been accumulated, which was deemed to have occurred on 31 March 2002.

On 13 September 2009 the contractors of the Dartford River Crossing (Le Crossing) changed to Connect Plus M25, which again is made up of a consortium of Atkins, Egis, Skanska, and Balfour Beatty.

From April 2010 to March 2011, 50,939,941 vehicles used the crossing, at a daily average of 139,545 vehicles - 5184 an hour averaged out. This represented a fall back to pre-2002 levels, from averages approaching 150,000 since the turn of the millennium. The highest recorded daily usage was 181,990 vehicles on 23 July 2004.

As part of the Government’s spending review in 2010 they proposed new actions to improve traffic flow at the crossing.

These included suspension of charges in the case of severe congestion and a review into additional capacity – either at the Dartford Crossing or with a new crossing of the Thames.

The Government also announced its intention to introduce new payment technology which would allow for the removal of the existing toll booths and barriers. The Highways Agency consulted on legislation changes related to the new scheme in November 2012.